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bioRxiv · 10.1101/2020.07.23.217836

Inter-annual stability and age-dependent changes in plasma testosterone levels in a longitudinally monitored free-living passerine bird

Tesicky, M.·Krajzingrova, T.·Elias, J.·Velova, H.·Svobodova, J.·Bauerova, P.·Albrecht, T.·Vinkler, M.
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Abstract

While seasonal trends in the testosterone-driven hormonal regulation of resource allocation are known from cohort population samples, data on the inter-annual individual stability of blood plasma testosterone levels in wild birds are lacking, and our understanding of age-dependent changes is limited. We assessed plasma testosterone levels in 105 samples originating from 49 repeatedly captured free-living great tits (Parus major) to investigate their relative long-term stability and lifetime changes. Furthermore, we examined the inter-annual stability of selected condition-related traits (carotenoid- and melanin-based plumage ornamentation, ptilochronological feather growth rate, body mass, and haematological heterophil/lymphocyte ratio) and their relationships to testosterone levels. We show that testosterone levels in both sexes are inter-annually repeatable, both in their absolute values and individual ranks (indicating the maintenance of relative status in a population), yet with higher stability in females. Despite this stability, in males we found a quadratic dependence of testosterone levels on age, with a peak in midlife. In contrast, female testosterone levels showed no lifetime trend. The inter-annual stability of condition-related traits was mostly moderate and unrelated to plasma testosterone concentrations. However, males with elevated testosterone had significantly higher carotenoid-pigmented yellow plumage brightness, presumably serving as a sexually selected trait. Showing inter-annual stability in testosterone levels, this research opens the way to further understanding of the causes of variation in fitness-related traits. Based on a unique longitudinal dataset, this study demonstrates that male plasma testosterone undergoes age-related changes that may regulate resource allocation. Our results thus demonstrate that male birds undergo hormonal senescence similar to mammals.

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Tesicky, M., Krajzingrova, T., Elias, J., Velova, H., Svobodova, J., Bauerova, P., Albrecht, T., Vinkler, M.. 2020-07-24. Inter-annual stability and age-dependent changes in plasma testosterone levels in a longitudinally monitored free-living passerine bird. https://doi.org/10.1101/2020.07.23.217836

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