Phylogeography of Omus (Coleoptera: Cicindelidae): Testing the ring species hypothesis

Ring species have long fascinated biologists, as their study provides insight into the speciation processes under a geographic context. The flightless tiger beetle, Omus californicus, exhibits a circular distribution around the Central Valley of California, with three subspecies occupying different regions. Thus, O. californicus may represent a novel example of a ring species. In this study, we aim to test the ring species hypothesis by assessing: (1) How many populations are there in the O. californicus complex? (2) Does an isolation by distance model explain the population differentiation patterns? (3) How many good species, if any, are in the complex? We generated genomic-scale data in the form of ultraconserved elements (UCEs) in order to reconstruct the phylogeographic history of the species and perform species-delimitation. Under the ring species hypothesis, we would predict a northern origin for the group, with non-monophyly of the currently recognized subspecies. From our UCE data, single nucleotide polymorphisms (SNPs) data sets were also generated for additional non-parametric testing of gene flow or admixture. These tests will help identify distinct populations, and evidence of gene flow between them, which should be minimal between good species. Finally, we also tested for isolation by distance, as this should be present under a ring diversification scenario wherein populations and the two ends of the ring should be the most distinct.