No evidence for behavioural syndrome and genetic basis for three personality traits in a wild bird population

Constitutive gene expression differs in three brain regions important for cognition in neophobic and non-neophobic house sparrows (Passer domesticus)

Neophobia (aversion to new objects, food, and environments) is a personality trait that affects the ability of wildlife to adapt to new challenges and opportunities. Despite the ubiquity and importance of this trait, the molecular mechanisms underlying repeatable individual differences in neophobia in wild animals are poorly understood. We evaluated wild-caught house sparrows (Passer domesticus) for neophobia in the lab using novel object tests. We then selected a subset of neophobic and non-neophobic individuals (n = 3 of each, all females) and extracted RNA from four brain regions involved in learning, memory, threat perception, and executive function: striatum, caudal dorsomedial hippocampus, medial ventral arcopallium, and caudolateral nidopallium (NCL). Our analysis of differentially expressed genes (DEGs) used 11,889 gene regions annotated in the house sparrow reference genome for which we had an average of 25.7 million mapped reads/sample. PERMANOVA identified significant effects of brain region, phenotype (neophobic vs. non-neophobic), and a brain region by phenotype interaction. Comparing neophobic and non-neophobic birds revealed constitutive differences in DEGs in three of the four brain regions examined: hippocampus (12% of the transcriptome significantly differentially expressed), striatum (4%) and NCL (3%). DEGs included important known neuroendocrine mediators of learning, memory, executive function, and anxiety behavior, including serotonin receptor 5A, dopamine receptors 1, 2 and 5 (downregulated in neophobic birds), and estrogen receptor beta (upregulated in neophobic birds). These results suggest that some of the behavioral differences between phenotypes may be due to underlying gene expression differences in the brain. The large number of DEGs in neophobic and non-neophobic birds also implies that there are major differences in neural function between the two phenotypes that could affect a wide variety of behavioral traits beyond neophobia.

Unravelling the causes and consequences of dispersal syndromes in a wild passerine

Evidence accumulates that dispersal is correlated with individual behavioural phenotype (dispersal syndrome). The evolutionary causes and consequences of such covariation depend on the degree of plasticity versus inheritance of the traits, which requires challenging experiments to implement in mobile organisms. Here, we combine a forced dispersal experiment, natural colonization and longitudinal data to establish if dispersal and aggression levels are integrated and to test their adaptive nature in pied flycatchers (Ficedula hypoleuca). We found that (forced) dispersers behaved more aggressively in their first breeding year after dispersal and decreased their aggression in following years. Strength of dispersal syndrome and direction of fecundity selection on aggression in newly colonized areas varied between years. We propose that the net benefits of aggression for dispersers increase under harsh conditions (e.g. low food abundance). This hypothesis now warrants further testing. Overall, this study provides unprecedented experimental evidence that dispersal syndromes can be remodelled via adaptive plasticity depending on the individuals' local breeding experience and/or year-specific ecological conditions. It highlights the importance of individual behavioural variation in population dynamics.

A transient reduction in circulating corticosterone reduces object neophobia in male house sparrows

Aversive reactions to novelty (or "neophobia") have been described in a wide variety of different animal species and can affect an individual's ability to exploit new resources and avoid potential dangers. However, despite its ecological importance, the proximate causes of neophobia are poorly understood. In this study, we tested the role of glucocorticoid hormones in neophobia in wild-caught house sparrows (Passer domesticus, n = 11 males) by giving an injection of the drug mitotane that reduced endogenous corticosterone for several days or a vehicle control, and then examined the latency to feed when the food dish was presented with or without a novel object in, on, or near the dish. Each sparrow was exposed to multiple novel object and control trials and received both vehicle control and mitotane treatments, with a week between treatments to allow the drug to wash out. As found previously, all novel objects significantly increased sparrows' latency to feed compared to no object present. Reducing corticosterone using mitotane significantly reduced the latency to feed in the presence of novel objects. In control trials without objects, mitotane had no significant effects on feeding time. Although we have shown that corticosterone affects neophobia, further studies using specific receptor agonists and antagonists will help clarify the neurobiological mechanisms involved and determine whether baseline or stress-induced corticosterone is driving this effect. These results suggest that increased glucocorticoids (e.g., due to human-induced stressors) could increase neophobia, affecting the ability of individuals to exploit novel resources, and, ultimately, to persist in human-altered environments.

Assortative mating for between-patch dispersal status in a wild bird population: Exploring the role of direct and indirect underlying mechanisms

Previous studies have reported functional integration between dispersal and other phenotypic traits allowing individuals to alleviate dispersal costs, and such associations can affect dispersal evolution in return. In sexually reproducing species, assortative mating according to dispersal can shape the maintenance of such trait associations. Despite the potentially crucial consequences of dispersal in natural populations, assortative mating for dispersal and its underlying mechanisms remain largely unexplored. Here, we assessed assortative mating for between-patch dispersal status in a fragmented population of a small passerine bird, the collared flycatcher, and explored whether such assortative mating could result from (i) direct mate choice based on dispersal-related behavioural (aggressiveness and boldness) and morphological traits (tarsus and wing length), (ii) biased mating due to spatio-temporal heterogeneity in the distribution of dispersal phenotypes and/or (iii) post-mating adjustment of dispersal phenotype or dispersal-related traits. We found intrinsic assortative mating (i.e. positive among-pair correlation) for current dispersal status (in the year of mating) but not for natal dispersal status, even though we could not exclude it due to limited power. We also found assortative mating for boldness and age category (yearlings vs. older adults), and the probability for pair members to be assorted for current dispersal status was higher when both pair members were of similar boldness score and of the same age compared with mixed-age pairs. Mate choice based on boldness and age thus appears as a possible mechanism underlying assortative mating for dispersal status. Our analyses however remained correlative, and only an experimental manipulation of these traits could allow inferring causal links. Non-random mating for dispersal-related traits may affect the evolution of dispersal syndromes in this population. More work is nevertheless needed to fully assess the evolutionary implications of age- and behaviour-based assortative mating for dispersal.

