Examining the role of introgressive hybridization on novel host-plant use in a recent evolutionary radiation of grasshoppers

Abstract

Introgressive hybridization can introduce genetic novelty into recipient lineages, induce important phenotypic changes and, ultimately, result in the formation of new species. The conditions in which hybridization is more prone to occur and its potential evolutionary consequences have been long discussed, nevertheless empirical examples revealing introgression accompanied by adaptive phenotypic changes are still scarcely documented in the literature. Here, we address these questions using as study system a recent radiation of grasshoppers (Chorthippus binotatus species complex) composed by eight taxa and two major clades, one primarily graminivorous (Saulcyi clade) and the other feeding on scrub legumes from the tribe Genisteae (Binotatus clade). While these two clades are phylogenetically well supported, the position of one of the taxa (Chorthippus saulcyi algoaldensis) in relation to the main two groups is unclear on the basis of different sources of genomic and phenotypic information. Despite C. s. algoaldensis is nowadays placed within the graminivorous Saulcyi group, it exhibits an intermediate morphology between the two clades and facultatively feeds on scrub legumes. Here, we employ genome-wide SNP data and a comprehensive suite of analytical methods to investigate introgression among the different taxa within the complex and, specifically, test the hypothesis that C. s. algoaldensis acquired its capacity to use alternative host-plants through historical hybridization and introgression from parapatric taxa of the Binotatus clade. By extensive sampling of populations from all linages of the species complex and comparing them in a population and phylogenomic context, our preliminary analyses revealed widespread introgression between the two main clades and highlighted the interest of this system to study the role of introgression on the acquisition of potentially adaptive traits and species diversification processes.