Population Genetics and Effective Population Size of the Brazilian Free-Tailed Bat, Tadarida brasiliensis (Chiroptera: Molossidae)

The Mexican free-tailed bat, Tadarida brasiliensis mexicana, exhibits variation in migratory behavior over its range. Some populations undergo seasonal long-distance migrations to warmer climates in winter, whereas others are resident through the winter in more northern regions and hibernate. Variation is also exhibited among populations in their migratory routes, and long-term banding studies document that populations are largely faithful to a single migratory route. These observations have led to the prediction that behaviorally defined migratory groups make up structured gene pools. Tests of this prediction using allozyme markers have documented high levels of gene flow among migratory groups, with no evidence for the structuring of gene pools. I use phylogenetic and population genetic analyses of mitochondrial DNA sequence data to examine genetic structuring among three of the four previously defined migratory groups. I find no evidence supporting the maintenance of separate gene pools within this subspecies, and conclude that sufficient gene flow occurs among colonies to genetically homogenize the entire subspecies. These analyses imply that the entire T. b. mexicana subspecies evolves as a single, very large population.