Out of the neotropics: A new species of spider ants, Leptomyrmex (Hymenoptera: Formicidae: Dolichoderinae) sheds light on the origin of the genus

Spider ants, Leptomyrmex (Dolichoderinae), are conspicuous elements of Australasian mesic forests. Multiple biogeographic hypotheses have been proposed for Leptomyrmex based on the fossil taxa L. neotropicus Emery, Usomyrma mirabilis Dlussky et al., and Leptomyrmula maravignae, from Dominican, Danish, and Sicilian amber, respectively. Leptomyrmex is proposed to have originated in either the Neotropics or Palearctic, and to have dispersed to the Australasian region via transoceanic dispersal from South America, or transcontinental dispersal from Europe. We test these hypotheses by placing a newly discovered species from central Brazil (L. relictus sp. n.) in the phylogeny of the Dolichoderinae and Leptomyrmex based on sequences from 10 nuclear genes, and via reevaluation of the Palearctic fossil taxa Usomyrma and Leptomyrmula. We recover L. relictus as a member of the Leptomyrmex clade and sister to the extant Australasian species with high support. Leptomyrmex is sister to the Neotropical genera Dorymyrmex and Forelius, which themselves form a clade. We infer a Neotropical origin for the genus and estimate a Mid Eocene (46 Ma, 95% CI 56-36 My) origin for the crown genus, and an Oligocene origin for the Australasian clade (29 Ma, 95% CI 40-19 My). Leptomyrmex neotropicus is confirmed as a member of the genus, but reject a close relationship of Usomyrma and Leptomyrmula, considering them incertae sedis in the subfamily. Our results support a Neotropical origin for the spider ants with dispersal to Australia, likely via the Antarctic land bridge. In contrast to the mesophilic Australasian species, L. relictus inhabits dry cerrado (Brazilian savannah).