Meeting Abstract
22.3 Thursday, Jan. 3 Hormonally-mediated maternal effects � the mother�s perspective TRAVERS, M.*; CLINCHY, M.; WILLIAMS, T.D.; ZANETTE, L.; SFU & UWO; UWO; SFU; UWO mtravers@sfu.ca
Hormonally-mediated maternal effects involve transfer of hormones from the mother�s circulation to offspring via egg yolk. Hormones that have potential �adaptive� effects in offspring also have important functional roles in female reproduction. However, it has been suggested that these same hormones can have negative pleiotropic effects in mothers (e.g. immunosuppression, anemia). Therefore, a mother�s ability to alter an offspring�s phenotype via hormones may be constrained by costs that the mother incurs from exposure to those hormones. Zanette et al.s (2006) finding of a strong negative correlation between the number of clutches laid and clutch size in song sparrows provides evidence that there may be a cost of exposure to endogenous reproductive hormones. The decline in clutch size occurred both in birds fed a very high quality diet and unfed birds, suggesting a non-resource based explanation (e.g. pleiotropic effects of reproductive hormones). We manipulated the number of hormonal cycles (i.e. clutches laid) that female song sparrows (Melospiza melodia) were exposed to during a breeding season, creating a high and a low clutch treatment, while supplementing all females with a high quality diet. Our goals were: 1) to experimentally demonstrate a cost (i.e. decrease in clutch size) of increased number of hormonal cycles 2) to investigate if a reduction in clutch size was due to repeated exposures to reproductive hormones. High clutch number females laid significantly smaller clutches compared with low clutch females. We predicted that females with more clutches (i.e. greater hormonal exposure) would also be in poorer physiological condition. We report the physiological condition of high and low clutch females as measured by oxidative stress, corticosterone, anemia, immunoglobulin, leukocytes and plasma metabolites.
