Diversification and phylogeographic structure in widespread Azteca plant-ants from the northern Neotropics

The Neotropical myrmecophytic tree Cordia alliodora hosts symbiotic Azteca ants in most of its widespread range. The taxonomy of the genus Azteca is notoriously difficult, which has frequently obscured species identity in ecological studies. We used sequence data from one mitochondrial and four nuclear loci to infer phylogenetic relationships, patterns of geographic distribution, and timing of diversification for 181 colonies of Azteca from Mexico to Colombia. We identified at least eight lineages of C. alliodora-dwelling Azteca, including at least five lineages within the most abundant and specialized species, Azteca pittieri. Mitochondrial and nuclear data were concordant at the species level, but not within species; comparison of the two datasets suggested that both introgression and incomplete lineage sorting contributed to these inconsistencies. Divergence time analyses estimated that C. alliodora-dwelling Azteca shared a common ancestor approximately 9-18 million years ago, coinci...