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Environmental heterogeneity and the evolution of personality traits in blue tits (Cyaniste caeruleus)

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Abstract

Environmental heterogeneity, spatial variation in selection pressure and gene flow are known to be important for shaping intra-specific variation and local adaptations. However, their roles as drivers of variation and divergence in behavioral traits have seldom been studied. Here, we studied the phenotypic divergence of breeding and fledgling blue tits (Cyanistes caeruleus) for personality traits across three wild populations situated in contrasted habitats yet connected by gene flow. We first compared the mean personality phenotype of each population. Second, using common garden, reciprocal transplant and cross-fostering experiment we investigated the genetic basis of the observed divergence. Third, we determined the selection pressure acting on the personality phenotype in each population. We found phenotypic and genetic difference between populations and our results suggested that these divergences result from the local selection regime in each habitat. Overall, our results highlight the importance of environmental heterogeneity in the maintenance of small-scale intra-specific variation for behavioral traits.

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Local adaptation has been a major focus of evolutionary ecologists working across diverse systems for decades. However, little of this research has explored variation at microgeographic scales because it has often been assumed that high rates of gene flow will prevent adaptive divergence at fine spatial scales. Here, we establish a quantitative definition of microgeographic adaptation based on Wright's dispersal neighborhood that standardizes dispersal abilities, enabling this measure to be compared across species. We use this definition to evaluate growing evidence of evolutionary divergence at fine spatial scales. We identify the main mechanisms known to facilitate this adaptation and highlight illustrative examples of microgeographic evolution in nature. Collectively, this evidence requires that we revisit our understanding of the spatial scale of adaptation and consider how microgeographic adaptation and its driving mechanisms can fundamentally alter ecological and evolutionary dynamics in nature.
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The direction of covariation in behavioral traits (a behavioral syndrome) is typically the same in males and females, although intersexual differences in life history could lead to intersexual heterogeneity in syndrome structure. We explored whether a behavioral syndrome was the same in both sexes. We recorded 2 metrics of nest defense in wild blue tits Cyanistes caeruleus: 1) Nest defense of a female around the time her eggs hatch (hatching defense), 2) nest defense of the male and female parent when their offspring was 16 days old (nestling defense), and 3) handling aggression. We used repeated records of these behaviors collected on 392 females and 363 males during 2007–2012 in a hierarchical mixed model to separate the between-individual from the residual (co)variances. We find that 1) hatching defense is not repeatable across breeding seasons (but highly repeatable within years). 2) Nestling defense intensity is 38% repeatable in males and females. 3) Contrary to our expectation, females that defended their nestlings more intensively were less aggressive when being handled (negative between-individual correlation), but 4) nestling defense and handling aggression showed a positive between-individual correlation in males although nonsignificantly. These correlations were completely masked on the phenotypic level by a low residual correlation. Individuals may hence display repeatable and correlated aggressive behavior in different contexts, but the direction of this syndrome may differ between the sexes. Intersexual heterogeneity in animal personality and syndrome structure remains poorly understood, and our findings hence urge future work to explicitly consider this heterogeneity.
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Environmental heterogeneity can result in spatial variation in selection pressures that can produce local adaptations. The pace-of-life syndrome hypothesis predicts that habitat-specific selective pressures will favor the coevolution of personality, physiological, and lifehistory phenotypes. Few studies so far have compared these traits simultaneously across different ecological conditions. In this study, we compared 3 personality traits (handling aggression, exploration speed in a novel environment, and nest defense behavior) and 1 physiological trait (heart rate during manual restraint) across 3 Corsican blue tit (Cyanistes caeruleus) populations. These populations are located in contrasting habitats (evergreen vs. deciduous) and are situated in 2 different valleys 25 km apart. Birds from these populations are known to differ in life-history characteristics, with birds from the evergreen habitat displaying a slow pace-of-life, and birds from the deciduous habitat a comparatively faster pace-of-life. We expected personality to differ across populations, in line with the differences in pace-of-life documented for life-history traits. As expected, we found behavioral differences among populations. Despite considerable temporal variation, birds exhibited lower handling aggression in the evergreen populations. Exploration speed and male heart rate also differed across populations, although our results for exploration speed were more consistent with a phenotypic difference between the 2 valleys than between habitats. There were no clear differences in nest defense intensity among populations. Our study emphasizes the role of environmental heterogeneity in shaping population divergence in personality traits at a small spatial scale.
