Biology ETDs

Publication Date

12-10-1985

Abstract

Relationships among populations of the desert tortoise, Gopherus agassizi, were assessed using starch-gel electrophoresis. Concurrently, tortoises obtained for the electrophoretic study were used in a preliminary morphological analysis. Morphologically, males differed from females in the gular shape and anal scutes, front foot width, carapacial doming, and the posterior curvature of the carapace. Only anal notch depth differed among habitats for female tortoises, while differences in gular length, front foot width, anal notch depth and width, and carapacial flatness were detected among males. Differences in foot and gular shape may reflect their importance in male:male agonistic encounters. Shell shape differences between sexes may reflect different growth rates in response to cost of egg production in females, while differences among habitats may reflect forage availability in different habitats. Electrophoretic data were analyzed in two fashions: 1) the analysis of 16 blood proteins for 17 sample sites and 2) the analysis of 24 proteins from heart, liver, kidney, and blood for 10 sample sites. No fixed genetic differences were detected between samples and, overall, desert tortoises were genetically similar. Phenograms based on [illegible] analysis of genetic similarity and genetic distance values, grouped 1) most samples from the Mojave Desertscrub (west of the Colorado River), and 2) samples from the Sonoran Desertscrub, Sinaloan Thornscrub, and Sinaloan Deciduous Forest (east of the Colorado River). Exceptions were noted. Stepwise regression analysis of genetic distance values with geographical and ecological variables indicated that the Colorado River and rainfall patterns had significant predictive powers on the relatedness of tortoise populations. The Colorado River may be a barrier to gene exchange between tortoises. Environmental bottlenecks induced by low rainfall on the west side of the river may have exaggerated genetic differences. Low heterozygosity values from samples west of the Colorado River support this bottleneck hypothesis.

Language

English

Keywords

Desert tortoise

Document Type

Thesis

Degree Name

Biology

Level of Degree

Masters

Department Name

UNM Biology Department

Download

Included in

Biology Commons

Share

COinS