Phylogeny of the Formicoxenus genus-group (Hymenoptera: Formicidae) reveals isolated lineages of Leptothorax acervorum in the Iberian Peninsula predating the Last Glacial Maximum

<p dir="ltr">The Formicoxenus genus-group comprises six genera within the tribe Crematogastrini. The</p><p dir="ltr">group is well known for repeated evolution of social parasitism among closely related taxa</p><p dir="ltr">and cold-adapted species with large distribution ranges in the Nearctic and Palearctic</p><p dir="ltr">regions. Previous analyses based on nuclear markers (ultraconserved elements, UCEs) and</p><p dir="ltr">mitochondrial genes suggest close relationship between Formicoxenus Mayr, 1855,</p><p dir="ltr">Leptothorax Mayr, 1855 and Harpagoxenus Forel, 1893. However, scant sampling has</p><p dir="ltr">limited phylogenetic assessment of these genera. Also, previous phylogeographic analyses</p><p dir="ltr">of L. acervorum (Fabricius, 1793) have been limited to its West-Palearctic range of</p><p dir="ltr">distribution, which has provided a narrow view on recolonization, population structure and</p><p dir="ltr">existing refugia of the species. Here, we inferred the phylogenenetic history of genera</p><p dir="ltr">within the Formicoxenus genus-group and reconstructed the phylogeography of L.</p><p dir="ltr">acervorum with more extensive sampling. We employed three datasets, one data set</p><p dir="ltr">consisting of whole mitochondrial genomes, and two data sets of sequences of the COI-5P</p><p dir="ltr">(658 bp) with different number of specimens. The topologies of previous nuclear and our</p><p dir="ltr">inferences based on mitochondrial genomes were overall congruent. Further, Formicoxenus</p><p dir="ltr">may not be monophyletic. We found several monophyletic lineages that do not correspond</p><p dir="ltr">to the current species described within Leptothorax, especially in the Nearctic region. We</p><p dir="ltr">identified a monophyletic L. acervorum lineage that comprises both Nearctic and Palearctic</p><p dir="ltr">locations. The most recent expansion within L. acervorum probably occurred within the</p><p dir="ltr">last 0.5 Ma with isolated populations predating the Last Glacial Maximum (LGM), which</p><p dir="ltr">are localized in at least two refugial areas (Pyrenean and Northern plateau) in the Iberian</p><p dir="ltr">Peninsula. The patterns recovered suggest a shared glacial refugium in the Iberian Peninsula</p><p dir="ltr">with cold-adapted trees that currently share high-altitude environments in this region.</p>