Science

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.

Guest Post: Crowdfunded study of maternal care in leaf beetles

The following is a guest post by entomologist Guillaume Dury.

In the tropical forests of South America, survival can be tough for a small larva. Ravenous predators are on the prowl and deadly parasites soar nearby. Even faced with these threats, most species simply abandon their offspring, usually eggs. My favourite solution to survival of offspring is maternal care, but this raises the question: “Why do some insects care for their young while most do not?”

Comparatively few people study maternal care in insects and I’d like your help to be one of them. Insects are my passion, below is a photo of me at 4 years old, in the Swiss Alps with my insect net. Since then, I’ve obtained a B.Sc. in biology and ecology and I’ve finished my M.Sc. working on leaf beetles. I’m a BugShot 2012 alumnus and love insect photography, you can find my portfolio and my complete research C.V. on my website: http://www.gjdury.com/

gd2
Guillaume, 4 years old, with his insect gear in the Swiss Alps.

My project is partially funded by a National Geographic Young Explorer’s grant. I’m collaborating with Dr. Windsor of the Smithsonian Tropical Research Institute and Dr. Bede of McGill University, we propose a series of observations and experiments to determine how Proseicela vittata Fabricius (Chrysomelidae: Chrysomelinae) mothers defend their offspring, and from what threats, and how it differs from a closely related species without maternal care.

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Proseicela vittata guarding a brood of larvae. Photo by Dr. Donald Windsor.

Leaf beetles feed on leaves exposed to predators and parasites, parents of some species guard their progeny. The picture above is a mother Proseicela vittata with her larvae. In P. vittata, the mother beetle protects her eggs by gestating them, then, after giving birth to small larvae, she remains with them for all of their development.

The mother beetle doesn’t feed her larvae, but prepares their first meal. She will cut the veins of the first leaf the larvae eat. The leaves are those of the toxic Solanum morii (Solanaceae), and no one is certain about why the mothers cut the veins, we think it makes the leaves less toxic for the newborn larvae.

If you can share my project and spare a few dollars, it will make a big difference for me and I’ll do my very best to give back the best science I can! I am collecting funds through an Indiegogo campaign:

https://www.indiegogo.com/projects/study-of-maternal-care-in-leaf-beetles

The Many Talents of Trap-Jaw Ants…

…include swimming gracefully across water. Astounding:

This, from a new study by Steve Yanoviak in the Journal of Experimental Biology:

Abstract: Upon falling onto the water surface, most terrestrial arthropods helplessly struggle and are quickly eaten by aquatic predators. Exceptions to this outcome mostly occur among riparian taxa that escape by walking or swimming at the water surface. Here we document sustained, directional, neustonic locomotion (i.e. surface swimming) in tropical arboreal ants. We dropped 35 species of ants into natural and artificial aquatic settings in Peru and Panama to assess their swimming ability. Ten species showed directed surface swimming at speeds >3 body lengths s−1, with some swimming at absolute speeds >10 cm s−1. Ten other species exhibited partial swimming ability characterized by relatively slow but directed movement. The remaining species showed no locomotory control at the surface. The phylogenetic distribution of swimming among ant genera indicates parallel evolution and a trend toward negative association with directed aerial descent behavior. Experiments with workers of Odontomachus bauri showed that they escape from the water by directing their swimming toward dark emergent objects (i.e. skototaxis). Analyses of high-speed video images indicate that Pachycondylaspp. and O. bauri use a modified alternating tripod gait when swimming; they generate thrust at the water surface via synchronized treading and rowing motions of the contralateral fore and mid legs, respectively, while the hind legs provide roll stability. These results expand the list of facultatively neustonic terrestrial taxa to include various species of tropical arboreal ants.

source: Yanoviak, SP, Frederick, DN. 2014. Water surface locomotion in tropical canopy ants. J Exp Biol 217, 2163-2170. doi: 10.1242/​jeb.101600

Bringing Ants to a Wider Audience

Or, not:

Open Access

I don’t generally pick on scientists for not making their articles freely available. Publication is expensive, after all. But surely some types of articles merit more of an Open Access effort?

(More seriously, the article is about AntWiki, an open ant biology site that will be increasingly valuable as myrmecologists add content.)

A Project For The Lazy Myrmecologist

Here’s a big, useful question: How does human activity affect ant populations across landscapes?

