Meeting Abstract

29.5  Jan. 5  A novel experimental test of the relationship between plasma and yolk testosterone levels in the house sparrow EGBERT, Jeremy R.*; SCHWABL, Hubert G.; Washington State University, School of Biological Sciences, Pullman, WA jeremyegbert@wsu.edu

One example of a maternal non-genomic effect is the accumulation of maternally-derived steroids in the yolks of avian eggs, which have been shown to affect offspring growth and competitive ability. Higher female-female competition during breeding has been shown to correlate with increased yolk androgen levels, but the mechanism of this accumulation remains unknown. Competition between females may increase follicular steroidogenesis, after which the lipophilic steroids might either diffuse into circulation and into yolk in roughly equal proportions, or steroid concentrations in circulation and yolk could be regulated independently through active processes. To examine these possible relationships, captive, laying female House Sparrows were either challenged at the nest box by a novel female or left unchallenged. Yolks from subsequently laid eggs were fixed and stained so that a sample could be obtained from the yolk layer that was being formed at the time of the treatment period and blood sampling. Females responded behaviorally to the challenge by perching near the intruder and often exhibiting aggression. Concentrations of testosterone in the plasma and yolk layer were not different between treatments, which could indicate follicular steroidogenesis was not altered by the challenge. However, yolk testosterone concentrations were significantly more variable in challenged females. This might suggest a context-dependent effect of social competition on follicular steroidogenesis and subsequent yolk androgen levels. Since testosterone concentrations in the yolk layer and plasma were not correlated with each other, their levels may be regulated independently.