Sweeney, B.W., D.H. Funk, and R.L. Vannote. 1986. Journal of the North American Benthological Society 5(4):253-262.
The population genetic structure of two species of mayflies was studied using protein electrophoresis at eight locations in the headwater region of the Delaware River drainage basin. Study sites were located upstream and downstream from two large reservoirs. The working hypothesis was that little or no genetic differentiation occurs between conspecific populations within and among tributaries of the same drainage basin. A total of 24 and 28 loci were examined for Eurylophella verisimilis and Ephemerella subvaria respectively. Geographic differentiation was significant for three of nine polymorphic loci (average FST=0.028) for Ep. subvaria when all populations were compared. Spatial variation in allele frequencies among populations of Ep. subvaria was substantially higher in the West Branch than in the East Branch of the Delaware River. The spatial cline of allele frequencies for certain loci of Ep. subvaria paralleled environmental gradients in the vicinity of the two reservoirs but no cause-effect relationship can be implied without more extensive data. Regardless, the results for Ep. subvaria failed to support the hypothesis. In contrast, geographic differentiation for Eu. verisimilis was low, being limited to one locus and caused by allelic abnormalities at one site (average FST=0.008). No significant spatial clines were observed for Eu. verisimilis among study sites. These data seem to be consistent with the hypothesis. There was no indication of disrupted gene flow caused by the reservoirs acting as barriers to dispersal by larval drift or adult flight in either species. However, additional data on species in drainage basins without potential barriers to gene flow are needed to adequately test the hypothesis.