Those of you familiar with South American ants know the distinction between the two great lineages of leafcutters. Acromyrmex comprises the smaller, stubbier, spinier species, while Atta contains the larger, leggier, and less spiny species. This dichotomy is marked enough even to be recognized in the local vernacular. The Guaraní called the former Akêkê and the latter Ysaú, which Brazilians have modified into the Portuguese Quemquem and Sauva. When preliminary phylogenetic work appeared to confirm the duality, I was pleased by the concordance of cultural and phylogenetic classifications.
A new study in PLoS One by Maykon Passos Cristiano et al added the unusual species Acromyrmex striatus to the phylogenetic framework, and- surprise!- it’s not like the others. Acromyrmex striatus chromosomes appear more similar to those of Atta than to those of its own congeners, and a phylogenetic reconstruction based on several protein-coding genes suggests this species may be a third, distinct lineage.
The authors state that more sampling is needed. Fair enough. But based on these data I would not be surprised if this taxonomic mismatch is eventually resolved by condensing leafcutters into a single monophyletic Atta.
update (3/26): See comment by Terry Nuhn, below.
source: Cristiano MP, Cardoso DC, Fernandes-Salomão TM (2013) Cytogenetic and Molecular Analyses Reveal a Divergence between Acromyrmex striatus (Roger, 1863) and Other Congeneric Species: Taxonomic Implications. PLoS ONE 8(3): e59784. doi:10.1371/journal.pone.0059784