UC San Diego

This thesis examines mitochondrial DNA variation exhibited by Aphaenogaster patruelis, an ant species that is confined to five oceanic islands off the coast of southern California and Baja California. The aims of this study are to assess inter-island relationships and to determine if there is cytonuclear discordance. Aphaenogaster patruelis is a putative relict known only from San Clemente Island, Santa Catalina Island, San Nicolas Island, Santa Barbara Island, and Isla Guadalupe. Samples were collected from each of the islands, and DNA extraction was performed to sequence the 12S and CO1 mitochondrial genes. Based on these sequence data, I constructed median-joining haplotype networks and a CO1 phylogenetic tree. Samples on three islands were represented by a single haplotype, but samples on two islands were represented by two, distinct haplotypes. The presence of two, distinct haplotypes suggests multiple colonization events on these islands and indicates the presence of cytonuclear discordance as the split is not evident in previous analyses based on nuclear DNA. Given the lack of an extant mainland population of Aphaenogaster patruelis, reconstructing evolutionary relationships among island populations is not possible, but our results do suggest repeated colonization on individual islands, either through movements between islands or between islands and a now extinct mainland population.