Parallel adaptation to climate above the 35th parallel

Abstract

Independent or parallel evolution of similar traits is key to understanding the genetics and limitations of adaptation. Adaptation from the same genetic changes in different populations defines parallel evolution. Such genetic changes can derive from standing ancestral variation or de novo mutations and excludes instances of adaptive introgression. In this issue of Molecular Ecology, Walden et al.(2020) investigate the scale of parallel climate adaptation from standing genetic variation between two North American Arabidopsis lyrata lineages, each formed by a distinct evolutionary history during the last glacial cycle. By identifying adaptive variants correlated with three ecologically significant climatic gradients, they show that instead of the same genetic variants or even genes, parallel evolution is only observed at the level of biological processes. The evolution of independent adaptive variants to climate in two genetically close lineages is explained by their different post‐glacial demographic histories. Separate glacial refugia and strong population bottlenecks were probably sufficient to change the landscape of shared allele frequencies, hindering the possibility of parallel evolution.

The relevance of genetic structure in ecotype designation and conservation management

“…In theory, this might represent either one or multiple ecotypes. Possibly, previous gradual environmental changes permitted evolution of traits involving many variants with small fitness effects, which could have facilitated parallel evolution, but that are often difficult to detect with standard statistical approaches (Burns & Novikova, 2020 ). However, the situation may be different for the rapid changes occurring at present, where standing variation provides important raw material for selection, but the speed of change exceeds the possibility of adaptation even with the aid of novel variation (Burns & Novikova, 2020 ).…”

Capturing the rapidly evolving study of adaptation

“…In general, evolutionary biologists tend to use cases of repeated, parallel evolution of genes, phenotypes, or ecotypes to infer that (a) similar environments exert similar selection pressures, (b) selection favours only a few solutions and (c) the genes or traits that evolve in parallel are adaptations (Bolnick et al, 2018). However, the repeatability of these natural experiments in evolution is debated, and evidence for strong selection playing a role in parallel evolution at the genetic level is often equivocal because many different genetic routes can produce similar phenotypic outcomes (Bailey et al, 2016;Burns & Novikova, 2020).…”