Connecting the dots: Genetic differentiation among conservation areas

Background/Question/Methods

Population connectivity is vital for the maintenance of gene flow and metapopulation dynamics.  Migration among populations promotes allelic diversity within populations, reduces the effects of genetic drift, and contributes to each population’s ability to evolve in a dynamic world.  However, successful migration is dependent upon both species vagility as well as the intervening habitat matrix. As such, the distances between suitable habitat patches as well as the quality and configuration of the landscape can act as substantial barriers to movement. Isolated populations, in turn, may suffer from low interpopulation migration rates by experiencing reduced genetic variation and increased risk of local extinction.  Populations residing within conservation areas are no exception.  Conservation areas are typically isolated from one another by large expanses of unprotected land.  Therefore, they are separated not only by distance, but often by highly fragmented, inhospitable habitats as well.  These factors suggest that significant genetic differentiation may exist between conservation areas.  The wood frog (Rana sylvatica), a Missouri species of conservation concern, exhibits metapopulation structure and is known to be a philopatric breeder with moderate dispersal abilities.  In this study, 10 microsatellite primers were used to assess genetic differentiation within and among nine wood frog breeding ponds (n=210).  Three ponds were sampled at each of three conservation areas that were separated by an average of 8 km in east-central Missouri.    

Results/Conclusions

Analysis of molecular variance (AMOVA) results reveal significant genetic differentiation among both conservation areas and populations within conservation areas.  In addition, allelic richness varied significantly with the following observations:  the western most area contained the fewest alleles, the central area had an intermediate number of alleles, and the eastern most area—representing the conservation area closest to the core of Missouri’s wood frog distribution—exhibited the greatest number of alleles.  A similar pattern was revealed in observed heterozygosities, where decreasing values again correlated with distance from the core range.  Our data illustrates the negative effects of population isolation as facilitated by habitat discontinuity.  In order for conservation areas to be successful in promoting genetic diversity and species persistence, efforts should be made to connect island populations.   As such, vulnerable species, including the wood frog, may benefit from corridors that promote migration and gene flow between the isolated patches that comprise conservation areas.