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The fungus‐growing ants and their fungal cultivars constitute a classic example of a mutualism that has led to complex coevolutionary dynamics spanning c. 55–65 Ma. Of the five agricultural systems practised by fungus‐growing ants, higher‐attine agriculture, of which leaf‐cutter agriculture is a derived subset, remains poorly understood despite its relevance to ecosystem function and human agriculture across the Neotropics and parts of North America. Among the ants practising higher‐attine agriculture, the genus Trachymyrmex Forel, as currently defined, shares most‐recent common ancestors with both the leaf‐cutter ants and the higher‐attine genera Sericomyrmex Mayr and Xerolitor Sosa‐Calvo et al. Although previous molecular‐phylogenetic studies have suggested that Trachymyrmex is a paraphyletic grade, until now insufficient taxon sampling has prevented a full investigation of the evolutionary history of this group and limited the possibility of resolving its taxonomy. Here we describe the results of phylogenetic analyses of 38 Trachymyrmex species, including 27 of the 49 described species and at least 11 new species, using four nuclear markers, as well as phylogenetic analyses of the fungi cultivated by 23 species of Trachymyrmex using two markers. We generated new genetic data for 112 ants (402 new gene sequences) and 95 fungi (153 new gene sequences). Our results corroborate previous findings that Trachymyrmex, as currently defined, is paraphyletic. We propose recognizing two new genera, Mycetomoelleriusgen.n. and Paratrachymyrmexgen.n., and restricting the continued use of Trachymyrmex to the clade of nine largely North American species that contains the type species [Trachymyrmex septentrionalis (McCook)] and that is the sister group of the leaf‐cutting ants. Our fungal cultivar phylogeny generally corroborates previously observed broad patterns of ant–fungus association, but it also reveals further violations of those patterns. Higher‐attine fungi are divided into two groups: (i) the single species Leucoagaricus gongylophorus (Möller); and (ii) its sister clade, consisting of multiple species, recently referred to as Leucoagaricus Singer 'clade B'. Our phylogeny indicates that, although most non‐leaf‐cutting higher‐attine ants typically cultivate species in clade B, some species cultivate L. gongylophorus, whereas still others cultivate fungi typically associated with lower‐attine agriculture. This indicates that the attine agricultural systems, which are currently defined by associations between ants and fungi, are not entirely congruent with ant and fungal phylogenies. They may, however, be correlated with as yet poorly understood biological traits of the ants and/or of their microbiomes. [ABSTRACT FROM AUTHOR]

Ants are widely recognized as ecologically important members of many low- to mid-latitude ecosystems. Surprisingly, there is very little phylogeographical information on ants at regional scales. We examine here the phylogeography of two partially sympatric species of Trachymyrmex ( Trachymyrmex septentrionalis and Trachymyrmex turrifex) ants in southeastern North America. We test the hypothesis that all Trachymyrmex species found in the USA expanded into North America from refugial populations located in northern Mexico as the post- Pleistocene climate warmed. Phylogeographical theory predicts that these northward-expanding species should exhibit higher genetic diversity in regions closer to Mexico and less diversity in more northern regions. We also examine, in the widely distributed T. septentrionalis, the hypothesis of vicariance that occurred at the formation of the Mississippi Embayment. Phylogeographical patterns indicate that T. septentrionalis has an eastern origin because diversity was highest east of the Mississippi, whereas T. turrifex probably has a Mexican origin because it lacked mitochondrial DNA (mt DNA) variation throughout its range and is currently absent from eastern North America. Both species are characterized by reduced haplotypic variation in the western coastal plain of the Gulf of Mexico ( Texas and Louisiana), which may indicate recent expansion and/or bottlenecks associated with increased aridity and drought in these western regions. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114, 689-698. [ABSTRACT FROM AUTHOR]

We developed 23 polymorphic microsatellite markers for the symbiotic fungi cultivated by leaf cutter ants, then assessed allelic variation in North American leafcutter-fungus populations (Mexico, Cuba, USA). Polyploidy was indicated by 21 of the 23 loci, consistent with the multinucleate nature of leafcutter fungi. Microsatellite fingerprinting can now assess fungal genetic variation within leafcutter nests to test for monoculture of the cultivated fungi. [ABSTRACT FROM AUTHOR]