phylogeny

A Myrmicine Phylogeny Shakes Things Up

Monomorium kiliani
Monomorium kiliani, an Australian myrmicine. The narrow, two-segmented waist is characteristic of this subfamily.

We’re only halfway through the year, but already 2014 will be remembered as pivotal for studies of ant evolution and classification. Following right on the heels of Schmidt & Shattuck’s massive ponerine revision comes an important new study from the Ant Tree of Life group. Ward, Brady, Fisher, and Schultz (2014) have reconstructed the first thorough genus-level phylogeny of the great ant subfamily Myrmicinae.

How important is this study?

Roughly half of all ants are myrmicines, both in abundance and in species diversity. Their numbers include fire ants, harvester ants, leafcutter ants, big-headed ants, acrobat ants, and so on, to the tune of some 6,000+ species.

So… Boom! Suddenly, we’ve been given a detailed picture of the evolution of half the ants. This is big. It is so big I cannot cover the paper in detail. Instead, I’ll just give a few preliminary thoughts, as follows:

1. This is a well executed study, as we’ve come to expect from the Ant Tree of Life team, applying a thorough analysis to over 250 carefully selected taxa and 11 genes. It’s also a shining example of an older generation of genetic techniques, alas, and while I am confident the stronger results will mostly endure, be aware that an incoming next-gen tide of full genomes, and the 6,000 yet-unsampled myrmicine species, may yet overturn some of the findings.

2. The deep history of Myrmicinae, starting 100 million or so years ago, mostly occurred on those continents that drifted to become the Americas. Echos of these earliest divisions are heard in six clear, genetically distinct groups that Ward et al have formally set the up as a new system of tribes, replacing an earlier, messier scheme. The six groups are listed here in their order of divergence: Myrmicini (MyrmicaManica), Pogonomyrmecini (Hylomyrma & Pogonomyrmex), Stenammini (AphaenogasterMessorStenamma, and relatives), and three sprawling groups with thousands of species: Solenopsidini, Attini, and Crematogastrini. 

mtree1
The myrmicine big picture. (Sharpie on office paper, 2014, limited edition print available, unless I recycle it).

3. The news is not all good. The clarity deep in Ward et al‘s tree fades for slightly younger events. Early relationships within some of the the six tribes are discouragingly ambiguous. This study has resolved some problems, myrmicine taxonomists face a difficult road ahead. Many of the world’s greatest genera do not form natural groups and will have to be redone. These include Aphaenogaster, Pheidole, Tetramorium, and especially Monomorium, which splatters almost comically across the Solenopsidines.

What, really, is Monomorium? Modified from Figure 1 of Ward et al (2014).

Distressingly, fuzzy resolution in a data set with this many markers and taxa means achieving proper resolution, if at all, will likely be expensive. Myrmicines may have speciated so explosively that we may never be able to reconstruct what happened with confidence.

4. The authors correct a few of the more obvious instances of paraphyly. Notably, the New World “Messor“, being unrelated to their old world doppelgangers, were moved to a revived Veromessor, and several social parasites like Protomognathus and Anergates have been sunk into the host genera from whence they evolved: Temnothorax and Tetramorium, respectively. There are other changes, too; they are listed in the abstract

Most of the identified problems- such as what to do with Monomorium and Aphaenogaster were left for targeted future research.

5. Remember the dispute over Pyramica vs. Strumigenys? The argument was fundamentally over how ant mandibles evolve. Apparently, high energy trap-jaws arise easier than anyone imagined. According to Ward  et al, not only is the assemblage of trap-jaw ants formerly included in dacetini a polyphyletic splatter, even within the genus Strumigenys the trap jaw has arisen at least twice.

ward1
A phylogram of Strumigenys, modified from Figure 1 in Ward et al 2014, showing strong support for the parallel evolution of trap-jaws in the genus.

6. The rare and bizarre African myrmicine genus Ankylomyrma is not a myrmicine at all! Rather, Ward et al‘s results unambiguously tie it to the equally bizarre Tatuidris of the Neotropics, sitting on a distant branch of the ant tree. Peas in a poneromorph pod…

Ultimately, Ward et al have crafted a sobering view of how little we still know about ant evolution, and how much remains to be done.

fulva10j
Aphaenogaster fulva, photographed in Illinois.

source: Ward PS, Brady SG, Fisher BL, Schultz TR (2014) The evolution of myrmicine ants: phylogeny and biogeography of a hyperdiverse ant clade (Hymenoptera: Formicidae). Systematic Entomology, online early. DOI: 10.1111/syen.12090

disclosure: I received my Ph.D. from Phil Ward’s lab where much of this study was completed, and I contributed a few of the samples, but I was long gone by the time the study was initiated and have had no other involvement with the research.

Genomic data reveal that ants and bees are close relatives

Current Biology has just published what is surely among the most significant papers this year on insect evolutionary relationships:

Aculeates1
Cladogram depicting relationships among major groups of aculeate wasps, based on analyses of 308 aligned nuclear genes. Branch color represents parasitism (=green) or predation/nest-building (=yellow). Adapted from Figure 3 of Johnson et al (2013).

The importance of the paper derives from a combination of hitting a controversial topic with a much-needed phylogeny, and doing so with a staggering amount of information. The 300 or so genes employed to create the genomic tree is orders of magnitude more data than that used in any previous effort, and the result finally brings clarity to a question that’s been nagging a lot of Hymenopterists: what are the closest relatives of ants?

Probably, bees and spheciform wasps.

That’s not necessarily the relationship I would have guessed, but it holds under multiple modes of analysis.

