Male-like testosterone levels inhibit oviposition in a female parrot: A breeding experiment in budgerigars

Abstract

Abstract Studies in several songbird species have shown that treating females with the androgenic steroid hormone testosterone (T) can negatively affect female reproductive behaviors and breeding success. As the effects of T on females appear to be species-specific, it is not clear if similar effects of high T occur in non-songbird species. Here, we studied the effects of T supplementation on female reproductive behavior and oviposition in the budgerigar, Melopsittacus undulatus, a small monogamous parrot species with distinct sex differences in parental behavior. We experimentally increased T concentrations to male-like levels in T-treated females compared to controls and we allowed females to breed. We found no significant effects of treatment on the latency to enter the nestbox but T treatment significantly interfered with oviposition. Our results show that T-treated females were seven times less likely to produce a clutch than control females. As we found that T treatment had a strong inhibitory effect on oviposition, our results indicate that female budgerigars suffer fitness costs from male-like plasma T levels. Therefore, it may be possible that, also in non-songbird species, selection for higher T levels in males is constrained by a correlated response to selection which imposes fitness costs on females in terms of reproduction. Evaluating whether or not this is indeed the case requires further work combining different approaches to the study of the evolution of male and female testosterone levels.