| My recent 14 yr survey of the hybrid zone between the ground crickets Allonemobius fasciatus and A. socius in eastern North America revealed two patterns. First, the zone has moved north in one transect through the Appalachian Mountains, possibly due to climate warming since the ranges of both taxa are temperature dependent. Second, throughout the Mountain transect, and another transect along the East Coast, mixed-species populations harbored hybrids and backcrosses, yet were bimodally dominated by parentals, implying that introgression was not eroding the identity of parentals, who were separated by strong but incomplete reproductive isolation. In this dissertation I explore these patterns in detail. I genetically analyzed long-term samples from a third transect through Illinois with the expectation that this transect, farther from oceanic climate-buffering than the Mountain transect, should experience greater warming and greater movement. Most Illinois populations registered greater genotypic changeovers consistent with reaction to warming, but unexpected reverse changeovers implied the zone may react to climate at local scales. Additionally, Illinois mixed populations were bimodal, bolstering evidence from the original survey that parental taxa throughout the zone retain identity despite introgressive hybridization. I investigated the possibility that conspecific sperm precedence (CSP), the preferential utilization of conspecific sperm by females mated to both conspecific and heterospecific males, between A. fasciatus and A. socius, accounted for bimodality. Using East Coast transect populations and AFLPs I undertook quantitative trait locus (QTL) experiments describing genetic architecture of CSP, pinpointing CSP QTLs and identifying linkage groups in both species, thereby developing candidate species-specific AFLP markers. I surveyed the East Coast transect for AFLP linkage groups and QTLs at regional and local scales and found that many markers held up as species-specific, although results varied at different scales of gene flow and geography. Mating trials with East Coast transect crickets showed a weak relationship between sperm utilization and empirically derived species-specific AFLP linkage groups and QTLs. |
