Population Genetic Structure of Very Large Populations: The Brazilian Free-Tailed Bat, Tadarida brasiliensis

摘要

Species with restricted distributions or low potential for movement often are distinguished by population structures that can be readily defined by geographical distribution. By contrast, highly vagile or migratory species such as many birds, bats, insects, and marine organisms, are often characterized by population structures that are much harder to predict. Using published data from allozymes and from mitochondrial DNA (mtDNA) sequences, we present an analysis of genetic structuring in the Brazilian free-tailed bat, Tadarida brasiliensis, a highly vagile mammal that is characterized by extremely large population sizes. We compare molecular genetic analyses between and within subspecies with structure that has been inferred from morphological, behavioral, and ecological data. Mitochondrial DNA sequence data indicate that significant differences exist between populations in North America and those in Soutth America. A cladistic analysis of gene flow suggests genetic structuring among females in North America that is not consistent with the current subspecific taxonomy. Neither allozyme nor mtDNA data support distinction between the North American subspecies, nor do they support the genetic uniqueness of Cockrum's (1969) hypothesized migratory groups of T. b. mexicana. Data indicate that this subspecies has evolved as a single genetic unit, with an extremely large effective population size. Effective population sizes of the magnitude suspected for these bats are extremely rare for mammalian species.