The gang-of-four ready to take over the ant world. From left: Philip Ward, Seán Brady, Ted Schultz and Brian Fisher at the IUSSI congress in Sapporo, Japan.

It was at the XIV international meeting of the International Union for the Study of Social Insects in 2002 that the “gang of four” decided to join forces to reconstruct the phylogenetic history of ants using molecular data.  Four years later Brady et al. 2006 was published.

Red Hot Chilli Peppers? No, dentiform setae in the labrum of an Onychomyrmex doddi worker (Scanning Electron Micrograph, Roberto Keller/AMNH)

Just as the anterior margin of an ant’s cranium can sometimes be armed with rows of dentiform clypeal setae (that is, especially modified hairs), the lid that closes the insect’s mouth called labrum can bear identical structures. The image above shows two of these specialized teeth-like pieces (in red) flanking an empty broad socket where a third piece used to be inserted.

The labrum and part of the clypeus of an Onychomyrmex doddi worker. A row of dentiform setae adorn the labrum (in red) and the clypeus (in yellow; Scanning Electron Micrograph, Roberto Keller/AMNH)

Although these dentiform setae vary in size and shape quite considerably from species to species, when they are present in different parts of the body within an individual they show the same morphology, suggesting that they are the result of a similar developmental program that switches on at the different positions.

Head of the African subterranean ant Apomyrma stygia showing the hypertrophied dentiform setae in the labrum (in red; Scanning Electron Micrograph, Roberto Keller/AMNH)

Moreover, there is a interesting similarity between dentiform setae that have developed in similar but apparently independent (non-homologous) conditions. The hugely grown dentiform setae restricted to the labrum in Apomyrma stygia are identical to the similarly hypertrophied ones found in Amblyopone pluto but that occur exclusively in the clypeus (see last image on this post). Though not sisters, these two taxa belong to the same Amblyoponinae clade.

Lastly, a couple of comments regarding a recent paper describing the ant fossil Gerontoformica, which has similar detiform setae in both the clypeus and labrum. Nel and coworkers¹ mention that dentiform setae in extant ants are found either in the clypeus or in the labrum but never in combination. This is not the case as can be seen in the example of Onychomyrmex pictured above. There is also the suggestion that Probolomyrmex, a non-amblyoponine genus, has dentiform setae on the labrum. However, close inspection revels that this is also not the case. Rather, most setae covering the body in this genus, including the few stout ones on the labrum surface, are short and scale-like and can easily be confused with pegs at low magnification.

So far, in extant taxa these peculiar dentiform setae arming the clypeus and/or labrum are only known to occur within the subfamily Amblyoponinae.

References

First, it must be explained why the name of the bee appears in the title as two words, though “honeybee” is the customary form in the literature of apiculture. Regardless of dictionaries, we have in entomology a rule for insect common names that can be followed. It says: If the insect is what its name implies, write the two words separately; otherwise run them together. Thus we have such names as house fly, blow fly, and robber fly contrasted with dragonfly, caddicefly, and butterfly, because the latter are not flies, just as an aphislion is not a lion and a silverfish is not a fish. The honey bee is an insect and is pre-eminently a bee; “honeybee” is equivalent to “Johnsmith.” [vii]

It is an interesting paragraph, full of common sense.

In myrmecology, we do write acacia ant, army ant, carpenter ant, fire ant, harvester ant, weaver ant, and wood ant. However, we also refer to non-formicids like Mutillidae wasps as velvet ants and Isoptera (=termites) as white ants.

I always feel a little queasy over conventions that seek to regulate the proper use of common names from a scientific standpoint; such names, after all, belong to the common, not to the self-absorbed scientist. Snodgrass’ grammatical rule presupposes that the person using a common name has a good grasp of the taxonomy of the group. The same feeling goes for the insistence by some anthropologically-inclined taxonomists that one should compile and list all the existing common names for a given taxonomic group while preparing a monograph, flora or fauna (if you ever worked in an area with a rich ethnographic diversity you know this would require a dissertation work in itself). If we as scientists wish to talk science or convince the public to do so, if we seek taxonomic correctness, we should then use and promote our system of scientific names designed specifically for this purpose.

In other words, go try to convince geneticists that, if they won’t call their beloved model organism vinegar fly, at least they should call it fruitfly. Wait, does this applies?

Reference

Everybody likes popular science stories with clear and simple eureka moments. In the case of Charles Darwin’s theory of Evolution his voyage on board the H.M.S. Beagle and exploration of the Galapagos archipelago usually serves for such narrative purpose.

