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Journal Cover Journal of Evolutionary Biology
  [SJR: 2.009]   [H-I: 98]   [23 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1010-061X - ISSN (Online) 1420-9101
   Published by John Wiley and Sons Homepage  [1592 journals]
  • Conserved roles of Osiris genes in insect development, polymorphism, and
           protection
    • Authors: Chris R. Smith; Claire Morandin, Moataz Noureddine, Swati Pant
      Abstract: Much of the variation among insects is derived from the different ways that chitin has been molded to form rigid structures, both internal and external. In this study, we identify a highly conserved expression pattern in an insect-only gene family, the Osiris genes, that is essential for development, but also plays a significant role in phenotypic plasticity and in immunity/toxicity responses. The majority of Osiris genes exist in a highly syntenic cluster, and the cluster itself appears to have arisen very early in the evolution of insects. We used developmental gene expression in the fruit fly, Drosophila melanogaster, the bumble bee, Bombus terrestris, the harvester ant, Pogonomyrmex barbatus, and the wood ant, Formica exsecta, to compare patterns of Osiris gene expression both during development, and between alternate caste phenotypes in the polymorphic social insects. Developmental gene expression of Osiris genes is highly conserved across species, and correlated with gene location and evolutionary history. The social insect castes are highly divergent in pupal Osiris gene expression. Sets of co-expressed genes that include Osiris genes are enriched in gene ontology terms related to chitin/cuticle and peptidase activity. Osiris genes are essential for cuticle formation in both embryos and pupae, and genes co-expressed with Osiris genes affect wing development. Additionally, Osiris genes and those co-expressed seem to play a conserved role in insect toxicology defences and digestion. Given their role in development, plasticity, and protection we propose that the Osiris genes play a central role in insect adaptive evolution.This article is protected by copyright. All rights reserved.
      PubDate: 2018-01-10T23:12:37.141464-05:
      DOI: 10.1111/jeb.13238
       
  • Evolution of morphology and locomotor performance in anurans:
           Relationships with microhabitat diversification
    • Authors: Jessyca Michele Citadini; Renata Brandt, Craig R. Williams, Fernando Ribeiro Gomes
      Abstract: The relationships between morphology, performance, behavior and ecology provide evidence for multiple and complex phenotypic adaptations. The anuran body plan, for example, is evolutionarily conserved and shows clear specializations to jumping performance back at least to the early Jurassic. However, there are instances of more recent adaptation to habit diversity in the post‐cranial skeleton, including relative limb length. The present study tested adaptive models of morphological evolution in anurans associated with the diversity of microhabitat use (aquatic, arboreal, fossorial, torrent, and terrestrial) in species of anuran amphibians from Brazil and Australia. We use phylogenetic comparative methods to determine which evolutionary models, including Brownian motion (BM) and Ornstein‐Uhlenbeck (OU) are consistent with morphological variation observed across anuran species. Furthermore, this study investigated the relationship of maximum distance jumped as a function of components of morphological variables and microhabitat use. We found there are multiple optima of limb lengths associated to different microhabitats with a trend of increasing hindlimbs in torrent, arboreal, aquatic, whereas fossorial and terrestrial species evolve toward optima with shorter hindlimbs. Moreover, arboreal, aquatic and torrent anurans have higher jumping performance and longer hindlimbs, when compared to terrestrial and fossorial species. We corroborate the hypothesis that evolutionary modifications of overall limb morphology have been important in the diversification of locomotor performance along the anuran phylogeny. Such evolutionary changes converged in different phylogenetic groups adapted to similar microhabitat use in two different zoogeographical regions.This article is protected by copyright. All rights reserved.
      PubDate: 2018-01-03T07:01:27.911585-05:
      DOI: 10.1111/jeb.13228
       
  • Interactions between host sex and age of exposure modify the
           virulence‐transmission trade‐off
    • Authors: Stephen A.Y. Gipson; Matthew D. Hall
      Abstract: The patterns of immunity conferred by host sex or age represent two sources of host heterogeneity that can potentially shape the evolutionary trajectory of disease. With each host sex or age encountered, a pathogen's optimal exploitative strategy may change, leading to considerable variation in expression of pathogen transmission and virulence. To date, these host characteristics have been studied in the context of host fitness alone, overlooking the effects of host sex and age on the fundamental virulence‐transmission trade‐off faced by pathogens. Here we explicitly address the interaction of these characteristics and find that host sex and age at exposure to a pathogen affect age‐specific patterns of mortality and the balance between pathogen transmission and virulence. When infecting age‐structured male and female Daphnia magna with different genotypes of Pasteuria ramosa, we found that infection increased mortality rates across all age classes for females, whereas mortality only increased in the earliest age class for males. Female hosts allowed a variety of trade‐offs between transmission and virulence to arise with each age and pathogen genotype. In contrast, this variation was dampened in males, with pathogens exhibiting declines in both virulence and transmission with increasing host age. Our results suggest that differences in exploitation potential of males and females to a pathogen can interact with host age to allow different virulence strategies to coexist, and illustrate the potential for these widespread sources of host heterogeneity to direct the evolution of disease in natural populations.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-29T23:40:31.043746-05:
      DOI: 10.1111/jeb.13237
       
  • Can Ebola Virus evolve to be less virulent in humans'
    • Authors: Mircea T. Sofonea; Lafi Aldakak, Luis Fernando Boullosa, Samuel Alizon
      Abstract: Understanding Ebola Virus (EBOV) virulence evolution is not only timely but also raises specific questions because it causes one of the most virulent human infections and it is capable of transmission after the death of its host. Using a compartmental epidemiological model that captures three transmission routes (by regular contact, via dead bodies and by sexual contact), we infer the evolutionary dynamics of case fatality ratio (CFR) on the scale of an outbreak and on the long term. Our major finding is that the virus's specific life cycle imposes selection for high levels of virulence and that this pattern is robust to parameter variations in biological ranges. In addition to shedding a new light on the ultimate causes of EBOV's high virulence, these results generate testable predictions and contribute to informing public health policies. In particular, burial management stands out as the most appropriate intervention since it decreases the R0 of the epidemics, while imposing selection for less virulent strains.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-29T23:00:40.463679-05:
      DOI: 10.1111/jeb.13229
       
  • Mixed evidence for early bursts of morphological evolution in extant
           clades
    • Authors: Mark N. Puttick
      Abstract: Macroevolutionary theory predicts high rates of evolution should occur early in a clade's history as species exploit ecological opportunity. Evidence from the fossil record has shown a high prevalence of early bursts in morphological evolution, but recent work has provided little evidence for early high rates in the evolution of extant clades. Here I test the prevalence of early bursts in extant data using phylogenetic comparative methods. Existing models are extended to allow a shift from a background Brownian motion (BM) process to an early burst process within sub‐clades of phylogenies, rather than an early burst being applied to an entire phylogenetic tree. This nested early burst model is compared to other modes of evolution that can occur within sub‐clades, such as evolution with a constraint (Ornstein‐Uhlenbeck model) and nested BM rate shift models. These relaxed models are validated using simulations and then are applied to body size evolution of three major clades of amniotes (mammals, squamates, and aves) at different levels of taxonomic organisation (order, family). Applying these unconstrained models greatly increases the support for early bursts within nested sub‐clades, and so early bursts are the most common model of evolution when only one shift is analysed. However, the relative fit of early burst models is worse than models that allow for multiple shifts of the BM or OU process. No single shift or homogenous model is superior to models of multiple shifts in BM or OU evolution, but the patterns shown by these multi‐rate models are generally congruent with patterns expected from early bursts.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-29T01:50:30.102356-05:
      DOI: 10.1111/jeb.13236
       
