Revisiting comparisons of genetic diversity in stable and declining species: assessing genome-wide polymorphism in North American bumble bees using RAD sequencing.

Genetic variation is of key importance for a species' evolutionary potential, and its estimation is a major component of conservation studies. New DNA sequencing technologies have enabled the analysis of large portions of the genome in nonmodel species, promising highly accurate estimates of such population genetic parameters. Restriction site-associated DNA sequencing (RADseq) is used to analyse thousands of variants in the bumble bee species Bombus impatiens, which is common, and Bombus pensylvanicus, which is in decline. Previous microsatellite-based analyses have shown that gene diversity is lower in the declining B. pensylvanicus than in B. impatiens. RADseq nucleotide diversities appear much more similar in the two species. Both species exhibit allele frequencies consistent with historical population expansions. Differences in diversity observed at microsatellites thus do not appear to have arisen from long-term differences in population size and are either recent in origin or may result from mutational processes. Additional research is needed to explain these discrepancies and to investigate the best ways to integrate next-generation sequencing data and more traditional molecular markers in studies of genetic diversity.

Molecular markers reveal strong geographic, but not host associated, genetic differentiation in Aphidius transcaspicus, a parasitoid of the aphid genus Hyalopterus.

Host plant associated genetic differentiation is a common phenomenon in phytophagous insects, but the degree to which such associations sequentially drive diversification at higher trophic levels is not as well understood. A recent study examining neutral molecular markers in Hyalopterus aphids revealed that genetic structure in this genus is strongly determined by primary host plant use (Prunus spp.). In this paper, we take a similar approach to determine whether this host plant specificity has affected genetic structure in the parasitoid Aphidius transcaspicus, an important natural enemy of Hyalopterus spp. in the Mediterranean. Mitochondrial DNA (428 bp) and seven microsatellite loci were examined in parasitoids collected from aphid populations on almond, apricot, peach and plum trees from Spain and Greece. In contrast to the previous findings for Hyalopterus from the same regions, here we find no evidence for host associated diversification in A. transcaspicus at the species level or below, though geographic structure between regional populations is exceptionally high. These findings have several implications for our understanding of the ecology and evolution of A. transcaspicus as well as for its use as a biological control agent for Hyalopterus, suggesting that a consideration of host plant specificity may be less critical than factors such as climatic suitability or geographic origins of invasive populations.