Sex roles in birds : phylogenetic analyses of the influence of climate, life histories and social environment

Sex roles describe sex differences in courtship, mate competition, social pair-bonds and parental care. A key challenge is to identify associations among the components and the drivers of sex roles. Here, we investigate sex roles using data from over 1800 bird species. We found extensive variation and lability in proxies of sex roles, indicating remarkably independent evolution among sex role components. Climate and life history showed weak associations with sex roles. However, adult sex ratio is associated with sexual dimorphism, mating system and parental care, suggesting that social environment is central to explaining variation in sex roles among birds. Our results suggest that sex differences in reproductive behaviour are the result of diverse and idiosyncratic responses to selection. Further understanding of sex roles requires studies at the population level to test how local responses to ecology, life histories and mating opportunities drive processes that shape sex role variation among higher taxa

Telomere length reveals cumulative individual and transgenerational inbreeding effects in a passerine bird

Inbreeding results in more homozygous offspring that should suffer reduced fitness, but it can be difficult to quantify these costs for several reasons. First, inbreeding depression may vary with ecological or physiological stress and only be detectable over long time periods. Second, parental homozygosity may indirectly affect offspring fitness, thus confounding analyses that consider offspring homozygosity alone. Finally, measurement of inbreeding coefficients, survival and reproductive success may often be too crude to detect inbreeding costs in wild populations. Telomere length provides a more precise measure of somatic costs, predicts survival in many species and should reflect differences in somatic condition that result from varying ability to cope with environmental stressors. We studied relative telomere length in a wild population of Seychelles warblers (Acrocephalus sechellensis) to assess the lifelong relationship between individual homozygosity, which reflects genome-wide inbreeding in this species, and telomere length. In juveniles, individual homozygosity was negatively associated with telomere length in poor seasons. In adults, individual homozygosity was consistently negatively related to telomere length, suggesting the accumulation of inbreeding depression during life. Maternal homozygosity also negatively predicted offspring telomere length. Our results show that somatic inbreeding costs are environmentally dependent at certain life stages but may accumulate throughout life.</p

Causes and consequences of telomere lengthening in a wild vertebrate population

Telomeres have been advocated to be important markers of biological age in evolutionary and ecological studies. Telomeres usually shorten with age and shortening is frequently associated with environmental stressors and increased subsequent mortality. Telomere lengthening – an apparent increase in telomere length between repeated samples from the same individual – also occurs. However, the exact circumstances, and consequences, of telomere lengthening are poorly understood. Using longitudinal data from the Seychelles warbler (Acrocephalus sechellensis), we tested whether telomere lengthening – which occurs in adults of this species – is associated with specific stressors (reproductive effort, food availability, malarial infection and cooperative breeding) and predicts subsequent survival. In females, telomere shortening was observed under greater stress (i.e., low food availability, malaria infection), while telomere lengthening was observed in females experiencing lower stress (i.e., high food availability, assisted by helpers, without malaria). The telomere dynamics of males were not associated with the key stressors tested. These results indicate that, at least for females, telomere lengthening occurs in circumstances more conducive to self-maintenance. Importantly, both females and males with lengthened telomeres had improved subsequent survival relative to individuals that displayed unchanged, or shortened, telomeres – indicating that telomere lengthening is associated with individual fitness. These results demonstrate that telomere dynamics are bidirectionally responsive to the level of stress that an individual faces, but may poorly reflect the accumulation of stress over an individuals lifetime

Breeding biology of two populations of Chinese penduline tits

The phenotypes and breeding behavior in one species may be different between populations. The local environments, social interactions can all lead to some variations in life history. The thorough investigations of breeding biology over populations can provide insights for us to understand the evolution and diversifications of breeding systems and phenotypic traits from multiple perspectives other than drawing monotonous associations between a factor and a trait. In this study, we explored two Chinese penduline populations, Liaohekou (LHK) and Xianghai (XH), both in the northeast of China located 550 km away from each other. A comparative study of the breeding biology was carried on in the two populations. We found that the climate has no obvious difference in these two populations but has different habitats. Nest emergence and egg-laying were earlier in the more northern population XH. Males in XH has a lower chance of pairing up with a female and exhibit mainly biparental care pattern instead uniparental care that we reported in LHK. The chick fledgling success in the biparental care nests was higher than in the uniparental care nests in XH, but no difference to the uniparental care nests in LHK. Besides, the penduline tits in the two populations were also significantly different in their wing length, tail length and beak shape. These incongruences suggested different food availability, adult sex ratio and migration distances of the two populations. Future studies should experimentally investigate the joint influences of breeding perspectives on the evolution of parental care and mating system

Effects of season length and uniparental care efficiency on the evolution of parental care

Parental care patterns differ enormously among and even within species. In Chinese penduline tits (Remiz pendulinus), for example, biparental care, female-only care, male-only care, and biparental desertion all occur in the same population; moreover, the distribution of care patterns differs systematically between populations. By means of an individual-based model, we show that such diversity can readily evolve. We report five main findings. First, under a broad range of parameters, different care patterns (e.g. male care and biparental care) coexist at equilibrium. Second, for many parameters, alternative evolutionary outcomes are possible; this can explain differences in care patterns across populations. Third, rapid evolutionary transitions can occur between alternative equilibria; this can explain the often-reported evolutionary lability of parental care patterns. Fourth, season length has a strong but non-monotonic effect on the evolved care patterns. Fifth, when uniparental care efficiency is low, biparental care tends to evolve; however, in many scenarios uniparental care is still common at equilibrium. Our study sheds new light on Triver’s hypothesis that the sex with the highest pre-zygotic investment is predestined to invest a lot post-zygotically as well. We also discuss the implications of climate change, which simultaneously affects season length and efficiency of parental care

