UC Davis

The subfamily Leptanillinae (Hymenoptera: Formicidae) consists of miniscule subterranean ants, most diverse in Southeast Asia, but known throughout the Old World tropics and subtropics. Phylogenomic inference demonstrates that the Leptanillinae are sister to all, or nearly all, other extant Formicidae. Little is known of leptanilline behavior, with the few observations that exist indicating that these ants are specialist predators of geophilomorph centipedes or forcepstails (Diplura: Japygidae), with Leptanilla displaying a legionary biology reminiscent of army ants of the subfamily Dorylinae, along with larval hemolymph feeding (LHF) like that observed in the vampire ants (Amblyoponinae). Contrary to the collecting bias observed in most ants, male leptanilline specimens are acquired more easily than workers or queens. The sexes are almost never collected in association, and many subclades within the Leptanillinae are known from male specimens only. These restrictions plague our understanding of the Leptanillinae with probable taxonomic redundancy. My dissertation constitutes a systematic revision of the Leptanillinae that is informed by phylogeny inferred from both genotype and phenotype and integrates morphological data from both sexes. Chapter 1 presents the results of total-evidence Bayesian inference from 11 nuclear loci and 33 binary male morphological characters, which unequivocally support the synonymy of the monotypic genus Phaulomyrma Wheeler & Wheeler, known only from a single male specimen, with Leptanilla Emery. Chapter 2 describes Yavnella laventa Griebenow et al., the first species belonging to the genus Yavnella Kugler for which the worker caste is known, identified as Yavnella by maximum-likelihood (ML) and Bayesian phylogenomic inference from ultra-conserved elements (UCEs). Chapter 3 provides detailed descriptions of the male genital skeletomusculature of 9 leptanilline morphospecies and 3 outgroups across the Formicidae, based on scans acquired by micro-computed tomography, and using a novel nomenclature for male genital musculature compatible with topographical main-group nomenclature already created for other anatomical regions and extensible across the whole of the Hymenoptera. Chapter 4 is a comprehensive revision of generic and tribal boundaries in the Leptanillinae, reciprocally illuminated by the results of phylogenetic inference presented in Chapter 5, and worker and male phenotypes; this chapter also includes worker- and male-based dichotomous keys to all described leptanilline species. Finally, Chapter 5 presents the results of phylogenomic inference, including examples of all major leptanilline clades, under frequentist and Bayesian statistical frameworks, along with a coalescent-based approach to accommodate discordant phylogenetic signal among gene trees; plus the results of Bayesian total-evidence (from 58 UCE loci and 64 binary male morphological characters) to resolve the phylogenetic positions of aberrant lineages for which only male morphology is known, including Scyphodon Brues.