The Effect of Sex Steroids on Primary and Secondary Sex Differentiation in the Sexually Dichromatic Reedfrog (Hyperolius argus: Hyperolidae) from the Arabuko Sokoke Forest of Kenya

Abstract

The current study examined the role of steroids in primary and secondary sex differentiation in the African reedfrog (Hyperolius argus: Hyperolidae). This species is sexually dimorphic: males have a solid green dorsum and females are reddish-brown with large white spots. This study is the first to report the effects of sex steroids on the development of a sexually dichromatic species and the first to examine the role of sex steroids on development of the vocal sac. Both males and females metamorphosed solid green without spots. Approximately 2 months after metamorphosis, control females transformed to the female-typical color pattern. Control males never developed this color pattern (remained green), but developed vocal sacs. To examine the role of sex steroid hormones on primary (gonadal differentiation) and secondary (vocal sac development and dorsal coloration) sex differentiation, testosterone (T) or estradiol-17β (E2) were administered throughout larval development. At metamorphosis, 53% of the controls were males, based on gross gonadal morphology and histology of a subsample. Both doses of T produced 100% males. All E2-treated animals had ovarian cavities and/or follicles when examined histologically (at both doses) but 50% had testicular tissue in addition to these ovarian characteristics. Both doses of T induced vocal sac development and both doses of E2 induced female coloration. Thus, both T and E2 induced secondary sex characteristics (vocal sac development and dorsal color change, respectively) but E2 produced hermaphroditic gonads, whereas T induced complete sex reversal.