Data from: Evolution of defense against depletion of local food resources in a mechanistic foraging model

Abstract Models of resource defense are usually based on the assumption that individuals fight over the possession of discrete food items. In many territorial species however conflicts occur over access to an area in space that contains resources rather than the resources themselves. We investigate under which conditions defense against depletion of local resources instead of single resource items can evolve from a non-aggressive ancestral population using a spatially explicit mechanistic model with resource dynamics and individual movement. We find that in general details of the model assumptions have a great influence on the costs and benefits of different behavior in the model. For patchy resources defense evolves if fighting costs are very high or if individuals can not avoid conflicts. If resources are distributed uniformly defense appears only if individuals can make their behavior dependent on distance to their opponent. Introducing role asymmetries during conflicts in general increases the frequency of contests but reduces the probability that they escalate. If losers of a fight control how far they run aggressiveness disappears or is greatly reduced for patchy resources but increases significantly for uniform resource distribution. Our results show how defense of space and territoriality could evolve even if resources are neither discrete nor clumped. The fact that seemingly minor differences in how individuals make decisions during encounters lead to huge differences in model outcome highlights the need for more mechanistic models of animal conflicts.,simulation source files. Complete C++ sources for the simulation program described in the article.src.zip

Data from: No effect of partner age and lifespan on female age-specific reproductive performance in blue tits

Studies of age-specific reproductive performance are fundamental to our understanding of population dynamics and the evolution of life-history strategies. In species with bi-parental care, reproductive ageing trajectories of either parent may be influenced by their partner's age, but this has rarely been investigated. We investigated within-individual age-specific performance (laying date and number of eggs laid) in wild female blue tits Cyanistes caeruleus and evaluated how the age and longevity of their male partner indirectly influenced the females' reproductive performance. Females showed clear age-dependence in both laying date and number of eggs laid. We found that female reproductive performance improved in early life, before showing a decline. Longer-lived females had an earlier laying date throughout their lives than shorter-lived females, but there was no difference in number of eggs laid between longer- and shorter-lived females. Within breeding pairs, the female's (age-specific) reproductive performance was not dependent on the age and longevity of the male partner. We conclude that the age and quality of the male partner may be of little importance for traits that are under direct female control. The data package contains one dataset: -Amininasab_etal_JAB_Dryad This data was used for analyses on manuscript entitled :No effect of partner age and lifespan on female age-specific reproductive performance in blue tit

Data from: The cost of prospecting for dispersal opportunities in a social bird

Understanding why individuals delay dispersal and become subordinates within a group is central to studying the evolution of sociality. Hypotheses predict that dispersal decisions are influenced by costs of extra-territorial prospecting that are often required to find a breeding vacancy. Little is known about such costs, partly because it is complicated to demonstrate them empirically. For example, prospecting individuals may be of inferior quality already before prospecting and/or have been evicted. Moreover, costs of prospecting are mainly studied in species where prospectors suffer from predation risk, so how costly prospecting is when predators are absent remains unclear. Here, we determine a cost of prospecting for subordinate Seychelles warblers, Acrocephalus sechellensis, in a population where predators are absent and individuals return to their resident territory after prospecting. Prospecting individuals had 5.2% lower body mass than non-prospecting individuals. Our evidence suggests this may be owing to frequent attacks by resident conspecifics, likely leading to reduced food intake by prospectors. These results support the hypothesis that energetic costs associated with dispersal opportunities are one factor influencing dispersal decisions and shaping the evolution of delayed dispersal in social animals.,Data_Kingma_etal_ProspectingCostsBody condition data of resident and prospecting individuals. All additional data used in the analyses are included.

Data from: Covariance of paternity and sex with laying order explains male bias in extra-pair offspring in a wild bird population

It has been hypothesized that parents increase their fitness by biasing the sex ratio of extra-pair offspring (EPO) towards males. Here, we report a male bias among EPO in a wild population of blue tits (Cyanistes caeruleus). This resulted from a decline in both the proportion of males and EPO over the laying order of eggs in the clutch. However, previous studies suggest that, unlike the decline in EPO with laying order, the relationship between offspring sex ratio and laying order is not consistent between years and populations in this species. Hence, we caution against treating the decline in proportion of males with laying order, and the resulting male bias among EPO, as support for the above hypothesis. Variable patterns of offspring sex and paternity over the laying order may explain inconsistent associations between offspring sex and paternity, between and within species. The data package contains one dataset: - Laying order, sex and paternity of blue tit hatchlings in 2009 Laying order, sex and paternity of 743 blue tit hatchlings in 2009, from 68 broods

The impact of breeding experience and social status on group interactions and fitness in a communally breeding species

In group breeding species, not only prior breeding experiences, but also an individual’s social status and that of the group members it interacts with, may influence an individual’s future behaviour and fitness. Here, we report an experimental study on the facultatively communal breeding burying beetles, Nicrophorus vespilloides, in which we tested the combined effects of prior breeding experience and dominance status (dominant vs. subordinate) of focal individuals and those of other group members on aggressive interactions, parental investment and fitness during a future breeding event. In the presence of inexperienced subordinates, there was less aggressiveness towards experienced dominants than to inexperienced dominants, which resulted in a lower injury degree of dominants. Compared to inexperienced dominant or subordinate individuals, experienced dominants with prior breeding experience increased their parental investment, whereas experienced subordinates reduced their parental investment and by doing so avoid the escalation of aggressive interactions. Consequently, dominants may benefit from the presence of experienced subordinates because they gain enhanced benefits in reproduction, or suffer less from aggressive interactions with others. Our results highlight the importance of an individual’s own breeding experience and social status and that of other group members for mediating individual behaviour and social interactions in groups resulting in higher net fitness.,See ReadMe file.