The devil is in the details: genetic variation in introduced populations and its contributions to invasion

Abstract

The influence of genetic variation on invasion success has captivated researchers since the start of the field of invasion genetics 50 years ago. We review the history of work on this question and conclude that genetic variation-as surveyed with molecular markers-appears to shape invasion rarely. Instead, there is a significant disconnect between marker assays and ecologically relevant genetic variation in introductions. We argue that the potential for adaptation to facilitate invasion will be shaped by the details of genotypes affecting phenotypes, and we highlight three areas in which we see opportunities to make powerful new insights. (i) The genetic architecture of adaptive variation. Traits shaped by large-effect alleles may be strongly impacted by founder events yet more likely to respond to selection when genetic drift is strong. Large-effect loci may be especially relevant for traits involved in biotic interactions. (ii) Cryptic genetic variation exposed during invasion. Introductions have strong potential to uncover masked variation due to alterations in genetic and ecological environments. (iii) Genetic interactions during admixture of multiple source populations. As divergence among sources increases, positive followed by increasingly negative effects of admixture should be expected. Although generally hypothesized to be beneficial during invasion, admixture is most often reported among sources of intermediate divergence, supporting the possibility that incompatibilities among divergent source populations might be limiting their introgression. Finally, we note that these details of invasion genetics can be coupled with comparative demographic analyses to link genetic changes to the evolution of invasiveness itself.

Invasions and extinctions through the looking glass of evolutionary ecology

“…When adaptive variants from a genetically distinct population introgress, natural selection can act on this enhanced standing variation without waiting for new mutations to arise de novo [57]. For these reasons, and because invasive species frequently experience novel selective environments in their introduced range, admixture has been implicated as a potential factor fuelling rapid evolution and the generation of novel invasive genotypes [33,48,58]. Nevertheless, direct evidence of a link between introgressed variation and the evolution of invasiveness is largely lacking to date.…”

The population genomic basis of geographic differentiation in North American common ragweed (Ambrosia artemisiifolia L.)

“…When multiple introductions occur from different locations, formerly disparate genotypes have opportunities to form hybrids that may better exploit niches than parent genotypes (Ellstrand and Schierenbeck 2000; Dlugosch et al. 2015). …”

Reticulate evolution is favored in influenza niche switching

“…Beyond the viral world, recent reviews have asserted the importance of reticulate evolutionary events as a driver of speciation and niche diversification (22,23), and recent studies have illustrated heightened fitness effects in hybrid populations (24,25). However, none have quantitatively tested the importance of reticulate evolutionary strategies in enabling ecological niche switches on a global scale, especially in comparison with clonal adaptation under drift and selection (a task feasible only in fast-evolving organisms).…”