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The use of regression techniques for estimating the direction and magnitude of selection from measurements on phenotypes has become widespread in field studies. A potential problem with these techniques is that environmental correlations between fitness and the traits examined may produce biased estimates of selection gradients. This report demonstrates that the phenotypic covariance between fitness and a trait, used as an estimate of the selection differential in estimating selection gradients, has two components: a component induced by selection itself and a component due to the effect of environmental factors on fitness. The second component is shown to be responsible for biases in estimates of selection gradients. The use of regressions involving genotypic and breeding values instead of phenotypic values can yield estimates of selection gradients that are not biased by environmental covariances. Statistical methods for estimating the coefficients of such regressions, and for testing for biases in regressions involving phenotypic values, are described.
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We tested the two main evolutionary hypotheses for an association between immunity and personality. The risk-of-parasitism hypothesis predicts that more proactive (bold, exploratory, risk-taking) individuals have more vigorous immune defenses because of increased risk of parasite exposure. In contrast, the pace-of-life hypothesis argues that proactive behavioral styles are associated with shorter lifespans and reduced investment in immune function. Mechanistically, associations between immunity and personality can arise because personality differences are often associated with differences in condition and stress responsiveness, both of which are intricately linked with immunity. Here we investigate the association between personality (measured as proactive exploration of a novel environment) and three indices of innate immune function (the non-specific first line of defense against parasites) in wild superb fairy-wrens Malurus cyaneus. We also quantified body condition, hemoparasites (none detected), chronic stress (heterophil:lymphocyte ratio) and circulating corticosterone levels at the end of the behavioral test (CORT, in a subset of birds). We found that fast explorers had lower titers of natural antibodies. This result is consistent with the pace-of-life hypothesis, and with the previously documented higher mortality of fast explorers in this species. There was no interactive effect of exploration score and duration in captivity on immune indices. This suggests that personality-related differences in stress responsiveness did not underlie differences in immunity, even though behavioral style did modulate the effect of captivity on CORT. Taken together these results suggest reduced constitutive investment in innate immune function in more proactive individuals.
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Predators can affect prey both directly (consumptive effects) and indirectly (nonconsumptive effects), with a growing body of literature showing the latter may have pronounced effects. Prey populations are comprised of individuals that differ in perception of and willingness to take risk; therefore, studying how different types of individuals respond to predation risk is necessary to fully understand prey dynamics. Playbacks were used to experimentally manipulate perceived predation risk in nest-box populations of wild great tits (Parus major) to examine the nonconsumptive effects of avian predators on prey behavior and morphology, and to explore individual differences in prey response. Individuals responded to our treatment, and responses differed depending on both treatment and premanipulation behavioral type. Birds in areas exposed to predator playback tended to decrease in body mass more than birds exposed to nonthreatening (control) playback. Differences between treatment groups were mainly driven by initially fast exploring birds: In the control treatment, fast explorers increased in mass, whereas the initially fast exploring birds in the predation treatment decreased in mass. Furthermore, birds exposed to predator playback decreased exploratory tendency compared with controls. These findings demonstrate that predation risk alters great tit behavior (exploration) and morphology (body mass) and that plasticity in response to risk relates to an individual’s willingness to take risks. Our findings suggest that individuals differ in susceptibility to predation risk, causing adaptive individual differences in responsiveness to changes in predation risk. Acknowledging individuality in responses to perceived predation risk has important consequences for understanding prey dynamics.
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This book had its origin when, about five years ago, an ecologist (MacArthur) and a taxonomist and zoogeographer (Wilson) began a dialogue about common interests in biogeography. The ideas and the language of the two specialties seemed initially so different as to cast doubt on the usefulness of the endeavor. But we had faith in the ultimate unity of population biology, and this book is the result. Now we both call ourselves biogeographers and are unable to see any real distinction between biogeography and ecology.
