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Abstract: Consistent inter-individual differences in behaviour are thought to be related to consistency in social network position. There is also evidence that network structures can show predictable temporal dynamics, suggesting that consistency in social network position across time does not preclude some form of plasticity in response to environmental variation. To better consider variation in network position and plasticity simultaneously, we investigate the extension of the behavioural reaction norm (BRN) to dynamic social networks. Our aim is to estimate both an individual’s position and plasticity within a network across an environmental gradient (i.e. to generate a network reaction norm (NRN)). We show that it is possible to account for the non-independence of network measures using covariance structures but that, in cases where the independent variables are group-level environmental measures, a standard multilevel model is sufficient. We therefore outline when a standard multilevel model is appropriate for NRNs and highlight the benefits and limitations to this approach. As an illustrative example, we used an NRN approach on 7 years of behavioural data on chacma baboons to quantify both the consistency with which individuals maintained social behaviour (node strength) and central positions (eigenvector centrality) within the social network. We found evidence for individual plasticity for node strength but little evidence for eigenvector centrality. Conversely, we found evidence of consistent individual differences in eigenvector centrality but not strength. These results suggest that individual node strengths are influenced by environmental changes, but the social structure of the group remains remarkably stable nevertheless. We suggest that expanding from measures of repeatability in social networks to network reaction norms will provide a more contextually nuanced way to investigate social phenotypes, leading to a better understanding of the development and maintenance of social structures in changing environments. Significance statement An individual’s position within a social network can have consequences for its fitness, resulting in great interest into how individuals develop and maintain particular network positions. Here, we extend the notion of behavioural reaction norms to include social network data. Given the non-independence of network data, however, the application of BRNs is not straightforward. Consequently, we have developed an alternative statistical extension that uses covariance structures to account for non-independence. Although we find that under one specific set of assumptions, it is possible to apply the standard BRN to network data. Applying this approach to data from a social group of chacma baboons, we found individual social behaviours shifted in response to environmental variables, yet the social structure of the group remained remarkably stable. PubDate: 2023-03-15
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Abstract: Animals capable of rapid (i.e., physiological) body color change may use color to respond quickly to changing social or physical environments. Because males and females often differ in their environments, the sexes may use changes in body color differently, reflecting sexual dimorphism in ecological, behavioral, or morphological traits. Green anole lizards, Anolis carolinensis, frequently switch their dorsal body color between bright green and dark brown, a change that requires only seconds, but little is known regarding sexual dimorphism in their color change. We tested three hypotheses for the function of body color (thermoregulation, camouflage via background-matching, and social communication) to determine the ecological role(s) of physiological color change in anoles. First, we examined instantaneous body color to determine relationships between body color and body temperature, substrate color and type, and whether these varied between the sexes. Next, we examined the association between color change and behavioral displays. Altogether, we found that males were more likely to be green than females, and larger lizards were more often green than smaller ones, but there was no evidence that anole body color was associated with body temperature or background color during the summer breeding season. Instead, our results show that although the sexes change their color at approximately the same rates, males changed color more frequently during social displays, while females remained green when displaying. In sum, social communication appears to be the primary function of anole color change, although the functions of body color may differ in the nonbreeding season. Significance statement Many animals can change their body color in response to their environments, and in many species, males and females experience different environments. In this study, we examined whether the sexes of green anole lizards use the ability to rapidly change their body color between green and brown for different functions. We found that, when a lizard was first sighted, its body color did not appear to match its background color in either sex (suggesting that color change does not contribute to avoidance of detection by potential predators), and body color was not associated with temperature for either sex (i.e., color was unlikely to influence body temperature). Yet, males changed color more often when performing social displays to other lizards, while females remained green during social displays. Thus, rapid color change plays an important role in social communication in both sexes, highlighting how males and females may use the same behavior to convey different messages. PubDate: 2023-03-11
