IS THERE A GENETIC BASIS FOR THE PHENOTYPIC DIFFERENCES AMONG BAETIS SPP. IN FISH AND FISHLESS STREAMS?

B.L. Peckarsky^1,2, J.M. Hughes³, and A.C. Encalada^1,2. ¹Department of Entomology, Cornell University, Ithaca, NY, ²Rocky Mountain Biological Laboratory, P.O. box 519, Crested Butte, CO, ³Cooperative Research Centre for Freshwater Ecology, Australian School of Environmental Studies, Griffith University, Nathan, Queensland, Australia

Populations of Baetis bicaudatis living in high elevation Colorado streams behave differently and undergo different developmental pathways in fish and fishless streams. In streams with brook trout, larvae are more nocturnal and develop faster resulting in smaller and less fecund adults emerging from trout streams than from fishless streams. These phenotypic differences in behavior and development can be induced experimentally by exposing fishless stream Baetis in mesocosms and in natural streams to chemical cues from brook trout. These experiments suggest that Baetis traits associated with fish and fishless streams are phenotypically plastic, and that populations in both fish and fishless streams have the genetic capability to respond to fish. To test this hypothesis, during summer 2001 we collected Baetis larvae from multiple fish and fishless streams, and from fish and fishless sections of the same streams. We used allozymes and a fragment of the COI mitochondrial gene to examine genetic variation of Baetis individuals within and among streams. Results showed that genetic variation among populations of Baetis from different streams was not explained by the presence or absence of fish. These data suggest that populations of Baetis bicaudatis living in fish and fishless streams are not genetically distinct.