Personality and urbanization: behavioural traits and DRD4 SNP830 polymorphisms in great tits in Barcelona city

Urban and rural male song sparrows (Melospiza melodia) differ in territorial aggression and activation of vasotocin neurons in response to song challenge

When living in urban habitats, 'urban adapter' species often show greater aggression toward conspecifics, yet we do not understand the mechanisms underlying this behavioral shift. The neuroendocrine system regulates socio-sexual behaviors including aggression and thus could mediate behavioral responses to urbanization. Indeed, urban male song sparrows (Melospiza melodia), which are more territorially aggressive, also have greater abundance of the neuropeptide arginine vasotocin (AVT) in nodes of the brain social behavior network. Higher abundance of AVT could reflect long-term synthesis that underlies baseline territoriality or short-term changes that regulate aggression in response to social challenge. To begin to resolve the timeframe over which the AVT system contributes to habitat differences in aggression we used immediate early gene co-expression as a measure of the activation of AVT neurons. We compared Fos induction in AVT-immunoreactive neurons of the bed nucleus of the stria terminalis (BSTm) and paraventricular nucleus of the hypothalamus (PVN) between urban and rural male song sparrows in response to a short (< 5 min.) or long (> 30 min.) song playback to simulate territorial intrusion by another male. We found that urban males had a higher proportion of Fos-positive AVT neurons in both brain regions compared to rural males, regardless of the duration of song playback. Our results suggest that AVT neurons remain activated in urban males, independently of the duration of social challenge. These findings that Fos induction in AVT neurons differs between rural and urban male song sparrows further implicate this system in regulating behavioral responses to urbanization.

Candidate gene polymorphisms are linked to dispersive and migratory behaviour: Searching for a mechanism behind the "paradox of the great speciators"

The "paradox of the great speciators" has puzzled evolutionary biologists for over half a century. A great speciator requires excellent dispersal propensity to explain its occurrence on multiple islands, but reduced dispersal ability to explain its high number of subspecies. A rapid reduction in dispersal ability is often invoked to solve this apparent paradox, but a proximate mechanism has not been identified yet. Here, we explored the role of six genes linked to migration and animal personality differences (CREB1, CLOCK, ADCYAP1, NPAS2, DRD4, and SERT) in 20 South Pacific populations of silvereye (Zosterops lateralis) that range from highly sedentary to partially migratory, to determine if genetic variation is associated with dispersal propensity and migration. We detected genetic associations in three of the six genes: (i) in a partial migrant population, migrant individuals had longer microsatellite alleles at the CLOCK gene compared to resident individuals from the same population; (ii) CREB1 displayed longer average microsatellite allele lengths in recently colonized island populations (<200 years), compared to evolutionarily older populations. Bayesian broken stick regression models supported a reduction in CREB1 length with time since colonization; and (iii) like CREB1, DRD4 showed differences in polymorphisms between recent and old colonizations but a larger sample is needed to confirm. ADCYAP1, SERT, and NPAS2 were variable but that variation was not associated with dispersal propensity. The association of genetic variants at three genes with migration and dispersal ability in silvereyes provides the impetus for further exploration of genetic mechanisms underlying dispersal shifts, and the prospect of resolving a long-running evolutionary paradox through a genetic lens.

Urbanization is associated with non-coding polymorphisms in candidate behavioural genes in the Eurasian coot