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Abstract: Neighbour-stranger discrimination plays a crucial role in territorial animals and is expressed as either the dear enemy phenomenon or the nasty neighbour effect. Previous evidence showed that the size of intruding groups affected the expression of neighbour-stranger discrimination. However, few studies have compared neighbour-stranger discrimination between individual-level and group-level intrusions in conspecifics. In this study, we used playback experiments to investigate whether the western black crested gibbon (Nomascus concolor) discriminates intruding neighbours from strangers via vocal signal and explore the effect of intruder type (individual versus group) on neighbour-stranger discrimination. We found that the focal gibbons responded more intensively to neighbours versus strange intruders with shorter movement delay time and longer counter-singing duration. Furthermore, the intruder type had a pronounced influence on subjects’ response intensity. The focal gibbons reacted with faster movement velocity and shorter locomotor duration to individual intruders than to group intruders. Our results provide the first empirical evidence for the nasty neighbour effect in Hylobatidae. These results also suggest that group intruders are not necessarily more threatening than individual intruders, and that the perceived threat posed by intruders is affected by ecological factors and social contexts. Significance statement Neighbour-stranger discrimination (NSD) is widespread in territorial animals. However, few studies have compared the differences in NSD between individual-level and group-level intrusions in conspecifics. We studied the effect of intruder type (individual versus group) on NSD dynamics using acoustic playback experiments in free-ranging western black crested gibbons (Nomascus concolor). We provide the first experimental evidence for the nasty neighbour effect in Hylobatidae. Our findings support the threat level hypothesis and suggest that the threat level of the intruder depends on ecological factors and social contexts. We also suggest that group intruders do not necessarily have a higher threat level than individual intruders, at least among the western black crested gibbons. PubDate: 2023-03-09
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Abstract: Nesting behavior is an important part of reproduction that affects maternal fitness. Females of most oviparous species choose microhabitats for nesting that have positive effects on embryo development. However, choosing suitable nest microhabitats could be challenging in environments that fluctuate unpredictably. In many reptiles, females avoid nesting in dry microhabitats because eggs rapidly desiccate. In nature, however, microhabitats with suitable hydric conditions at the time of oviposition may eventually become lethally dry during incubation. We designed an experiment to test whether female lizards (Anolis sagrei) avoid nesting in locations with unpredictable fluctuations in substrate moisture and choose sites with stable moist conditions. We provided captive lizards three nest conditions to choose among: 1) substrate that predictably alternated between suitable and lethal moisture conditions, 2) substrate that fluctuated unpredictably between suitable and lethal conditions, and 3) substrate with moisture levels that remained constant. For the constant choice, some females could choose moist substrate (which is suitable for embryos), and others could choose dry substrate (which rapidly desiccates eggs). Females always nested in substrates that were moist at the time of oviposition, regardless of the level of predictability. Additionally, while constantly dry substrate was avoided, females did not distinguish between predictable and unpredictable options, both of which resulted in 100% egg mortality. These results suggest that nest site choice is based on immediate environmental cues, rather than the level of predictability of future conditions of nest sites, which in turn can have negative consequences when environments fluctuate between suitable and unsuitable conditions. Significance statement Fluctuating environments pose challenges to females when seeking suitable locations for laying eggs. Female brown anole lizards choose moist nest conditions that facilitate embryo development. However, because moisture levels of nest substrate can unpredictably change, females that avoid nesting in microhabitats with unpredictable moisture fluctuations may have increased fitness. We tested the ability of females to select sites based on moisture predictability by providing them with options where substrate moisture remained stable, fluctuated predictably, and fluctuated unpredictably. Females did not discriminate among stable and fluctuating substrates. Rather, they always nested in moist substrates that were present at the time of oviposition, even if their nest site eventually fluctuated towards lethally dry conditions. Our results show that extreme fluctuations lead to poor choices of nest sites, which is problematic under global change where fluctuations in ambient conditions are expected to increase. PubDate: 2023-03-08
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Abstract: In species where conflict is costly, individuals adopt alternative movement tactics to minimise the risk of competitive interactions. Dominant males often maintain defined territories, while less competitive males may be forced to adopt alternative tactics to maximise fitness and reduce conflict. However, the extent to which males switch tactics according to current social or physiological status is poorly understood. Using implanted acoustic tags and a fixed array of tracking receivers, we investigated how the behaviour of 78 male estuarine crocodiles (Crocodylus porosus) shifted over an 11-year period in relation to ontogeny, body condition, and the extent of physical injuries. We discovered that male crocodiles sorted into three common movement classes, with 51% of males maintaining the same movement class across consecutive years (max = 9 years). Males > 4 m in total length maintained confined territories both within and across years and had the greatest extent of injuries and the highest condition score, indicative of territory holders. In contrast, smaller males sorted into high movement roamer or low movement site-philopatric tactics, where the tactic an individual adopted was less stable between years and did not correlate with condition or external injuries. Our study reveals the socio-biological