Adaptive Genetic Divergence along Narrow Environmental Gradients in Four Stream Insects

Abstract

A central question linking ecology with evolutionary biology is how environmental heterogeneity can drive adaptive genetic divergence among populations. We examined adaptive divergence of four stream insects from six adjacent catchments in Japan by combining field measures of habitat and resource components with genome scans of non-neutral Amplified Fragment Length Polymorphism (AFLP) loci. Neutral genetic variation was used to measure gene flow and non-neutral genetic variation was used to test for adaptive divergence. We identified the environmental characteristics contributing to divergence by comparing genetic distances at non-neutral loci between sites with Euclidean distances for each of 15 environmental variables. Comparisons were made using partial Mantel tests to control for geographic distance. In all four species, we found strong evidence for non-neutral divergence along environmental gradients at between 6 and 21 loci per species. The relative contribution of these environmental variables to each species' ecological niche was quantified as the specialization index, S, based on ecological data. In each species, the variable most significantly correlated with genetic distance at non-neutral loci was the same variable along which each species was most narrowly distributed (i.e., highest S). These were gradients of elevation (two species), chlorophyll-a, and ammonia-nitrogen. This adaptive divergence occurred in the face of ongoing gene flow (F st = 0.01–0.04), indicating that selection was strong enough to overcome homogenization at the landscape scale. Our results suggest that adaptive divergence is pronounced, occurs along different environmental gradients for different species, and may consistently occur along the narrowest components of species' niche.

Signatures of selection in mammalian clock genes with coding trinucleotide repeats: Implications for studying the genomics of high‐pace adaptation

“…In the recent past, there has been an advancement in empirical studies implicating climatic and environmental gradients in the generation and maintenance of adaptive genetic diversity through selection, even in the face of ongoing gene flow between populations (DeFaveri et al., 2013; Fang et al., 2013; Watanabe, Kazama, Omura, & Monaghan, 2014). Clock genes in particular have been demonstrated to be important targets of selection, as they are likely to provide a means by which species can adapt to seasonal changes or adjust to novel environments (Kondratova et al., 2010).…”

Comparative tests of the species‐genetic diversity correlation at neutral and nonneutral loci in four species of stream insect

“…We focused on four species of freshwater insect for which genetic data (AFLP variation) were reported by Watanabe et al. (). We also analyzed the stream invertebrate communities in which they occur in six adjacent watersheds in Northeast Japan.…”

Catchment‐scale modeling of riverine species diversity using hydrological simulation: application to tests of species‐genetic diversity correlation

“…We used empirical AFLP genetic data for three caddisflies (Insecta: Trichoptera), Hydropsyche orientalis (Ho), Stenopsyche marmorata (Sm) and H. albicephala (Ha), and a mayfly (Insecta: Ephemeroptera), Ephemera japonica (Ej), as reported by Watanabe et al (). The two caddisfly species, Ho and Sm, were broadly distributed (present at 26 sites and 20 sites), whereas Ha and Ej were only sampled in upstream/ headwater regions and small tributaries (present at 13 sites and 11 sites) from the 39 sampling sites across the study catchment (see Figure S2).…”

“…We used different biological datasets for constructing and validating the model to verify our practical approach, which applies a priori the model estimated from local data to an estimation of species diversity covering the catchment. We used empirical Amplified Fragment Length Polymorphism (AFLP) data (Watanabe, Kazama, Omura, & Monaghan, ) to calculate the genetic diversity of four stream invertebrate species (three caddisflies and one mayfly). Subsequently, we examined the SGDCs using the estimated species diversity and the genetic diversity.…”