Extensive transformation of natural land cover into urbanized areas enhances accumulation of phenotypic differences between animals from urban and nonurban populations, but there is little information on whether these changes, especially in terms of animal behaviour and circadian rhythm, have a genetic basis. The aim of this study was to investigate genetic background of behavioural differences between four pairs of urban and nonurban populations of a common waterbird, the Eurasian coot Fulica atra. For this purpose, we quantified polymorphisms in personality-related candidate genes, previously reported to be associated with avian circadian rhythms and behavioural traits that may be crucial for urban life. We found general associations between landscape urbanization level and polymorphisms in 3'UTR region of CREB1 gene encoding transcriptional factor, which participates in development of cognitive functions and regulation of circadian rhythm. We also found significant differentiation between urban and nonurban populations in the intronic region of CKIɛ gene responsible for regulation of circadian clock. Although we lacked evidence for linkage of this intronic variation with coding polymorphisms, genetic differentiation between urban populations was significantly stronger at CKIɛ intron compared with neutral microsatellite markers, suggesting possible local adaptations of CKIɛ expression regulation to specific urban sites. Our results indicate that behavioural differentiation between urban and nonurban coot populations may be the effect of habitat-specific selective pressure resulting in genetic adaptations to urban environment and supporting the microevolutionary scenario. These adaptations, however, prevailed in non-coding regulatory rather than coding gene regions and showed either general or local patterns, revealing high complexity of associations between behaviour and landscape urbanization in birds.

The Epigenetics of Animal Personality

Animal personality, consistent individual differences in behaviour, is an important concept for understanding how individuals vary in how they cope with environmental challenges. In order to understand the evolutionary significance of animal personality, it is crucial to understand the underlying regulatory mechanisms. Epigenetic marks such as DNA methylation are hypothesised to play a major role in explaining variation in phenotypic changes in response to environmental alterations. Several characteristics of DNA methylation also align well with the concept of animal personality. In this review paper, we summarise the current literature on the role that molecular epigenetic mechanisms may have in explaining personality variation. We elaborate on the potential for epigenetic mechanisms to explain behavioural variation, behavioural development and temporal consistency in behaviour. We then suggest future routes for this emerging field and point to potential pitfalls that may be encountered. We conclude that a more inclusive approach is needed for studying the epigenetics of animal personality and that epigenetic mechanisms cannot be studied without considering the genetic background.

Coping with novelty across an urban mosaic: Provisioning latency increases closer to roads and is associated with species-specific reproductive success in two urban adapters

Most research on urban avian ecology has focused on population- and community-level phenomena, whereas fewer studies have examined how urbanization affects individual behavioral responses to a sudden and novel stimulus, and how those translate to fitness. We measured between-individual variation in provisioning latency in two urban adapters - great tits and blue tits - in response to an infrared camera installed in the nestbox, encountered when offspring in the nest were at the peak of food demand (9-10-days old). For each nestbox, we quantified urbanization as intensity in human activity, distance to road and proportion of impervious surface area. In both species, provisioning latency increased closer to roads. Moreover, increased provisioning latency when exposed to a novel object was associated with higher reproductive success in great tits whose nestboxes were surrounded by high amounts of impervious surface. In contrast, increased provisioning latency was consistently associated with lower reproductive success in blue tits. Our results suggest that provisioning latency changes in relation to the environment surrounding the nest, and may be context- and species-specific when exposed to a novel stimulus, such as a novel object in the nest. To better understand the role of initial behavioral responses towards novelty across an individual's lifetime and, ultimately, its impact on fitness in the urban mosaic, further research explicitly testing different behavioral responses across the entire breeding cycle in wild model systems is needed.

Urban Individuals of Three Rove Beetle Species Are Not More Exploratory or Risk-Taking Than Rural Conspecifics

Urbanization is creating changes in environmental and habitat conditions, as well as creating disturbance and threats to urban-associated species. Some traits, such as high exploratory and risk-taking behavior, are beneficial to allow colonization of urban habitats and coping with urbanization-derived pressures. In this study the exploratory and risk-taking behavior of rural and urban individuals of three forest-associated rove beetle species were tested during their main reproductive period by five frequently used behavioral measures. Individuals of all studied species were similarly ranked by all behavioral measures, indicating that the studied rove beetles responded consistently in the different contexts. However, the behavior of beetles was consistent over time for all/most studied species only by using two measures of exploratory behavior. These provide evidence for the existence of the exploratory dimension of personality in rove beetles. We found a higher exploratory behavior in males than females in Ocypus nitens which can be explained by the active searching of males for mating partners. There were no urbanization-related differences in the exploratory behavior of individuals, suggesting that behavioral changes (being more exploratory) may not yield additional fitness benefits in these rove beetle species with good dispersal capacity.

