Out of the Neotropics: newly discovered relictual species sheds light on the biogeographical history of spider ants (Leptomyrmex, Dolichoderinae, Formicidae)

Abstract

Spider ants of the genus Leptomyrmex Mayr (Hymenoptera: Formicidae: Dolichoderinae) are conspicuous species of Australasian rainforests, with putative fossil relatives in the Neotropics and Europe. There is longstanding debate over the biogeographical history of the genus, with the Palaearctic and Neotropical regions proposed as alternate centres of origin. We propose a resolution of this debate with the recent discovery and analysis of an extant species from central Brazil, L. relictus sp.n., which we describe from workers, males and brood. We sequence ten nuclear genes in the new species and in several Australian Leptomyrmex species, and append these data to a 54-taxon, 10-gene data matrix previously generated for the subfamily Dolichoderinae. We conduct phylogenetic and divergence dating analyses, and re-evaluate the fossil record of the group. We recover Leptomyrmex relictus sp.n. as a member of the Leptomyrmex clade with high support. It is sister to the Australasian species, and the genus Leptomyrmex is, in turn, sister to a pair of Neotropical genera, Forelius and Dorymyrmex. We infer a Neotropical origin for the genus and estimate a mid-Eocene (46 Ma, 95% CI 56 to 36 Ma) origin for the crown genus and an Oligocene origin for the Australasian clade (29 Ma, 95% CI 40 to 19 Ma). We confirm placement of the Dominican amber species †L. neotropicus Baroni Urbani in the genus but reject a close relationship with the Palaearctic fossil taxa †Leptomyrmula Emery and †Usomyrma Dlussky, Radchenko & Dubovikoff, considering them incertae sedis in the subfamily (Dolichoderinae). In contrast to the mesophilic preferences of the Australasian species of Leptomyrmex, the new Brazilian species inhabits cerrado (dry savannah). Our results support a Neotropical origin for spider ants with dispersal to Australia. Rafting on west-bound currents and/or a historical diversity imbalance between Australia and South America are proposed as alternate hypotheses to explain a pattern of biased E-W mid-Tertiary dispersal for ants with austral distributions. This pattern is suggested by our results in conjunction with observations of other ant clades. Overall, our findings highlight the value of integrated taxonomy, critical interpretation of morphology, and a comparative phylogenetic framework when conducting palaeontological and biogeographical studies of insect species. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid: zoobank.org:pub

A global phylogenetic analysis of trap‐jaw ants, Anochetus Mayr and Odontomachus Latreille (Hymenoptera: Formicidae: Ponerinae)

“…According to Boudinot et al . (2016), overland dispersal with subsequent Antarctic extinctions is roughly corroborated by similar minimum age estimates of ∼30 Ma for trans‐Antarctic interchanges of multiple arthropod groups, including chironomid midges (Krosch et al ., 2011), colletid bees (Almeida et al ., 2012), euophryine spiders (Zhang & Maddison, 2013), window flies (Winterton & Ware, 2015) and various stoneflies (McCulloch et al ., 2016).…”

“…(2016) estimated that Anochetus + Odontomachus originated in the Neotropical or Indomalayan region, also based on the DEC model. A study of Leptomyrmex spider ants similarly supports a Neotropical origin with dispersal to Australia (Boudinot et al ., 2016). A route through Antarctica could explain the radiation of Anochetus and Odontomachus ancestors originating in the Neotropical region during the late Cretaceous.…”

Taxon cycle predictions supported by model‐based inference in Indo‐Pacific trap‐jaw ants (Hymenoptera: Formicidae: Odontomachus)

“…A Gondwanan vicariant origin of the Indo‐Pacific and New World clades, which would have left a similar biogeographical pattern, is ruled out by evidence from both fossil (Barden, ) and molecular divergence times (see also Moreau & Bell, ; Schmidt, ). Dispersal from South America to Australia via Antarctica (see Boudinot, Probst, Brandão, Feitosa, & Ward, ) is also ruled out given our biogeographical inferences; Australian Odontomachus derive from Melanesian lineages and not the other way around which would be expected if the ants arrived first to Australia (Figure ).…”

Sistemática y diversidad de las hormigas neotropicales

“…Internal explorations in the subfamilies have been carried out in Amblyoponinae (Ward and Fisher 2016), Dolichoderinae (Ward et al 2010;Boudinot et al 2016), Dorylinae (Brady et al 2014;Borowiec 2019), Formicinae (Blaimer et al 2015), Myrmicinae (Ward et al 2015), Ponerinae (Schmidt 2013), and Pseudomyrmecinae (Ward and Downie 2005). 5/20…”