Tuesday, August 29, 2006

Some comments on the ant phylogenetics symposium held at Washington D.C. Part II.

Ant phylogenetics: New molecular trees to address old problems in ant biology. XV Congress IUSSI. August 1, 2006. Washington D.C.

Part I dealt only with the first four talks of the symposium; those happened to be the talks addressing phylogenetic problems at the highest hierarchical levels within Formicidae. The rest concentrated mostly on single genera or less inclusive clades with an improvement on detail. As such, they also highlighted the reasons behind phylogenetic reconstruction: improve taxonomy (Schöning et al.; LaPolla and Schultz; Wild); test predictions about the evolution of behavior (Savolainen and Vepsäläinen; Peeters); and introduce a historical component to ecological questions (Crozier et al.; Schultz and Brady; Solomon and Mueller). Rather than reviewing each of the remaining talks here I want to comment on two of them.

Alex Wild (Tucson, Arizona) presented part of his work on Linepithema. The revision of this genus is important not only because the taxonomy of the included species was outdated, but also because the Argentine ant, Linepithema humile (Mayr), is a predominant invasive ant worldwide. What is worth noting is Wild’s integrative approach to species delimitation. He draws data from morphology, mitochondrial and nuclear molecular markers and combines the information looking for agreement. The project is a painful reminder of the current state in ant species-level taxonomy; while female workers are the most commonly collected and therefore used cast in classification studies, adult males seem to display the greatest morphological diversity useful at the species level. Incidentally, Wild also showed that pure molecular approaches may be insufficient for the task, as with the use of a short COI barcode where calibrating an adequate threshold to reflect species circumscribed by an integrative approach proved daunting. Wild states in print that he explicitly follows E. Mayr’s biological species concept (Phil Ward’s fault I suppose), however it seems to me that by searching for congruence of the different lines of evidence he is really reconstructing species as historical units of the sort advocated by the phylogenetic species concept, a result that is conveniently more in line with phylogenetic reconstruction in general.

Riitta Savolainen (Helsinki) talk presented some preliminary results on a phylogenetic study of the host-parasite association between Formica and Polyergus. Previous phylogenetic work using both morphology and molecular data support a close or sister relationship between these two genera. My understanding is that the possibility exists that Polyergus may be a derived subgroup within the large Formica genus. It was puzzling to see, therefore, that a phylogeny for each genus was reconstructed independently, even though the molecular markers used were the same. Even if both genera are monophyletic, the best reconstruction within each genus will be achieved by pooling together all the species into a single matrix and rooting the result at the branch between them or using the more distant outgroups originally included.

In comparison with the similar symposium held at the previous IUSSI meeting in Sapporo (2002), the number, scope and quality of the talks presented at Washington D.C. was far superior and reflects the long overdue incorporation of cladistic methods at all levels of ant taxonomy. We have to congratulate Sean Brady and Riitta Savolainen for organizing such a stimulating symposium.

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