Bold or shy? Examining the risk–taking behavior and neophobia of invasive and non–invasive house sparrows

Behavior provides a useful framework for understanding specialization, with animal personality aiding our understanding of the invasiveness of birds. Invasions imply dispersion into unknown areas and could require changes in behavior or spatial clustering based on personality. Reduced neophobia and increased exploring behavior could allow individuals to colonize new areas as they test and use non–familiar resources. Here, we hypothesized that house sparrow (Passer domesticus) individuals from invasive populations would exhibit bolder behavior than in non–invasive populations. We assessed risk taking and neophobia in male house sparrows in Barcelona (where it is considered native) and in Mexico City (where it has become widely invasive), captured in two different habitats, urban and non–urban. We assessed latency to enter an experimental cage and to explore it, and latency to feed and feeding time in the presence of a novel object. We found that sparrows from Mexico City, both from urban and non–urban areas, were quicker to enter the experimental cage than the sparrows from Barcelona. The time it took the birds to start exploring the cage gave a similar result. We found no differences between cities or habitats in the latency to feed and feeding time while exposed to a novel object. Our results partially support the view that the invader populations from Mexico City are bolder than those from Barcelona. Behavior is an important component of plasticity and its variability may have an important effect on adaptation to local situations. Future studies should disentangle the underlying mechanisms that explain the different personalities found in populations of different regions, contrasting populations of different densities, and taking different food availability scenarios into account.

The Behavioral Responses of the Chiguanco Thrush to Urbanization in a Neotropical City Comes From Preadapted Behavioral Traits

Several animal species can survive within cities by changing their behavior; such changes could be the result of evolutionary adaptation, epigenetic effects, or come from preadapted traits through phenotypic plasticity or non-random dispersal. Exploring whether behavioral preadapted traits are present in non-urbanized populations could improve our understanding of the processes that allow animals to cope with urbanization. We compared the boldness, neophobia, and solving-test skills of adult individuals of the Chiguanco Thrush (Turdus chiguanco) between urban and extra-urban habitats in La Paz (Bolivia), a high-altitude Neotropical city. The urban Chiguanco Thrushes were bolder, less neophobic, and performed better in problem-solving tests. Extra-urban individuals varied significantly more among them in boldness and neophobia, and although a smaller proportion of individuals were able to solve the simplest problem-solving test, they did so in the same way as the urban ones. This evidence suggests that the behavioral responses of the Chiguanco Thrush to urbanization in La Paz come from preadapted traits.

Great Tits Learn Odors and Colors Equally Well, and Show No Predisposition for Herbivore-Induced Plant Volatiles

Ability to efficiently localize productive foraging habitat is crucial for nesting success of insectivorous birds. Some bird species can use olfaction to identify caterpillar-infested trees by detection of herbivore induced plant volatiles (HIPVs), but these cues probably need to be learned. So far, we know very little about the process of olfactory learning in birds, whether insectivorous species have a predisposition for detecting and learning HIPVs, due to the high ecological significance of these odors, and how olfaction is integrated with vision in making foraging decisions. In a standardized setup, we tested whether 35 wild-caught great tits (Parus major) show any preference for widely abundant HIPVs compared to neutral (non-induced) plant odors, how fast they learn to associate olfactory, visual and multimodal foraging cues with food, and whether the olfactory preferences and learning speed were influenced by bird sex or habitat (urban or rural). We also tested how fast birds switch to a new cue of the same modality. Great tits showed no initial preference for HIPVs compared to neutral odors, and they learned all olfactory cues at a similar pace, except for methyl salicylate (MeSA), which they learned more slowly. We also found no differences in learning speeds between visual, olfactory and multimodal foraging cues, but birds learned the second cue they were offered faster than the first one. Bird sex or habitat had no effect on learning speed or olfactory preference, but urban birds tended to learn visual cues more slowly. We conclude that insectivorous birds utilize olfactory and visual cues with similar efficiency in foraging, and that they probably don‘t have any special predisposition toward the tested HIPVs. These results confirm that great tits are flexible foragers with good learning abilities.

