Homoploid hybrid speciation between cryptic species of a hidden snout weevil

Hybridisation 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, geographic and phenotypic dimensions within which hybrid populations evolve RI against parental species is still limited. Here, we describe HHS 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 speciation, where the hybrid lineage originated from historical admixture between parental lineages. Genome-wide estimates of heterozygosity and individual-based simulations of hybrid speciation provide further support for an ancient, rather than recent origin of the hybrid species. We leverage geographic patterns of genomic relatedness between hybrid and parental individuals to identify the likely origin within a hybrid swarm that was geographically isolated from both parental species. We argue that hybridisation is not just a driver of speciation, but may also act as a facilitator by enhancing the pathway to RI above that expected within a strictly allopatric model.