Hybrid species evolution between cryptic and sympatric weevil species

Hybridization may generate a variety of evolutionary outcomes, including novel hybrid species without a change in ploidy. Within this process, referred to as homoploid hybrid speciation (HHS), selection on recombinant traits is often invoked as the driver of reproductive isolation (RI) between hybrid and parental species. However, our understanding of the temporal, geographical and phenotypic dimensions within which hybrid populations evolve RI against parental species is still limited. Here, we describe speciation following hybridization within a beetle species complex that presents no obvious phenotypical or ecological differences among hybrid and parental species, and where all occur sympatrically. Demographic modelling supports hybrid species origin, where the hybrid lineage originated from historical admixture between parental lineages. Genome-wide estimates of heterozygosity and individual-based simulations of hybrid species origin provide further support for an ancient, rather than recent origin of the hybrid species. We use geographical patterns of genomic relatedness between hybrids and parentals to identify the probable origin of the hybrid species within a hybrid swarm that was geographically isolated from both parental species. We then discuss our results within the context of HHS theory to highlight predictions for an HHS origin that can be tested when an appropriate reference genome becomes available.