Genetic introgression as a potential to widen a species' niche: Insights from alpine Carex curvula

Abstract

Understanding what causes the decreasing abundance of species at the margins of their distributions along environmental gradients has drawn considerable interest, especially because of the recent need to predict shifts in species distribution patterns in response to climatic changes. Here, we address the ecological range limit problem by focusing on the sedge, Carex curvula, a dominant plant of high-elevation grasslands in Europe, for which two ecologically differentiated but crosscompatible taxa have been described in the Alps. Our study heuristically combines an extensive phytoecological survey of alpine plant communities to set the niche attributes of each taxon and a population genetic study to assess the multilocus genotypes of 177 individuals sampled in typical and marginal habitats. We found that ecological variation strongly correlates with genetic differentiation. Our data strongly suggest that ecologically marginal populations of each taxon are mainly composed of individuals with genotypes resulting from introgressive hybridization. Conversely, no hybrids were found in typical habitats, even though the two taxa were close enough to crossbreed. Thus, our results indicate that genotype integrity is maintained in optimal habitats, whereas introgressed individuals are favored in marginal habitats. We conclude that gene flow between closely related taxa might be an important, although underestimated, mechanism shaping species distribution along gradients.alpine flora ͉ evolutionary ecology ͉ introgressive hybridization ͉ local adaptation ͉ niche theory

Adaptation to Marginal Habitats

“…Finally, heritable variation for phenological traits that allowed the tephritid fly Rhagoletis to broaden its host range may have originated by introgression of chromosomal inversions from a formerly allopatric population (Xie et al 2007). Similar cases have been reported in an alpine sedge (Choler et al 2004), mosquitoes, and trypanosomes (Arnold 2004). Horizontal gene transfer, though involving different mechanisms, is in some ways an analogous phenomenon, playing an important role in the evolution of ecological niches of prokaryotes (Koonin et al 2001).…”

Natural hybridization between Elymus repens and E. hispidus assessed by AFLP analysis

“…As stated, ecological marginal populations of Carex curvula are mainly composed of individuals with genotypes resulting from introgressive hybridization. Genotype integrity of this species is maintained in optimal habitats, while introgressed individuals are favoured in marginal habitats (Choler et al 2004). Studies on flooding tolerance of Elytrigia repens, E. intermedia and their hybrids have shown that hybridization may lead to the enrichment of hybrids gene pools with genes responsible for the survival of the parental species under extreme conditions (Mahelka 2006).…”

Reticulate Evolution of the Rye Genome

“…Diploid hybrid species of sunflower (Helianthus annuus) exhibited a selective advantage over their parental species in more extreme habitats, as demonstrated by resynthesized hybrid species (Rieseberg et al, 2003). In the sedge species Carex curvula, it has been postulated that interspecies hybrid formation could have provided an advantage under changing environmental conditions (Choler et al, 2004). Furthermore, chromosomal aberrations and spontaneous aneuploidy were observed to occur at higher frequency in Aegilops speltoides populations in marginal environments (Belyayev and Raskina, 2013).…”