Genetic population structure of Gnathium minimum (Coleoptera: Meloidae): core and peripheral populations

A recent generic revision and a statewide survey of the meloid fauna of Wisconsin show a widespread distribution of Gnathium minimum throughout the Great Plains and western United States but with isolated records in southwestern Wisconsin. To investigate the degree of isolation and divergence between the core (western U.S.) and peripheral (WI) populations, we used amplified fragment length polymorphism (AFLP) to compare the magnitudes of genetic variability and genetic differentiation among sampling locations. Specimens from the Great Plains were obtained from 14 locations covering a relatively large geographic distance. However, we only found (and collected) G. minimum individuals at 11 locations in a 43 km stretch of sandy soils adjacent to the Wisconsin River. This limited distribution in Wisconsin is likely in part due to the adult foraging specifically on Few-leaf Sunflower (Helianthus occidentalis), although other species of sunflower are used in the Great Plains. A comparison of core and peripheral populations, but also between some sampling locations within each of these areas, resulted in statistically significant genetic differentiation. This differentiation suggests that gene flow may be restricted, especially between the WI and Great Plains sampling locations.