Here’s the abstract (emphasis mine):

Eusocial behavior has arisen in few animal groups, most notably in the aculeate Hymenoptera, a clade comprising ants, bees, and stinging wasps. Phylogeny is crucial to understanding the evolution of the salient features of these insects, including eusociality. Yet the phylogenetic relationships among the major lineages of aculeate Hymenoptera remain contentious. We address this problem here by generating and analyzing genomic data for a representative series of taxa. We obtain a single well-resolved and strongly supported tree, robust to multiple methods of phylogenetic inference. Apoidea (spheciform wasps and bees) and ants are sister groups, a novel finding that contradicts earlier views that ants are closer to ectoparasitoid wasps. Vespid wasps (paper wasps, yellow jackets, and relatives) are sister to all other aculeates except chrysidoids. Thus, all eusocial species of Hymenoptera are contained within two major groups, characterized by transport of larval provisions and nest construction, likely prerequisites for the evolution of eusociality. These two lineages are interpolated among three other clades of wasps whose species are predominantly ectoparasitoids on concealed hosts, the inferred ancestral condition for aculeates. This phylogeny provides a new framework for exploring the evolution of nesting, feeding, and social behavior within the stinging Hymenoptera.

Source:  Brian R. Johnson, Marek L. Borowiec, Joanna C. Chiu, Ernest K. Lee, Joel Atallah, Philip S. Ward (2013) Phylogenomics Resolves Evolutionary Relationships among Ants, Bees, and Wasps. Current Biology, Available online 3 October 2013. http://dx.doi.org/10.1016/j.cub.2013.08.050

A Phylogeny for the Dolichoderine Ants

Leptomyrmex darlingtoni, Australia

A big day for ant evolution! The Ant Tree of Life research group (AToL) has published their dolichoderine phylogeny in the journal Systematic Biology.

Dolichoderines are one of the big ant subfamilies, comprising just under ten percent of the world’s ant species. These are dominant, conspicuous ants noted for having ditched the heavy ancestral ant sting and armor in favor of speed, agility, and refined chemical weaponry. Most dolichoderines live in large colonies with extensive trail networks, and they fuel their frenetic lifestyle through copious consumption of hemipteran honeydew.

The paper is unfortunately behind a subscription barrier, but I’ve reproduced the primary finding below. (more…)

TimeTree of Life

I see that the TimeTree of Life project is now public.  This collaborative project draws on the research of dozens of biologists to estimate the timing of past evolutionary divergences.  The work is available as a book, but the online version has an interactive section that allows the user to name two organisms and get back the date the two last shared an ancestor.

For instance,

Ants vs. Bees: 163.5 million years ago

A word of caution, though.  While the output is extremely precise (i.e., it gives exact dates with decimal places), precision is not necessarily accuracy.  The given dates are really the midpoints across a range of estimates, and for appropriate scientific caution you’re still best off consulting the referenced papers themselves. In our insect example, the work was done by the Smithsonian Institution’s Seán Brady.

Still, it’s a fun little tool.

Specimen Request: Simopelta Army Ants

Simopelta nr. pergandei, Venezuela
Simopelta sp. nr. pergandei, Venezuela

I’ve just started a project in collaboration with Daniel Kronauer, Jack Longino, and Andy Suarez to infer the phylogeny of species in the Neotropical ponerine genus Simopelta.  If you happen to have any DNA-quality specimens of these unusual ants in your keep, we’d greatly appreciate a donation.

Why Simopelta?  These insects are among the “other” army ants, the barely-known lineages that have also evolved the specialized nomadic lifestyle that characterizes the well-known, photogenic, and oft-televised ecitonine and doryline army ants.  Yet Simopelta are ponerines, a completely different subfamily of ants.   Because they acquired their traits independently, Simopelta will add power to statistical tests of various hypotheses about how army ants came to be.  That, and they’re really interesting critters in their own right.

Ideally, specimens will have been collected into strong (>90%) ethanol and stored in a cool place, but these ants are rare enough that we’ll take whatever we can get.  Send to:

Alex Wild
Department of Entomology
320 Morrill Hall
University of Illinois at Urbana-Champaign
505 S Goodwin Ave
Urbana, IL 61801 USA

David Attenborough’s Tree of Life

Explaining the evolutionary tree of life is always a tricky proposition, as narratives are inherently linear but evolution spirals outwards in countless messy directions at once.  To tell a story from the tangled bank requires picking a single thread and following it, yet it is precisely our tendency to follow single threads that causes so much misunderstanding of how evolution works.

Attenborough grapples with the problem using an animation that permeates the video, showing graphically the complexity of an ever dividing tree in the background as he traverses time from ancient to modern.  Yet I don’t think he is entirely successful.  The problem is that the story he tells is the same one that’s always told: the vertebrate descent from early chordates to primates.  There is lip service paid to other lineages, but probably not enough.  The more the same vertebrate story is repeated as the preferred exemplar of evolution, the more we reinforce the incorrect ladder-like narrative of linear evolutionary progression.

The same sort of video could be made that ends at sea cucumbers, or rotifers, or grasses, and it would be every bit as accurate as the same old primate one that we see again and again.

(h/t Pharyngula)

Phylogeny of Linepithema

Argentine ants tending scale insects

Three years after finishing my Ph.D., I have finally published the last bit of work from my dissertation.  It’s a multi-locus molecular phylogeny of the ant genus Linepithema, a group of mostly obscure Neotropical ants that would be overlooked if they didn’t happen to contain the infamous Argentine Ant.  In less jargony language, what I’ve done is reconstruct the evolution of an ant genus using genetic data.  Here’s the citation:

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