28th Annual Meeting and Symposium of the
Desert Tortoise Council, February 21-23, 2003
Abstracts

STUDENT PAPER

Analysis of Gene Flow Among Sonoran Desert Tortoise Populations Using Molecular Techniques and Radiotelemetry

¹Taylor Edwards, ^2,1Cecil R. Schwalbe, ³Don E. Swann, ¹Caren S. Goldberg, and ¹Eric W. Stitt
¹School of Renewable Natural Resources, University of Arizona, Tucson, AZ 85721
²U.S. Geological Survey, Southwestern Biological Science Center, University of Arizona, Tucson, AZ 85721
³Saguaro National Park, Tucson, AZ 85730

We used molecular techniques and radiotelemetry to examine movement patterns of desert tortoises, Gopherus agassizii, in southern Arizona. We collected blood samples from 170 individuals in 9 mountain ranges surrounding Tucson. We analyzed mitochondrial DNA sequences and developed 6 novel microsatellite markers useful for conservation genetic studies of this species. Two microsatellite loci exhibited only marginal variability (2-3 alleles), but four were highly variable (8-27 alleles). Five of these markers successfully cross-amplified in Mojave Desert samples and may be applicable to studies of other congeners. Genetic differentiation among Sonoran populations was low, indicating that gene flow occurred historically among populations. Gene flow estimates among populations suggest that tortoises exchanged individuals historically at a rate greater than one migrant per generation. We found a positive correlation between genetic and geographic distance of population pairs, a pattern characteristic of isolation by distance. During the study, we observed a radiotelemetered tortoise make an inter-population movement (>32km) and documented the anthropogenic barriers it encountered. Desert tortoises are capable of and sometimes motivated to disperse great distances and these movements result in the exchange of genetic material among adjacent populations. Because many historic dispersal routes are no longer available to desert tortoises as a result of anthropogenic landscape change, informed management strategies need to be in place to facilitate the long-term persistence of Sonoran desert tortoise populations.