mechanisms by which estuarine crocodiles coexist within a restricted habitat. Significance statement Identifying individual-level differences in movement helps us predict which individuals are more likely to be involved in human-wildlife interactions. However, studying long-term shifts in movement is challenging, as large datasets of co-occurring individuals tracked in their natural environment over multiple years are required. We tracked a population of 78 male estuarine crocodiles (1030–4687 mm total length) in a shared environment over 11 years and assessed how eight movement traits were linked to body size and physical condition. At the population level, males sorted into different movement tactics according to ontogeny, with large territorial males having better body condition yet a greater incidence of injury. However, 49% of males showed variability across years, suggesting that tactics were conditional relative to environmental variability and a male’s own status. Our study provides insights into the mechanisms and costs of movement tactics in wild crocodile populations. PubDate: 2023-03-04
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Abstract: Numerous studies have examined the correlation between offspring quantity and quality, and many have found that the most common brood size is often smaller than broods with the highest offspring quality or production. However, the reasons why these small broods with lower offspring quality are produced are still poorly explained. Using data spanning 29 years, we investigated the effects of brood size on nestlings’ body mass and the lifetime fitness for those offspring as adults (as proxies of offspring quality) in the Crested Ibis (Nipponia nippon). We also examined the temporal variation of brood size. We found that overall offspring quality increases with brood size and that individuals from broods of three had the highest quality, as quantified by larger body mass, higher adult survival, and lifetime reproductive success. Furthermore, the brood size of an individual pair significantly varied across years, and the proportion of broods containing two offspring increased while broods of three decreased after 2000 when the population dispersed to low-quality habitat. These findings indicate that spatiotemporal variation in resources may impact variation in brood size and subsequent fitness consequences, and that small broods are more common in resource-poor years or low-quality habitats. In contrast, parents with access to high-quality resources produce larger broods of nestlings that achieve higher body mass and subsequently experience higher adult survival and lifetime fitness. This study highlights how variation in life history traits can be influenced by resource condition and provides an insight into particular habitats that need conservation for Crested Ibis. Significance statement Although life history theory predicts a trade-off between offspring quantity and quality, and that fewer, high-quality offspring are expected to be more common to prolong one’s own survival prospect in long-lived species, birds, mammals, and humans often show a positive correlation for these traits. Why do parents produce small broods with lower offspring quality' Here, we found that offspring quality—such as nestlings’ body mass, survival, and the lifetime reproductive success of offspring as adults—increased overall with brood size, up to broods of three of Crested Ibis. Brood size varied across years; in particular, pairs appear to produce smaller broods of nestlings that have lower body mass and lifetime fitness in resource-poor years or lower-quality habitats. This long-term study helps to advance our understanding of the fitness consequences and ecological mechanisms that impact offspring quantity and quality in long-lived animals. PubDate: 2023-03-02
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Abstract: Conspecific cues often provide social information on habitat quality that is considered when deciding to settle at a specific site. The type of sensory cues useful for this will depend on the environment. For amphisbaenians, reptiles adapted to an underground life with highly reduced sight, chemoreception is especially useful to recognize conspecifics. Here, we first analyzed the lipophilic compounds from precloacal gland secretions of the amphisbaenian Blanus cinereus, showing that there were sex- and size-related variations in the proportions of the three major compounds. Then, we tested in the laboratory whether there was an underground site selection based on conspecific chemical cues (substrate scent marks) in two different contexts. In loose substrates, both male and female amphisbaenians tended to choose first the scent-marked substrates more often when the individual that produced the scent, independently of its sex, was relatively larger than the focal individual. In contrast, inside semi-permanent galleries, males, but not females, chose the scent-marked gallery more often when the scent donor, independently of its sex, was relatively smaller. These results suggest that the proportions of compounds in scent marks may allow amphisbaenians to estimate the body size of the producer and that this information affects their site selection decisions. However, the different substrate-dependent responses suggest a different meaning and usefulness of scent marks depending on the context. Significance statement The presence of your conspecific in a site may indicate that this is a “quality” site to live in. If you are blind and live underground, smell is one of the best options for detecting conspecifics and assessing how good are your surroundings. Here, we test whether a blind amphisbaenian reptile that spends its life buried in sandy substrates uses conspecific chemical stimuli to choose where to settle. We found that this decision is influenced by the microhabitat type, sex, and the size difference between the individual that sniffs and the producer of the scent. Amphisbaenians seem to detect and assess conspecific traits based on the differences in compounds in their odors. Therefore, using conspecific scent to assess habitat quality may help fossorial animals to live underground. PubDate: 2023-02-24
