FINE-SCALE POPULATION GENETIC STRUCTURE IN AUSTRALIAN CADDISFLIES: AN EMPIRICAL TEST OF THE PATCHY RECRUITMENT HYPOTHESIS.

A.S. Schultheis¹ and J.M. Hughes². ¹Department of Biology, Stetson University, DeLand, FL , USA 32724-8264, ²Australian School of Environmental Studies, Griffith University, Nathan, QLD , Australia, 4111

Stream insect populations from SE Queensland exhibit an unusual pattern of genetic structure. In these streams, the highest levels of genetic differentiation occur at the smallest spatial scales and there are stochastic deviations from Hardy-Weinberg Equilibrium (HWE) across populations and loci. The 'patchy recruitment' hypothesis (PRH) states that this pattern results from the asynchronous adult emergence, low invertebrate density, and limited larval movement typical of SE Queensland streams. We tested the PRH by comparing spatial patterns of genetic differentiation in two species of caddisfly (Trichoptera: Tasimiidae), one from SE Queensland, and another from Victoria. Because adult emergence tends to be more synchronous and larval density is often greater in temperate streams, we predicted that the genetic structure of the Victorian populations would more closely resemble that of North American populations, i.e., that genetic distance would tend to increase with geographic distance, and that there would be little deviation from HWE. Population genetic structure was determined by sequencing a portion of the COI region of mtDNA and deviations from HWE were tested using two microsatellite loci. Although the pattern was not as pronounced as it has been in other species, the overall results were consistent with the predictions of the PRH.