  • Fixed effect variance and the estimation of repeatabilities and
           heritabilities: Issues and solutions
    • Authors: Pierre de Villemereuil; Michael B. Morrissey, Shinichi Nakagawa, Holger Schielzeth
      Abstract: Linear mixed effects models are frequently used for estimating quantitative genetic parameters, including the heritability, as well as the repeatability, of traits. Heritability acts as a filter that determines how efficiently phenotypic selection translates into evolutionary change, while repeatability informs us about the individual consistency of phenotypic traits. As quantities of biological interest, it is important that the denominator, the phenotypic variance in both cases, reflects the amount of phenotypic variance in the relevant ecological setting. The current practice of quantifying heritabilities and repeatabilities from mixed effects models frequently deprives their denominator of variance explained by fixed effects (often leading to upward‐bias of heritabilities and repeatabilities) and it has been suggested to omit fixed effects when estimating heritabilities in particular. We advocate an alternative option of fitting models incorporating all relevant effects, while including the variance explained by fixed effects into the estimation of the phenotypic variance. The approach is easily implemented and allows optimising the estimation of phenotypic variance, for example by the exclusion of variance arising from experimental design effects while still including all biologically relevant sources of variation. We address the estimation and interpretation of heritabilities in situations in which potential covariates are themselves heritable traits of the organism. Furthermore, we discuss complications that arise in generalised and non‐linear mixed models with fixed effects. In these cases, the variance parameters on the data scale depend on the location of the intercept and hence on the scaling of the fixed effects. Integration over the biologically relevant range of fixed effects offers a preferred solution in those situations.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-28T22:50:32.656883-05:
      DOI: 10.1111/jeb.13232
       
  • Sex‐antagonistic genes, XY recombination, and feminized Y
           chromosomes
    • Authors: Elisa Cavoto; Samuel Neuenschwander, Jérôme Goudet, Nicolas Perrin
      Abstract: The canonical model of sex‐chromosome evolution predicts that sex‐antagonistic (SA) genes play an instrumental role in the arrest of XY recombination and ensuing Y‐chromosome degeneration. Although this model might account for the highly differentiated sex chromosomes of birds and mammals, it does not fit the situation of many lineages of fish, amphibians or non‐avian reptiles, where sex chromosomes are maintained homomorphic through occasional XY recombination and/or high turnover rates. Such situations call for alternative explanatory frameworks. A crucial issue at stake is the effect of XY recombination on the dynamics of SA genes and deleterious mutations. Using individual‐based simulations, we show that a complete arrest of XY recombination actually benefits females, not males. Male fitness is maximized at different XY‐recombination rates depending on SA selection, but never at zero XY recombination. This should consistently favor some level of XY recombination, which in turn generates a recombination load at sex‐linked SA genes. Hill‐Robertson interferences with deleterious mutations also impede the differentiation of sex‐linked SA genes, to the point that males may actually fix feminized phenotypes when SA selection and XY recombination are low. We argue that sex chromosomes might not be a good localization for SA genes, and sex conflicts seem better solved through the differential expression of autosomal genes.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-28T18:06:07.313324-05:
      DOI: 10.1111/jeb.13235
       
  • Disparate patterns of thermal adaptation between life stages in temperate
           vs. tropical Drosophila melanogaster
    • Authors: Brent L. Lockwood; Tarun Gupta, Rosemary Scavotto
      Abstract: Many terrestrial ectothermic species exhibit limited variation in upper thermal tolerance across latitude. However, these trends may not signify limited adaptive capacity to increase thermal tolerance in the face of climate change. Instead, thermal tolerance may be similar among populations because behavioral thermoregulation by mobile organisms or life stages may buffer natural selection for thermal tolerance. We compared thermal tolerance of adults and embryos among natural populations of Drosophila melanogaster from a broad range of thermal habitats around the globe to assess natural variation of thermal tolerance in mobile vs. immobile life stages. We found no variation among populations in adult thermal tolerance, but embryonic thermal tolerance was higher in tropical strains than in temperate strains. We further report that embryos live closer to their upper thermal limits than adults—i.e., thermal safety margins are smaller for embryos than adults. F1 hybrid embryos from crosses between temperate and tropical populations had thermal tolerance that matched that of tropical embryos, suggesting dominance of heat‐tolerant alleles. Together our findings suggest that thermal selection has led to divergence in embryonic thermal tolerance but that selection for divergent thermal tolerance may be limited in adults. Further, our results suggest that thermal traits should be measured across life stages in order to better predict adaptive limits.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-28T18:05:44.296701-05:
      DOI: 10.1111/jeb.13234
       
  • Temperature fluctuations during development reduce male fitness and may
           limit adaptive potential in tropical rainforest Drosophila
    • Authors: Andrew D. Saxon; Eleanor K. O'Brien, Jon R. Bridle
      Abstract: Understanding the potential for organisms to tolerate thermal stress through physiological or evolutionary responses is crucial given rapid climate change. Although climate models predict increases in both temperature mean and variance, such tolerances are typically assessed under constant conditions. We tested the effects of temperature variability during development on male fitness in the rainforest fly Drosophila birchii, by simulating thermal variation typical of the warm and cool margins of its elevational distribution, and estimated heritabilities and genetic correlations of fitness traits. Reproductive success was reduced for males reared in warm (mean 24°C) fluctuating (± 3°C) versus constant conditions but not in cool fluctuating conditions (mean 17°C), although fluctuations reduced body size at both temperatures. Male reproductive success under warm fluctuating conditions was similar to that at constant 27°C, indicating that briefly exceeding critical thermal limits has similar fitness costs to continuously stressful conditions. There was substantial heritable variation in all traits. However, reproductive success traits showed no genetic correlation between treatments reflecting temperature variation at elevational extremes, which may constrain evolutionary responses at these ecological margins. Our data suggest that even small increases in temperature variability will threaten tropical ectotherms living close to their upper thermal limits, both through direct effects on fitness and by limiting their adaptive potential.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-28T01:55:38.905393-05:
      DOI: 10.1111/jeb.13231
       
  • Experimental evolution of infectious behaviour in a facultative
           ectoparasite
    • Authors: Emily S. Durkin; Lien T. Luong
      Abstract: Parasitic lifestyles have evolved many times in animals, but how such life-history strategies evolved from free-living ancestors remains a great puzzle. Transitional symbiotic strategies, such as facultative parasitism, are hypothesized evolutionary stepping-stones towards obligate parasitism. However, to consider this hypothesis, heritable genetic variation in infectious behaviour of transitional symbiotic strategies must exist. In this study, we experimentally evolved infectivity and estimated the additive genetic variation in a facultative parasite. We performed artificial selection experiments in which we selected for either increased or decreased propensity to infect in a facultatively parasitic mite (Macrocheles muscaedomesticae). Here, infectiousness was expressed in terms of mite attachment to a host (Drosophila hydei) and modeled as a threshold trait. Mites responded positively to selection for increased infectivity; realized heritability of infectious behaviour was significantly different from zero and estimated to be 16.6% (±4.4% SE). Further, infection prevalence was monitored for 20 generations post-selection. Selected lines continued to display relatively high levels of infection demonstrating a degree of genetic stability in infectiousness. Our study is the first to provide an estimate of heritability and additive genetic variation for infectious behaviour in a facultative parasite, which suggests natural selection can act upon facultative strategies with important implications for the evolution of parasitism.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-28T01:50:31.557089-05:
      DOI: 10.1111/jeb.13227
       
