Analysis of Morphology and Asymmetry in Bluegill Sunfish (Lepomis macrochirus) in the Southeastern United States

Two bluegill subspecies in the southeastern United States are found to be morphologically and genetically distinguishable, and an intergrade zone between the subspecies ranges is delimited. It has been hypothesized that populations in zones of hybridization between two forms should show higher levels of asymmetry than comparable populations of the parent forms. Bluegill populations from the intergrade zone showed no higher levels of asymmetry than either parent subspecies. This lack of difference may be due to the genomes of the two subspecies being very similar, or to genome coadaptation having evolved independently in drainages inhabited by intergrade populations. Morphological data and allelic frequencies at a marker locus give complementary information about the subspecies ranges. Present patterns of morphological and genetic differentiation are best explained by degrees of isolation among bluegill populations.