Biology subjects

Tomasek, O.

Publications and source records attributed to Tomasek, O..

6 recordsLinked to original sources

bioRxiv2026

Feather corticosterone is not associated with feather growth rate or quality across tropical and temperate passerines, but possibly linked to elevation

Moult is a challenging stage in the life of birds. Small passerines replace plumage, substantial part of their body mass, annually to preserve its vital functions. Surprisingly, most species tend to downregulate corticosterone, major mediator of energy metabolism and stress response, during this energetically demanding period. Experimental studies suggest corticosterone has detrimental effect on feather quality and, within species, slows feather growth rate (FGR), prolonging the period when plumage functions are compromised. However, how exactly corticosterone affects moult in natural populations or on macroecological scale is not yet fully understood. In this study, we analysed corticosterone deposited in tail feathers (fCORT), a corticosterone cumulative measure across multiple days relevant to the moult, on an unprecedented sample of 87 passerine species from Europe and Afrotropics. Our data showed moderate between and high within-species repeatability, strengthening the usefulness of fCORT as a tress record across multiple species. We did not find any association of fCORT with either FGR or fault bar occurrence. Unlike circulating corticosterone, fCORT did not differ between latitudes. However, our data suggested higher fCORT in high elevation tropical species. More research is needed to understand how birds regulate corticosterone during moult and how it affects moult in natural populations.

ecology↗

bioRxiv2025

Comparative analysis of plasma steroid hormone levels reveals lower concentrations in Afrotropical than Palearctic temperate zone passerines

Latitudinal changes in environmental conditions shape the evolution of avian life history traits: tropical bird species typically exhibiting prolonged breeding seasons, a slower pace of life, lower annual investment in reproduction and increased annual survival compared to their temperate counterparts. Major shifts in physiology, reflecting these differences, are expected to be mediated by endocrine regulation, yet comparative data on the sources of inter-specific variation in hormone concentrations remain sparse, especially outside the Nearctic-Neotropic system. We examined variation in two key steroid hormones, corticosterone and testosterone, across 100 passerine species from Europe and the Afrotropics, sampled using standardized field protocols. Baseline levels of both hormones were consistently lower in tropical species, as expected. While stress-induced corticosterone reactivity did not differ between latitudes, it declined with migration distance. Testosterone levels were higher in males than females and declined with migration distance. In tropical species, neither hormone was associated with elevation, another source of environmental variation, but both varied during the breeding cycle, challenging the view of tropical aseasonality. This study broadens the perspective on endocrine correlates of avian life history evolution by testing their generality in an understudied Afrotropical-Palearctic system. The results support the hypothesis that steroid hormone profiles co-evolve with latitude.

ecology↗

bioRxiv2025

Conspecific brood parasitism in the barn swallow (Hirundo rustica)

Conspecific brood parasitism (CBP) has been reported in many altricial avian species, yet its prevalence and underlying behavioural mechanisms remain poorly understood. We studied CBP in the barn swallow (Hirundo rustica), a species in which conspecific brood parasitism has been reported. We conducted parentage analysis on 1945 barn swallow broods involving 7816 offspring. Samples were collected over 12 breeding seasons at 5 colonies/populations. Contrary to expectations, we identified only six cases of CBP (0.3 % of broods). By identifying all individuals involved, i.e. the parasitic females, the female hosts and the males that fathered the parasitic eggs, we determined these cases of CBP resulted most likely from either a failed nest take-over (three times), the disappearance of a female partner or a disruption caused by researchers while only one case could be interpreted as a result of females mixed reproductive tactic. Based on a review of the literature on CBP in seven other Hirundinidae, we conclude that the only reliable evidence for CBP comes from cliff swallows (Petrochelidon pyrrhonata). Studies on other species either failed to identify the parasitic females or do not present sufficient evidence supporting the occurrence of CBP. Several studies relied on the appearance of two eggs in a nest within 24 hours to conclude that CBP occurred. However, based on the parentage analysis, we show that CBP only occurred in one out of 11 such cases in our barn swallow data. Our findings highlight that CBP is rare in our barn swallow populations, and have been likely overestimated in other studies. We emphasize the importance of frequent nest checks and rigorous genetic validation in CBP research. Overall, our results challenge existing assumptions about the prevalence of CBP and provide insights into the behavioural mechanisms that lead to CBP, with ecological and evolutionary implications.

