TESTS OF THE PATCHY RECRUITMENT HYPOTHESIS IN BAETID MAYFLIES FROM THREE DIFFERENT ENVIRONMENTS.

J.M. Hughes¹, M. Hillyer¹, P. Mather², S.E. Bunn¹, and B.L. Peckarsky³. ¹Cooperative Research Centre for Freshwater Ecology, Australian School of Environmental Studies, Griffith University, Nathan, Queensland, Australia, ²School of Natural Sciences, Queensland University of Technology, Brisbane, Queensland, Australia, ³Department of Entomology, Cornell University, Ithaca, NY, U.S.A.

Recent studies of the genetic structure of populations of insects in Australian subtropical streams have shown that the greatest amount of genetic variation is at the smallest spatial scale; i.e., among populations from pools within the same stream. These results may indicate patchy recruitment into pools and limited larval dispersal. It has been proposed that these patterns should be most pronounced in environments where emergence of adults is asynchronous. We compared the genetic structure of baetid mayflies from subtropical and temperate streams in Australia and montane streams in the Rocky Mountains, Colorado. We predicted that small-scale variation and deviations from Hardy-Weinberg proportions would be greatest in subtropical streams, where adults emerge gradually all year and drift rates are low, and smallest in montane streams, where adult emergence is more synchronous and drift rates are high. We used allozymes and a fragment of the COI mitochondrial gene to examine genetic variation within and among streams and allozymes to assess the patterns of deviation from Hardy-Weinberg proportions. Patterns of genetic variation were similar in the Victorian species and that in Queensland streams, despite predicted higher rates of drift. In both species, adult emergence is asynchronous, occurring throughout much of the year, and could lead to patchy recruitment. This is unlikely to be the case in the North American species, which shows greater synchrony of larval development and adult emergence and is a renouned drifter.