Search

Invasive species offer outstanding opportunities to identify the genomic sources of variation that contribute to rapid adaptation, as well as the genetic mechanisms facilitating invasions. The Eurasian plant yellow starthistle (Centaurea solstitialis) is highly invasive in North and South American grasslands and known to have evolved increased growth and reproduction during invasion. Here, we develop new genomic resources for C. solstitialis and map the genetic basis of invasiveness traits. We present a chromosome-scale (1N = 8) reference genome using PacBio CLR and Dovetail Omni-C technologies, and functional gene annotation using RNAseq. We find repeat structure typical of the family Asteraceae, with over 25% of gene content derived from ancestral whole-genome duplications (paleologs). Using an F2 mapping population derived from a cross between native and invading parents, with a restriction site-associated DNA (RAD)-based genetic map, we validate the assembly and identify 13 quantitative trait loci underpinning size traits that have evolved during invasion. We find evidence that large effects of quantitative trait loci may be associated with structural variants between native and invading genotypes, including a variant with an overdominant and pleiotropic effect on key invader traits. We also find evidence of significant paleolog enrichment under two quantitative trait loci. Our results add to growing evidence of the importance of structural variants in evolution, and to understanding of the rapid evolution of invaders. [ABSTRACT FROM AUTHOR]

Aim: Hybridization is thought to have played an important role in shaping the evolutionary history of diverse island taxa. Here, we propose an ecological and evolutionary framework for understanding the causes and consequences of heterospecific mating on islands—with and without introgressive hybridization. We use this framework to support our main contention that cases of secondary contact among endemic species should commonly result in introgressive hybridization whereas cases of contact between endemic and introduced species should commonly result in reproductive interference (RIN)—resulting in two qualitatively different faces of secondary contact on islands. Location: Canary Islands, Galapagos, New Zealand, Caribbean and Hawaii. Taxa: 705 vertebrate, invertebrate and plant species spanning 167 genera and 99 families. Methods: Using a quantitative analysis of empirical research on secondary contact on islands, we weigh evidence for the causes and consequences of secondary contact and heterospecific mating on islands. In particular, we compare cases of secondary contact between endemic species versus secondary contact between endemic and introduced species. Results: We find that the drivers of secondary contact and heterospecific mating on islands most frequently reported in the literature are disturbance, long‐distance (e.g. inter‐island) dispersal and compromised assortative mating. We find support for the hypothesis that extensive introgression is a more common outcome between endemic species while RIN is a more common outcome between endemic and introduced species. Main Conclusions: We conclude that there are biological reasons to predict secondary contact and heterospecific mating to be common on islands for all taxa, but that the consequence of secondary contact is categorically different for contact between endemic species and contact between endemic and introduced species. We conclude that the former likely explains the apparent frequency of hybridization on islands, while the latter presents a cryptic and underappreciated conservation threat. [ABSTRACT FROM AUTHOR]