Meeting Abstract

35.5  Thursday, Jan. 5  Development time, seasonality, and body size clines in insects: a general explanation? DILLON, M.E.*; FRAZIER, M.R.; University of Wyoming, Laramie; U.S. EPA, Western Ecology Division, Newport, OR Michael.Dillon@uwyo.edu

Body size clines and their underlying mechanisms have long fascinated ecologists. Bergmann originally documented consistent increases in body size with latitude among endotherm species. But his rule has since been extended to non-endotherms and both inter- and intraspecific patterns. Insects seem to be equally likely to show either increasing or decreasing size across altitude and latitude, a pattern that contradicts the general one and begs explanation. The body size cline an insect species expresses along latitudinal and altitudinal gradients has been hypothesized to depend on the species’ development time relative to the growing season. Species with relatively long generation times and relatively short growing seasons run the greatest risk of running out of time or resources prior to completing development. To avoid this, populations living in colder environments may reduce development times by maturing at smaller body sizes. Based on this hypothesis, we predicted that: 1) insect species with longer development times are more likely to be smaller at high altitudes (i.e., negative body size cline); and 2) insects living in regions with short growing seasons are more likely to be smaller at high altitudes. We compiled studies measuring intraspecific changes in body size along altitudinal gradients and used both conventional and phylogenetically corrected analyses to test these predictions. Overall, preliminary analyses support the hypothesis, suggesting a general explanation for body size clines in insects.