Epigenetics and the city: Non-parallel DNA methylation modifications across pairs of urban-forest Great tit populations

Identifying the molecular mechanisms involved in rapid adaptation to novel environments and determining their predictability are central questions in evolutionary biology and pressing issues due to rapid global changes. Complementary to genetic responses to selection, faster epigenetic variations such as modifications of DNA methylation may play a substantial role in rapid adaptation. In the context of rampant urbanization, joint examinations of genomic and epigenomic mechanisms are still lacking. Here, we investigated genomic (SNP) and epigenomic (CpG methylation) responses to urban life in a passerine bird, the Great tit (Parus major). To test whether urban evolution is predictable (i.e. parallel) or involves mostly nonparallel molecular processes among cities, we analysed both SNP and CpG methylation variations across three distinct pairs of city and forest Great tit populations in Europe. Our analyses reveal a polygenic response to urban life, with both many genes putatively under weak divergent selection and multiple differentially methylated regions (DMRs) between forest and city great tits. DMRs mainly overlapped transcription start sites and promotor regions, suggesting their importance in modulating gene expression. Both genomic and epigenomic outliers were found in genomic regions enriched for genes with biological functions related to the nervous system, immunity, or behavioural, hormonal and stress responses. Interestingly, comparisons across the three pairs of city-forest populations suggested little parallelism in both genetic and epigenetic responses. Our results confirm, at both the genetic and epigenetic levels, hypotheses of polygenic and largely nonparallel mechanisms of rapid adaptation in novel environments such as urbanized areas.

Serotonin transporter (SERT) polymorphisms, personality and problem-solving in urban great tits

Understanding underlying genetic variation can elucidate how diversity in behavioral phenotypes evolves and is maintained. Genes in the serotonergic signaling pathway, including the serotonin transporter gene (SERT), are candidates for affecting animal personality, cognition and fitness. In a model species, the great tit (Parus major), we reevaluated previous findings suggesting relationships between SERT polymorphisms, neophobia, exploratory behavior and fitness parameters, and performed a first test of the relationship between single nucleotide polymorphisms (SNPs) in SERT and problem-solving in birds. We found some evidence for associations between SERT SNPs and neophobia, exploratory behavior and laying date. Furthermore, several SNPs were associated with behavioral patterns and success rates during obstacle removal problem-solving tests performed at nest boxes. In females, minor allele homozygotes (AA) for nonsynonymous SNP226 in exon 1 made fewer incorrect attempts and were more likely to problem-solve. In both sexes, there was some evidence that minor allele homozygotes (CC) for SNP84 in exon 9 were more likely to problem-solve. Only one SNP-behavior relationship was statistically significant after correcting for multiple comparisons, but several were associated with substantial effect sizes. Our study provides a foundation for future research on the genetic basis of behavioral and cognitive variation in wild animal populations.

Are There Personality Differences between Rural vs. Urban-Living Individuals of a Specialist Ground Beetle, Carabus convexus?

Simple Summary

Urbanization causes substantial changes in environmental and habitat conditions. These, as well as more frequent disturbance events accompanying urbanization constitute selective forces acting on various reactions of urban-associated species, including behavior. In this study, rural and urban individuals of a forest specialist ground beetle, Carabus convexus were tested for their exploratory and risk-taking behavior. Beetles responded consistently in the different contexts, and also over time, demonstrating that they had personalities. Carabus convexus is the second ground beetle species in which the existence of personality was demonstrated. By agglomerative cluster analysis, we identified two groups of behavioral traits: the exploratory and the risk-taking dimensions of personality. Urban females were significantly more exploratory than urban males which can be an adaptation to find high quality food needed to mature eggs, as well as to find favorable microsites for oviposition. Moreover, urban females and males showed higher level of risk-taking behavior than rural females. Urban beetles with higher risk-taking behavior may be better able to cope with new conditions created by frequent urbanization-driven disturbance events.