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Linking population genetic variation to the spatial heterogeneity of the environment is of fundamental interest to evolutionary biology and ecology, in particular when phenotypic differences between populations are observed at biologically small spatial scales. Here, we applied restriction-site associated DNA sequencing (RAD-Seq) to test whether phenotypically differentiated populations of wild blue tits (Cyanistes caeruleus) breeding in a highly heterogeneous environment exhibit genetic structure related to habitat type. Using 12 106 SNPs in 197 individuals from deciduous and evergreen oak woodlands, we applied complementary population genomic analyses, which revealed that genetic variation is influenced by both geographical distance and habitat type. A fine-scale genetic differentiation supported by genome- and transcriptome-wide analyses was found within Corsica, between two adjacent habitats where blue tits exhibit marked differences in breeding time while nesting < 6 km apart. Using redundancy analysis (RDA), we show that genomic variation remains associated with habitat type when controlling for spatial and temporal effects. Finally, our results suggest that the observed patterns of genomic differentiation were not driven by a small proportion of highly differentiated loci, but rather emerged through a process such as habitat choice, which reduces gene flow between habitats across the entire genome. The pattern of genomic isolation-by-environment closely matches differentiation observed at the phenotypic level, thereby offering significant potential for future inference of phenotype-genotype associations in a heterogeneous environment.
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Behavioural syndromes, i.e. correlated behaviours, may be a result from adaptive correlational selection but in a new environmental setting the trait correlation might act as an evolutionary constraint. However, knowledge about the quantitative genetic basis of behavioural syndromes, and the stability and evolvability of genetic correlations under different ecological conditions is limited. We investigated the quantitative genetic basis of correlated behaviours in the freshwater isopod Asellus aquaticus. In some Swedish lakes, A. aquaticus has recently colonised a novel habitat and diverged into two ecotypes, presumably due to habitat specific selection from predation. Using a common garden approach and animal model analyses, we estimated quantitative genetic parameters for behavioural traits, and compared the genetic architecture between the ecotypes. We report that the genetic covariance structure of the behavioural traits has been altered in the novel ecotype, demonstrating divergence in behavioural correlations. Thus, our study confirms that genetic correlations behind behaviours can change rapidly in response to novel selective environments. This article is protected by copyright. All rights reserved.
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Individual differences in personality affect behavior in novel or challenging situations. Personality traits may be subject to selection because they affect the ability to dominate others. We investigated whether dominance rank at feeding tables in winter correlated with a heritable personality trait (as measured by exploratory behavior in a novel environment) in a natural population of great tits, Parus major. We provided clumped resources at feeding tables and calculated linear dominance hierarchies on the basis of observations between dyads of color-ringed individuals, and we used an experimental procedure to measure individual exploratory behavior of these birds. We show that fast-exploring territorial males had higher dominance ranks than did slow-exploring territorial males in two out of three samples, and that dominance related negatively to the distance between the site of observation and the territory. In contrast, fast-exploring nonterritorial juveniles had lower dominance ranks than did slow-exploring nonterritorial juveniles, implying that the relation between dominance and personality is context-dependent in the wild. We discuss how these patterns in dominance can explain earlier reported effects of avian personality on natal dispersal and fitness. Copyright 2004.
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(1) The aim of this paper is to estimate the shape of the curve relating first year survival to nestling weight in individual great tits (Parus major) and to study the causality of this relationship. (2) Data were collected in a mainland and an island population. Nestlings were weighed and sexed in the nest when 2 weeks old. A recapture programme provided data for recapture-rate estimates in the winter. Local survival until next breeding season was estimated by capturing the breeding population. Brood-size manipulation experiments were performed in the mainland population in order to manipulate nestling weights. (3) The relation between local recapture rate and nestling weight was described using logistic regression techniques. The descriptive model included positive weight and negative squared weight regression coefficients, if controlled for year, sex and date. Recapture rate approached zero at weights of c. 70% of the adult body weight. The curves for both populations showed an approximately linear part over a rather long range of weights. At high weights, the curve levelled off in the mainland population and curved down in the island population. (4) Survival from weighing till fledging and recapture rate from fledging till winter were related to nestling weight, but recapture rate from winter till breeding was not. (5) The effect of brood-size manipulation on nestling weight and subsequent recapture rate suggests causality of the recapture rate-nestling weight curve. Additional information from a comparison of the association between recapture rate and nestling weight within and between broods leads to the conclusion that weight does play a causal role in this relationship. Recapture rate-nestling weight curves can thus be estimated from non-experimental data.
