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Genetics and Life History Traits of Big Brown Bats

Recent genetic studies documented the occurrence of several geographically distinct mitochondrial (mt) DNA lineages of the big brown bat (Eptesicus fuscus) in North America. Individuals from two of these lineages, an eastern and a western form, co-occur within maternity colonies in Fort Collins, Colorado.

Geographically distinct mitochondrial (mt) DNA lineages of the big brown bat (Eptesicus fuscus) in North America.

This discovery of two divergent mtDNA lineages in sympatry has prompted a host of ecological questions regarding possible differences between haplotypes in a number of life history characters, including the rabies virus variant found in each type, distribution, litter size, morphology, and roosting behavior. We captured big brown bats at maternity roosts throughout Fort Collins and several locations elsewhere in Colorado. Data on life-history traits were sampled and wing biopsies were collected for genetic analysis.

Forearm measurement

Tissue sample (biopsy)

Color comparison

Sequence analysis and restriction digests of the ND2 region of the mtDNA molecule were employed to determine lineage of individual bats. In addition, intron 1 of the b-globin gene was used to determine if the two mtDNA lineages are hybridizing. Eastern and western lineages differ at approximately 10% sequence divergence and genetic data suggest population expansion for both lineages. Overall there is a relatively equal proportion of the two lineages but differences in distribution seem to occur along the Colorado Front Range, with an increasing proportion of western haplotypes occurring farther south.

Lineages did not differ greatly in their choice of roosts or overwintering behavior and no outstanding distinctiveness has been found between the mtDNA haplotypes in most life history characters examined. Additionally, results from the nuclear intron demonstrated hybridization between the two lineages. Pleistocene climate changes likely lead to the separation of this species into isolated eastern and western populations, and secondary contact, with subsequent interbreeding, was possibly facilitated by urbanization and water development activities. Although at two rabies virus variants were found to be circulating in Colorado big brown bat populations, these variants were not associated with the mtDNA haplotypes of infected bats.

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