Do brood sex ratio, nestling development and sex affect fledging timing and order? An experimental study on great tits

The process of nest leaving (fledging) in hole-breeding passerines is largely unexplored, although it is potentially an important facet of reproduction. We used the great tit, Parus major, to investigate whether fledging timing and order were affected by nestling development and sex, as well as the sex ratio in the brood the nestlings were raised in. Because of the difference in size and competitiveness between male and female nestlings, we expected to find an effect of sex and brood sex ratio (BSR) on the process of fledging. To explore its effect on fledging experimentally, we manipulated BSR by swapping 6-day-old nestlings of both sexes. We implanted transponders in all 14-day-old nestlings to determine timing and order of fledging. The brood age at fledging was best explained by average wing length of the brood (negative), average body mass of the brood (positive) and hatching date (negative). In contrast to our hypothesis, BSR did not affect fledging time. Also, the asynchrony of fledging within broods did not depend on BSR. Within broods, fledging order was not affected by sex or by the interaction between sex and BSR. Nestlings with long wings on day 14 fledged earlier than nestmates with shorter wings. Although females were lighter at day 14, they had similar length wings as their male nestmates. Nestlings should keep up with their nestmates during development, because developmental status relative to nestmates, rather than sex-specific competition, influenced the process of fledging.

Reproductive effort affects spatial distribution in Great tits

Poster at The Sixth International Hole Nesting Bird Conference. Oxford. Great Britain. July 201

Seasonal variation in the response to a toxin-producing cyanobacteria in Daphnia

Many populations of water fleas (Daphnia) are exposed to algal blooms dominated by microcystin-producing cyanobacteria. However, the severity of these effects on Daphnia fitness remain poorly understood in natural populations. We investigated seasonal changes in body size, reproduction and survival of D. longispina individuals from five eutrophic lakes in southern Sweden. We tested whether individuals collected before, during or following algal blooms differed in their reproduction and survival when experimentally exposed to microcystin-producing cyanobacteria. The concentration of microcystin in the lakes was significantly higher during summer and autumn compared to spring, but there were substantial differences between lakes. The reproductive output of individuals declined consistently over the season, and this decline was stronger for Daphnia collected during periods of, or from lakes with, high microcystin concentration. There was little evidence that individuals adapted to the toxin over the season. The strong seasonal changes in body size, reproduction and survival in these D. longispina appear to be caused partly by variation in the abundance of toxin-producing cyanobacteria. Populations were unable to adapt sufficiently quickly during summer and autumn to recover from the negative effects of microcystin. We therefore suggest that seasonal increases in tolerance to microcystin-producing cyanobacteria have limited effects on the eco-evolutionary dynamics between Daphnia and phytoplankton

A field experiment reveals seasonal variation in the Daphnia gut microbiome

The gut microbiome is increasingly recognized for its impact on host fitness, but it remains poorly understood how naturally variable environments influence gut microbiome diversity and composition. We studied changes in the gut microbiome of ten genotypes of water fleas Daphnia magna in submerged mesocosm enclosures in a eutrophic lake over a period of 16 weeks, from early summer to autumn. The microbial diversity increased when Daphnia were reintroduced from the laboratory to the lake, and the composition of gut microbes drastically changed. Both gut microbiome diversity and composition continued to change over the 16-week period, with alpha diversity peaking in late summer. The gut microbiome community was clearly distinct from that of the surrounding water, and temporal changes in the two communities were independent of each other. There were no consistent differences in the gut microbiomes among Daphnia genotypes in the lake environment. The change in gut microbiome over the season was accompanied by a decline in reproductive output and survival. There were weak, but statistically supported, effects of microbiota composition on Daphnia fitness, but there was no evidence that natural variation in microbiome diversity or composition was associated with tolerance to the cyanotoxin microcystin. We conclude that the gut microbiome of Daphnia is highly dynamic in a natural lake environment, but that host genetic effects on microbiome diversity and composition between genotypes within a population can be vanishingly small. These results emphasize that establishing the ecological effects of gut microbiota will require large-scale experiments under natural conditions

