Kalathomyrmex: New Genus, Old Species

Kalathomyrmex emeryi (Forel 1907), Argentina.

In Zootaxa last week, Christiana Klingenberg and Beto Brandão introduced to the world an entirely new genus of fungus-growing ant, Kalathomyrmex.  Yet the single species, K. emeryi, is a widespread neotropical insect that has been known for over a century.  In fact, I photographed it twice during my recent trip to Argentina.  How does this happen, a new genus devoid of novel species?

The answer is understandable in light of the distinct pattern of evolution among the fungus growing ants, revealed in a 2008 study by Ted Schultz and Sean Brady:

Simplified phylogeny of the attini, from Schultz & Brady 2008

The history of the attine ants is marked by a series of innovations.  Ants associate with fungus.  Ants develop specialized relations with different types of fungus. Ants start to harvest live vegetation. Ants develop  morphological worker subcastes.  And so on.

At each change, the novel trait is accompanied by morphological alterations.  The renovated lineages possessing the new traits evolve away from the older forms.  It's a delightful evolutionary tale.  Yet it's also the perfect storm to foment a taxonomist's nightmare: morphologically distinct groups that are not each other's closest relatives but instead the residue of lineages that simply never acquired the new adaptations.

Consequently many of the existing attine genera- Mycetophylax, Mycetosoritis, Cyphomyrmex, Trachymyrmex- are not natural groupings but artifacts of evolution.  The leftovers, as it were.

The small entrance mound of a K. emeryi nest in a sandy road.

Bringing attine taxonomy into accord with the phylogeny will not be an easy task.  It will necessarily entail finding characters among groups of markedly similar ants.  Klingenberg & Brandão's paper is the first salvo in the effort: they've tackled the forms previously included in Mycetophylax. 

Kalathomyrmex was erected to house the oldest lineage in the disorderly phylogenetic splatter that was Mycetophylax and comprises a single species, emeryi, first described by the Swiss myrmecologist Forel.  It is defined by a pattern of clypeal setae not shared by the others.  Not the most obvious character, but it does seem to work.

Stronger than you: a K. emeryi worker performs nest maintenance.

K & B also resurrected an older genus, Paramycetophylax, for the rare Argentinian ant P. bruchi.  Mycetophylax in the strict sense now includes only a smattering of species that nest in the sand along Brazil's coastlines and rivers, as well as a species or two that had been waylaid in Cyphomyrmex for a few decades.  With any luck this new scheme, firmly rooted in phylogeny, will herald a new era of stability for the taxonomy of fungus-growing ants.

Incidentally, I've discovered that I should never leave the computer for more than a week, ever again. The sheer volume of new ant research during my absence will be impossible to catch up with, much less blog about.

Source: Klingenberg, K., Brandao, C. R. F. 2009. Revision of the fungus-growing ant genera Mycetophylax Emery and Paramycetophylax Kusnezov rev. stat., and description of Kalathomyrmex n. gen. (Formicidae: Myrmicinae: Attini). Zootaxa 2052: 1-31.