  • Two different strategies of host manipulation allow parasites to persist
           in intermediate-definitive host systems
    • Authors: Lana J. de Vries; Frank van Langevelde
      Abstract: Trophically-transmitted parasites start their development in an intermediate host, before they finish the development in their definitive host when the definitive host preys on the intermediate host. In intermediate-definitive host systems, two strategies of host manipulation have been evolved: increasing the rate of transmission to the definitive host by increasing the chance that the definitive host will prey on the intermediate host, or increasing the lifespan of the parasite in the intermediate host by decreasing the predation chance when the intermediate host is not yet infectious. As the second strategy is less well studied than the first, it is unknown under what conditions each of these strategies are prevailed and evolved. We analysed the effect of both strategies on the presence of parasites in intermediate-definitive host systems with a structured population model. We show that the parasite can increase the parameter space where it can persist in the intermediate-definitive host system by using one of these two strategies of host manipulation. We found that when the intermediate host or the definitive host have life-history traits that allow the definitive host to reach large population densities, i.e. high reproduction rate of the intermediate host or high conversion efficiency of the definitive host (efficiency at which the uninfected definitive host converts caught intermediate hosts into offspring) respectively, evolving manipulation to decrease the predation chance of the intermediate host will be more beneficial than manipulation to increase the predation chance to enhance transmission. Furthermore, manipulation to decrease the predation chance of the intermediate host results in higher population densities of infected intermediate hosts than manipulation that increases the predation chance to enhance transmission. Our study shows that host manipulation in early stages of the parasite development to decrease predation might be a more frequently evolved way of host manipulation than is currently assumed.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-28T01:50:24.850081-05:
      DOI: 10.1111/jeb.13230
       
  • When do trade‐offs occur' The roles of energy constraints and trait
           flexibility in a bushcricket
    • Authors: F. Barbosa; D. Rebar, M. D. Greenfield
      Abstract: In many animal species, the expression of sexually‐selected traits is negatively correlated with survival traits such as immune function, a relationship termed a ‘trade‐off’. But an alternative in which sexually‐selected traits are positively correlated with survival traits is also widespread. The nature of inter‐trait relationships may be largely determined by overall energy expenditure, energy availability, and trait flexibility, with trade‐offs expected when individuals are subject to energy constraints. We tested this hypothesis in Ephippiger diurnus, a European bushcricket in which males are distinguished by two prominent sexually‐selected traits, acoustic calls and a large spermatophore transferred to the female at mating, and where immune function may be critical in survival. E. diurnus are distributed as small, isolated populations that are differentiated genetically and behaviorally. We analyzed songs, spermatophores, and the immune function in male individuals from eight populations spanning a range of song types. As predicted, we only found trade‐offs in those populations that expended more energy on song and were less flexible in their ability to adjust that expenditure. Ultimately, energy constraints and resulting trade‐offs may limit the evolution of song exaggeration in E. diurnus populations broadcasting long calls comprised of multiple ‘syllables’.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-23T03:20:33.747981-05:
      DOI: 10.1111/jeb.13221
       
  • Robustness of the Approximate Likelihood of the Protracted Speciation
           Model
    • Authors: Camille Anna Simonet; Raphaël Scherrer, Artur Rego-Costa, Rampal S. Etienne
      Abstract: The protracted speciation model presents a realistic and parsimonious explanation for the observed slowdown in lineage accumulation through time, by accounting for the fact that speciation takes time. A method to compute the likelihood for this model given a phylogeny is available and allows estimation of its parameters (rate of initiation of speciation, rate of completion of speciation, and extinction rate) and statistical comparison of this model to other proposed models of diversification. However this likelihood computation method makes an approximation of the protracted speciation model to be mathematically tractable: it sometimes counts fewer species than one would do from a biological perspective. This approximation may have large consequences for likelihood‐based inferences: it may render any conclusions based on this method completely irrelevant. Here we study to what extent this approximation affects parameter estimations. We simulated phylogenies from which we reconstructed the tree of extant species according to the original, biologically meaningful protracted speciation model and according to the approximation. We then compared the resulting parameter estimates. We found that the differences were larger for high values of extinction rates and small values of speciation‐completion rates. Indeed, a long speciation‐completion time and a high extinction rate promote the appearance of cases to which the approximation applies. However, surprisingly, the deviation introduced is largely negligible over the parameter space explored, suggesting that this approximate likelihood can be applied reliably in practice to estimate biologically relevant parameters under the original protracted speciation model.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-22T23:20:33.359628-05:
      DOI: 10.1111/jeb.13233
       
  • Predation drives morphological convergence in the Gambusia panuco species
           group among lotic and lentic habitats
    • Authors: Eric K. Moody; Ma. de Lourdes Lozano-Vilano
      Abstract: Fish morphology is often constrained by a trade‐off between optimizing steady vs. unsteady swimming performance due to opposing effects of caudal peduncle size. Lotic environments tend to select for steady swimming performance, leading to smaller caudal peduncles, while predators tend to select for unsteady swimming performance, leading to larger caudal peduncles. However, it is unclear which aspect of performance should be optimized across heterogeneous flow and predation environments and how this heterogeneity may affect parallel phenotypic evolution. We investigated this question among four Gambusia species in northeastern Mexico, specifically the riverine G. panuco, the spring endemics G. alvarezi and G. hurtadoi, and a fourth species, G. marshi, found in a variety of habitats with varying predation pressure in the Cuatro Ciénegas basin and Río Salado de Nadadores. We employed a geometric morphometric analysis to examine how body shapes of both male and female fish differ among species and habitats and with piscivore presence. We found that high‐predation and low‐predation species diverged morphologically, with G. marshi exhibiting a variable, intermediate body shape. Within G. marshi, body morphology converged in high‐predation environments regardless of flow velocity, and fish from high‐predation sites had larger relative caudal peduncle areas. However, we found that G. marshi from low‐predation environments diverged in morphology between sub‐basins of Cuatro Ciénegas, indicating other differences among these basins that merit further study. Our results suggest that a morphological trade‐off promotes parallel evolution of body shape in fishes colonizing high‐predation environments and that changing predation pressure can strongly impact morphological evolution in these species.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-20T10:30:21.746121-05:
      DOI: 10.1111/jeb.13226
       
