CHRISTIANS, J.K.; WILLIAMS, T.D. *: Effects of porcine follicle-stimulating hormone on the reproductive performance of female zebra finches (Taeniopygia guttata)

It has been suggested that follicle-stimulating hormone (FSH) may play a role in egg size/number trade-offs in oviparous vertebrates. We tested this hypothesis in an avian species by administering porcine FSH (pFSH) to intact, captive female zebra finches (Taeniopygia guttata) during egg formation. We predicted that 1) low doses of pFSH would increase yolk deposition and so increase egg mass; 2) higher doses of pFSH would increase the number of ovarian follicles recruited into rapid yolk development, and so increase clutch size; and 3) an increase in clutch size at high doses would lead to a reduction in egg size. Although a range of pFSH doses decreased egg mass by ca. 10% in three separate experiments, the reduction in egg mass occurred in the absence of an increase in clutch size. Porcine FSH actually reduced the number of eggs laid, although only the difference in median clutch size (and not mean clutch size) was statistically significant in two experiments. The results of this study did not support the hypothesis that FSH mediates a trade-off between egg size and clutch size in birds.