Inferring haplotype diversity and population structure of the mite Spinturnix americanus between two host species, M. lucifugus and M. septentrionalis, via cytochrome b sequencing

Abstract

The wing mite Spinturnix americanus is a sanguivorous and obligate ectoparasite on bats of the genus Myotis, including Myotis lucifugus (little brown bat) and Myotis septentrionalis (northern long-eared bat). These hosts have different social structures and life histories with respect to roost group size, travel distances between roosts and hibernacula, roost social behavior, foraging behavior, and specialist versus generalist roost tendencies. Genetic analyses conducted on similar European Spinturnix species found that these host life history traits influence the genetic diversity and genetic structure of their parasite populations. Using samples collected from M. lucifugus and M. septentrionalis hosts captured at the entrance of Hayes cave (Nova Scotia) during swarming in August-September 2006. I sequenced cytochrome-b and estimated genetic diversity (gene diversity and nucleotide diversity) and genetic differentiation (F[subscript ST], and [Phi subscript ST]) levels in parasites collected from both host species. Twelve haplotypes were characterized from 28 individuals (20 from S. americanus mites collected from M. lucifugus, and 8 collected from M. septentrionalis), with 11 present in the M. lucifugus group, and 2 in M. septentrionalis group. One haplotype was found in 15 (54%) of the mites, (8 collected from M. lucifugus, 7 from M. septentrionalis). Estimates of gene diversity were 0.8421 and 0.2500, and nucleotide diversity were 0.0056 and 0.0023, for mites on M. lucifugus and M. septentrionalis respectively, indicating greater haplotype diversity in mites from M. lucifugus. FST and [Phi subscript ST] values were 0.1059 (p= 0.0498), and -0.0235 (p= 0.6353) suggesting some degree, but not uninhibited, gene flow between the parasites on each species, leading to some degree of genetic differentiation. The larger F[subscript ST] value compared to [Phi subscript ST] suggests that the movement rate is higher than the mutation rate, with mites spreading new mutations (haplotypes) among host species. The measures of genetic diversity suggest that M. lucifugus’ life history factors of larger roost groups, longer roost to hibernacula migration distances, and more generalist roosting tendencies may facilitate more opportunity for mite interbreeding, and therefore greater genetic diversity. Future studies should be conducted to determine definitive degree of differentiation between the host groups, and to assess if they qualify as subpopulations with minimal or no gene flow between them, and observe how population dynamics have changed after the white-nose syndrome epidemic.