  • Experimental Manipulation of Population‐level MHC Diversity Controls
           Pathogen Virulence Evolution in Mus musculus
    • Authors: Douglas H. Cornwall; Jason L. Kubinak, Elisabeth Zachary, Derek L. Stark, Dustan Seipel, Wayne K. Potts
      Abstract: The virulence levels attained by serial passage of pathogens through similar host genotypes are much higher than observed in natural systems, however, it is unknown what keeps natural virulence levels below these empirically demonstrated maximum levels. One hypothesis suggests that host diversity impedes pathogen virulence, because adaptation to one host genotype carries tradeoffs in the ability to replicate and cause disease in other host genotypes. To test this hypothesis, with the simplest level of population diversity within the loci of the major histocompatibility complex (MHC), we serially passaged Friend Virus Complex (FVC) through two rounds, in hosts with either the same MHC genotypes (pure passage) or hosts with different MHC genotypes (alternated passage). Alternated passages showed a significant overall reduction of viral titer (31%) and virulence (54%) when compared to pure passages. Furthermore, a resistant host genotype initially dominated any effects due to MHC diversity, however, when FVC was allowed to adapt to the resistant host genotype, predicted MHC effects emerged, i.e. alternated lines show reduced virulence. These data indicate serial exposure to diverse MHC genotypes is an impediment to pathogen adaptation, suggesting genetic variation at MHC loci is important for limiting virulence in a rapidly evolving pathogen and supports negative frequency‐dependent selection as a force maintaining MHC diversity in host populations.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-20T09:55:27.269836-05:
      DOI: 10.1111/jeb.13225
       
  • Linking genotype to phenotype in a changing ocean: inferring the genomic
           architecture of a blue mussel stress response with genome‐wide
           association
    • Authors: Sarah E. Kingston; Pieter Martino, Marko Melendy, Floyd A. Reed, David B. Carlon
      Abstract: A key component to understanding the evolutionary response to a changing climate is linking underlying genetic variation to phenotypic variation in stress response. Here we use a genome‐wide association approach (GWAS) to understand the genetic architecture of calcification rates under simulated climate stress. We take advantage of the genomic gradient across the blue mussel hybrid zone (Mytilus edulis and Mytilus trossulus) in the Gulf of Maine (GOM) to link genetic variation with variance in calcification rates in response to simulated climate change. Falling calcium carbonate saturation states are predicted to negatively impact many marine organisms that build calcium carbonate shells ‐ like blue mussels. We sampled wild mussels and measured net calcification phenotypes after exposing mussels to a “climate change” common garden, where we raised temperature 3°C, decreased pH by 0.2 units, and limited food supply by filtering out planktonic particles > 5 μm, compared to ambient GOM conditions in the summer. This climate change exposure greatly increased phenotypic variation in net calcification rates compared to ambient conditions. We then used regression models to link the phenotypic variation with over 170,000 single nucleotide polymorphism loci (SNPs) generated by genotype by sequencing to identify genomic locations associated with calcification phenotype, and estimate heritability and architecture of the trait. We identified at least one of potentially 2‐10 genomic regions responsible for 30% of the phenotypic variation in calcification rates that are potential targets of natural selection by climate change. Our simulations suggest a power of 13.7% with our study's average effective sample size of 118 individuals and rare alleles, but a power of > 90% when effective sample size is 900.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-20T08:45:21.151994-05:
      DOI: 10.1111/jeb.13224
       
  • Macroecological patterns of sexual size dimorphism in turtles of the world
    • Authors: Mickey Agha; Joshua R. Ennen, A.Justin Nowakowski, Jeffrey E. Lovich, Sarah C. Sweat, Brian D. Todd
      Abstract: Sexual size dimorphism (SSD) is a well‐documented phenomenon in both plants and animals; however, the ecological and evolutionary mechanisms that drive and maintain SSD patterns across geographic space at regional and global scales are understudied, especially for reptiles. Our goal was to examine geographic variation of turtle SSD and to explore ecological and environmental correlates using phylogenetic comparative methods. We use published body size data on 135 species from nine turtle families to examine how geographic patterns and the evolution of SSD are influenced by habitat specialization, climate (annual mean temperature and annual precipitation) and climate variability, latitude, or a combination of these predictor variables. We also found that geographic variation, magnitude, and direction of turtle SSD are best explained by habitat association, annual temperature variance, and annual precipitation. Use of semi‐aquatic and terrestrial habitats was associated with male‐biased SSD, whereas use of aquatic habitat was associated with female‐biased SSD. Our results also suggest that greater temperature variability is associated with female‐biased SSD. In contrast, wetter climates are associated with male‐biased SSD compared with arid climates that are associated with female‐biased SSD. We also show support for a global latitudinal trend in SSD, with females being larger than males towards the poles, especially in the families Emydidae and Geoemydidae. Estimates of phylogenetic signal for both SSD and habitat type indicate that closely related species occupy similar habitats and exhibit similar direction and magnitude of SSD. These global patterns of SSD may arise from sex‐specific reproductive behavior, fecundity, and sex‐specific responses to environmental factors that differ among habitats and vary systematically across latitude. Thus, this study adds to our current understanding that while SSD can vary dramatically across and within turtle species under phylogenetic constraints, it may be driven, maintained, and exaggerated by habitat type, climate, and geographic location.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-14T14:25:50.426649-05:
      DOI: 10.1111/jeb.13223
       
  • Evolution of larval competitiveness and associated life history traits in
           response to host shifts in a seed beetle
    • Authors: Charles W. Fox; Frank J. Messina
      Abstract: Resource competition is frequently strong among parasites that feed within small discrete resource patches, such as seeds or fruits. The properties of a host can influence the behavioral, morphological, and life history traits of associated parasites, including traits that mediate competition within the host. For seed parasites, host size may be an especially important determinant of competitive ability. Using the seed beetle, Callosobruchus maculatus, we performed replicated, reciprocal host shifts to examine the role of seed size in determining larval competitiveness and associated traits. Populations ancestrally associated with either a small host (mung bean) or a large one (cowpea) were switched to each other's host for 36 generations. Compared to control lines (those remaining on the ancestral host), lines switched from the small host to the large host evolved greater tolerance of co‐occurring larvae within seeds (indicated by an increase in the frequency of small seeds yielding two adults), smaller egg size, and higher fecundity. Each change occurred in the direction predicted by the traits of populations already adapted to cowpea. However, we did not observe the expected decline in adult mass following the shift to the larger host. Moreover, lines switched from the large host (cowpea) to the small one (mung bean) did not evolve the predicted increase in larval competitiveness or egg size, but did exhibit the predicted increase in body mass. Our results thus provide mixed support for the hypothesis that host size determines the evolution of competition‐related traits of seed beetles; evolutionary responses to the two host shifts were consistent among replicate lines but the evolution of larval competition was asymmetric, with larval competitiveness evolving as predicted in one direction of host shift, but not the reverse. Nevertheless, our results indicate that switching hosts is sufficient to produce repeatable and rapid, but asymmetric, changes in the competition strategy and fitness‐related traits of insect populations.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-08T17:30:32.062072-05:
      DOI: 10.1111/jeb.13222
       
