Alligator physiology and life history: the importance of temperature

Abstract

Alligators are the most northerly distributed of the extant Crocodilia. Reproducing populations are found as far north as 35° latitude in the freshwater marshes and rivers of coastal North Carolina, and as far south as 25° latitude in the Florida Keys. Thus different populations are exposed to very different annual thermal cycles. Alligators stop eating when ambient temperature drops below 16 °C. This anorexia lasts at least 6 months at 35° latitude. In southwest Louisiana alligators stop feeding in October and do not resume feeding until late March or early April. It is only during the warmer months when actively feeding that growth occurs. Even with this restricted growing season Louisiana alligators grow about 30 cm a year for the first 6 years. When alligators reach sexual maturity at about 1.85 m total length growth slows in both sexes, but is significantly slower in females than males. As a result of differences in thermal regime sexual maturity is estimated at around 18 years in North Carolina and about 10 years in Louisiana. Females lay one clutch of around 40 eggs in June, but the time of nesting is also tightly linked to temperature. In a cool spring nesting can occur as late as July 5th, and in a warm spring as early as June 5th. Immature male alligators undergo a seasonal hormonal cycle similar to fully mature breeding males, but testosterone levels differ by an order of magnitude. The number of mature females reproducing each year is rarely greater than 50%, but data on internest interval is lacking. Immature female alligators show no seasonal hormonal cycle.