Founder events and subsequent genetic bottlenecks underlie karyotype evolution in the Ibero - North African endemic Carex helodes

Abstract

BACKGROUND AND AIMS: Despite chromosomal evolution being one of the major drivers of diversification in plants, we do not yet have a clear view of how new chromosome rearrangements become fixed within populations, which is a crucial step forward for understanding chromosomal speciation.

METHODS: In this study, we test the role of genetic drift in the establishment of new chromosomal variants in the context of hybrid dysfunction models of chromosomal speciation. We genotyped a total of 178 individuals from seven populations (plus 25 seeds from one population) across the geographic range of Carex helodes (Cyperaceae). We also characterized karyotype geographic patterns of the species across the distribution range. For one of the populations, we performed a detailed study of the fine scale, local spatial distribution of its individuals and their genotypes and karyotypes.

KEY RESULTS: Synergistically, phylogeographic and karyotypic evidence show two main genetic groups: southwestern Iberian Peninsula vs. northwestern African populations, and within Europe our results suggest a west-to-east expansion with signals of genetic bottlenecks. Additionally, we have inferred a pattern of descending dysploidy, plausibly as a result of a west-to-east process of post-glacial colonization in Europe.

CONCLUSIONS: Our results give experimental support to the role of geographic isolation, drift, and inbreeding in the establishment of new karyotypes which is key in the speciation models of hybrid dysfunction.