Biology subjects

Hau, M.

Publications and source records attributed to Hau, M..

6 recordsLinked to original sources

bioRxiv2026

Individual variation in glucocorticoid plasticity to temperature is not associated with reproductive success in a wild songbird population

Vertebrates cope with rapid temperature fluctuations by plastically adjusting their behaviour and physiology. This phenotypic plasticity is partly mediated by plastic changes in glucocorticoid levels; however, whether individual differences in endocrine plasticity are associated with fitness remains unknown. Here, we examined the relationship between individual variation in glucocorticoid plasticity in response to air temperature changes and reproductive success in a wild great tit population (Parus major). Over nine years, we collected repeated measurements of baseline and stress-induced corticosterone during nestling rearing. We found consistent reaction norm patterns in hormone response to temperature variation -- as shown in a previous study conducted over a shorter period. This provides robust evidence of individual differences in average hormone levels (intercepts) and the strength of the plastic response (slopes), indicating potential for evolution. However, neither intercepts nor slopes were associated with reproductive success (fledgling number or brood mass), suggesting that individual variation in endocrine plasticity was not under natural selection, at least within the environmental conditions experienced. This study provides a first empirical test of the evolutionary implications of endocrine plasticity in the wild and highlights the need to assess its fitness relevance under more extreme conditions, such as those expected under future climate scenarios.

evolutionary biology↗

bioRxiv2026

A capture-handling-restraint protocol elicits short-term stress responses in female and male parental wild great tits (Parus major) but has little impact on reproductive success

Capturing and handling wild animals is essential for ecological and evolutionary research, yet their effects on physiology, behaviour, and reproductive success remain poorly understood. We investigated short-and longer-term consequences of a capture-handling-restraint protocol in wild great tits (Parus major) over three breeding seasons. To assess short-term responses, we measured circulating corticosterone, a metabolic hormone that responds to unpredictable challenges, and automatically recorded provisioning behaviour. We also explored whether environmental and individual traits were related to provisioning latency (i.e., time to resume provisioning after capture). To evaluate longer-term effects, we monitored provisioning in the days following capture and related it to reproductive success (fledgling number and body condition). We predicted that longer handling would increase stress-induced corticosterone and provisioning latency, that these variables would be positively correlated, and that higher corticosterone and longer latencies would be associated with lower reproductive success. After capture, great tits showed elevated corticosterone and delayed provisioning. Contrary to our predictions, handling duration was negatively associated with stress-induced corticosterone in males (but not females) and did not affect provisioning latency. Provisioning latency was unrelated to corticosterone, environmental, or individual variables. Following capture, parents resumed provisioning, and short-term responses had little influence on reproductive success. We show that parental behaviour and physiology are affected by capture restraint protocols on the short term, but offspring condition and survival are not. However, these results should be interpreted cautiously, as our study lacks an uncaptured control group. Our findings highlight that evaluating welfare impacts requires rigorous study design incorporating both immediate and longer-term behavioural and fitness effects.

physiology↗

bioRxiv2025

Variation in seed abundance predicts yolk fatty acid composition in a wild population of birds

Bird embryos develop inside eggs, which contain maternal substances that can shape offspring phenotype and fitness. Yolk fatty acids are a key energy source for the developing embryo, with omega-6 ({omega}-6) and omega-3 ({omega}-3) polyunsaturated fatty acids (PUFAs) obtained exclusively from the diet. Therefore, food availability during the breeding season is expected to influence yolk fatty acid composition and, consequently, embryo development and growth. However, the effects of dietary variation on yolk fatty acids remain unexplored in wild birds. We investigated inter-annual variation in yolk fatty acid composition of free-living great tits (Parus major) in relation to fluctuations in beech (Fagus sylvatica) fructification--their preferred food--across two years differing strongly in seed abundance. We hypothesized that differences in beech seed availability would alter yolk fatty acid composition between years of high and low fructification, with corresponding correlations to the fatty acid profiles of available seeds. Hence, we analyzed fatty acids from seeds of beech and two conifers (Picea abies and Pinus sylvestris), which account for most of the tree cover in the study area, and from 112 eggs collected from 107 nests over two years. Beech seeds contained higher proportions of saturated (SFA), monounsaturated (MUFA), and {omega}-3 PUFAs, and lower proportions of {omega}-6 PUFAs than conifer seeds. Correspondingly, egg yolks had more SFA, MUFA, and {omega}-3 PUFAs in the year of high beech abundance, and more {omega}-6 PUFAs in the year of low abundance. Notably, the proportion of the conifer-associated {omega}-6 PUFA pinolenic acid was 64.25 times higher in years of low compared to high beech fructification, suggesting marked inter-annual variation in yolk fatty acid composition, likely reflecting shifts in maternal diet. Future experiments need to establish causal links between diet and yolk composition and assess the fitness consequences of different seed resources for breeding females and their offspring.

