Biology subjects

Kauzalova, T.

Publications and source records attributed to Kauzalova, T..

3 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↗

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↗