Abstract

The world-wide, rapid urbanization is leading to substantial changes in environmental and habitat conditions. These changes, as well as disturbances accompanying urbanization have considerable effects at various levels of the biological organization on wildlife. Understanding behavioral responses to such changes is essential for identifying which organisms may successfully adapt to the altered conditions. In this study, individuals of a forest specialist ground beetle, Carabus convexus, from rural and urban forest patches were tested for their exploratory and risk-taking behavior. Beetles responded consistently in the different contexts; furthermore, by behaving consistently over time, demonstrated that they had personalities. Agglomerative cluster analysis identified two groups of behavioral traits: the exploratory and the risk-taking dimension of personality. Urban females were significantly more exploratory than urban males which can be an adaptation to find high quality food needed to mature eggs in urban habitats, as well as to select favorable microsites for oviposition. Moreover, urban females and males showed more risk-taking behavior than rural females. Urban beetles with more risk-taking behavior may be better able to cope with frequent urbanization-driven disturbance events.

Genetic association with boldness and maternal performance in a free-ranging population of grey seals (Halichoerus grypus)

Individual variation in quantitative traits clearly influence many ecological and evolutionary processes. Moderate to high heritability estimates of personality and life-history traits suggest some level of genetic control over these traits. Yet, we know very little of the underlying genetic architecture of phenotypic variation in the wild. In this study, we used a candidate gene approach to investigate the association of genetic variants with repeated measures of boldness and maternal performance traits (weaning mass and lactation duration) collected over an 11- and 28-year period, respectively, in a free-ranging population of grey seals on Sable Island National Park Reserve, Canada. We isolated and re-sequenced five genes: dopamine receptor D4 (DRD4), serotonin transporter (SERT), oxytocin receptor (OXTR), and melanocortin receptors 1 (MC1R) and 5 (MC5R). We discovered single nucleotide polymorphisms (SNPs) in each gene; and, after accounting for loci in linkage disequilibrium and filtering due to missing data, we were able to test for genotype-phenotype relationships at seven loci in three genes (DRD4, SERT, and MC1R). We tested for association between these loci and traits of 180 females having extreme shy-bold phenotypes using mixed-effects models. One locus within SERT was significantly associated with boldness (effect size = 0.189) and a second locus within DRD4 with weaning mass (effect size = 0.232). Altogether, genotypes explained 6.52-13.66% of total trait variation. Our study substantiates SERT and DRD4 as important determinants of behaviour, and provides unique insight into the molecular mechanisms underlying maternal performance variation in a marine predator.

Nonlinear maternal effects on personality in a rodent species with fluctuating densities

Consistent among-individual variation in behavior, or animal personality, is present in a wide variety of species. This behavioral variation is maintained by both genetic and environmental factors. Parental effects are a special case of environmental variation and are expected to evolve in populations experiencing large fluctuations in their environment. They represent a non-genetic pathway by which parents can transmit information to their offspring, by modulating their personality. While it is expected that parental effects contribute to the observed personality variation, this has rarely been studied in wild populations. We used the multimammate mouse Mastomys natalensis as a model system to investigate the potential effects of maternal personality on offspring behavior. We did this by repeatedly recording the behavior of individually housed juveniles which were born and raised in the lab from wild caught females. A linear correlation, between mother and offspring in behavior, would be expected when the personality is only affected by additive genetic variation, while a more complex relationship would suggests the presence of maternal effects. We found that the personality of the mother predicted the behavior of their offspring in a non-linear pattern. Exploration behavior of mother and offspring was positively correlated, but only for slow and average exploring mothers, while this correlation became negative for fast exploring mothers. This may suggests that early maternal effects could affect personality in juvenile M. natalensis, potentially due to density-dependent and negative frequency-dependent mechanisms, and therefore contribute to the maintenance of personality variation.