zoology↗

bioRxiv2024

Do egg hormones have fitness consequences in wild birds? A systematic review and meta-analysis

Egg-laying species are key models for understanding the adaptive significance of maternal effects, with egg hormones proposed as an important underlying mechanism. However, even thirty years after their discovery, the evolutionary consequences of hormone-mediated maternal effects remain unclear. Using evidence synthesis, we tested the extent to which increased prenatal maternal hormone deposition in eggs relates to fitness in wild birds (19 species, 438 effect sizes, 57 studies). Egg androgens, glucocorticoids, and thyroid hormones showed an overall near-zero mean effect for both maternal and offspring fitness proxies. However, heterogeneity was high, suggesting that egg hormone effects on fitness are context-dependent. Hormone type and age did not explain much of the observed variance, nor did methodological factors such as type of study or experimental design. Heterogeneity decomposition showed that differences in effect sizes were mostly driven by within-study variability and phylogenetic relationships. Our study provides the most comprehensive investigation to date of the relationship between egg hormones and fitness in vertebrates. By synthesizing current knowledge, we aim to overcome theoretical shortcomings in the field of maternal effects via egg hormone deposition and inspire new research into its many intriguing aspects.

evolutionary biology↗

bioRxiv2022

Great tits differ in glucocorticoid plasticity in response to spring temperature

Fluctuations in environmental temperature affect energy metabolism, stimulating the expression of phenotypic plasticity in behavioral and physiological traits. Vertebrate hormonal signals like glucocorticoids underpin environmentally-induced phenotypic plasticity, with changes in circulating concentrations orchestrating plastic changes in diverse traits. Climate change is predicted to alter temperature variation globally, making it imperative to evaluate whether free-living animal populations can cope adaptively. To evaluate their potential to respond to ongoing global change, we quantified individual variation in glucocorticoid plasticity to ambient temperature in wild great tits (Parus major). Using a reaction norm approach, we repeatedly sampled individuals for circulating glucocorticoid concentrations across five years. As expected, baseline and stress-induced glucocorticoid concentrations increased with lower ambient temperatures at the population and within-individual level. Moreover, we provide unique evidence that free-living individuals differ significantly in their plastic responses to temperature variation for both glucocorticoid traits, with some displaying greater plasticity than others. Average concentrations and degree of plasticity covaried for baseline glucocorticoids, indicating that these two reaction norm components are linked. Hence, individual variation in glucocorticoid plasticity to an important environmental factor exists in a wild population, representing a crucial step to assess the adaptive potential of vertebrates to endure current temperature fluctuations.

physiology↗

bioRxiv2018

Female variation in allocation of steroid hormones, antioxidants and fatty acids: a multilevel analysis in a wild passerine bird

The environment where an embryo develops can be influenced by components of maternal origin, which can shape offspring phenotypes and therefore maternal fitness. In birds that produce more than one egg per clutch, females differ in the concentration of components they allocate into the yolk along the laying sequence. However, identification of processes that shape female yolk allocation and thus offspring phenotype still remains a major challenge within evolutionary ecology. A way to increase our understanding is by acknowledging that allocation patterns can differ depending on the level of analysis, such as the population versus the among-female (within-population) level. We employed mixed models to analyze at both levels the variation in allocation along the laying sequence of four steroid hormones, three antioxidants, and four groups of fatty acids present in the egg yolks of wild great tits (Parus major). We also quantified repeatabilities for each component to study female consistency. At a population level, the concentrations/proportions of five yolk components varied along the laying sequence, implying that the developmental environment is different for offspring developing in first versus last eggs. Females varied substantially in the mean allocation of components and in their plasticity along the laying sequence. For most components, these two parameters were negatively correlated. Females were also remarkably repeatable in their allocation. Overall, our data emphasize the need to account for female variation in yolk allocation along the laying sequence at multiple levels, as variation at a population level is underpinned by different individual patterns. Our findings also highlight the importance of considering both levels of analysis in future studies investigating the causes and fitness consequences of yolk compounds. Finally, our results on female repeatability confirm that analyzing one egg per nest is a suitable way to address the consequences of yolk resource deposition for the offspring.

physiology↗