Testosterone metabolism and its testosterone-dependent activation in the uropygial gland of quail

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

While seasonal trends in testosterone levels are known from cross-cohort studies, data on testosterone inter-annual individual repeatability in wild birds are rare. Also, our understanding of hormonal age-dependent changes in testosterone levels is limited. We assessed plasma testosterone levels in 105 samples originating from 49 repeatedly captured free-living great tits (Parus major) sampled during the nesting to investigate their relative long-term repeatability and within-individual changes. Furthermore, we examined the inter-annual repeatability of 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 are inter-annually repeatable in females, with a non-significant pattern in males, both in absolute values and individual ranks (indicating the maintenance of relative status in a population). In males, we found a quadratic dependence of testosterone levels on age, with a peak in midlife. In contrast, female testosterone levels showed no age-dependent trends. The inter-annual repeatability of condition-related traits ranged from zero to moderate and was mostly unrelated to plasma testosterone concentrations. However, males with elevated testosterone had significantly higher carotenoid-pigmented yellow plumage brightness, a trait presumably involved in mating. Showing inter-annual repeatability in testosterone levels, this research opens the way to further understanding the causes of variation in condition-related traits. Based on a longitudinal dataset, this study demonstrates that male plasma testosterone undergoes age-related changes that may regulate resource allocation. Our results thus suggest that, unlike females, male birds undergo hormonal senescence similar to mammals.

Arterial Vascularization of the Uropygial Glands (Gl. Uropygialis) in the Rock Partridge (Alectoris graeca) Living in Turkey

This study aims to observe the morphological characteristics of the uropygial gland (Glandula uropygialis), specifically the arterial vascularization, in rock partridges (Alectoris graeca) living in Turkey. Coloured-latex-injected animals were dissected and the gland and related arteries were observed. Mostly, the fourth paired caudal segmental arteries (Aa. segmentales caudales) arising from the median caudal artery (A. mediana caudae) were specified as the uropygial gland arteries. These arteries, in turn, gave the following rami: the muscular ramus (Ramus muscularis) to the levator coccygeus and lateral caudal muscles, the lateral ramus (Ramus lateralis) to the lateral coccygeus muscle and a small ventro-lateral division of the caudal component of the gland, and the medial rami (Ramus medialis) to the dorsal surface of the gland.