Sharing the burden : on the division of parental care and vocalizations during incubation

In species with biparental care, individuals only have to pay the costs for their own parental investment, whereas the contribution of their partner comes for free. Each parent hence benefits if its partner works harder, creating an evolutionary conflict of interest. How parents resolve this conflict and how they achieve the optimal division of parental tasks often remains elusive. In this study, we investigated whether lesser black-backed gulls (Larus fuscus) divide parental care during incubation equally and whether this correlates with the extent of vocalizations between pair-members during incubation. We then investigated whether pairs showing more evenly distributed incubation behavior had a higher reproductive success. To this end, we recorded incubation behavior and vocalizations for 24-h time periods. Subsequently, we experimentally increased or decreased brood sizes in order to manipulate parental effort, and followed offspring development from hatching till fledging. Although incubation bouts were, on average, slightly longer in females, patterns varied strongly between pairs, ranging from primarily female incubation over equal sex contributions to male-biased incubation. Pairs contributing more equally to incubation vocalized more during nest relief and had a higher reproductive output when brood sizes were experimentally increased. Thus, vocalizations and a more equal division of parental care during incubation may facilitate higher levels of care during the nestling period, as suggested by a greater reproductive success when facing high brood demand, or they indicate pair quality

Nest predation in Afrotropical forest fragments shaped by inverse edge effects, timing of nest initiation and vegetation structure

High levels of nest predation influence the population dynamics of many tropical birds, especially when deforestation alters nest predator communities. The consequences of tropical forest fragmentation on nest predation, however, remain poorly understood, as natural predation patterns have only been well documented in a handful of tropical forests. Here, we show the results of an extensive study of predation on natural nests of Cabanis's Greenbul (Phyllastrephus cabanisi) during 3 years in a highly fragmented cloud forest in SE Kenya. Overall predation rates derived from 228 scrub nests averaged 69 %, matching the typical high predation level on tropical bird species. However, predation rates strongly varied in space and time, and a model that combined timing effects of fragment, edge, concealment, year and nest was best supported by our data. Nest predation rates consistently increased from forest edge to interior, opposing the classic edge effect on nest predation, and supporting the idea that classic edge effects are much rarer in Afrotropical forests than elsewhere. Nest concealment also affected predation rates, but the strength and direction of the relationship varied across breeding seasons and fragments. Apart from spatial variation, predation rates declined during the breeding season, although the strength of this pattern varied among breeding seasons. Complex and variable relationships with nest predation, such as those demonstrated here, suggest that several underlying mechanisms interact and imply that fixed nesting strategies may have variable-even opposing-fitness effects between years, sites and habitats

Modelling developmental instability as the joint action of noise and stability: a Bayesian approach

BACKGROUND: Fluctuating asymmetry is assumed to measure individual and population level developmental stability. The latter may in turn show an association with stress, which can be observed through asymmetry-stress correlations. However, the recent literature does not support an ubiquitous relationship. Very little is known why some studies show relatively strong associations while others completely fail to find such a correlation. We propose a new Bayesian statistical framework to examine these associations RESULTS: We are considering developmental stability – i.e. the individual buffering capacity – as the biologically relevant trait and show that (i) little variation in developmental stability can explain observed variation in fluctuating asymmetry when the distribution of developmental stability is highly skewed, and (ii) that a previously developed tool (i.e. the hypothetical repeatability of fluctuating asymmetry) contains only limited information about variation in developmental stability, which stands in sharp contrast to the earlier established close association between the repeatability and developmental instability. CONCLUSION: We provide tools to generate valuable information about the distribution of between-individual variation in developmental stability. A simple linear transformation of a previous model lead to completely different conclusions. Thus, theoretical modelling of asymmetry and stability appears to be very sensitive to the scale of inference. More research is urgently needed to get better insights in the developmental mechanisms of noise and stability. In spite of the fact that the model is likely to represent an oversimplification of reality, the accumulation of new insights could be incorporated in the Bayesian statistical approach to obtain more reliable estimation