ecology↗

bioRxiv2025

Recent breeding experience improves egg ejection behaviour

Recognizing ones own eggs is crucial for birds, especially for hosts of brood parasites that must identify and reject different-looking parasitic eggs. While birds seem to possess a template image of their eggs, whether it is innate or learnt remains unclear. We addressed this question by experimentally inserting either artificial mimetic eggs (ME) or non-mimetic eggs (NME) into the nests of barn swallows (Hirundo rustica) during pre-laying stage. Our individually marked population allowed a unique comparison between naive first-time breeders and experienced females, as well as females with old (from a previous season) and recent (from the previous breeding attempt within the same season) experience allowing to investigate the role of memory. We found that both naive and experienced females ejected ME and NME at similar rates, indicating that the template image is neither innate nor learnt and does not play a primary role in egg recognition. Instead, our findings suggest that awareness of own egg-laying is the crucial mechanism at play, and may facilitate nest sanitation behaviour. Finally, we provide the first evidence that this mechanism improves with recent breeding experience. Future studies should investigate the role of non-visual factors that may modulate nest sanitation, such as endocrine regulation.

animal behavior and cognition↗

bioRxiv2023

Birds escape the oxidative stress costs of high blood glucose levels

Chronically high blood glucose levels (hyperglycaemia) can compromise healthy ageing and lifespan at the individual level. Elevated oxidative stress can play a central role in hyperglycaemia-induced pathologies. Nevertheless, the lifespan of birds shows no species-level association with blood glucose. This suggests that the potential pathologies of high blood glucose levels can be avoided by adaptations in oxidative physiology at the macroevolutionary scale. However, this hypothesis remains unexplored. Here, we examined this hypothesis using comparative analyses controlled for phylogeny, allometry and fecundity based on data from 51 songbird species (681 individuals with blood glucose and 1021 individuals with oxidative state data). We measured blood glucose at baseline and after stress stimulus and computed glucose stress reactivity as the magnitude of change between the two time points. We also measured three parameters of non-enzymatic antioxidants (uric acid, total antioxidants and glutathione) and a marker of oxidative lipid damage (malondialdehyde). We found no clear evidence for blood glucose concentration being correlated with either antioxidant or lipid damage levels at the macroevolutionary scale, as opposed to the hypothesis postulating that high blood glucose levels entail oxidative costs. The only exception was the moderate evidence for species with a stronger stress-induced increase in blood glucose concentration evolving moderately lower investment into antioxidant defence (uric acid and glutathione). Neither baseline nor stress-induced glucose levels were associated with oxidative physiology. Our findings support the hypothesis that birds evolved adaptations preventing the (glyc)oxidative costs of high blood glucose observed at the within-species level. Such adaptations may explain the decoupled evolution of glycaemia and lifespan in birds and possibly the paradoxical combination of long lifespan and high blood glucose levels relative to mammals. Summary statementHigh blood glucose levels can harm organisms by causing oxidative stress. We show that, at the macroevolutionary level, songbirds defy this expectation, as their glucose levels and oxidative physiology are uncoupled.

evolutionary biology↗

bioRxiv2020

The sources of sex differences in aging in annual fishes

Sex differences in lifespan and aging are widespread among animals, with males usually the shorter-lived sex. Despite extensive research interest, it is unclear how lifespan differences between the sexes are modulated by genetic, environmental and social factors. We combined comparative data from natural populations of annual killifishes with experimental results on replicated captive populations, showing that females consistently outlived males in the wild. This sex-specific survival difference persisted in social environment only in two most aggressive species, and ceased completely when social and physical contacts were prevented. Demographically, neither an earlier start nor faster rate of aging accounted for shorter male lifespans, but increased baseline mortality and the lack of mortality deceleration in the oldest age shortened male lifespan. The sexes did not differ in any measure of functional aging we recorded. Overall, we demonstrate that sex differences in lifespan and aging may be ameliorated by modulating social and environmental conditions.

evolutionary biology↗