Meeting Abstract

P2.124  Friday, Jan. 4  Does digit ratio correlate with gonad function or morphological characters in a songbird? CAIN, K.E.*; BERGEON, C.M.; KETTERSON, E.D.; Indiana University; Indiana University; Indiana University caink@indiana.edu

The hormonal environment an animal experiences during development can have profound long-term effects on its morphology, physiology, and behavior. Because birds are unable to alter the hormonal environment of the egg once it is laid, they serve as an excellent model for understanding these effects. Studies of mammals, including humans, have found a relationship between testosterone (T) exposure in utero and the relative lengths of digits, or digit ratios (DR). Lower DR values have been associated with greater uterine exposure to T, owing perhaps to the co-regulatory roles of the HOXA and HOXD homeobox genes on both digit and uro-genital development. Because these genes are highly conserved, similar relationships have been sought in other taxa, including birds, in which females are known to vary in the amount of T they deposit in eggs. If the DR does reflect the developmental environment, it may also reflect gonadal function and thus vary with other measures, such as the ability of the testes/ovaries to respond indirectly to a Gonadotropin Releasing Hormone (GnRH) challenge, or the extent to which testosterone regulated phenotypic characters are expressed. In this study I evaluated three sub-species of a weakly dimorphic songbird, the dark-eyed junco (Junco hyemalis), for correlations between DR and circulating levels of T, response to a GnRH challenge, and morphological characters. Results to date indicate variation in DR within and among populations, which is consistent with geographic variation in the developmental environment. Preliminary evidence also suggests a relationship between DR and morphological characters. Implications for the development of sexual dimorphism and the divergence of morphological characters among sub-species will be discussed.