  • Effects of prior exposure to antibiotics on bacterial adaptation to phages
    • Authors: Flor I. Arias-Sánchez; Richard C. Allen, Alex R. Hall
      Abstract: Understanding adaptation to complex environments requires information about how exposure to one selection pressure affects adaptation to others. For bacteria, antibiotics and viral parasites (phages) are two of the most common selection pressures and are both relevant for treatment of bacterial infections: increasing antibiotic resistance is generating significant interest in using phages in addition or as an alternative to antibiotics. However, we lack knowledge of how exposure to antibiotics affects bacterial responses to phages. Specifically, it is unclear how the negative effects of antibiotics on bacterial population growth combine with any possible mutagenic effects or physiological responses to influence adaptation to other stressors such as phages, and how this net effect varies with antibiotic concentration. Here, we experimentally addressed the effect of pre‐exposure to a wide range of antibiotic concentrations on bacterial responses to phages. Across 10 antibiotics, we found a strong association between their effects on bacterial population size and subsequent population growth in the presence of phages (which in these conditions indicates phage‐resistance evolution). We detected some evidence of mutagenesis among populations treated with fluoroquinolones, quinolones and β‐lactams at sub‐lethal doses, but these effects were small and not consistent across phage treatments. These results show that, although stressors such as antibiotics can boost adaptation to other stressors at low concentrations, these effects are weak compared to the effect of reduced population growth at inhibitory concentrations, which in our experiments strongly reduced the likelihood of subsequent phage‐resistance evolution.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-08T03:26:17.388203-05:
      DOI: 10.1111/jeb.13220
       
  • Disentangling sex allocation in a viviparous reptile with
           temperature‐dependent sex determination: a multifactorial approach
    • Authors: Jodie Gruber; George D. Cunningham, Geoffrey M. While, Erik Wapstra
      Abstract: Females are predicted to alter sex allocation when ecological, physiological and behavioural variables have different consequences on the fitness of male and female offspring. Traditionally, tests of sex allocation have examined single causative factors, often ignoring possible interactions between multiple factors. Here we used a multi‐factorial approach to examine sex allocation in the viviparous skink, Niveoscincus ocellatus. We integrated a 16‐year observational field study with a manipulative laboratory experiment to explore whether the effects of the maternal thermal environment interact with the resources available to females for reproduction to affect sex allocation decisions. We found strong effects of temperature on sex allocation in the field, with females born in warm conditions and males in cold conditions, however, this was not replicated in the laboratory. In contrast, we found no effect of female resource availability on sex allocation, either independently, or in interaction with temperature. These results corresponded with an overall lack of an effect of resource availability on any of the life history traits that we predicted would mediate the benefits of differential sex allocation in this system, suggesting that selection for sex allocation in response to resource availability may be relatively weak. Combined, these results suggest that temperature may be the predominant factor driving sex allocation in this system.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-01T01:45:40.918291-05:
      DOI: 10.1111/jeb.13219
       
  • Parasites favor intermediate nestling masses and brood sizes in cliff
           swallows
    • Authors: Charles R. Brown; Mary Bomberger Brown
      Abstract: A challenge of life‐history theory is to explain why animal body size does not continue to increase, given various advantages of larger size. In birds, body size of nestlings and the number of nestlings produced (brood size) have occasionally been shown to be constrained by higher predation on larger nestlings and those from larger broods. Parasites also are known to have strong effects on life‐history traits in birds, but whether parasitism can be a driver for stabilizing selection on nestling body size or brood size is unknown. We studied patterns of first‐year survival in cliff swallows (Petrochelidon pyrrhonota) in western Nebraska in relation to brood size and nestling body mass in nests under natural conditions and in those in which hematophagous ectoparasites had been removed by fumigation. Birds from parasitized nests showed highest first‐year survival at the most common, intermediate brood‐size and nestling‐mass categories, but cliff swallows from non‐parasitized nests had highest survival at the heaviest nestling masses and no relationship with brood size. A survival analysis suggested stabilizing selection on brood size and nestling mass in the presence (but not in the absence) of parasites. Parasites apparently favor intermediate offspring size and number in cliff swallows and produce the observed distributions of these traits, although the mechanisms are unclear. Our results emphasize the importance of parasites in life‐history evolution.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-30T11:25:21.509785-05:
      DOI: 10.1111/jeb.13218
       
  • Associations of Stream Geomorphic Conditions and Prevalence of Alternative
           Reproductive Tactics Among Sockeye Salmon Populations
    • Authors: Lukas B. DeFilippo; Daniel E. Schindler, Jackie L. Carter, Timothy E. Walsworth, Timothy J. Cline, Wesley A. Larson, Thomas Buehrens
      Abstract: In many species, males may exhibit alternative life histories to circumvent the costs of intrasexual competition and female courtship. While the evolution and underlying genetic and physiological mechanisms behind alternative reproductive tactics are well studied, there has been less consideration of the ecological factors that regulate their prevalence. Here, we examine six decades of age composition records from thirty‐six populations of sockeye salmon (Oncorhynchus nerka) to quantify associations between spawning habitat characteristics and the prevalence of precocious sneakers known as ‘jacks’. Jack prevalence was independent of neutral genetic structure among stream populations, but varied among habitat types and as a function of continuous geomorphic characteristics. Jacks were more common in streams relative to beaches and rivers, and their prevalence was negatively associated with stream width, depth, elevation, slope and area, but positively related to bank cover. Behavioral observations showed that jacks made greater use of banks, wood, and shallows than guard males, indicating that their reproductive success depends on the availability of such refuges. Our results emphasize the role of the physical habitat in shaping reproductive tactic frequencies among populations, likely through local adaptation in response to variable fitness expectations under different geomorphic conditions.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-30T08:36:23.905324-05:
      DOI: 10.1111/jeb.13217
       
  • Bigger testes increase paternity in a simultaneous hermaphrodite,
           independently of the sperm competition level
    • Authors: N. Vellnow; L. Marie-Orleach, K. S. Zadesenets, L. Schärer
      Abstract: Hermaphroditic animals face the fundamental evolutionary optimization problem of allocating their resources to their male vs. female reproductive function (e.g. testes and sperm vs. ovaries and eggs), and this optimal sex allocation can be affected by both pre‐ and post‐copulatory sexual selection. For example, local sperm competition (LSC) – the competition between related sperm for the fertilization of a partner's ova – occurs in small mating groups and can favour a female‐biased sex allocation, because, under LSC, investment into sperm production is predicted to show diminishing fitness returns. Here, we test whether higher testis investment increases an individual's paternity success under sperm competition, and whether the strength of this effect diminishes when LSC is stronger, as predicted by sex allocation theory. We created two subsets of individuals of the simultaneously hermaphroditic flatworm Macrostomum lignano – by sampling worms from either the highest or lowest quartile of the testis investment distribution – and estimated their paternity success in group sizes of either three (strong LSC) or eight individuals (weak LSC). Specifically, using transgenic focal individuals expressing a dominant green‐fluorescent protein marker, we showed that worms with high testis investment sired 22% more offspring relative to those with low investment, corroborating previous findings in M. lignano and other species. However, the strength of this effect was not significantly modulated by the experienced group size, contrasting theoretical expectations of more strongly diminishing fitness returns under strong LSC. We discuss the possible implications for the evolutionary maintenance of hermaphroditism in M. lignano.
      PubDate: 2017-11-30T06:55:31.58454-05:0
      DOI: 10.1111/jeb.13212
       