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Abstract: Understanding the main factors driving the evolution of mating systems is a major goal of behavioral ecology. In ungulates, the transition from forests to open habitats and the accompanying clustered spatial distribution of females are thought to have promoted an evolutionary shift from monogamy to polygyny. However, no field-based studies to date have tested in the field whether such changes in ecological conditions promote a shift from monogamy to polygyny. We investigated mating systems of the Japanese serow, which is an evolutionarily ancestral and solitary species among caprids, living in the area with subalpine forest and alpine meadows over 7 years. We evaluated the effects of habitat characteristics on mating systems using within population comparisons. In this site, females form solitary territories in subalpine forests but group territories in alpine meadows. Males defended most of their home ranges as territories, and both social monogamy (29.6%; one male with one female) and polygyny (70.4%; one male with 2–5 females) were observed. Males in alpine meadows formed mating units with more females, whereas males in subalpine forests formed mating units with single females. We show that open habitats promote the transition from social monogamy to polygyny and a higher degree of social polygyny. Our findings suggest that the main factor affecting the mating system is the spatial dispersion of females (solitary territory or group territory), which depends on habitat structure (closed or open). Significance statement The Japanese serow is an ungulate that mainly inhabits forests and is assumed to possess the ancestral social systems for caprids, such as solitary and monogamous with territory. We found that open habitats, such as alpine meadows, promote the transition from monogamous to polygynous territory in the Japanese serow. In the study site, alpine meadows promote the transition from solitary territory to group territory of females. Thus, our results suggest that the main factor affecting the mating system is the spatial dispersion of females (solitary or group territory), which depends on habitat structure (subalpine forests or alpine meadows). Our findings provide evidence for a social evolutionary pattern in caprids, whereby the spread of forest-dwelling ancestors into open mountains promote evolution from social monogamy to polygyny. PubDate: 2023-02-23
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Abstract: Morphological and behavioural differences between the sexes often make one sex of a species more vulnerable to predation than the other. Onomarchus uninotatus, a canopy katydid, forms an important component of the diet of the insectivorous bat Megaderma spasma. Examination of culled prey remains in M. spasma roosts suggested that female O. uninotatus may be at higher risk of predation than males. As in many insects, the females of O. uninotatus are larger and heavier and might be easier for predators to detect and capture and/or preferred for their higher nutritive value. We tested these hypotheses by conducting behavioural experiments in an outdoor enclosure, examining the bat predator approach to free-flying O. uninotatus and their capture success. We found that the flying female and male katydids were equally likely to be approached, but males were captured more by M. spasma, with a weak effect. This indicates that females may have a better escape strategy after being approached. We then asked whether females were at higher risk of predation because they moved more often or for longer durations across trees than males, in search of mates and egg-laying sites. We investigated landscape-level movement patterns of O. uninotatus females and males using VHF radio-telemetry. Females had 1.6 times higher frequency of movement and 1.8 times greater displacement across trees than males. This difference may be ecologically important and cause higher bat predation risk on females. Significance statement Studying the factors affecting sex-specific levels of predation risk is crucial to better understand the natural selection and the hypothesised causes and consequences of sexual dimorphism. Katydid females, including Onomarchus uninotatus, are at a higher risk of bat predation than males, and flying is one of the most risky prey behaviours. Onomarchus uninotatus females are larger than males, which could make them easier to detect and capture. Our experiments involving free-flying bats and katydids showed, however, that bat approaches are similar for flying females and males. Females might be better at escaping bat captures after being approached. Katydid males typically broadcast acoustic signals, and females move towards these signals, potentially placing females at higher predation risk. Radio-telemetry studies revealed that on average, females were likely to move more often with greater displacements across trees, which may place them at higher risk of predation. PubDate: 2023-02-20
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Abstract: Given that organismal performance (e.g., sprint speed, endurance) sets the “envelope” within which behaviour is possible, there are likely many co-adaptations between suites of performance and behavioural traits. On one hand, performance might “compensate” for behaviours that increase predation risk, such that bold and active individuals should be able to sprint faster and/or for longer. On the other hand, performance could be “co-specialised” with behaviour to reduce overall predation risk, such that shy and inactive individuals should be able to sprint faster and for longer. Here, we repeatedly measured multiple aspects of locomotor performance (sprint speed and swimming performance) and behaviour (exploration, voluntary wheel running, and home-cage activity) in 51 female white-footed mice (Peromyscus leucopus). All six among-individual correlations between the behavioural and performance traits were negative. Sprint speed was significantly negatively correlated with both voluntary wheel running and home-cage