Of course Darwin’s story is much more complex, richer and interesting. Something seldom mentioned is Darwin the taxonomist. He published extensive monographs revising the classification of extant and extinct barnacles (Cirripedia). Taxonomic work at that scale amounted the study of morphology, ontogeny and biogeography across many species in a comparative framework. It does provides a great perspective that was an influential piece in Darwin’s synthesis.

It is with great pleasure then that I see that this week’s Science Magazine cover portraits plates of Darwin’s monographs for their special issue on speciation.

Further reading

Stott, Rebecca. 2003. Darwin and the Barnacle: The Story of One Tiny Creature and History’s Most Spectacular Scientific Breakthrough. W.W. Norton, 309 pages.
ISBN 0393057453, 9780393057454

Darwin’s monographs:

• Darwin, C. 1851-54. A Monograph on the Sub-Class Cirripedia. 2 vols. Ray Society.
• ————  1851. A Monograph on the Fossil Lepadidae. , or, Pedunculated Cirripedes of Great Britain. Palaeontographical Society.
• ————  1854. A Monograph of the Fossil Balanidae and Verrucidae of Great Britain. Palaeontographical Society.

Courtesy of Rabeling & Verhaagh/PNAS. Used with permission.

The recent description of the new and unusual ant species from Brazil Martialis heureka, caused furor in the popular media. It was entertaining to watch how, like the children’s game of Chinese whispers, the report rapidly deteriorated and became increasingly sensationalistic as it spun through news agencies around the globe. Reports ranged from accurate and informative to down right silly, with some newspapers almost claiming that the species actually originated in Mars (You can read more about it at Myrmecos blog and comments therein).

I have to say, I appreciate the medias attention to insect science no matter how distorted it gets. But now that the news storm has settle we can point out some other good news about Rabeling, Brown, and Verhaagh’s paper.  News that may not make for a good newspaper headline but that are nevertheless relevant to specialists in ant systematics.

Martialis heureka is the first ant species to be placed into our existing scheme of classification for the ant family in a strict phylogenetic way, with the use of quantitative methods, since the publication of the large scale phylogenetic projects for ants by Moreau et al. (2006) and Brady et al. (2006). That is, we now have a system in place, with enough molecular markers across enough ant taxa, that makes possible taking an ant species from which we know nothing about and “plug it in” to find out its evolutionary position relative to the rest of the family. These are good news also because it shows that the large scale Tree-of-life efforts for Formicidae are working as intended: rather than been the final saying about ant phylogeny, they created a platform from which our taxonomic knowledge can grow phylogenetically as more species are added to the pool of data.

One can agree or disagree about M. heureka position as sister to the rest of extant ants (I have my reservations, subject for another post), but that is beyond the point. The data is there and the methods are transparently laid out for anyone to scrutinize, reproduce and tinker with if so one wishes. This contrast with the still common way of doing taxonomy base of notions of overall similarity or favoring some characters over another without a clear method. These taxonomic decisions can be very well informed guesses, made by specialists with decades of experience, but they are guesses nevertheless, and as such difficult to assess (or challenge) by the rest of the community.

Not all is glossy though. The paper on M. heureka also highlights a big piece that is missing in our system: morphology. Our vast knowledge of ant morphology is not yet structured into a coherent system equal to the molecular one. Ideally, such system would allows us to plug-in a species by comparing its anatomical features to a pool of existing morphological data, score characters, and combine it with molecular markers for phylogeny reconstruction.

Courtesy of Rabeling & Verhaagh/PNAS. Used with permission.

The impact of this vacuum is apparent in M. heureka‘s paper. What constitute unique derived features in this species and which ones are shared primitive (and potentially ancestral to all ants) remains speculative- surely those specialized mandibles (unique among ants) are derived, but it is not clear that having one tibial spur per leg (as opposed to two) is an apomorphy for this lineage, for example, since this character occurs on and off scattered across the family.  Such uncertainty greatly impacts our attempts to reconstruct how ants first evolved and how they looked like, even when we have what seems to be a vital piece of the puzzle. And I am not even bringing up the f-word.

All in all, ant systematics seems to have gotten into great shape in the last couple of years and the publication of M. heureka by Rabeling and coworkers is a welcome attest to this.

References

Rabeling, C., Brown, J. M., and Verhaagh, M. (2008). Newly discovered sister lineage sheds light on early ant evolution. Proceedings of the National Academy of Sciences. doi: 10.1073/pnas.0806187105

Brady SG, Fisher BL, Schultz TR, Ward PS (2006). Evaluating alternative hypotheses for the early evolution and diversification of ants. Proc Natl Acad Sci USA 103:18172–18177. doi: 10.1073/pnas.0605858103

Moreau CS, Bell CD, Vila R, Archibald SB, Pierce NE (2006). Phylogeny of the ants: Diversification in the age of angiosperms. Science 312:101–104. doi: 10.1126/science.112489