One could design any number of studies to answer this question, most involving lots of trudging about in the mud, or through swarms of mosquitoes, or laboring outside cell tower coverage (gasp!). Or, one could just sit back in one’s ergonomic office chair and harvest ant data from Google Earth.

ants_from_space

This satellite photograph shows land in the Paraguayan chaco under various amounts of disturbance. It also shows nests of the chaco leafcutter ant, Atta vollenweideri, erupting in white spots across the heavily disturbed land like pimples before a prom.

Several decades ago, J.C.M. Jonkman used aerial photographs from the same region to conclude that leafcutter nests accelerate succession from pasture back to forest. But there is a lot more that could be done, relatively easily, from Google’s massive archive. It’d make a tidy side project for the lazy myrmecologist.

 

A Novel Use For Formic Acid

fulva5
Nylanderia fulva, the tawny crazy ant (photographed in Paraná, Brazil).

 

Ant guy Ed LeBrun has a paper out in Science today documenting a novel defensive use for formic acid: detoxifying the venom of competing fire ants:

Abstract: As tawny crazy ants (Nylanderia fulva) invade the southern USA, they often displace imported fire ants (Solenopsis invicta). Following exposure to S. invicta venom, N. fulva applies abdominal exocrine gland secretions to its cuticle. Bioassays reveal that these secretions detoxify S. invicta venom. Further, formic acid, from N. fulva venom, is the detoxifying agent. N. fulva exhibits this detoxification behavior after conflict with a variety of ant species; however, it expresses it most intensely after interactions with S. invicta. This behavior may have evolved in their shared South American native range. The unique capacity to detoxify a major competitor’s venom likely contributes substantially to its ability to displace S. invicta populations, making this behavior a causative agent in the ecological transformation of regional arthropod assemblages.

Normally, formic acid from the ants’ venom gland is applied to an opponent as a potent volatile weapon, but this sort of self-medication is novel. I haven’t read the paper in depth, but it looks fascinating.

I’ve long been interested in the invasion of North America by a suite of highly-competitive species from the same region of Argentina. Some of the most dominant ants in along the gulf coast are imports: fire ants, Argentine ants, tawny crazy ants, Pheidole obscurithorax, and rover ants all know each other, so to speak, from their interactions along the banks of the Paraná river. Thus, this detoxification behavior likely originated long before any of these ants hitchhiked to North America.


Source: LeBrun EG, Jones NT, Gilbert LE (2014) Chemical Warfare Among Invaders: A Detoxification Interaction Facilitates an Ant Invasion. Science, online early. doi: 10.1126/science.1245833

Fossils and DNA tell different stories about ant evolution. Or do they?

Did modern ants evolve up from subterranean ancestors? Or did they diversify from above-ground species?

This straightforward question about ant history does not have a straightforward answer. If we look at early ant fossils, most sport the long limbs and large eyes typical of surface-dwelling species. Consider the Cretaceous ant Haidomyrmex:

fossil_ant_scan
Haidomyrmex scimitarus (via antweb.org)

If the fossils tell a tale of large-eyed, surface-dwelling ancestors spawning the modern ant fauna, genetic data from modern species give an apparently conflicting story. A recent paper by Andrea Lucky and others in PLOS ONE took the known habits of modern ants and triangulated back over an evolutionary tree to infer the ancestral state. The odds of a subterranean ancestor were more than 90%:

Modified from Figure 1 of Lucky et al 2014.

 

Which story do we believe?

Possibly, both. The existence of a conflict depends on how the extinct, large-eyed species are related to modern ants. Many of them are in the subfamily Sphecomyrminae, and their phylogenetic position is not known with certainty. If sphecomyrmines are merely another ant lineage contained within the other known ants, as beautifully illustrated in the below diagram that took  at least 2 minutes to sketch, then we indeed have a conflict.

tree2

If, instead, sphecomyrmines are a separate lineage that diverged earlier in ant evolution, then there isn’t  a conflict at all. tree

In this latter scenario, one particular lineage went underground (where they were less likely to be preserved as amber fossils) and from there radiated into the ants we know and love today. Meanwhile, their sphecomyrmine sisters persisted, large-eyed and above ground, until extinction. It is entirely possible that the diversity and success of modern ants traces to modifications forced by this subterranean existence.

Finally, the underground result of Lucky et al depends on particular assumptions of how traits evolve. Specifically, that above- and below-ground species go extinct at similar rates. If subterranean ants tend, on average, to go extinct less often than their above-ground relatives, then many of the surviving members of older lineages will be subterranean and we might infer a subterranean ancestor as an artifact.