  • Phenotypic plasticity in response to environmental heterogeneity
           contributes to fluctuating asymmetry in plants: first empirical evidence
    • Authors: Branka Tucić; Sanja Budečević, Sanja Manitašević Jovanović, Ana Vuleta, Christian Peter Klingenberg
      Abstract: Fluctuating asymmetry (FA) is widely used to quantify developmental instability (DI) in ecological and evolutionary studies. It has long been recognized that FA may not exclusively originate from DI for sessile organisms such as plants, because phenotypic plasticity in response to heterogeneities in the environment might also produce FA. This study provides the first empirical evidence for this hypothesis. We reasoned that solar irradiance, which is greater on the southern side than on the northern side of plants growing in the temperate zone of the northern hemisphere, would cause systematic morphological differences and asymmetry associated with the orientation of plant parts. We used geometric morphometrics to characterize the size and shape of flower parts in Iris pumila grown in a common garden. The size of floral organs was not significantly affected by orientation. Shape and particularly its asymmetric component differed significantly according to orientation for three different floral parts. Orientation accounted for 10.4% of the total shape asymmetry within flowers in the falls, for 11.4% in the standards, and for 2.2% in the style branches. This indicates that phenotypic plasticity in response to a directed environmental factor, most likely solar irradiance, contributes to FA of flowers under natural conditions. That FA partly results from phenotypic plasticity and not just from DI needs to be considered by studies of FA in plants and other sessile organisms.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-28T01:40:33.742315-05:
      DOI: 10.1111/jeb.13207
       
  • Women's attractiveness is linked to expected age at menopause
    • Authors: Jeanne Bovet; Mélissa Barkat-Defradas, Valérie Durand, Charlotte Faurie, Michel Raymond
      Abstract: A great number of studies have shown that features linked to immediate fertility explain a large part of the variance in female attractiveness. This is consistent with an evolutionary perspective, as men are expected to prefer females at the age at which fertility peaks (at least for short‐term relationships) in order to increase their reproductive success. However, for long‐term relationships, a high residual reproductive value (the expected future reproductive output, linked to age at menopause) becomes relevant as well. In that case, young age AND late menopause are expected to be preferred by men. However, the extent to which facial features provide cues to the likely age at menopause has never been investigated so far. Here, we show that expected age at menopause is linked to facial attractiveness of young women. As age at menopause is heritable, we used the mother's age at menopause as a proxy for her daughter's expected age of menopause. We found that men judged faces of women with a later expected age at menopause as more attractive than those of women with an earlier expected age at menopause. This result holds when age, cues of immediate fertility and facial ageing were controlled for. Additionally, we found that the expected age at menopause was not correlated with any of the other variables considered (including immediate fertility cues and facial ageing). Our results show the existence of a new correlate of women's facial attractiveness, expected age at menopause, which is independent from immediate fertility cues and facial ageing.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T10:21:02.027122-05:
      DOI: 10.1111/jeb.13214
       
  • Stronger selective constraint on downstream genes in the oxidative
           phosphorylation pathway of cetaceans
    • Authors: Ran Tian; Shixia Xu, Simin Chai, Daiqing Yin, Harold Zakon, Guang Yang
      Abstract: The oxidative phosphorylation (OXPHOS) pathway is an efficient way to produce energy via adenosine triphosphate (ATP), which is critical for sustaining an energy supply for cetaceans in a hypoxic environment. Several studies have shown that natural selection may shape the evolution of the genes involved in OXPHOS. However, how network architecture drives OXPHOS protein sequence evolution remains poorly explored. Here, we investigated the evolutionary patterns of genes in the OXPHOS pathway across six cetacean genomes within the framework of a functional network. Our results show a negative correlation between the strength of purifying selection and pathway position. This result indicates that downstream genes were subjected to stronger evolutionary constraints than upstream genes, which may be due to the dual function of ATP synthase in the OXPHOS pathway. Additionally, there was a positive correlation between codon usage bias and omega (ω = dN/dS) and a negative correlation with synonymous substitution rate (dS), indicating that the stronger selective constraint on genes (with less biased codon usage) along the OXPHOS pathway is attributable to an increase in the rate of synonymous substitution. Surprisingly, there was no significant correlation between protein‐protein interactions and the evolutionary estimates, implying that highly connected enzymes may not always show greater evolutionary constraints. Compared with that observed for terrestrial mammals, we found that the signature of positive selection detected in five genes (ATP5J, LHPP, PPA1, UQCRC1, UQCRQ) was cetacean‐specific, reflecting the importance of OXPHOS for survival in hypoxic, aquatic environments.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-24T18:06:17.425486-05:
      DOI: 10.1111/jeb.13213
       
  • Testing hypotheses for maternal effects in Daphnia magna
    • Authors: C. M. Coakley; E. Nestoros, T. J. Little
      Abstract: Maternal effects are widely observed, but their adaptive nature remains difficult to describe and interpret. We investigated adaptive maternal effects in a clone of the crustacean Daphnia magna, experimentally varying both maternal age and maternal food and subsequently varying food available to offspring. We had two main predictions: that offspring in a food environment matched to their mothers should fare better than offspring in unmatched environments, and that offspring of older mothers would fare better in low food environments. We detected numerous maternal effects, for example offspring of poorly fed mothers were large, while offspring of older mothers were both large and showed an earlier age at first reproduction. However, these maternal effects did not clearly translate into the predicted differences in reproduction. Thus, our predictions about adaptive maternal effects in response to food variation were not met in this genotype of Daphnia magna.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-22T00:10:33.477487-05:
      DOI: 10.1111/jeb.13206
       
  • A biomechanical analysis of prognathous and orthognathous insect head
           capsules: Evidence for a many to one mapping of ridge strain to head
           strain
    • Abstract: Insect head shapes are remarkably variable but the influences of these changes on biomechanical performance are unclear. Among “basal” winged insects, such as dragonflies, mayflies, earwigs, and stoneflies, some of the most prominent anatomical changes are the general mouthpart orientation, eye size and the connection of the endoskeleton to the head. Here, we assess these variations as well as differing ridge and sclerite configurations using modern engineering methods including multibody dynamics modelling and finite element analysis in order to quantify and compare the influence of anatomical changes on strain in particular head regions and the whole head.We show that a range of peculiar structures such as the genal/subgenal, epistomal, and circumoccular areas are consistently highly loaded in all species, despite drastically differing morphologies in species with forward projecting (prognathous) and downwards projecting (orthognathous) mouthparts. Sensitivity analyses show that the presence of eyes has a negligible influence on head capsule strain if a circumoccular ridge is present. In contrast, the connection of the dorsal endoskeletal arms to the head capsule especially affects overall head loading in species with downward projecting mouthparts. Analysis of the relative strains between species for each head region reveals that concerted changes in head substructures such as the subgenal area, the endoskeleton and the epistomal area lead to a consistent relative loading for the whole head capsule and vulnerable structures such as the eyes in prognathous and orthognathous insects. It appears that biting‐chewing loads are managed by a system of strengthening ridges on the head capsule irrespective of the general mouthpart and head orientation. Concerted changes in ridge and endoskeleton configuration allow for more radical anatomical changes such as the general mouthpart orientation which could be an explanation for the variability of this trait among insects. In an evolutionary context, many to one mapping of strain patterns onto a relatively similar overall head loading indeed could have fostered the dynamic diversification processes seen in insects.This article is protected by copyright. All rights reserved.
       
