Population genetic structure of aquatic insects with varying dispersal abilities in fragmented desert streams

Background/Question/Methods

Streams occur as fragmented habitats across the arid southwest of North America. The spatial distribution of these streams and their differing degrees of flow permanence have likely influenced the population genetic structures of aquatic invertebrates in this region. We sampled populations of three co-distributed, stream-dwelling insects in Arizona— Abedus herberti (Hemiptera), Mesocapnia arizonensis (Plecoptera), and Stictotarsus aequinoctialis (Coleoptera)— with the aim of comparing intraspecific patterns genetic differentiation among these species (20 populations each, 30 individuals per population). These insects differ in their habitat requirements and dispersal abilities. A. herberti requires perennial water for all life stages and is flightless. M. arizonensis is found in intermittent streams and may be capable of dispersing moderate distances via adult flight (males are brachypterous). Adult S. aequinoctialis are strong flyers; this species occurs in ephemeral, intermittent, and perennial habitats. Among the three insects, we expected to find contrasting patterns of population structure that correlate with the spatial distributions of the stream habitats as well as with the species’ dispersal abilities.

Results/Conclusions

Analysis of data from 10 microsatellite loci in A. herberti (617 individuals from 20 populations) found evidence of strong population genetic structure in this species and a pattern of isolation by distance among populations. These patterns likely reflect the limited dispersal ability of A. herberti. A landscape genetics analysis of this species revealed an association between gene flow and landscape curvature. Landscape curvature describes the extent to which local topography is either convex or concave. Gene flow in A. herberti appears to be relatively high across areas with concave topography, such as stream drainages, gullies, and passes between watersheds. We have developed seventeen and eleven microsatellite loci for M. arizonensis and S. aequinoctialis, respectively. With data for all three species, we aim to forecast how the population genetics of stream-dwelling insects might be altered by regional climate change.