Meeting Abstract
Glucocorticoids fuel energetically demanding life-history stages, but can also suppress reproduction. In many taxa, reciprocal hormone-behavior interactions make it difficult to assess the effects of glucocorticoids on gonad function independently from changes in reproductive behavior (e.g., sexual experience itself can alter sex steroids). In this study, we used a dissociated breeder, red-sided garter snakes (Thamnophis sirtalis parietalis), to determine if glucocorticoids alter two measures of testis function: sex steroid hormone synthesis and spermatogenesis. Because males mate during the spring and undergo spermatogenesis during the summer, the influence of glucocorticoids on gonad function can be determined independently of breeding activity. As in our prior studies, we manipulated glucocorticoids with subcutaneous elastomer implants mixed with corticosterone, metyrapone (a glucocorticoid synthesis inhibitor), or no hormone. Blood samples were collected at 0, 3 and 6 wks post-implant treatment; a subset of snakes in each group was euthanized at 3 and 6 wks post-treatment and the testes were sliced on a cryostat and counterstained. Seminiferous tubule diameter was measured for 25 tubules per snake as an indirect assessment of spermatogenesis. Similar to previous studies, plasma corticosterone did not differ significantly among groups, indicating strong endogenous control of corticosterone. However, androgens increased over the course of the experiment and were significantly elevated in metyrapone-treated snakes. Seminiferous tubule diameter did not differ among groups despite the differences in androgens. These data suggest that corticosterone suppresses gonadal sex steroid synthesis but not spermatogenesis in this dissociated breeder.