Phenotypic signatures of urbanization are scale-dependent : a multi-trait study on a classic urban exploiter

Understanding at which spatial scales anthropogenic selection pressures operate most strongly is a prerequisite for efficient conservation and management of urban biodiversity. Heterogeneity in findings on the strength and direction of urbanization effects may result from a lack of consensus on which spatial scales are most adequate when studying biotic effects of urbanization. Therefore, here, using the house sparrow (Passer domesticus) as model, we test the hypothesis that more than one spatial scale will explain variation among phenotypic stress markers. By applying a unique hierarchical sampling design enabling us to differentiate between local and regional effects of urbanization, we here show that the strength and direction of relationships with the percentage of built-up area - a simple structural measure of urbanization - vary among phenotypic stress markers and across the spatial range over which urbanization is measured. While inverse relationships with scaled body mass and bill height of adult house sparrows (Passer domesticus) were strongest when the degree of urbanization was quantified at city-level, similar relationships with corticosterone concentrations in feathers were only detected at the scale of individual home ranges. In contrast, tarsus length, wing length, and two measures of feather development were not significantly related to urbanization at any spatial scale. As the suite of phenotypic stress markers applied in this study revealed signatures of urbanization over a broad spatial range, we conclude that measures aimed at mitigating impacts of urbanization on free-ranging populations should best be implemented at multiple spatial scales too

Diet contributes to urban-induced alterations in gut microbiota : experimental evidence from a wild passerine

Urban sprawl increasingly affects the ecology of natural populations, including host-microbiota interactions, with observed differences in the gut microbiota between urban and rural hosts. While different mechanisms could explain this pattern, dietary uptake constitutes a likely candidate. To assess the contribution of diet in explaining urban-rural variation in gut microbiota, we performed an aviary experiment in which urban and rural house sparrows were fed with mimics of urban or rural diets. Before the experiment, rural sparrows hosted more diverse gut communities, with a higher relative abundance of Enterococcaceae and Staphylococcaceae and lower abundance of genes involved in xenobiotic degradation and lipid metabolism than their urban counterparts. The experimental diets significantly altered gut microbiota alpha- and beta-diversity and taxonomic composition, with the strongest shifts occurring in individuals exposed to contrasting diets. Overall, diet-induced shifts resembled initial differences between free-ranging urban and rural hosts. Furthermore, rural diet had a positive impact on urban host body mass but only in hosts with the highest initial gut diversity. Overall, our results indicate that diet constitutes an important factor contributing to differences in gut microbiota along the urbanization gradient and provide new insights on possible fitness consequences of a reduced gut diversity in urban settings

Dynamics of gut microbiota diversity during the early development of an avian host : evidence from a cross-foster experiment

Despite the increasing knowledge on the processes involved in the acquisition and development of the gut microbiota in model organisms, the factors influencing early microbiota successions in natural populations remain poorly understood. In particular, little is known on the role of the rearing environment in the establishment of the gut microbiota in wild birds. Here, we examined the influence of the nesting environment on the gut microbiota of Great tits (Parus major) by performing a partial cross-fostering experiment during the intermediate stage of nestling development. We found that the cloaca! microbiota of great tit nestlings underwent substantial changes between 8 and 15 days of age, with a strong decrease in diversity, an increase in the relative abundance of Firmicutes and a shift in the functional features of the community. Second, the nesting environment significantly influenced community composition, with a divergence among separated true siblings and a convergence among foster siblings. Third, larger shifts in both microbiota diversity and composition correlated with lower nestling body condition. Our results shed new light on the dynamics of microbial diversity during the ontogeny of avian hosts, indicating that the nest environment continues to shape the gut microbiota during the later stages of nestling development and that the increase in gut diversity between hatching and adulthood may not be as linear as previously suspected. Lastly, the microbiota changes incurred during this period may have implications for nestling body condition which can lead to long-term consequences for host fitness