MAYFLIES IN HEADWATER STREAMS: PATTERNS OF SPATIAL SEPARATION THAT MAY AFFECT GENE FLOW AMONG LOCAL POPULATIONS.

L.C. Alexander, W.O. Lamp, and D.J. Hawthorne. Department of Entomology, University of Maryland, College Park, Maryland 20742

Drainage basin morphology and the unidirectional flow of stream water may be viewed as natural fragmentation processes capable of structuring aquatic invertebrate populations at the landscape-scale. Headwater streams in the central piedmont region of Maryland historically formed dense, highly-branched networks that are now being reduced in number and complexity as watersheds are developed. We ask how the population structure of mayflies living in headwater streams may be affected by loss of neighboring streams, and whether the historic levels of connectivity among Maryland's headwaters are important to the persistence of these aquatic species. Using mitochondrial and nuclear DNA markers to assess migration and gene flow, we test for changes in the population genetic structure of mayflies living in intact and disturbed headwater stream networks.