Landscape genetics of the threatened gopher tortoise, Gopherus polyphemus

Background/Question/Methods

The main aim of this study is to use a landscape genetics approach to identify the major determinants of population structure in the federally threatened gopher tortoise (Gopherus polyphemus). Previous ecological studies on habitat suitability and movement patterns indicate features such as rivers and major highways may impede gene flow, while upland ridges and favorable soil types may function as dispersal corridors. However, no genetic data is currently available on how these landscape variables affect patterns of gene flow and population connectivity in gopher tortoises. By identifying landscape features that constitute barriers to gene flow, information from this study will be used to formulate much-needed translocation guidelines for tortoise populations subject to habitat fragmentation and encroachment by development. Furthermore, this species is threatened by emerging infectious diseases so that knowledge of landscape features that promote tortoise movement and population connectivity is critical to future management of disease transmission. This project will utilize multi-locus genotypic data, geographic information systems, and several analytical approaches recently introduced to the field of landscape genetics including partial Mantel tests, least-cost path analysis, and generalized linear modeling. These methods will be used to test for a significant correlation between landscape features and population differentiation.

Results/Conclusions

Preliminary results showed no evidence that rivers were significantly correlated with genetic distance indicating that rivers may not be major barriers to dispersal as previously assumed. In contrast, major roads were significantly correlated with genetic distance suggesting that recent rather than historical barriers may be shaping current population structure. Information from this study will be used to improve species management by providing guidelines for relocation and the delineation of management units. Tortoises should not be translocated across features that have historically impeded dispersal. In contrast, roads may create artificial impediments and if so, appropriate management actions need to be taken to maintain natural population connectivity. Results from this study will also improve the management of chelonian diseases in natural populations through better understanding of tortoise movement. This includes the upper respiratory tract disease (URTD) that has been implicated in population declines. In conclusion, this research promises to impact species management and therefore improve the long-term population viability of gopher tortoises.