Biologia Futura: adaptive changes in urban populations

Cities represent novel environments where altered ecological conditions can generate strong selection pressures leading to the evolution of specific urban phenotypes. Is there evidence for such adaptive changes in urban populations which have colonized their new environments relatively recently? A growing number of studies suggest that rapid adaptations may be widespread in wild urban populations, including increased tolerance to various anthropogenic stressors, and physiological, morphological and behavioural changes in response to the altered resources and predation risk. Some of these adaptive changes are based on genetic differentiation, although other mechanisms, such as phenotypic plasticity and epigenetic effects, are also frequently involved.

Experimental evidence for a role of dopamine in avian personality traits

There is increasing interest in the genetic and physiological bases of behavioural differences among individuals, namely animal personality. One particular dopamine (DA) receptor gene (the dopamine receptor D4 gene) has been used as candidate gene to explain personality differences, but with mixed results. Here, we used an alternative approach, exogenously manipulating the dopaminergic system and testing for effects on personality assays in a social bird species, the common waxbill (Estrilda astrild). We treated birds with agonists and antagonists for DA receptors of both D1 and D2 receptor pathways (the latter includes the D4 receptor) and found that short-term manipulation of DA signalling had an immediate effect on personality-related behaviours. In an assay of social responses (mirror test), manipulation of D2 receptor pathways reduced time spent looking at the social stimulus (mirror image). Blocking D2 receptors reduced motor activity in this social assay, while treatment with a D2 receptor agonist augmented activity in this social assay but reduced activity in a non-social behavioural assay. Also, in the non-social assay, treatment with the D1 receptor antagonist markedly increased time spent at the feeder. These results show distinct and context-specific effects of the dopaminergic pathways on waxbill personality traits. Our results also suggest that experimental manipulation of DA signalling can disrupt a behavioural correlation (more active individuals being less attentive to mirror image) that is habitually observed as part of a behavioural syndrome in waxbills. We discuss our results in the context of animal personality, and the role of the DA system in reward and social behaviour.

Human recreation reduces clutch size in great tits Parus major regardless of risk-taking personality

Recreation negatively affects wildlife by influencing animal behavior vital to reproduction and survival. Such nonconsumptive effects of perceived predation risk are mainly studied in ground-breeding birds. However, if antipredator responses characterize bird species generally, so should nonconsumptive effects of perceived predation associated with human recreation. Moreover, as individuals consistently differ in behaviors linked to antipredator responses, they should also differ in responses to recreation, with bolder birds being less affected. To test this key prediction, we quantified effects of human recreation pressure on a cavity-breeding passerine. We uniquely quantified human recreation pressure over a substantial (8-year) period within 12 nest box populations of the great tit Parus major, assayed annually for reproductive parameters. We detected considerable spatial variation in recreation pressure. In plots with high recreation pressure, we found strong support for birds breeding further away from highly frequented paths and birds producing smaller clutches; we also found moderate support for birds producing fewer fledglings. These detrimental effects did not vary with behavioral proxies of an individual’s risk-taking phenotype (exploratory activity). This implies that effects of recreation pressure apply to the average bird, and extend to species (like forest birds) not previously considered.

Behavioural correlations of the domestication syndrome are decoupled in modern dog breeds

Domestication is hypothesized to drive correlated responses in animal morphology, physiology and behaviour, a phenomenon known as the domestication syndrome. However, we currently lack quantitative confirmation that suites of behaviours are correlated during domestication. Here we evaluate the strength and direction of behavioural correlations among key prosocial (sociability, playfulness) and reactive (fearfulness, aggression) behaviours implicated in the domestication syndrome in 76,158 dogs representing 78 registered breeds. Consistent with the domestication syndrome hypothesis, behavioural correlations within prosocial and reactive categories demonstrated the expected direction-specificity across dogs. However, correlational strength varied between dog breeds representing early (ancient) and late (modern) stages of domestication, with ancient breeds exhibiting exaggerated correlations compared to modern breeds across prosocial and reactive behaviours. Our results suggest that suites of correlated behaviours have been temporally decoupled during dog domestication and that recent shifts in selection pressures in modern dog breeds affect the expression of domestication-related behaviours independently.

