Endemic ants from the California Channel Islands result from divergent evolutionary processes

Insular endemism can result from a variety of processes. Island endemics can be the products of post-colonization evolution, through in situ differentiation driven by founder effects, genetic drift, and novel selection pressures (autochthonous endemism), or they can evolve elsewhere but become restricted to islands through processes such as relictualization (allochthonous endemism). Molecular tools provide insights into the evolutionary origins of insular endemics and can be used to distinguish between these two alternative scenarios. Here we use high-throughput sequencing of ultraconserved elements (UCEs) to conduct phylogenomic and phylogeographic analyses of the evolutionary origins of four ant taxa endemic to the California Channel Islands: Camponotus bakeri, C. sp. nr. yogi, C. sp. nr. vicinus, and Aphaenogaster patruelis. These taxa represent multi-island (C. bakeri, A. patruelis) and single-island (C. sp. nr. vicinus, C. sp. nr. yogi) endemics. RAxML and SNAPP analyses provide evidence for three different routes to endemism: in situ differentiation on the Channel Islands and subsequent interisland dispersal (C. bakeri), relictualization following the presumed extinction of an ancestral mainland population (A. patruelis), and in situ differentiation on a single island (C. sp. nr. vicinus., C. sp. nr. yogi). Population genetic analyses and STRUCTURE plots further show that ongoing gene flow is lacking between island endemic and sister taxa. These findings illustrate how endemic taxa from the same region can result from divergent evolutionary processes. Through the use of genomics tools, our study provides new insights into the evolutionary processes that can lead to endemism in insular systems.