Monday, August 21, 2006

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

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

The general mood of the symposium was good. In part this had to do with the fact that the venue was adequate for the event; a large and well-lit conference room at its full capacity. Phil Ward (Davis, California) opened the symposium talking about their Ant-AToL project clearly feeling grand about the full attendance and with the advantage of presenting before Moreau et al.’s talk, yet with characteristic lusterless. Their result so far is the same as the one recently published by Moreau et al.’s in Science (and it better be, since they have practically the same taxon sampling and genes, except using EF1-alpha instead of CO-I), but, unlike the Science report, they voiced the concern that the ant tree may be rooting in the wrong place; an analysis including just the ant sequences results in a topology that cannot be rooted to achieve the same results as with outgroups included. Basically there cannot be a Poneroid clade independent of Leptanillinae (see Moreau et al. 2006). They proceeded to constrain the root at different places within the ingroup comparing the parsimony/likelihood/probability scores (Lumberg-rooting style) to argue that in any case placing the root inside the large Formicoid cluster produces highly suboptimal results. I fail to see the point of this exercise since the global optimal solution for these data (including the ingroup and outgroup sequences simultaneously) already showed that the root doesn’t end up inside that clade. At the end recovering a highly supported Formicoid clade seems to be what most excites the AtoL group.

Corrie Moreau (Harvard) followed Ward's talk. She gave a good and fluid talk and stood pleased even though it was a repetition of results from the previous talk (yet already published by her group), but including the part of dating and correlation with the diversification of Angiosperms. She also cast doubts on the root position, mentioning the fact that both Myrmecia and Amblyopone have been hypothesized as the most primitive ants even though you cannot have both, since they occur well nested inside unrelated groups. Both her and Ward said that it will probably be necessary to sequence the other nominal Leptanillinae taxa to break the assumed long-branch attraction artifact. However the question remains if the problem if confined to Leptanillinae alone or if the whole so-called Poneroid clade is acting as an “attractor” of the divergent outgroup sequences and thus the ant tree is getting rooted upside-down. After all this “clade” contains several long branches (e.g., what is the lone Paraponera clavata doing in the middle of it?). A more promising solution would be to balance the outgroup portion of the analysis, but we will have to wait for the HymATol team for this.

Chris Schmidt (Tucson, Arizona) talked next. He is working on a phylogeny of the Ponerinae sensu Bolton and not wasting any time since he downloaded many sequences from Moreau's et al. to include as many outgroups as ingroup terminals. This talk was much more sophisticated than the rest in the symposium in terms of phylogenetic methods (probably under the influence of D. Maddison), and talked about the use of mixed models instead of the traditional way of applying the same model across a given gene or a priori codon partition. The results on the tree topology are very different, with the exception of Platythyrea that always comes as a long branch sister to Ponerini. The use of mixed models seems to be a good trend among researches fond of model-base approaches, and I wonder how far will they go before realizing they came back full circle to the realm of parsimony. I only regret that C. Schmidt omitted a discussion of the taxonomic and nomenclatural problems of this group as advertised in his abstract, since sorting out taxa like Pachycondyla is going to be the real challenge for this subfamily.

After this came the second turn for the Ant-AtoL team with a talk by Sean Brady (Smithsonian), co-organizer of the symposium. In this talk the AtoL team addressed the issue of dating the molecular ant phylogeny. The results are, again, basically the same as the ones published and presented by Moreau et al. However Brady also showed that his team is exploring the sensibility of their estimations to different parameters like models, taxon sampling and tree topology. This is important given the apparent problems with the ant tree reconstruction itself discussed earlier.

I will end this already long first part noting that all of the above speakers in some way or another acknowledged the need to incorporate morphology into the picture. In part to ameliorate the issues of poor resolution and indecisiveness that the current molecular data is showing about the relationships among the ant subfamilies, but also to be able to incorporate the fossil information more precisely and achieve a more complete picture of the ant’s phylogenetic history. In all, this positive attitude towards morphology is the best thing coming out of a molecular phylogenetics symposium.

To Part II

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