activity, such that faster sprinters travelled less distance on the wheel and in their home cage. By contrast, the within-individual correlation between sprint speed and voluntary wheel running was positive and significant, providing another striking example of the importance of partitioning the correlations among labile traits. Our results suggest that the performance-behaviour link is not caused by methodological biases due to measurements in stressful situations (e.g., escape from human threat, exposure to a novel environment). Our study, combined with others on performance and behaviour, provide unequivocal support for co-specialisation in rodents, but also raises the interesting possibility that plastic within-individual changes in performance and behaviour follow a compensatory relationship. Significance statement To minimise predation risk, animals can behave in such a way to avoid exposure to predators and/or rely on their locomotor performance (to outrun predators). On one hand, bold individuals may compensate for higher predation risk by having greater locomotor performance whereas, on the other hand, behaviour and performance may be co-specialised, in which case shy individuals would have greater locomotor performance. Here we found that, on average, individuals that are more active have lower maximal sprint speed, but on a given day, individuals that are more active than usual display faster sprint speed (relative to their own individual average). Hence, performance and behaviour appear “co-specialised” at the among-individual level, but plastic changes in performance and behaviour follow a compensatory relationship, which highlights the importance of (co)variance partitioning to properly separate relationships at the among- and within-individual levels. PubDate: 2023-02-17
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Abstract: Sexual selection is a major force shaping morphological and behavioral diversity. Existing theory focuses on courtship display traits such as morphological ornaments whose costs and benefits are assumed be to fixed across individuals’ lifetimes. In contrast, empirically observed displays are often inherently dynamic, as vividly illustrated by the acrobatic dances, loud vocalizations, and vigorous motor displays involved in courtship behavior across a broad range of taxa. One empirically observed form of display flexibility occurs when signalers adjust their courtship investment based on the number of rival signalers. The predictions of established sexual selection theory cannot readily be extended to such displays because display expression varies between courtship events, such that any given display may not reliably reflect signaler quality. We thus lack an understanding of how dynamic displays coevolve with sexual preferences and how signalers should tactically adjust their display investment across multiple courtship opportunities. To address these questions, we extended an established model of the coevolution of a female sexual preference and a male display trait to allow for flexible, dynamic displays. We find that such a display can coevolve with a sexual preference away from their naturally selected optima, though display intensity is a weaker signal of male quality than for non-flexible displays. Furthermore, we find that males evolve to decrease their display investment when displaying alongside more rivals. This research represents a first step towards generalizing the findings of sexual selection theory to account for the ubiquitous dynamism of animal courtship. Significance statement Animal courtship displays are typically costly for survival: songs attract predators; dances are exhausting; extravagant plumage is cumbersome. Because of the trade-off between mating benefits and survival costs, displaying individuals often vary their displays across time, courting more intensely when the potential benefit is higher or the cost is lower. Despite the ubiquity of such adjustment in nature, existing theory cannot account for how this flexibility might affect the coevolution of displays with sexual preferences, nor for the patterns of tactical display adjustment that might result, because those models treat displays as static, with fixed costs and benefits. Generalizing a well-studied model of sexual selection, we find that a static display and a flexible display can evolve under similar conditions. Our model predicts that courtship should be less intense when more competitors are present. PubDate: 2023-02-16
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Abstract: Eusocial insect colonies act as a superorganism, which can improve their ability to buffer the negative impact of some anthropogenic stressors. However, this buffering effect can be affected by anthropogenic factors that reduce their colony size. A reduction in colony size is known to negatively affect several parameters like brood maintenance or thermoregulation, but the effects on behaviour and cognition have been largely overlooked. It remains unclear how a sudden change in group size, such as that which might be caused by anthropogenic stressors, affects individual behaviour within a colony. In this study, the bumblebee Bombus terrestris was used to study the effect of social group size on behaviour by comparing the associative learning capabilities of individuals from colonies that were unmanipulated, reduced to a normal size (a colony of 100 workers) or reduced to a critically low but functional size (a colony of 20 workers). The results demonstrated that workers from the different treatments performed equally well in associative learning tasks, which also included no significant differences in the learning capacity of workers that had fully developed after the colony size manipulation. Furthermore, we found that the size of workers had no impact on associative learning ability. The learning abilities of bumblebee workers were thus resilient to the colony reduction they encountered. Our study is a first step towards understanding how eusocial insect cognition can be impacted by drastic reductions in colony size. Significance statement While anthropogenic stressors can reduce the colony size of eusocial insects, the impact of this reduction is poorly studied, particularly among bumblebees. We hypothesised that colony size reduction would affect the cognitive capacity of worker bumblebees as a result of fewer social interactions or potential undernourishment. Using differential conditioning, we showed that drastic reductions in colony size have no effect on the associative learning capabilities of the bumblebee Bombus terrestris and that this was the same for individuals that were tested just after the colony reduction and individuals that fully developed under the colony size reduction. We also showed that body size did not affect learning capabilities. This resilience could be an efficient buffer against the ongoing impacts of global change. PubDate: 2023-02-16
