Genetic Variation in Stream Mayfly (Insecta: Ephemeroptera) Populations of Eastern North America

Abstract

We evaluated genetic variation in 40 populations (five species) of ephemerellid mayflies collected from streams in the Atlantic and Gulf drainages of eastern North America. The principal study species included Eurylophella funeralis (McDunnough), Eurylophella verisimilis (McDunnough), Ephemerella subvaria McDunnough, Ephemerella aurivillii (Bengtsson) and Ephemerella septentrionalis McDunnough. For the 40 populations, proportion of polymorphic loci averaged 22.3% (SEM = 2.0; range, 0–50%), with relatively low genie heterozygosity (ݲ ± SEM = 0.079 ± 0.006; range, 0–0.160). Nei's genetic distance (D) averaged 0.006 among conspecific mayfly populations and 1.434 among species. A genetic distance of 0.704 suggests that Eu. funeralis and Eu. verisimilis are distantly related congeners. Genetic distances among populations of the three principal Ephemerella species were even higher, with D values averaging >1.0. Genetic distance data for five additional Ephemerella species, Ephemerella dorothea Needham, Ephemerella excrucians Walsh, Ephemerella inconstans Traver, Ephemerella invaria (Walker), and Ephemerella rotunda Morgan, revealed that D values F_ST values ranging from 0.04 to 0.15 (average for five species = 0.10). Although one allele generally predominated at each polymorphic locus of a given species, there was significant variation in allele frequencies among populations. However, allele frequencies did not exhibit a geographic cline. Gene flow seems limited among most mayfly populations. A severe deficiency of heterozygotes at several loci for each species indicates substantial inbreeding in mayfly populations (average F_IS values ranged from 0.03 to 0.28). Heterogeneity of inbreeding values among loci in a given species suggests possible selection at some loci.