  • Environmental and genetic control of cold tolerance in the Glanville
           fritillary butterfly
    • Abstract: Thermal tolerance has a major effect on individual fitness and species distributions, and can be determined by genetic variation as well as phenotypic plasticity. We investigate the effects of developmental and adult thermal conditions on cold tolerance, measured as chill coma recovery (CCR) time, during the early and late adult stage in the Glanville fritillary butterfly. We also investigate the genetic basis of cold tolerance by associating CCR variation with polymorphisms in candidate genes that have a known role in insect physiology. Our results demonstrate that a cooler developmental temperature leads to reduced cold tolerance in the early adult stage, whereas cooler conditions during the adult stage lead to increased cold tolerance. This suggests that adult acclimation, but not developmental plasticity, of adult cold tolerance is adaptive. This could be explained by the ecological conditions the Glanville fritillary experiences in the field, where temperature during early summer, but not spring, is predictive of thermal conditions during the butterfly's flight season. In addition, an amino acid polymorphism (Ala‐Glu) in the gene flightin, which has a known function in insect flight and locomotion, was associated with chill coma recovery. These amino acids have distinct biochemical properties and may thus affect protein function and/or structure. To our knowledge, our study is the first to link genetic variation in flightin to cold tolerance, or thermal adaptation in general.This article is protected by copyright. All rights reserved.
       
  • Digging their own macroevolutionary grave: Fossoriality as an evolutionary
           dead‐end in snakes
    • Abstract: The tree of life is highly asymmetrical in its clade wise species richness and this has often been attributed to variation in diversification rates either across time or lineages. Variations across lineages are usually associated with traits that increase lineage diversification. Certain traits can also hinder diversification by increasing extinction and such traits are called evolutionary dead‐ends. Ecological specialization has usually been considered as an evolutionary dead‐end. However, recent analyses of specializations along single axes have provided mixed support for this model. Here, we test if fossoriality, a trait that forces specialization at multiple axes, acts as an evolutionary dead‐end in squamates (lizards and snakes) using recently developed phylogenetic comparative methods. We show that fossoriality is an evolutionary dead‐end in snakes but not in lizards. Fossorial snakes exhibit reduced speciation and increased extinction compared to non‐fossorial snakes. Our analysis also indicates that transition rates from fossoriality to non‐fossoriality in snakes are significantly lower than transition rates from non‐fossoriality to fossoriality. Overall our results suggest that broad scale ecological interactions that lead to specialization at multiple axes limit diversification.This article is protected by copyright. All rights reserved.
       
  • Fitness variation among host species and the paradox of ineffective
           rhizobia
    • Abstract: Legumes can preferentially select beneficial rhizobial symbionts and sanction ineffective strains that fail to fix nitrogen. Yet paradoxically, rhizobial populations vary from highly beneficial to ineffective in natural and agricultural soils. Classic models of symbiosis focus on the single dimension of symbiont cost‐benefit to sympatric hosts, but fail to explain the widespread persistence of ineffective rhizobia. Here we test a novel framework predicting that spatio‐temporal and community dynamics can maintain ineffective strains in rhizobial populations. We used clonal and multistrain inoculations and quantitative culturing to investigate the relative fitness of four focal Bradyrhizobium strains varying from effective to ineffective on Acmispon strigosus. We found that an ineffective Bradyrhizobium strain can be sanctioned by its native A. strigosus host across the host's range, forming fewer and smaller nodules compared to beneficial strains. But the same ineffective Bradyrhizobium strain exhibits a nearly opposite pattern on the broadly sympatric host A. wrangelianus, forming large nodules in both clonal and multistrain inoculations. These data suggest that community‐level effects could favor the persistence of ineffective rhizobia and contribute to variation in symbiotic nitrogen fixation.This article is protected by copyright. All rights reserved.
       
  • Laboratory maintenance does not alter ecological and physiological
           patterns among species: a Drosophila case study
    • Abstract: Large comparative studies in animal ecology, physiology and evolution often use animals reared in the laboratory for many generations; however, the relevance of these studies hinges on the assumption that laboratory populations are still representative for their wild living conspecifics. In this study, we investigate whether laboratory‐maintained and freshly collected animal populations are fundamentally different and whether data from laboratory‐maintained animals are valid to use in large comparative investigations of ecological and physiological patterns. Here, we obtained nine species of Drosophila with paired populations of laboratory‐maintained and freshly collected flies. These species, representing a range of ecotypes, were assayed for four stress‐tolerance, two body‐size traits and six life‐history traits. For all of these traits, we observed small differences in species‐specific comparisons between field and laboratory populations; however, these differences were unsystematic and laboratory maintenance did not eclipse fundamental species characteristics. To investigate whether laboratory maintenance influence the general patterns in comparative studies, we correlated stress tolerance and life‐history traits with environmental traits for the laboratory‐maintained and freshly collected populations. Based on this analysis, we found that the comparative physiological and ecological trait correlations are similar irrespective of provenience. This finding is important for comparative biology in general because it validates comparative meta‐analyses based on laboratory‐maintained populations.
       
  • Issue Information
    •  
  • Low levels of hybridization in two species of African driver ants
    • Abstract: Hybridization in ants can have consequences different from those observed in most other species, with many of the potential deleterious effects being mitigated due to haplodiploidy and eusociality. In some species where colonies are either headed by multiple queens or single queens that mate with many males, hybridization is associated with genetic caste determination, where hybrids develop into workers and purebred individuals develop into queens. A previous study suggested that hybridization occurs between two Dorylus army ant species with multiply mated queens. However, the extent and exact pattern of hybridization has remained unclear, and its possible effect on caste determination has not been investigated. In this study we aimed to determine the extent and direction of hybridization by measuring how frequently hybrids occur in colonies of both species, and to investigate the possibility of genetic caste determination. We show that hybridization is bidirectional and occurs at equal rates in both species. Hybrid workers make up only 1‐2% of the population, and successful interspecific matings represent approximately 2% of all matings in both species. This shows that, while interspecific matings that give rise to worker offspring occur regularly, they are much rarer than intraspecific mating. Finally, we find no evidence of an association between hybridization and genetic caste determination in this population. This means that genetic caste determination is not a necessary outcome of hybridization in ants, even in species where queens mate with multiple males.This article is protected by copyright. All rights reserved.
       
  • Fluctuating selection and its (elusive) evolutionary consequences in a
           wild rodent population
    • Abstract: Temporal uctuations in the strength and direction of selection are often proposed as a mechanism that slows down evolution, both over geological and con‐temporary time‐scales. Both the prevalence of fluctuating selection and its relevance for evolutionary dynamics remain poorly understood however, especially on contem‐porary time scales: Unbiased empirical estimates of variation in selection are scarce, and the question of how much of the variation in selection translates into variation in genetic change has largely been ignored. Using long‐term individual‐based data for a wild rodent population, we quantify the magnitude of fluctuating selection on body size. Subsequently, we estimate the evolutionary dynamics of size, and test for a link between fluctuating selection and evolution. We show that, over the past 11 years, phenotypic selection on body size has fluctuated significantly. However, the strength and direction of genetic change have remained largely constant over the study period, i.e., the rate of genetic change was similar in years where total selection favored heavier versus lighter individuals. This result suggests that over shorter timescales, fluctuating selection does not necessarily translate into fluctuating evolution. Im‐portantly however, individual‐based simulations show that a precise estimation of the correlation between fluctuating selection and fluctuating evolution requires sub‐stantially more data. We identify new challenges in measuring the coupling between selection and evolution, and provide methods and guidelines to overcome them.This article is protected by copyright. All rights reserved.
       