Dog breeds differ in evolutionary age and admixture with wolves, enabling comparison across domestication stages. Here, Hansen Wheat et al. show that correlations among behaviours are decoupled in modern breeds compared to ancient breeds and suggest this reflects a recent shift in selection pressure.

Personality and plasticity in neophobia levels vary with anthropogenic disturbance but not toxic metal exposure in urban great tits: Urban disturbance, metal pollution and neophobia

Animal personalities, as defined by repeatable among individual differences in behavior, can vary across urbanization gradients. However, how urbanization affects personalities remains incompletely understood, especially because different urban stressors could affect personality traits in opposing ways, whereas most previous studies have considered only one urban disturbance factor. For instance, novel habitat features could favor reduced neophobia, whereas exposure to pollutants could increase risk sensitivity through neurotoxic or hormonal effects. To address this contingency, we studied object neophobia in four urban populations of great tits (Parus major) that vary in exposure to metal pollution and anthropogenic disturbance, as quantified by proximity to roads and pathways. We measured the return latency of incubating females when flushed from the nest and presented with up to two different novel objects, allowing quantification of behavioral repeatability and plasticity. To separate neophobia from sensitivity to disturbance, we also conducted baseline trials, in which females were flushed but no object was presented. We additionally measured exploration behavior and aggression (hissing) during nest defense, to explore whether suites of behaviors covary with urbanization, and examined whether neophobia affects reproductive success. Sensitivity to disturbance and neophobia were repeatable, and thus represent personality traits. Moreover, females occupying territories near roads and pathways had shorter return latencies during novel object but not baseline trials, suggesting a specific reduction in neophobia in disturbed areas. Plasticity in neophobia also increased with disturbance level. In contrast, metal exposure did not affect neophobia or sensitivity to disturbance, despite negatively correlating with exploration behavior. Neophobia correlated with exploration behavior, but not aggression or reproductive success. Results suggest that shifts in personality types in urbanized areas might involve specific reductions in neophobia, rather than general reductions in sensitivity to disturbance, and unexpectedly indicate no effect of toxic metals on risk sensitivity.

Variation in personality traits across a metal pollution gradient in a free-living songbird

Anthropogenic contaminants could alter traits central to animal behavioral types, or personalities, including aggressiveness, boldness and activity level. Lead and other toxic metals are persistent inorganic pollutants that affect organisms worldwide. Metal exposure can alter behavior by affecting neurology, endocrinology, and health. However, the direction and magnitude of the behavioral effects of metal exposure remain equivocal. Moreover, the degree to which metal exposure simultaneously affects suites of correlated behavioral traits (behavioral syndromes) that are controlled by common mechanisms remains unclear, with most studies focusing on single behaviors. Using a model species for personality variation, the great tit (Parus major), we explored differences in multiple behavioral traits across a pollution gradient where levels of metals, especially lead and cadmium, are elevated close to a smelter. We employed the novel environment exploration test, a proxy for variation in personality type, and also measured territorial aggressiveness and nest defense behavior. At polluted sites birds of both sexes displayed slower exploration behavior, which could reflect impaired neurological or physiological function. Territorial aggression and nest defense behavior were individually consistent, but did not vary with proximity to the smelter, suggesting that metal exposure does not concurrently affect exploration and aggression. Rather, exploration behavior appears more sensitive to metal pollution. Effects of metal pollution on exploration behavior, a key animal personality trait, could have critical effects on fitness.

A review of urban impacts on avian life-history evolution: Does city living lead to slower pace of life?