Genetics and developmental biology of cooperation

Despite essential progress towards understanding the evolution of cooperative behaviour, we still lack detailed knowledge about its underlying molecular mechanisms, genetic basis, evolutionary dynamics and ontogeny. An international workshop "Genetics and Development of Cooperation," organized by the University of Bern (Switzerland), aimed at discussing the current progress in this research field and suggesting avenues for future research. This review uses the major themes of the meeting as a springboard to synthesize the concepts of genetic and nongenetic inheritance of cooperation, and to review a quantitative genetic framework that allows for the inclusion of indirect genetic effects. Furthermore, we argue that including nongenetic inheritance, such as transgenerational epigenetic effects, parental effects, ecological and cultural inheritance, provides a more nuanced view of the evolution of cooperation. We summarize those genes and molecular pathways in a range of species that seem promising candidates for mechanisms underlying cooperative behaviours. Concerning the neurobiological substrate of cooperation, we suggest three cognitive skills necessary for the ability to cooperate: (i) event memory, (ii) synchrony with others and (iii) responsiveness to others. Taking a closer look at the developmental trajectories that lead to the expression of cooperative behaviours, we discuss the dichotomy between early morphological specialization in social insects and more flexible behavioural specialization in cooperatively breeding vertebrates. Finally, we provide recommendations for which biological systems and species may be particularly suitable, which specific traits and parameters should be measured, what type of approaches should be followed, and which methods should be employed in studies of cooperation to better understand how cooperation evolves and manifests in nature

Environmentally induced DNA methylation is inherited across generations in an aquatic keystone species

Transgenerational inheritance of environmentally induced epigenetic marks can have significant impacts on eco-evolutionary dynamics, but the phenomenon remains controversial in ecological model systems. We used whole-genome bisulfite sequencing of individual water fleas (Daphnia magna) to assess whether environmentally induced DNA methylation is transgenerationally inherited. Genetically identical females were exposed to one of three natural stressors, or a de-methylating drug, and their offspring were propagated clonally for four generations under control conditions. We identified between 70 and 225 differentially methylated CpG positions (DMPs) in F1 individuals whose mothers were exposed to a natural stressor. Roughly half of these environmentally induced DMPs persisted until generation F4. In contrast, treatment with the drug demonstrated that pervasive hypomethylation upon exposure is reset almost completely after one generation. These results suggest that environmentally induced DNA methylation is non-random and stably inherited across generations in Daphnia, making epigenetic inheritance a putative factor in the eco-evolutionary dynamics of freshwater communities

Hampered Foraging and Migratory Performance in Swans Infected with Low-Pathogenic Avian Influenza A Virus

It is increasingly acknowledged that migratory birds, notably waterfowl, play a critical role in the maintenance and spread of influenza A viruses. In order to elucidate the epidemiology of influenza A viruses in their natural hosts, a better understanding of the pathological effects in these hosts is required. Here we report on the feeding and migratory performance of wild migratory Bewick's swans (Cygnus columbianus bewickii Yarrell) naturally infected with low-pathogenic avian influenza (LPAI) A viruses of subtypes H6N2 and H6N8. Using information on geolocation data collected from Global Positioning Systems fitted to neck-collars, we show that infected swans experienced delayed migration, leaving their wintering site more than a month after uninfected animals. This was correlated with infected birds travelling shorter distances and fuelling and feeding at reduced rates. The data suggest that LPAI virus infections in wild migratory birds may have higher clinical and ecological impacts than previously recognised

Estimating heritability of social phenotypes from social networks

For understanding how social behaviour evolves and responds to selection, we need to be able to accurately estimate heritability with quantitative genetic models. More recently, this has moved into using node-specific statistics from social networks as social phenotypes. However, parameter estimation can be problematic because social phenotypes are not independent observations and standard models tend to ignore the uncertainties around their estimates. Here I present a framework using latent variable modelling to account for these dependencies and uncertainties. I use edge weights, rather than node-specific network statistics, as dependent variables. From these edge weights, two types of latent (i.e. unobserved) phenotypes are estimated: the individual tendency to be social (i.e. social tendency) and the relative contribution to associations (i.e. social governance). Effects of the social environment and indirect genetic effects are accounted for in the model and can be estimated post hoc. If edge weights are a proportion (e.g. simple ratio index) their uncertainty can be accounted for by a binomial sampling process. I illustrate this method in Stan, a flexible Bayesian inference library, using a publicly available dataset on bottlenose dolphin networks. This method not only accounts for dependencies and uncertainties, it also illuminates aspects of social evolution which are not observed with standard quantitative genetic models. For instance, indirect genetic effects models predict heritable variation in sociality (21.9%), while latent variable modelling shows heritability of social tendency (28.7%), but not for social governance (0.0%). Covariates at different levels in the model (edge and node level) highlight differences in sociality between different foraging strategies and the sexes. This example shows that not properly accounting for the assumptions underlying the use of social network statistics can have misleading effects on conclusions. Although some model assumption violations are less common, others are inherit to the study of (semi)wild populations. The presented framework offers solutions for some critical assumptions and is a flexible tool to further develop and tailor to the needs of specific studies, to ensure the proper fit to the study system