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Abstract: Border habitats such as interfaces and ecotones are promising research targets being likely areas of high species richness and genetic and phenotypic diversity. Springs are intriguing habitats exploited by both subterranean and surface species. For subterranean species, springs can provide higher trophic resources but can be risky in terms of predation and UV radiation, while for surface species, springs can be safer but less productive environments. We coupled field surveys and laboratory experiments to understand how predation risk and physical constraints, like light occurrence, affect spring exploitation by both a subterranean (Niphargus thuringius) and a surface crustacean amphipod species (Echinogammarus stammeri). From March to May 2021, we surveyed multiple springs and evaluated the activity (both during day and night) of the amphipods and of their predators. Furthermore, in a subterranean laboratory, we reared 80 N. thuringius and 80 E. stammeri under safe and risky conditions with both constant darkness and diel light variation assessing their activity and survival. Risky conditions were represented by the occurrence of meso-predators alone or coupled with the presence of a top predator. In the field, N. thuringius activity was negatively related to the density of predators, while laboratory experiments revealed a main role played by light treatments and night period. E. stammeri activity in the field was higher close to surface while in laboratory conditions decreased during time. In laboratory conditions, predation risk negatively affected survival of both amphipods. Our findings reveal that physical constraints play a key role in affecting the exploitation of ecotones and can mediate antipredator responses, thus providing selective pressures for the exploitation of border environments. Significance statement Understanding environmental pressures acting on ecotones is a key point to verify if new adaptations may occur at the border between two distinct habitats. Using both field and laboratory approaches, we show that, in springs, the behaviour of subterranean invertebrates is affected by surface physical constraints which can mediate the effects of predation risk. Behavioural strategies to avoid predation, such as nocturnal activity, may promote spring ecotone exploitation by groundwater animals, such as amphipod crustaceans. PubDate: 2023-02-14
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Abstract: Urban noise limits perception by masking acoustic signals, with negative consequences for communication. Although animals relying on acoustic communication are affected, they have developed different strategies to reduce the masking effect of urban noise. Theoretically, birdsong vocal learning confers behavioral plasticity, which may be important for adapting to life in urban environments. To understand the role of vocal learning for adjusting to noisy places, we performed a field study combined with a phylogenetic comparative analysis, comparing passerine species that typically exhibit song learning (oscines) and those that do not (suboscines). Under the premise that vocal learning confers behavioral plasticity, we hypothesized that (1) while oscine species would vary song traits (acoustic parameters), under noisy conditions, suboscines would remain consistent; (2) suboscines may vary birdsong activity in relation to noise; and (3) song learning functions as an exaptation for inhabiting noisy urban environments. We found that oscines only shifted the minimum frequency of their song and did not vary song activity in noisy areas. In contrast, suboscines shifted their complete song upwards and decreased song activity in cities. Our phylogenetic analysis indicated that foraging stratum and song frequency, not learning, best explain adaptation to cities in an evolutionary context. If city noise functions as an ecological filter, frequency traits may serve as an exaptation for colonizing noisy environments. We provided clear evidence that passerine species, depending on their song-learning ability, use different strategies to cope with noise, suggesting that vocal learning determines how birds cope with the masking effect of urban noise. Significance statement Since birdsong learning may confer behavioral flexibility, we studied its role for adapting to urban noisy environments. We studied passerines that vary in vocal learning ability combining field data with a phylogenetic comparative analysis. Our methodology may provide information on both the response and the evolutionary advantages of vocal learning for living in noisy urban environments. Although both learner and non-learner birds varied their responses, they displayed different strategies for coping with urban noise. Moreover, differences in vocal learning might not limit colonization of noisy environments, and ecological and acoustic traits may explain adaptation to urbanization. Frequency parameters are conserved evolutionary traits among birds living in cities and may function as a preadaptation that facilitates the colonization of urban environments. Our study suggests that the birdsong-learning program does not help birds colonize cities but determines how they cope with the masking effect of urban noise. PubDate: 2023-02-11
