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) pFSH would increase the number of ovarian follicles recruited into rapid yolk development and so increase clutch size, (2) an increase in clutch size would lead to a reduction in egg size, and (3) doses of pFSH that were not sufficient to increase clutch size would increase yolk deposition and so increase egg mass. 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 the number of eggs laid. Porcine FSH decreased mean clutch size significantly in one experiment and reduced median clutch size significantly in the other 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.