Species paraphyly and social parasitism: Phylogenomics, morphology, and geography clarify the evolution of the Pseudomyrmex elongatulus group (Hymenoptera: Formicidae), a Mesoamerican ant clade

Authors: WARD, PHILIP - University Of California, Davis; Branstetter, Michael

Submitted to: Insect Systematics and Diversity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2021
Publication Date: 1/25/2022
Citation: Ward, P.S., Branstetter, M.G. 2022. Species paraphyly and social parasitism: Phylogenomics, morphology, and geography clarify the evolution of the Pseudomyrmex elongatulus group (Hymenoptera: Formicidae), a Mesoamerican ant clade. Insect Systematics and Diversity. 6(1):1-31. Article 4. https://doi.org/10.1093/isd/ixab025.
DOI: https://doi.org/10.1093/isd/ixab025

Interpretive Summary: Species paraphyly and social parasitism: phylogenomics, morphology, and geography clarify the evolution of the Pseudomyrmex elongatulus group (Hymenoptera: Formicidae), a Mesoamerican ant clade: The tropical ant genus Pseudomyrmex contains over 200 known species and is of general interest to biologists because many species form mutualistic relationships with plants. Despite the interest, the taxonomy of Pseudomyrmex remains incomplete, with many species undescribed. In a new study, the taxonomy and evolution of the Pseudomyrmex elongatulus group was investigated using a combination of morphological and genome-scale molecular data. This integrative analysis revealed the existence of 13 species, nine of which are new to science, including two species that are social parasites of other species in the same group. The molecular data resolved evolutionary relationships among species and suggest that the group originated ~8 million years ago in Central America and Mexico. The study improves knowledge of ant biodiversity in the Americas and provides new information on ant biogeography and biology.

Technical Abstract: Using genetic, morphological, and geographical evidence, we investigate the species-level taxonomy and evolutionary history of the Pseudomyrmex elongatulus group, a clade of ants distributed from southwestern United States to Costa Rica. Through targeted enrichment of 2,524 UCE (ultraconserved element) loci we generate a phylogenomic data set and clarify the phylogenetic relationships and biogeographic history of these ants. The crown group is estimated to have originated ~8 Ma, in Mexico and/or northern Central America, and subsequently expanded into southern Central America and the southwestern Nearctic. The P. elongatulus group contains a mix of low- and high-elevation species, and there were apparently multiple transitions between these habitat types. We uncover three examples of one species—of restricted or marginal geographical distribution—being embedded phylogenetically in another species, rendering the latter paraphyletic. One of these cases involves an apparent workerless social parasite that occurs sympatrically with its parent species, with the latter serving as host. This suggests a sympatric origin of the parasite species within the distribution range of its host. Species boundaries were further tested using molecular delimitation approaches (SODA, bPTP) and these methods greatly inflated the number of species. In a formal taxonomic revision of the P. elongatulus group we recognize 13 species, of which nine are new: P. arcanus, sp. nov. (western Mexico); P. capillatus, sp. nov. (western Mexico); P. cognatus, sp. nov. (Chiapas, Mexico to Nicaragua); P. comitator, sp. nov. (Chiapas, Mexico); P. ereptor, sp. nov. (Veracruz, Mexico); P. exoratus, sp. nov. (southeastern Mexico, Honduras); P. fasciatus, sp. nov. (Chiapas, Mexico to Costa Rica); P. nimbus, sp. nov. (Costa Rica); and P. veracruzensis, sp. nov. (Veracruz, Mexico). Our study highlights the value of combining phylogenomic, phenotypic, and geographical data to resolve taxonomic and evolutionary questions.