Not much time to blog today owing to a busy photographic schedule, but I have to mention for the myrmecologists here a new PLoS One paper by Patrick Kück et al reanalyzing the phylogenetic position of Martialis:
Abstract: Martialinae are pale, eyeless and probably hypogaeic predatory ants. Morphological character sets suggest a close relationship to the ant subfamily Leptanillinae. Recent analyses based on molecular sequence data suggest that Martialinae are the sister group to all extant ants. However, by comparing molecular studies and different reconstruction methods, the position of Martialinae remains ambiguous. While this sister group relationship was well supported by Bayesian partitioned analyses, Maximum Likelihood approaches could not unequivocally resolve the position of Martialinae. By re-analysing a previous published molecular data set, we show that the Maximum Likelihood approach is highly appropriate to resolve deep ant relationships, especially between Leptanillinae, Martialinae and the remaining ant subfamilies. Based on improved alignments, alignment masking, and tree reconstructions with a sufficient number of bootstrap replicates, our results strongly reject a placement of Martialinae at the first split within the ant tree of life. Instead, we suggest that Leptanillinae are a sister group to all other extant ant subfamilies, whereas Martialinae branch off as a second lineage. This assumption is backed by approximately unbiased (AU) tests, additional Bayesian analyses and split networks. Our results demonstrate clear effects of improved alignment approaches, alignment masking and data partitioning. We hope that our study illustrates the importance of thorough, comprehensible phylogenetic analyses using the example of ant relationships.
The new tree is essentially the same as the earlier one (it is, after all, based on the same data), except that leptanillines & Martialis swap places as the oldest lineage, and the formicines collapse back to the formicoid polytomy. I read this as a reminder that phylogenetic trees are basically model projections, and like all model-based studies they are highly sensitive to the assumptions of the models and artifacts in the data. Change those assumptions and the inferred tree will change as well.
The way forward from the tangled roots of ant phylogeny will be to include more data. Now that an entire genome can be sequenced for a few thousand dollars, fully sequencing 15 or so of the relevant basal lineages is logistically plausible, perhaps as part of the i5k initiative.
source: Kück P, Hita Garcia F, Misof B, Meusemann K, 2011. Improved Phylogenetic Analyses Corroborate a Plausible Position of Martialis heureka in the Ant Tree of Life. PLoS ONE 6(6): e21031. doi:10.1371/journal.pone.0021031