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Abstract: Light availability is one of the key drivers of animal activity, and moonlight is the brightest source of natural light at night. Moon phase is commonly used but, while convenient, it can be a poor proxy for lunar illumination on the ground. While the moon phase remains effectively constant within a night, actual moonlight intensity is affected by multiple factors such as disc brightness, position of the moon, distance to the moon, angle of incidence, and cloud cover. A moonlight illumination model is presented for any given time and location, which is significantly better at predicting lunar illumination than moon phase. The model explains up to 92.2% of the variation in illumination levels with a residual standard error of 1.4%, compared to 60% explained by moon phase with a residual standard error of 22.6%. Importantly, the model not only predicts changes in mean illumination between nights but also within each night, providing greater temporal resolution of illumination estimates. An R package moonlit facilitating moonlight illumination modelling is also presented. Using a case study, it is shown that modelled moonlight intensity can be a better predictor of animal activity than moon phase. More importantly, complex patterns of activity are shown where animals focus their activity around certain illumination levels. This relationship could not be identified using moon phase alone. The model can be universally applied to a wide range of ecological and behavioural research, including existing datasets, allowing a better understanding of lunar illumination as an ecological resource. Significance statement Moon phase is often used to represent lunar illumination as an environmental niche, but it is a poor proxy for actual moonlight intensity on the ground. A model is therefore proposed to estimate lunar illumination for any given place and time. The model is shown to provide a significantly better prediction of empirically measured lunar illumination than moon phase. Importantly, it also has much higher temporal resolutions, allowing to not only detect selectiveness for light levels between nights but also within each night, which is not achievable with moon phase alone. This offers unprecedented opportunities to study complex activity patterns of nocturnal species using any time-stamped data (GPS trackers, camera traps, song meters, etc.). It can also be applied to historical datasets, as well as facilitate future research planning in a wide range of ecological and behavioural studies. PubDate: 2023-02-10
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Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Understanding the complex interplay of factors shaping polymorphic changes within individuals represents a longstanding conundrum in biology. Some crab spiders (Thomisidae) are examples of sit-and-wait predators that can change their body coloration. Many factors may influence crab spider color polymorphism with multiple explanations receiving various levels of support. Here we examined the daytime and nighttime activities and predator and prey interactions for two yellow-white polymorphic crab spiders, Thomisus labefactus and Ebrechtella tricuspidatus in the field. We thereupon conducted a manipulative experiment using dummies with color morphs visibly resembling the spiders when placed on background-matched flowers. We measured the spectra reflected from the dummies and their floral backgrounds and used insect visual models to determine if they are likely to be visible to a range of insects by night and day. We found that both color morphs of each species were more active by night than by day. Our visual models revealed that the spider’s bodies were unlikely to be cryptic. Together, these results suggest that the crab spiders might exploit flower colorations during the night but not during the day. They also indicated that explanations of why crab spiders utilize certain color polymorphs are context dependent and will vary with time, and whether predators, prey, or both, are present. Significance statement Crab spiders are an excellent model for investigating a long-standing challenge in evolutionary biology: understanding the causes and consequences of polymorphic coloration in animals. Studies have postulated a range of explanations with some support for each. Broader studies encompassing all interactions between spiders and their predators and prey across the day and night are urgently needed. Here we combined an around-the-clock spider activity survey with field experiments and insect visual models to show that the types of interactions between spider color morphs and their predators and prey differ over the day and night. Our study suggests that outcomes of experiments examining the adaptive drivers of polymorphisms may be dependent upon the context within which the observations were made, and that examining interactions across temporal contexts is required to fully uncover the various drivers of the polymorphisms. PubDate: 2023-02-02
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Abstract: The evolution of conspicuous ornamentation is often thought to be the consequence of sexual selection, but this might not always be the case. One such candidate is the contrasting pale-dark facial color patterns in front of eyes in predatory animals. The sight-line hypothesis proposes that the contrasting color between lore and forehead assists in tracking and capturing a fast-moving prey. However, this classic hypothesis has been criticized and thus ignored for several reasons including lack of formal statistical testing controlling for phylogenetic inertia and the confounding effect of the mere presence of dark facial markings that help reduce glare. Here, using a phylogenetic comparative approach, I tested the sight-line hypothesis and a widespread alternative explanation, the sexual selection hypothesis, in hirundines (Aves: Hirundinidae). I found no support for a sexual function of lore-forehead borderline in hirundines, because lore-forehead borderline was not positively related to indices of sexual selection. In contrast, I found consistent support for the sight-line hypothesis. Species