LANCE, V.A.; ELSEY, R.M.; TROSCLAIR, P.; San Diego State University; Louisiana Department of Wildlife and Fisheries; Louisiana Department of Wildlife and Fisheries: Sexual Maturation in Male American Alligators

Very little is known about the attainment of puberty in reptiles. In the American alligator (Alligator mississippiensis) males are assumed to be sexually mature at about 1.8 m in total length, but it is not clear at what size they produce testosterone, spermatozoa and mate successfully. The minimum size for sexual maturity is thought to be around 1.83 m, but social hierarchy favors breeding by male alligators over 2.13 m. We decided to re-examine this question by studying plasma testosterone levels in blood samples from a large sample of alligators (~1,500) collected in every month of the year and ranging in size from approximately 61 cm (2 ft) to 360 cm (11.5 ft). In addition a number of testicular samples were taken for histology from alligators (close to, and equal to 1.8 m total length) during the mating season to assess degree of spermatogenesis and gonadal maturation. Testosterone values ranged from 0.05 ng/ml to 115.41 ng/ml. All size classes of alligators exhibited a seasonal cycle in testosterone levels, but the concentration appeared to be size-dependent: the larger the alligator the higher the testosterone. In all size classes testosterone reached a peak in the breeding season (March-May). Mean testosterone in the largest size class during breeding was 75 ng/ml whereas in the smallest size class peak testosterone was less than 3 ng/ml. The smallest size class (61 � 89 cm) showed an additional rise in testosterone in late summer. The attainment of sexual maturity in alligators appears to be closely associated with growth and is a gradual process lasting several years. Sexually immature alligators show a seasonal pattern of testosterone secretion similar to that of adults, but the values are significantly lower.