The concept of a pace-of-life syndrome describes inter- and intraspecific variation in several life-history traits along a slow-to-fast pace-of-life continuum, with long lifespans, low reproductive and metabolic rates, and elevated somatic defences at the slow end of the continuum and the opposite traits at the fast end. Pace-of-life can vary in relation to local environmental conditions (e.g. latitude, altitude), and here we propose that this variation may also occur along an anthropogenically modified environmental gradient. Based on a body of literature supporting the idea that city birds have longer lifespans, we predict that urban birds have a slower pace-of-life compared to rural birds and thus invest more in self maintenance and less in annual reproduction. Our statistical meta-analysis of two key traits related to pace-of-life, survival and breeding investment (clutch size), indicated that urban birds generally have higher survival, but smaller clutch sizes. The latter finding (smaller clutches in urban habitats) seemed to be mainly a characteristic of smaller passerines. We also reviewed urbanization studies on other traits that can be associated with pace-of-life and are related to either reproductive investment or self-maintenance. Though sample sizes were generally too small to conduct formal meta-analyses, published literature suggests that urban birds tend to produce lower-quality sexual signals and invest more in offspring care. The latter finding is in agreement with the adult survival hypothesis, proposing that higher adult survival prospects favour investment in fewer offspring per year. According to our hypothesis, differences in age structure should arise between urban and rural populations, providing a novel alternative explanation for physiological differences and earlier breeding. We encourage more research investigating how telomere dynamics, immune defences, antioxidants and oxidative damage in different tissues vary along the urbanization gradient, and suggest that applying pace-of-life framework to studies of variation in physiological traits along the urbanization gradient might be the next direction to improve our understanding of urbanization as an evolutionary process.

Repeatability and degree of territorial aggression differs among urban and rural great tits (Parus major)

Animals in urban habitats face many novel selection pressures such as increased human population densities and human disturbance. This is predicted to favour bolder and more aggressive individuals together with greater flexibility in behaviour. Previous work has focussed primarily on studying these traits in captive birds and has shown increased aggression and reduced consistency between traits (behavioural syndromes) in birds from urban populations. However, personality (consistency within a behavioural trait) has not been well studied in the wild. Here we tested whether urban free-living male great tits show greater territorial aggression than rural counterparts. We also tested predictions that both behavioural syndromes and personality would show lower consistency in urban populations. We found that urban populations were more aggressive than rural populations and urban birds appeared to show lower levels of individual behavioural repeatability (personality) as predicted. However, we found no effect of urbanisation on behavioural syndromes (correlations between multiple behavioural traits). Our results indicate that urban environments may favour individuals which exhibit increased territorial aggression and greater within-trait flexibility which may be essential to success in holding urban territories. Determining how urban environments impact key fitness traits will be important in predicting how animals cope with ongoing urbanisation.

Evolution of life in urban environments

Our planet is an increasingly urbanized landscape, with over half of the human population residing in cities. Despite advances in urban ecology, we do not adequately understand how urbanization affects the evolution of organisms, nor how this evolution may affect ecosystems and human health. Here, we review evidence for the effects of urbanization on the evolution of microbes, plants, and animals that inhabit cities. Urbanization affects adaptive and nonadaptive evolutionary processes that shape the genetic diversity within and between populations. Rapid adaptation has facilitated the success of some native species in urban areas, but it has also allowed human pests and disease to spread more rapidly. The nascent field of urban evolution brings together efforts to understand evolution in response to environmental change while developing new hypotheses concerning adaptation to urban infrastructure and human socioeconomic activity. The next generation of research on urban evolution will provide critical insight into the importance of evolution for sustainable interactions between humans and our city environments.

Mary CM. Does the use of a multi-trait, multi-test approach to measure animal personality yield different behavioural syndrome results?

A multi-trait, multi-test approach to investigate the convergence or discrimination between behavioural tests putatively targeting the same or different animal personality traits has been recommended, yet whether and how the approaches affect the identification of behavioural syndrome(s), the suite of correlated personality traits, requires investigation. Here, we used behavioural measures collected from five commonly used behavioural tests targeting three personality traits, evaluated their convergence/discrimination through exploratory factor analysis (EFA), and then explored whether the identification of syndrome changed based on the approach we used to quantify personality traits. Our results indicated that tests presumably targeting the same personality trait actually measured distinct behavioural aspects. Syndrome defined using correlation changed due to how we identified personality traits, but not when using structural equation models (SEMs). Overall, this study emphasizes that it is critical to clarify the approach and terms we use for ‘personality traits’ in the field of animal personality.