SEXUAL DIMORPHISM IN THE GENITAL MORPHOLOGY OF YOUNG AMERICAN ALLIGATORS, ALLIGATOR-MISSISSIPPIENSIS

Egg temperature during incubation determines sex in the American allig ator (Alligator mississippiensis). Although juveniles and adults (>0.6 m) may be sexed effectively, smaller alligators are reportedly diffic ult to sex. We developed a method for sexing young alligators by inspe ction of the genitalia and quantified effects of incubation temperatur e on genital morphology. We predicted the sex of a hatchling by examin ing its genitalia within the cloaca. Our predictions were verified by inspecting the gonads macroscopically and histologically. The male cli tero-penis typically is red, round, and large (mean length = 4.1 mm) i n comparison with the female organ (mean length = 2.8 mm), which is wh ite and smaller. Sex identification by cloacal examination was highly reliable (accuracy greater than or equal to 96%). Clitero-penis dimens ions of hatchlings incubated at 29, 31, 32, 33, and 34 C increased sig nificantly with increasing incubation temperature, both within and bet ween sexes. Based on differences apparent in hatchlings, incubation te mperature seems to affect genital differentiation during development i n a graded fashion. During posthatching growth, size increased rapidly in males versus females; based on previous studies, we think that the se changes can be attributed to ontogenetic changes in the levels of c irculating sex steriods. Observable size differences in the genitalia of males versus females permit an accurate, noninvasive diagnosis of s ex in young alligators. Sex identification by this method will facilit ate experimental study, as well as the management of wild and captive alligators.