Bergmann's rule in the ant lion Myrmeleon immaculatus DeGeer (Neuroptera :Myrmeleontidae): geographic variation in body size and heterozygosity

Aim Geographic variation in body size and heterozygosity were surveyed for discrete populations of the ant lion, Myrmeleon immaculatus DeGeer, collect ed from the central and northeastern United States. Location Collection sites were located in the central and eastern United St ates ranging from western Oklahoma to northern New York. Methods We collected 872 M. immaculatus is larvae from thirty-four collecti ng sites. At each site, we randomly sampled ant lion pits and collected bet ween fifteen and fifty-two larvae in total. Larvae were preserved in 95% ET OH for morphological analysis and frozen in a -80 degrees C freezer for pro tein electrophoresis. We measured the body size of eighty-five preserved ad ult M. immaculatus obtained from museum collections using head width as an indicator of body size. Five enzymes [GPI (glucose phosphate isomerase), MD H (malate dehydrogenase), PEP (peptidase), DIA (diaphorase) and SOD (supero xide dismutase)] were used in the heterozygosity analyses. Results Larval and adult body size increased with latitude, bur decreased w ith elevation. Average heterozygosity, measured at five polymorphic loci, a lso increased significantly with latitude. Minimum temperature variance was the best predictor of body size, whereas precipitation and maximum tempera ture were the best predictors of heterozygosity. Populations were genetical ly differentiated from one another and showed a pattern of isolation by dis tance, as measured by Wright's F-st values and Nei's genetic distances. Main conclusions Sampling artifacts, heat conservation, character displacem ent, cell-size variation, density-dependent mortality, and differential dis persal probably cannot account for latitudinal variation in ant lion body s ize. Our results implicate the importance of diurnal photoperiod, which var ies with latitude, but not with elevation. Because photoperiod often contro ls growth, diapause, and metamorphosis, it may be an important determinant of latitudinal dines in body size and life history of insects.