Date of Award

Fall 12-2015

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Committee Chair

Jake Schaefer

Committee Chair Department

Biological Sciences

Committee Member 2

Jodie Jawor

Committee Member 2 Department

Biological Sciences

Committee Member 3

Carl Qualls

Committee Member 3 Department

Biological Sciences

Abstract

Federally threatened in Mississippi, gopher tortoise (Gopherus polyphemus) populations within the state have strongly variable recruitment and are generally in decline. Hatching success is significantly lower in Mississippi than in any other part of the species’ range , and most hatchlings die within the first year. There are few refuges where survival and hatching success is high. Here I compare two populations that differ in recruitment and offspring survival for differences in corticosterone. Corticosterone is a hormone that influences both energy availability and is released in elevated levels during stressful events, like living in poor quality habitat. Prolonged corticosterone elevation can impede growth and immune responses and result in early death. To assess adult stress, I utilized leukocyte profiles as they are influenced by prolonged elevation of corticosterone. A viable yolk sampling technique was used to collect yolk samples to determine levels of yolk CORT. Hatchlings were then kept in captivity for two years to observe growth rates and burrowing behavior before being released and monitored via radiotelemetry to monitor dispersal and survival. I found no differences in adult stress or egg yolk CORT between populations. This suggests adults are not excessively stressed. Survival of hatchlings did not differ between sites. Captive-reared hatchlings were larger and may have better survival than similar aged wild hatchlings. Overall, the poor survival of gopher tortoises may be more strongly linked to environmental variables such as soil structure than physiological ones.

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