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Frequency dependent selection is thought to be a major contributor to the maintenance of phenotypic variation. We tested for frequency dependent selection on contrasting behavioral strategies, termed here 'personalities', in three species of social spiders, each thought to represent an independent evolutionary origin of sociality. The evolution of sociality in the spider genus Anelosimus is consistently met with the emergence of two temporally-stable discrete personality types: an 'aggressive' or 'docile' form. We assessed how the foraging success of each phenotype changes as a function of its representation within a colony. We did this by creating experimental colonies of various compositions (6 aggressive, 3 aggressive and 3 docile, 1 aggressive and 5 docile, 6 docile), maintaining them in a common garden for three weeks, and tracking the mass gained by individuals of either phenotype. We found that both the docile and aggressive phenotype experienced their greatest mass gain in mixed colonies of mostly docile individuals. However, the performance of both phenotypes decreased as the frequency of the aggressive phenotype increased. Nearly identical patterns of phenotype-specific frequency dependence were recovered in all three species. Naturally-occurring colonies of these spiders exhibit mixtures dominated by the docile phenotype, suggesting that these spiders may have evolved mechanisms to maintain the compositions that maximize the success of the colony without compromising the expected reproductive output of either phenotype. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
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Extensive literature shows that lepidopteran larvae constitute the most important component of the diet of nestling tits (Parus spp.). In Blue Tits Parus caeruleus, breeding is usually timed to match the nestling stage to the period when caterpillars are most abundant. This is true even in places where caterpillars are not very numerous and many alternative prey types have to be used. In a study of a Corsican Blue Tit P. c. ogliastrae population, characterised by the extensive use of non-cater-pillar prey, we compared some aspects of the behaviour of nestlings when fed caterpillars, grasshoppers and spiders. The expectation deduced from ecological and behavioural literature that nestlings should be best able to swallow caterpillars was confirmed. Chick prey handling time could be ranked from caterpillars (the shortest time), through spiders to grasshoppers (the longest time). Handling time increased exponentially with prey size within each prey category and was to some extent subject to variation between broods. Consequently, the behaviour of nestlings provides new support for the idea that Blue Tits are best adapted to eating caterpillars and that mechanical constraints prevent them from using very big prey items, especially non-caterpillar prey, and that this is likely to affect their choice of prey. Such constraints may be less strict in Great Tits Parus major because of their larger body size.
Article
An exciting area in behavioural ecology focuses on understanding why animals exhibit consistent among-individual differences in behaviour (animal personal-ities). Animal personality has been proposed to emerge as an adaptation to individual differences in state vari-ables, leading to the question of why individuals differ consistently in state. Recent theory emphasizes the role that positive feedbacks between state and behaviour can play in producing consistent among-individual covari-ance between state and behaviour, hence state-dependent personality. We review the role of feedbacks in recent models of adaptive personalities, and provide guidelines for empirical testing of model assumptions and predictions. We discuss the importance of the me-diating effects of ecology on these feedbacks, and pro-vide a roadmap for including state–behaviour feedbacks in behavioural ecology research. State–behaviour feedbacks and the emergence of personality differences The past decade has seen tremendous interest in animal personalities [1–3], stemming from accumulating evidence for individual repeatability and significant correlations between various behaviours (e.g., boldness, aggres-siveness, activity, exploration, or sociability). Empirical studies show that animal personalities and behavioural syndromes (correlations across contexts) vary as a function of ecology [4,5]; for example, aggressiveness and boldness are often positively correlated but the strength of this correlation varies depending on the predation regime [6,7]. Variation in syndrome structure also exists across different temporal scales; for instance, early experiences (e.g., exposure to stressors) can have large effects on the development of personality structure but such effects can
Article
Climate change, habitat alteration, range expansions, and biological invasions are all predicted to require rapid shifts in multiple traits including behavior and life history, both for initial population establishment and subsequent adaptation. Hormonal mechanisms likely play a key role in facilitating or constraining plastic and genetic responses for suites of traits, but few studies have evaluated their role in shaping contemporary adaptation or diversification. We examined multiple phenotypic adjustments and associated hormonal changes following a recent (early 1980s) colonization event, in which a temperate-breeding songbird, the dark-eyed junco (Junco hyemalis), became established in the Mediterranean climate of San Diego, California. The milder climate has led to an extended breeding season and year-round residency, and we document shifts in multiple sexually selected behaviors and plumage traits. Testosterone titers in San Diego were elevated for longer but with a lower peak value compared to a nearby native-range population, and correlations between testosterone and related traits were similar within and among populations. A common garden study indicated that changes in testosterone likely represent plastic responses to the less seasonal environment of the city, providing the context against which subsequent genetic changes in morphology likely occurred. We argue that correlated shifts in multiple traits, organized by underlying physiology, may be a generally important element of many successful adjustments to changing environments.
