Abstract
Sexual size dimorphism was investigated in the African bullfrog (Pyxicephalus adspersus), a species in which adult males are about 2.5 times larger than females. Growth profile analysis revealed that males and females begin to diverge in growth rates at 4 weeks postmetamorphosis, concurrent with the appearance of differentiated gonads. At the end of 300 days, males were about 75% heavier and 20% longer than females (females remained previtellogenic). The difference was attributable primarily to an extended period of accelerated linear growth in males between days 166 and 195, and an extended period of accelerated weight gain between days 139 and 166. Surgical gonadectomy did not affect growth in males or females. Reduced plasma steroid levels, failure to show steroid response to GnRH injection, and abolishment of male agonistic behaviors confirmed the completeness of gonadectomy. In addition, there was no correlation between plasma steroid hormones and size or growth rate. The current study suggests that gonadal hormones may not play an “activational” role in establishing sexually dimorphic growth patterns. Sexual size dimorphism may be due to either “organizational” hormonal effects or genetic control of growth patterns. © 1992 Wiley‐Liss, Inc.