AFLP study of 5 macroinvertebrate species: Does range-size affect genetic diversity and differentiation?

Widely distributed species may contain greater genetic diversity than narrowly distributed species. We compared the genetic diversity and population structure among four caddisflies (Hydropsychidae: Hydropsyche orientalis and H. albicephala, Stenopsychidae: Stenopsyche marmorata, Rhyacophilidae: Rhyacophila towadensis) and one mayfly (Ephemeridae: Ephemera japonica) from six neighboring catchments in NE Japan using AFLP. Their geographic distribution varied from the widespread H. orientalis (41 out of the 73 study sites) to the rare R. towadensis (3 sites), with S marmorata (30 sites), H. albicephala (15) and E. japonica (12) all intermediate. Total genetic diversities were not significantly different among the species (H_T = 0.25 – 0.31), rejecting our hypothesis that widespread species have greater diversity than geographically restricted species. Genetic differentiation among subpopulations of the two narrowly distributed species (G_ST =　0.06 - 0.09, θ_ST=　0.03 - 0.06) was significantly lower than the other three (G_ST =　0.16 - 0.28, θ_ST=　0.12 - 0.13); however, diversity within subpopulations (H_S =　0.20 - 0.29) was negatively correlated with range size. The results indicate that widespread species maintained the genetic diversity mainly through turnover among subpopulations, whereas narrowly distributed species maintain diversity within populations. The result is no net difference in diversity throughout the distribution.