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Temporal variation in selection has long been proposed as a mechanism by which genetic variation could be maintained despite short-term strong directional selection and has been invoked to explain the maintenance of consistent individual differences in behaviour. We tested the hypothesis that ecological changes through time lead to fluctuating selection, which could promote the maintenance of variation in female behavioural traits in a wild population of North American red squirrels. As predicted, linear selection gradients on female aggression and activity significantly fluctuated across years depending on the level of competition among juveniles for vacant territories. This selection acted primarily through juvenile overwinter survival rather than maternal fecundity. Incorporating uncertainty in individual measures of behaviour reduced the magnitude of annual selection gradients and increased uncertainty in these estimates, but did not affect the overall pattern of temporal fluctuations in natural selection that coincided with the intensity of competition for vacant territories. These temporal fluctuations in selection might, therefore, promote the maintenance of heritable individual differences in behaviour in this wild red squirrel population.
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Animals with parental care defend their offspring with an intensity reflecting parental investment. Parental investment theory predicts that parents should take risks relative to their residual reproductive value. Therefore, parental defense should change consistently with age reaching a peak at middle age, and it should vary consistently with age at start and end of reproduction. We recorded the intensity of parental defense of offspring in 410 female goshawks Accipiter gentilis throughout their lives, ranging from timid females that barely approached a human intruder at the nest to aggressive females that physically attacked the human. Females were con-sistent in their level of defense throughout life, and aggressive females were mated to aggressive males. Investment in reproduction as reflected by laying date, clutch size, and brood size showed a bell-shaped relationship with age. Females that started to breed at a young age were less aggressive than females that started late. Likewise, females that finished reproduction at a young age behaved less aggressively than females that finished at an old age. The intensity of defense of offspring peaked at an intermediate age followed by a decrease into old age and senescence. Females that started to breed early during the season were more aggressive than late breeders. These findings are consistent with the hypothesis that the intensity of parental defense of their offspring reflects parental investment and patterns of aging.
Article
1. Here, I present a new, multifunctional phylogenetics package, phytools, for the R statistical computing environment. 2. The focus of the package is on methods for phylogenetic comparative biology; however, it also includes tools for tree inference, phylogeny input/output, plotting, manipulation and several other tasks. 3. I describe and tabulate the major methods implemented in phytools, and in addition provide some demonstration of its use in the form of two illustrative examples. 4. Finally, I conclude by briefly describing an active web-log that I use to document present and future developments for phytools. I also note other web resources for phylogenetics in the R computational environment.
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Behaviors are commonly correlated between individuals in so-called behavioral syndromes. Between-individual correlations of phenotypic traits can change the trajectories of evolutionary responses available to populations and even prevent evolutionary change if underpinned by genetic correlations. Whether behavioral syndromes also influence the course of evolution in this manner remains unknown. Here, we provide the first test of the degree to which evolutionary responses might be affected by behavioral syndrome structure. This test, based on a meta-analysis of additive genetic variancecovariance matrices, shows that behavioral syndromes constrain potential evolutionary responses by an average of 33%. For comparison, correlations between life-history or between morphological traits suggest constraints of 1318%. This finding demonstrates that behavioral syndromes might substantially constrain the evolutionary trajectories available to populations, prompts novel future directions for the study of behavioral syndromes, emphasizes the importance of viewing syndrome research from an evolutionary perspective, and provides a bridge between syndrome research and theoretical quantitative genetics.