The online early section of Molecular Phylogenetics and Evolution this week has the first comprehensive phylogeny of a rather important genus of ants: Myrmica.
Myrmica is ubiquitous in the colder climates of North America and Eurasia, with a few seemingly incongruous species inhabiting the mountains of tropical southeast Asia. The genus contains about 200 species, many that are common soil-nesting ants in lawns and gardens, and at least one damaging invasive species, M. rubra. The taxonomy ranks among the most difficult of any ant genus, as workers of different species tend to be numbingly similar to each other. And there are a lot of species.
Summary cladogram of the ant genus Myrmica, redrawn from Jansen et al 2010, depicting a parsimony reconstruction of the geographic distribution of the genus.
This phylogeny- part of Gunther Jansen's Ph.D. thesis- finally sets the systematics of Myrmica on a firm evolutionary footing. Jansen used genetic data from several loci and 106 specimens to infer the history of the genus, recovering a well-supported phylogeny spanning roughly half of the extant species. Considering the difficulties posed by a monotonous worker morphology, these molecular data provide a needed infusion of new information.
Jansen's primary findings are:
- In spite of the difficulty posed by morphology, most of the morphology-based species groups are recovered as clades.
- Much of the deeper history of Myrmica is preserved in North America, with what appears to be several independent dispersals across Beringia to Eurasia.
- Most social parasites are closely related to their hosts (see Emery's rule), but the exceptions suggest that socially parasitic lineages can persist beyond subsequent speciation events in their host lineage.
- Modern Myrmica shared a common ancestor about 30 to 45 million years ago, and the diversification appears to coincide with a global cooling around the Oligocene-Eocene boundary.
It's a solid paper, and a very welcome advance to the systematics of an important ant genus.
Source: Jansen, G., Savolainen, R., Vepsalainen, K., 2010. Phylogeny, divergence-time estimation, biogeography and social parasiteâhost relationships of the Holarctic ant genus Myrmica (Hymenoptera: Formicidae). Molecular Phylogenetics and Evolution, doi: http://dx.doi.org/10.1016/j.ympev.2010.01.029
Just read the paper -- very nice.
Now all we need is a good taxonomy for the North American fauna, comparable to the great work that has been completed in the last decade on the Eurasian ones.
Nice phylogeny. I'm only a bit disappointed by a lack of apparently close relative of M. sabuleti, M. lonae. Well, I guess that Myrmica sabuleti deserves a study of it's own. It's a quite variable species, and molecules could help to make sense of the diversity.
A nice but not discussed detail can be seen in the trees: M. tulinae appears in a clade with an undescribed species and M. hellenica, separate from both sabuleti and scabrinodis.
M.tulinae was described as a species with antennal scape structure of worker similar to that of sabuleti and male morphology as in scabrinodis. In a later reference it was even stated that when someone encounters what appears to be a nest of sabuleti workers with scabrinodis males, that must be tulinae. Bernhard Seifert treated this species with disbelief, and in his great 2007 book stated that "Der Fall muÃ mit objektiven Methoden geprÃ¼ft werden" and did not include the species in his key. I guess this proves the case with unbiased methods...
Well, it is still a pain to key Eurasian Myrmica, and frequent name and status changes (e.g., Radchenko A., Elmes G.W. 2009. Important alterations in the taxonomy of the ant genus Myrmica...) add to the confusion. Numerous (sometimes excellent, sometimes less so) descriptions of isolated taxa in the recent years make the taxonomy hard to comprehend. However, as I am told, there's light at the end of the tunnel: monograph of the Old World Myrmica is due out this year! Can't wait.
Oh, I omitted an important conclusion that can be drawn from the cladogram above. It finally tells us that Myrmica rugosa is the most p r i m i t i v e member of the genus! Just kidding ;)