Endocrine control of clutch size in reptiles: I. Effects of FSH on ovarian follicular size-gradation in Leiolopisma laterale and Anolis carolinensis

Abstract

The effects of follicle-stimulating hormone (FSH) on inactive ovarian follicles of different sizes were studied in two lizard species, Leiolopisma laterale and Anolis carolinensis. Each ovary of L. laterale possesses two germ lines, while each ovary of A. carolinensis possesses one germ line. In both ovaries of L. laterale, 1 μg of FSH daily for 21 days did not stimulate the growth of follicles. In the larger ovary, dosages of 10 and 50 μg of FSH did not stimulate growth of follicles less than 0.35 mm in diameter, but did stimulate growth of follicles greater than 0.43 mm (only 50μmg FSH) or 0.48 mm (10 and 50 μg FSH). FSH-induced follicular growth was biased; i.e., the larger the initial follicular size, the greater the hormonal effect. Similar FSH effects occurred in the smaller ovary, except (1) very small (0.25 mm) follicles responded to 10 and 50 μg FSH, and (2) biased growth of FSH-treated ovaries occurred in different initial follicular sizes in the larger and smaller germ lines (0.79 mm and 0.47 mm, respectively). In A. carolinensis, the effects of FSH treatment were similar to those seen in L. laterale except that (1) all follicles measured responded to 10 and 50 μg FSH. (2) 1 μg of FSH stimulated growth of larger follicles, and (3) biased growth occurred whenever the higher FSH dosages stimulated growth. These results are discussed in relation to proposed mechanisms controlling biased growth of some follicles but not others (“follicular selection”).