DISENTANGLING THE EFFECTS OF ECOLOGICAL AND EVOLUTIONARY PROCESSES ON THE GENETIC STRUCTURE OF ALPINE STREAM INSECTS.

M.T. Monaghan, P. Spaak, C.T. Robinson, and J.V. Ward. Department of Limnology, EAWAG/ETH, 8600 Duebendorf, Switzerland

Using neutral genetic markers to estimate gene flow requires consideration of processes occurring at both ecological and evolutionary time scales. Hierarchy theory suggests such processes manifest at local and regional spatial scales, respectively. We investigated the population genetic structure of two species of stream insects in the Swiss Alps at multiple spatial scales employing allozymes and AFLP markers. Rhithrogena loyolaea exhibited little genetic differentiation within (Fst = 0.01 to 0.03) and among (0.02 to 0.03) streams but significant differentiation among catchments (0.08), suggesting that most dispersal occurs within and among streams. Baetis alpinus exhibited moderate to substantial differentiation within streams fragmented by lakes and among streams within catchments (Fst = 0.083 to 0.394) but a distinct lack of genetic differentiation (0.01) among catchments (Rhine, Danube, Po). An identical pattern was observed for Baetis using AFLP markers: AMOVA results showed that 16% of the molecular variance occurred among streams and only ca 2% occurred among catchments. We suggest that pronounced genetic structure at local scales and limited genetic structure at regional scales may result from (1) historical gene flow that continues to mask reduced local dispersal, or (2) recurring processes of recruitment that lead to random differentiation among fragments.