(13) Impact of Variable Incubation Regimes on Genital Differentiation in Hatchling Alligators

How different are male and female hatching alligators? The external genitalia of adult alligators are quite different by sex, as to be expected. However, at hatching, this morphological difference of the clitero-penis (CTP) is... [ view full abstract ]

How different are male and female hatching alligators? The external genitalia of adult alligators are quite different by sex, as to be expected. However, at hatching, this morphological difference of the clitero-penis (CTP) is subtle, with males only being slightly more developed than females. While the gonadal sex of American alligators is determined by egg incubation temperature in the nest, development of external genitalia (clitoris or penis) is a more developmentally delayed, androgen-dependent process showing greater morphological variability within a given sex. Previous research has determined that a constant nest incubation temperature of 33℃ determines testis development and male genital formation. In contrast, 30℃ results in ovary development and cliteral formation. However, it is unclear how intermediate and/or fluctuating incubation temperatures could influence formation of external genitalia. We investigated this question in week-old hatchlings incubated under the following conditions: 1) Constant male producing temperature (33℃), 2) constant female producing temperature (30℃), 3) intermediate promoting temperature (31.2℃), and 4) intermediate promoting fluctuating temperatures one (31.2℃ +/- 0.6℃) and 4) intermediate promoting fluctuating temperature two (31.2 +/- 2.8℃). To better characterize morphological differences across incubation temperatures, we quantified lateral and ventral CTP dimensions of glands height (maximum vertical width at mid-section of the head), glands width (widest point of glands), and curve distance (from beginning of sulcus to end of tip). The results we present here expand our understanding of “normal” alligator CTP sexual dimorphisms. Our project illustrates how the environment intimately shapes crocodilian biology and increases our ability to detect altered development in wild populations.