  • Genetic variation in the shape of cold survival curves in a single fly
           population suggests potential for selection from climate variability
    • Abstract: Temperature variation is one of the primary challenges facing ectotherms, and the ability to tolerate a range of thermal environments is critical for setting current and future species distributions. Low temperature is particularly challenging for ectotherms because winter conditions have strong latitudinal and temporal variation. Lower lethal temperature (LLT) is a common metric of cold tolerance used in studies of local adaptation and plasticity. Comparisons of LLT across groups typically assume parallel S‐shaped survival curves, but genetic variation in the shape of survival vs. temperature curves has not been assessed. Here, we measured the ability of 36 lines of the Drosophila Genetic Reference Panel (DGRP) to survive a 1 h cold shock at seven ecologically relevant low temperatures (‐1 to ‐7°C) to create a high resolution response curve for each genotype. We observed surprising variation both in the magnitude of survival and the shapes of the response curves, with the curves clustering into four distinct shapes. To encompass variation in the shapes of these survival curves, we developed a new cold tolerance metric, Cumulative Cold Tolerance (CCT). By comparing our survival data with climatological data, we propose that variation in the shapes of cold survival curves arose from weak selection pressure to survive intermediate subzero temperatures in this mid‐latitude population of flies. Using publicly available genome sequence and transcript expression data for these lines, we identified several candidate genes associated with CCT, and using transgenic RNAi we confirmed a functional role for many of these genes.This article is protected by copyright. All rights reserved.
       
  • Male‐male aggression is unlikely to stabilize a poison frog
           polymorphism
    • Abstract: Phenotypic polymorphism is common in animals, and the maintenance of multiple phenotypes in a population requires forces that act against homogenizing drift and selection. Male‐male competition can contribute to the stability of a polymorphism when males compete primarily with males of the same phenotype. In and around a contact zone between red and blue lineages of the poison frog Oophaga pumilio, we used simulated territorial intrusions to test the non‐exclusive predictions that males would direct more aggression toward males of (i) their own phenotype and/or (ii) the phenotype that is most common in their population. Males in the monomorphic red and blue populations that flank the contact zone were more aggressive toward simulated intruders that matched the local coloration. However, males in the two polymorphic populations biased aggression toward neither their own color nor the color most common in their population. In sympatry, the rarer color morph gains no advantage via reduced male‐male aggression from territorial males in these O. pumilio populations, and so male aggression seems unlikely to stabilize color polymorphism on its own. More broadly, these results suggest that the potential for divergent male aggression biases to maintain phenotypic diversity depends on the mechanism(s) that generate the biases and the degree to which these mechanisms persist in sympatry.This article is protected by copyright. All rights reserved.
       
  • Dynamic sex chromosomes in Old World chameleons (Squamata: Chamaeleonidae)
    • Abstract: Much of our current state of knowledge concerning sex chromosome evolution is based on a handful of ‘exceptional’ taxa with heteromorphic sex chromosomes. However, classifying the sex chromosome systems of additional species lacking easily identifiable, heteromorphic sex chromosomes is indispensible if we wish to fully understand the genesis, degeneration, and turnover of vertebrate sex chromosomes. Squamate reptiles (lizards and snakes) are a potential model clade for studying sex chromosome evolution as they exhibit a suite of sex determining modes yet most species lack heteromorphic sex chromosomes. Only 3 (out of 203) chameleon species have identified sex chromosome systems (all with female heterogamety, ZZ/ZW). This study uses a recently developed method to identify sex‐specific genetic markers from restriction site‐associated DNA sequence (RADseq) data, which enables the identification of sex chromosome systems in species lacking heteromorphic sex chromosomes. We used RADseq and subsequent PCR validation to identify an XX/XY sex chromosome system in the veiled chameleon (Chamaeleo calyptratus), revealing a novel transition in sex chromosome systems within the Chamaeleonidae. The sex‐specific genetic markers identified here will be essential in research focused on sex‐specific, comparative, functional and developmental evolutionary questions, further promoting C. calyptratus’ utility as an emerging model organism.This article is protected by copyright. All rights reserved.
       
  • Differential visual ornamentation between brood‐parasitic and
           parental cuckoos
    • Abstract: The evolution of brood parasitism should affect adult phenotypic traits due to sexual selection as well as the parasite‐host interactions, though it is rarely focused on. Sexual selection theory predicts extravagant secondary sexual characteristics in brood parasites while immature‐like modest sexual characteristics in parental species. This is because juvenile‐like immature traits can attract mates by exploiting parental care for young (i.e. attraction to young), and because the good parent process, which favors traits that signal parental care ability, would constrain the evolution of costly secondary sexual characteristics due to evolutionary tradeoffs between parental investment and sexually selected traits. Using a phylogenetic comparative approach, we studied plumage and bare‐part characteristics of adults in relation to brood parasitism in cuckoos (family Cuculidae), in which brood parasitism together with loss of parental care has evolved three times. As predicted, we found that non‐parasitic cuckoos had plumage more similar to the juveniles than did brood parasitic cuckoos. Furthermore, non‐parasitic cuckoos had a higher probability of having additional bare skin, i.e. a seemingly less‐costly, hatchling‐like trait, than did brood parasitic cuckoos. This finding further supports the link between parental care and sexual selection, although the influence of a parasite‐host interaction cannot be excluded. The analysis of evolutionary pathways suggested inter‐dependent evolution of additional bare skin and brood parasitism. Brood parasitism together with the loss of parental care may facilitate the maintenance of a modest phenotype similar to the young, and vice versa in some cases.This article is protected by copyright. All rights reserved.
       
  • Casual movement speed but not maximal locomotor capacity predicts mate
           searching success
    • Abstract: Maximal locomotor performance is often used as a proxy for fitness. Maximal speed may be important under high‐threat conditions, such as during predator escape. However, animals do not always move at a speed that reflects their maximal physiological capacities when undisturbed. The physiological factors that determine the movement speed chosen by animals, such as minimisation of energy use, may be independent from maximal performance. As a result, the casual speed at which individuals move when undisturbed in a given context may better represent an individual's motivation to move. The casual speed may therefore be a better predictor of fitness in natural contexts than maximal performance capacity. We tested the hypothesis that casual movement speed rather than maximal speed predicts fitness in the golden orb‐web spider, Nephila plumipes. We measured fitness in two separate contexts, mate searching success and the positional rank near a female. We show that casual, but not maximal locomotor speed predicted both aspects of fitness. Casual speed was linearly related to maximal speed, indicating that casual speed is determined by physiological optimisation. Size and metabolic scope were not related to either maximal or chosen speeds, indicating that the supply of ATP does not limit locomotor performance in this species. Overall, our results demonstrate that locomotor performance is related to fitness, but suggest that different types of performance and not necessarily maximal physiological capacities are most relevant for particular ecologically relevant tasks.This article is protected by copyright. All rights reserved.
       
 
 
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