Male aggressiveness and risk-taking during reproduction are repeatable but not correlated in a wild bird population

Abstract

The existence of among-individual variation in behaviour within populations is poorly understood. Recent theory suggests that fine-scale individual differences in investment into current versus future reproduction may lead to a ‘slow-fast’-pace-of-life continuum, also referred to as the ‘pace-of-life-syndrome’ (POLS) hypothesis. According to this idea, individuals are predicted to differ in their level of risk-taking, which may drive among-individual variation and covariation of behaviours. Consistent individual differences in aggression, an ecologically relevant and potentially risky behaviour, have been reported across the animal kingdom. Here we test whether such individual differences in aggression are a manifestation of underlying differences in risk-taking. In a wild blue tit (Cyanistes caeruleus) population, we used standard behavioural tests to investigate if male territorial aggressiveness and risk-taking during breeding are positively related. At the start of breeding, we simulated conspecific territorial intrusions to obtain repeated measures of male aggressiveness. Subsequently, we measured male risk-taking as their latency to resume brood provisioning after presenting two different predators at their nest: human and sparrowhawk, a common predator of adult songbirds. First, we found substantial repeatability for male aggressiveness (R = 0.56 ± 0.08 SE). Second, while males took longer to resume provisioning after presentation of a sparrowhawk mount as compared to a human observer, risk-taking was repeatable across these two predator contexts (R = 0.51 ± 0.13 SE). Finally, we found no evidence for a correlation between male aggressiveness and risk-taking, thereby providing little support to a main prediction of the POLS hypothesis.

Significance statement

Consistent, and often correlated, individual differences in basal behaviours, such as aggression, exploration and sociability, are found across the animal kingdom. Why individuals consistently differ in their behaviour is poorly understood, as behavioural traits would seem inherently flexible. The ‘pace-of-life syndrome’ (POLS) hypothesis proposes observed behavioural variation to reflect differences in risk-taking associated with individual reproductive strategies. We tested this idea in a wild blue tit population by investigating whether individual males that were more aggressive toward territorial intruders also took more risk when provisioning their nestlings under a threat of predation. While we found consistent individual differences in both aggressiveness and risk-taking, these behaviours were not significantly correlated. Therefore, our study demonstrates among-individual variation in ecologically relevant behaviours in wild blue tits but provides little support for the POLS hypothesis.

Behavioural traits modulate the use of heterospecific social information for nest site selection: experimental evidence from a wild bird population

The use of social information for making decisions is common but can be constrained by behavioural traits via, for example, the ability to gather information. Such constrained information use has been described in foraging habitat selection; yet it remains unexplored in the breeding habitat selection context, despite potentially strong fitness consequences. We experimentally tested whether three behavioural traits (aggressiveness, boldness and neophobia) affected the use of heterospecific social information for nest site selection in wild collared flycatchers Ficedula albicollis. Flycatchers have previously been found to copy or reject an artificial apparent preference of tits (their main competitors) for a nest site feature: they preferred nest-boxes with the same or a different feature, depending on tit early reproductive investment. Here, we confirmed this result and showed that shy individuals and less aggressive old males (i.e. 2 years old or older) copied tit apparent preference, while more aggressive old males rejected the tit preference. Aggressiveness and boldness may allow males to access more information sources or affect males' interactions with dominant tits when selecting a nest site. Our study highlights the links between variation in behaviours and social information use for breeding habitat selection and calls for further work to explore underlying mechanisms.

Morphological Correlates of Personality in Female Asian Particolored Bats (Vespertilio sinensis)

Simple Summary

Personality emerges because of individual differences in repeatable state variables, such as metabolic rate, age, sex, or body size. Personality and its correlation with body size, however, have been relatively unexplored in bats. Our study showed that the exploration of female Asian particolored bats was significantly repeatable, but we did not find significant correlations among exploration, activity, and aggression. This finding suggested that female Asian particolored bats may not have a behavioral syndrome. Additionally, the body mass of female Asian particolored bats was correlated with aggression and activity, suggesting that body mass may have an impact on the behavioral characteristics of bats. Our findings not only added to the literature concerning personality in bats but are also helpful for understanding the maintenance of an animal’s personality.

Abstract

Personality traits represent a leading edge in the evolutionary process, as natural selection acts directly on variations in individual phenotypes within populations. Recent theoretical models have focused on the concept of adaptive state-dependent behavior, proposing that repeatable differences in behavior emerge because of individual differences in repeatable state variables, such as metabolic rate, age, sex, or body size. Personality and its correlation with body size, however, have been relatively unexplored in bats. We used female Asian particolored bats (Vespertilio sinensis) to investigate three personality characteristics (exploration, activity, and aggression) using the classic hole-board test and examined their relationships with body size using an information-theoretical approach. Our results showed that the exploration of female Asian particolored bats was significantly repeatable, but we did not find significant correlations among the three personality traits. This finding suggested that the female Asian particolored bat may not have a behavioral syndrome. In addition, the body mass of female Asian particolored bats was positively correlated with aggression but was negatively correlated with activity, suggesting that body mass was an important physiological basis affecting the behavioral characteristics of female Asian particolored bats.