Phylogeography of Amblycheila schwarzi (Coleoptera: Cicindelidae), supports the Colorado River as a leaky barrier

Geographic barriers to gene flow are of great interest to evolutionary biologists for their role in speciation. Speciation patterns in the Mojave have been influenced by barriers created through the dynamic geological events and paleoclimate cycling that shaped the current landscape. The Mojave Assemblage Model (MAM) proposes that vicariance events have significantly shaped the population structure of lineages inhabiting the Mojave. While research evaluating the MAM has focused on numerous vertebrates and few arthropods, insects–particularly beetles, remain understudied. This study tests the MAM’s hypothesis that vicariance associated with the formation of the Colorado River has significantly influenced population dynamics for the endemic Mojave giant tiger beetle, Amblycheila schwarzi Horn, 1904. This study presents the first instance of employing the Adephaga 2.9Kv1 probeset for shallow evolutionary scale analyses. We analyzed 33 fresh and museum specimens from 9 different localities across the Mojave using ultraconserved element (UCE) data. We investigate phylogeography using concatenated, coalescent-based, and single-nucleotide polymorphism (SNP) approaches. Results demonstrate that gene flow for A. schwarzi has not been affected by the formation of the Colorado River. The strength of barriers is highly reliant on the dispersal capabilities and adaptability of the taxa encountering them. In the case of A. schwarzi, barriers like the Colorado River within the Mojave may have served as leaky filters at best. This study demonstrates the versatility of UCEs and benefits of employing a tailored probeset to investigate both deep and shallow relationships, while also enabling the use of museum specimens to strengthen sampling datasets.