Population Structure, Phylogeography, and Conservation of Two North American Arctic (Oeneis spp.) Butterflies
The Macoun’s arctic butterfly [MA, Oeneis macounii (W. H. Edwards)] is distributed across northern North America. In contrast, the White Mountain arctic butterfly [WMA, Oeneis melissa semidea (Say)] is endemic to the alpine zone of the White Mountains, New Hampshire, USA, and is of conservation concern. Macoun’s arctic and WMA adults occupy fragmented habitats, and the extent of genetic exchange among their allopatric populations has never been assessed. Additionally, the MA and WMA are biennial, yet emerge every year over all or parts of their range as two sympatric, allochronic cohorts, likely reproductively isolated by their asynchronous adult emergence. Using mtDNA and AFLPs markers, I elucidated the spatial and temporal genetic population structures of the MA and the WMA to infer their demographic histories; conservation management requirements; and the extent of reproductive isolation among allopatric populations and between sympatric, allochronic cohorts. For the WMA, I also conducted a mark-release-recapture study to determine its adult distribution, dispersal patterns, and mating behaviour. The MA exhibited significant spatial genetic structuring, and dispersal and gene flow likely is limited among most allopatric populations. Patterns in mtDNA diversity and divergence suggested that the MA may have re-colonized from a single eastern refugium in association with jack pine. I found little evidence for genetic differentiation between sympatric, allochronic MA cohorts. My field observations revealed that the WMA likely does not exhibit a true lek mating system. I observed WMA adult movements among some meadows, and, correspondingly, there was no genetic differentiation among samples collected from each meadow. Therefore, the WMA can be managed spatially as a single population. Although the WMA allochronic cohorts were differentiated on the basis of AFLPs, further analyses are required to confirm that they are reproductively isolated. Presently, conservation management of the WMA should focus on increasing its population size. Finally, I reviewed existing studies of sympatric, allochronic divergence generated by asynchronous, biennial life cycles in insects. I discuss empirical knowledge gaps about biennial insect demography and life history, the answers to which will be crucial for concluding if allochrony acts as a significant reproductive isolating mechanism in sympatry for biennial insects.