Phylogeographic comparison of five large-bodied aquatic insect species across the western USA

Glacial legacy, barriers to migration, and dispersal abilities are important determinants of intraspecific genetic diversity. Genetic comparisons can elucidate the distribution of genetic variants among populations, but for many groups of organisms the concordance of population genetic structure and historical refugia among co-occurring species remains unclear. We compared phylogeographic histories of 4 stoneflies (Calineuria californica, Hesperoperla pacifica, Pteronarcys californica, and Pteronarcys princeps) and 1 caddisfly (Dicosmoecus gilvipes) across their species ranges. Study species had large body and wing sizes that suggest strong flying ability and dispersal potential. Nevertheless, riverine habitat restrictions and mating behaviors can inhibit dispersal. We used mitochondrial and nuclear gene sequences to examine population genetic structure relative to potential past and present barriers to dispersal in the western USA. North-south population genetic structure was present for each species but was more pronounced for 2 stoneflies (C. californica and P. californica) and the caddisfly. For these 3 species, phylogenies indicated concordant clades north and south of San Francisco Bay, a large, saltwater estuary in California. Basal phylogenetic nodes and regional centers of haplotype diversity suggested common historical refugia in northern California or southern Oregon, similar to that found in previous studies of salamanders. For 1 stonefly (C. californica) and the caddisfly, distinct populations in the Sierra Nevada Mountains suggested potential barriers to gene flow. The presence of population genetic structure suggests vulnerability to loss of intraspecific diversity under climate change scenarios, particularly for populations at high elevations.