Leptanilla6
Leptanilla is an ancient lineage of blind subterranean ants.

source: Lucky A, Trautwein MD, Guénard BS, Weiser MD, Dunn RR (2013) Tracing the Rise of Ants – Out of the Ground. PLoS ONE 8(12): e84012. doi:10.1371/journal.pone.0084012

Queen ants are a beautiful example of how form evolves with function

paripungens1
Thanks to expanded muscles in the front of the thorax, this Anochetus worker can hoist a heavy load.

Roberto Keller,  Christian Peeters, and Patrícia Beldade have published an intriguing new paper about ant thorax morphology. Worker ants lack wings, of course, so their thoraces are smaller. But this new study notes there is more to the thorax than mere reduction. Ant workers might not fly, but they do lift things with their heads, so the first segment- the pronotum- is enlarged to strengthen the neck. It’s essentially the factoid “ants can lift 50 times their own weight!!”, explained.

But I’m not blogging the paper for the worker necks. Workers are not the best part.

Rather, Keller et al also looked at queen ants, and here is where the study gets clever. Consider:

queen_morphology
Queen ants of most species fall into one of two body types.

Queens that hunt need strong, weight-bearing necks, so the thoracic segment anchoring neck muscles is enlarged as it is for workers. Queens that stay in the nest and don’t gather food don’t need neck strength, so the corresponding segment is reduced. Meanwhile, the segment associated with muscles that are metabolized to raise early workers is enlarged.

t1
Thoracic tergite #1 (T1), in blue, is much larger in queen ants that leave the nest to forage, while the second tergite (T2), in orange, is enlarged in queens that do not leave the nest. (Modified from Figure 2 of Keller et al).

While this pattern of claustral/non-claustral was generally known, Keller et al perform a more rigorous accounting. First, they quantified the phenomenon by measuring many species. Remarkably, the data did not form a continuum of values; rather, queens sort cleanly into one type or the other. Thus, queen ants really do come in two forms. It’s not just our imagination.

Then- and here’s the fun part- the authors tested for an evolutionary association of form and function. When thorax shape and colony-founding behavior are mapped on an evolutionary tree inferred from genetic data, we see two traits changing in concert rather than randomly. Ancestrally, queens forage and have an enlarged T1. Several times in evolution queens have shifted to claustral, non-foraging founding. When they do, the morphology also shifts.

That ant shape and ant behavior are intertwined should not be surprising, but I mention it because this study forms an especially nice example.

The form/function association has a practical use for ant-keepers, too. If you’ve caught a young queen and want to know if she requires feeding to raise her first workers, you can look at her thorax. A big T1 needs feeding, a small T1 is claustral and does not.


Source: Keller RA, Peeters C, Beldade P. 2014. Evolution of thorax architecture in ant castes highlights trade-off between flight and ground behaviors. eLife 2014;3:e01539 http://dx.doi.org/10.7554/eLife.01539

 

The jaws of Zigrasimecia

Behold the fearsome maw of the extinct ant Zigrasimecia ferox:

Zigrasimecia
modified from figure 7 (Perrichot 2014)

The image is from an upcoming paper by paleomyrmecologist Vincent Perrichot, and the preferred food of this spike-mouthed creature is unknown. One hopes, for the preys’ sake, that it wasn’t anything with a sensitive nervous system!

Sphecomyrmine ants like Zigrasimecia are puzzling for students of evolution. These extinct insects aren’t just a straightforward blend of ancestral wasp traits and derived ant traits. While these animals do possess a measure of each, they’ve also grown a uniquely sphecomyrmine suite of characteristics. Like, for example, highly specialized nightmare spiky death mouthparts.

These ants were surviving in the times of the dinosaurs doing something that no modern insects do- though exactly what that was is unclear- and given their strange appearance it is unlikely they were directly ancestral to today’s species. Instead, Zigrasimecia and relatives are probably an early offshoot on the ant tree, a manifestation of a predatory niche that worked until it didn’t. Here’s hoping against steep odds that someone uncovers an amber specimen holding the unfortunate mystery prey.


source:  Perrichot, V. 2014. A new species of the Cretaceous ant Zigrasimecia based on the worker caste reveals placement of the genus in the Sphecomyrminae (Hymenoptera: Formicidae). Myrmecological News pre-print, accessed via ResearchGate 1/5/2014.