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

Abstract

Aim Geographic variation in body size and heterozygosity were surveyed for discrete populations of the ant lion, Myrmeleon immaculatus DeGeer, collected from the central and northeastern United States.Location Collection sites were located in the central and eastern United States ranging from western Oklahoma to northern New York. MethodsWe collected 872 M. immaculatus larvae from thirty-four collecting sites. At each site, we randomly sampled ant lion pits and collected between fifteen and fifty-two larvae in total. Larvae were preserved in 95% ETOH for morphological analysis and frozen in a −80°C freezer for protein electrophoresis. We measured the body size of eighty-five preserved adult M. immaculatus obtained from museum collections using head width as an indicator of body size. Five enzymes [GPI (glucose phosphate isomerase), MDH (malate dehydrogenase), PEP (peptidase), DIA (diaphorase) and SOD (superoxide dismutase)] were used in the heterozygosity analyses. ResultsLarval and adult body size increased with latitude, but decreased with elevation. Average heterozygosity, measured at five polymorphic loci, also increased significantly with latitude. Minimum temperature variance was the best predictor of body size, whereas precipitation and maximum temperature were the best predictors of heterozygosity. Populations were genetically differentiated from one another and showed a pattern of isolation by distance, as measured by Wright's F st values and Nei's genetic distances.Main conclusions Sampling artifacts, heat conservation, character displacement, cell-size variation, density-dependent mortality, and differential dispersal probably cannot account for latitudinal variation in ant lion body size. Our results implicate the importance of diurnal photoperiod, which varies with latitude, but not with elevation. Because photoperiod often controls growth, diapause, and metamorphosis, it may be an important determinant of latitudinal clines in body size and life history of insects.

Investigating the poor performance of heather beetle, Lochmaea suturalis (Thompson) (Coleoptera: Chrysomelidae), as a weed biocontrol agent in New Zealand: Has genetic bottlenecking resulted in small body size and poor winter survival?

“…This pattern is consistent with Bergmann's Rule, although only homeotherms seem to show a consistent pattern of increased body size to counter climatic factors associated with increasing latitude (Arnett et al, 1999). The smaller size of heather beetle in NZ is also likely to be strongly influenced by genetics, but in this case from a major founder effect: all NZ heather beetles were derived from one or two field-collected females from one site in northern England.…”

Key themes in the study of seasonal adaptations in insects II. Life-cycle patterns

“…Although many geographic trends are complex (cf. Arnett and Gotelli, 1999), overall patterns of diapause are correlated especially with winter severity and duration of the growing season (e.g. Danks, 1987;Masaki, 1999).…”

Development of Myrmeleon brasiliensis (Navás) (Neuroptera, Myrmeleontidae), in laboratory, with different natural diets

“…Larvae pass through three instars, live up to two years, construct silk cocoons, and emerge as adults after approximately one month (ARNETT & GOTELLI 1999b. As the common name suggests, ants constitute most of the larval diet of the antlion, not by preference, but because they are usually the ABSTRACT.…”