Phylogeny, evolution, and classification of the ant genus Lasius, the tribe Lasiini, and the subfamily Formicinae (Hymenoptera: Formicidae)

Abstract

Within the Formicidae, the higher classification of nearly all subfamilies has been recently revised due to the findings of molecular phylogenetics. Here, we integrate morphology and molecular data to holistically address the evolution and classification of the ant genus Lasius, its tribe Lasiini, and their subfamily Formicinae. We accomplish this through a critical re-examination of morphology of extant and fossil taxa, molecular phylogenetic analyses, total-evidence dating under fossilized birth-death process, phylogeography, and ancestral state estimation. We use these results to provide revised taxonomic definitions for the Lasiini and select genera, and we provide a key to the genera of the Lasiini with emphasis on the Lasius genus group. We find that the crown Lasiini originated around the end of the Cretaceous on the Eurasian continent and is divisible into four morphologically distinct clades: Cladomyrma, the Lasius genus group, the Prenolepis genus group, and a previously undetected lineage we name XXX gen. n. The crown of the Lasius genus group is considerably younger than that of the Prenolepis genus group, indicating that extinction has played a major role in the evolution of the former clade. Lasius itself is divided into two well-supported monophyletic groups which are approximately equally speciose. We present evidence that temporary social parasitism and fungiculture arose in Lasius two times independently. Additionally, we recover the paraphyly of three Lasius subgenera and propose replacing all subgenera with an informal species group classification: Lasius = Acanthomyops syn. rev., = Austrolasius syn. n., = Cautolasius syn. n., = Chthonolasius syn. n., = Dendrolasius syn. n. Total-evidence analysis reveals that the Baltic-region amber fossil species {dagger}Lasius pumilus and {dagger}Pseudolasius boreus are misplaced to genus; we therefore designate {dagger}XXX gen. n. for the former and {dagger}XXX gen. n. for the latter. Further, we transfer {dagger}XXX and {dagger}Glaphyromyrmex out of the tribe, considering the former to be incertae sedis in the subfamily, and the latter a member of the Formicini (tribal transfer). Two final taxonomic actions are deemed necessary: synonymy of Lasius escamole Reza, 1925 with Liometopum apiculatum Mayr, 1870 syn. n. (subfamilial transfer), and transfer of Paratrechina kohli to Anoplolepis (tribal transfer, forming A. kohli (Forel, 1916) n. comb.). Summary of taxonomic actionsO_LISubgenera of Lasius synonymized: Lasius = Acanthomyops syn. rev. = Austrolasius syn. n. = Cautolasius syn. n. = Chthonolasius syn. n. = Dendrolasius syn. n. C_LIO_LILasius myrmidon transferred to XXX gen. n. (Lasiini, XXX genus group). C_LIO_LI{dagger}Lasius pumilus transferred to {dagger}XXX gen. n. (Lasiini, XXX genus group). C_LIO_LI{dagger}Pseudolasius boreus transferred to {dagger}XXX gen. n. (incertae sedis in Formicinae) (tribal transfer). C_LIO_LI{dagger}Glaphyromyrmex transferred to the Formicini from the Lasiini (tribal transfer). C_LIO_LILasius escamole Reza, 1925 synonymized with Liometopum apiculatum Mayr, 1870, syn. n. (subfamilial transfer). C_LIO_LIParatrechina kohli (Forel, 1916) transferred to Anoplolepis (Plagiolepidini) (genus and tribal transfer). C_LI