foraging on large active fliers (e.g., house flies) had more contrasting lore-forehead borderline than species foraging on small aerial planktons (e.g., midges). Furthermore, an analysis of evolutionary pathways provided a strong support for positively correlated evolution of lore-forehead borderline and prey size. These results remained significant when excluding species that lack dark lores and, thus, not mere presence of dark lores but contrasting color patterns may be important. To my knowledge, the current study is the first macroevolutionary support for the sight-line hypothesis. Significant statement Many predatory animals have contrasting pale and dark color pattern, or eyeline, in front of eyes. This color pattern might be adaptive as a “sight-line”, which can aid in tracking and capturing a fast-moving prey (sight-line hypothesis). This hypothesis has been ignored for decades, because eyeline has been misinterpreted as a form of dark facial feathers, which can aid in glare reduction at foraging. Here, I found that the sight-line hypothesis, but not glare-reducing effect of dark facial color marking, explained the macroevolution of contrasting pale-dark facial color patterns in swallows and martins, which commonly have dark facial feathers. The evolution of pale feathers above dark feathers in front of eyes had strong, positive evolutionary relationships with foraging on speedy preys. This study explains why many animals have eyelines instead of uniformally dark facial coloration. PubDate: 2023-02-01
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Abstract: Maintaining a good reputation is crucial for humans. Altruism, e.g. charity, may serve as a costly signal that enhances reputation based on the real or communicated cost. Fundraising via charity running triggers competitive altruism when potential donors donate in reaction to the reputation increase of the fundraiser. Using real-life data of marathonists and half-marathonists (388 runners) and their 9281 donors, the present research focuses on how the communicated cost and goal of a charity run affected the potential donors. We analysed the introductory texts of the runners presented online according to the cost and the social benefit of the fundraising communicated by them. We have shown that emphasizing more the subjective cost of running and the social benefit of the goal, or writing a longer text, attracted more donors and, even though the average amount of donation per donor did not increase, still lead to a greater amount of donations collected overall by the fundraiser. It was also shown that a higher communicated subjective cost resulted in a higher ratio of opposite-sex donors, both in the case of male and female runners, suggesting that the communication of the cost of an altruistic act might be the object of sexual selection. Significance statement A good reputation is crucial for humans, as a reputable person enjoys several benefits. One way to maintain a good reputation is to be altruistic, e.g. doing charity. A seemingly high cost and a socially accepted goal may result in a higher reputation. Using data from a charity running community we demonstrate that fundraisers who emphasize their subjective cost (how difficult to run), and emphasize the good goal of the charity, attract more donors, and even though the average amount of each donation does not increase, a higher number of donors results in a greater amount of donations collected overall. Talking about the difficulties of the charity run results in a higher ratio of opposite-sex donors. Our results may be helpful to plan more successful charity events or to make a human community more altruistic and cooperative in general. PubDate: 2023-01-20
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Abstract: In cooperatively breeding species, helpers take higher risks of getting lower return of investment than breeders due to the incongruity between helping and breeding. Helpers can deal with the risk by curtailing their investment or, if possible, claiming immediate rewards in the cooperation. Given breeders may rely largely on the aid of helpers to raise their offspring, it can be hypothesized that helpers are more likely to make adaptive responses to the incongruity-associated risk in adverse habitats than in good ones. This hypothesis was tested in the giant babax (Babax waddelli) by comparing helpers’ provisioning behaviors between two breeding populations in adverse high-altitude and good low-altitude environments. These two populations differed significantly in their egg size and nestlings’ growth patterns. Helpers in both populations made great contributions to the raising of offspring. During provisioning, helpers in the high-altitude population exhibited significantly higher feeding rates but delivered fewer insects per feeding bout than their counterparts in the low-altitude population. Helpers in both populations displayed a cheating strategy of “non-feeding” to reduce investment in provisioning. They pursued immediate excess rewards via kleptoparasitism of nestling fecal sacs in the high-altitude population but not in the low-altitude one. Accordingly, breeders made different antagonistic actions toward the cheating helpers between populations. Our findings confirm that helpers are prone to deceiving cooperation under poor breeding conditions, and that breeders’ tolerance of the cheating behavior of helpers is determined by their dependence on the helpers’ aid. Significance statement Giant babax is an obligated cooperatively breeding bird that breeds on the Tibetan Plateau. We found that helpers displayed cheating behaviors while they provisioned the brood. Although helpers in both high- and low-altitude populations adopt “non-feeding” strategy to reduce investment in the provisioning, they were more likely to perform contested kleptoparasitism to access the fecal sacs of nestling in the high-altitude population than in the low-altitude one. Our findings suggest that helpers in adverse high-altitude habitats are probable to claim immediate excess reward via cheating strategies. PubDate: 2023-01-17
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