Date of Award

8-1-1993

Document Type

Thesis

Degree Name

Master of Science (MS)

Abstract

I investigated the effects of incubation temperature, clutch, and sex on the morphometries, mass, and energy reserves of hatchling alligators. The effect of incubation temperature on hatchling genitalia was also studied. I evaluated and tested a method for determining the sex of hatchling alligators. Large scale incubation of alligator eggs allowed a study of inter-clutch variation in sex ratio of hatchlings incubated at the same temperature.

Aingator eggs were collected within several days of laying in June, 1991, at Rockefeller Wildlife Refuge, southwestern Louisiana, USA. Three clutches of eggs were incubated over the viable range of temperatures and the resulting hatchlings were measured and weighed. I examined sexual dimorphism of hatchling and juvenile alligators by comparing measurements and observations of the genitaha. In an additional study, I determined hatchling sex by cloacal examination and dissected specimens to verify the predicted sex with the gonadal detemiinations. The method of cloacal sex determination was used to analyze the sex ratios of multiple clutches incubated at the same temperature.

Incubation temperature affected the morphometries and residual yolk mass of hatchling alligators in a consistent, but complex pattern. Hatchling size was maximal at an intermediate temperature (32°C) and minimal at 29°C. Residual yolk mass was inversely related to yolk-free hatchling mass; higher yolk mass occurred at 31 and 33°C, and lower mass occurred at 29 and 32°C. Although the effects of temperature on body mass and fat mass parameters were not significant, temperature significantly affected the yolk-free hatchling mass of males. Strong clutch effects, temperature by clutch interactions, and sex effects were present for most variables.

Morphological differences in the genitalia of hatchlings were found between males and females. Males had significantly larger clitero-penis (CTP) dimensions than females. Differences in CTP size between sexes increased rapidly during post-hatching growth due to the accelerated growth of male genitalia compared to that of females. The method of sex determi tation b\ cloacal examination was highly reliable in hatchling alligators.

Considerable variation in sex ratio occurred among different clutches that were incubated at the same temperature. These results indicate that factors other than temperature influence sex determination in alligators.

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