Ants

Ant Research Roundup: Parasites Edition

One measure of the importance of ants is the number of parasites that have evolved to exploit their abundant resources. This week has seen a cluster of new ant parasite studies. Among them:

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Formica subintegra, photographed while raiding in upstate New York.

1. Socially parasitic Formica move nests during raiding season to richer hunting grounds. From the abstract of Apple et al (2014):

Five summers of monitoring the raiding behavior of 11–14 colonies of the slavemakers Formica subintegra and Formica pergandei revealed relatively frequent nest relocations: of 14 colonies that have been tracked for at least three of 5 years, all but one moved at least once by invading existing host nests. Movements tended to occur in the middle of the raiding season and were typically followed by continued raiding of nearby host colonies. Spatial patterns of movements suggest that their purpose is to gain access to more host colonies to raid.

source: Apple, J.L., Lewandowski, S.L., Levine, J.L. 2014. Nest relocation in the slavemaking ants Formica subintegra and Formica pergandei: a response to host nest availability that increases raiding success. Insectes Sociaux, doi: 10.1007/s00040-014-0359-1


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Myrmica queen in Arizona covered in mites.
2. Myrmica just can’t catch a break. A literature survey by Witek at al reports an array of about 40 parasites on these common holarctic ants, including butterfly larvae, socially parasitic ants, fly larvae, fungi, and others.

My sense is that Myrmica isn’t unusual in its parasite load; rather, Myrmica geography has lent itself to observation by natural-history obsessed northern Europeans. As myrmecology advances elsewhere, plenty of other ants will turn out to have lives just as miserable as Myrmica‘s.

source: Witek, M., Barbero, F., Markó, B. 2014. Myrmica ants host highly diverse parasitic communities: from social parasites to microbes. Insectes Sociaux, doi: 10.1007/s00040-014-0362-6


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Ophiocordyceps sp. on a Camponotus in Belize.

3. The famous ant-killing Ophiocordyceps fungus, when injected into a non-host species, fails to induce the stereotyped death-bite behavior. From the abstract of a paper by de Bekker et al:

…brain manipulation is species-specific seemingly because the fungus produces a specific array of compounds as a reaction to the presence of the host brain it has evolved to manipulate.

The real news here is the development of a technique to infect the fungus across species and monitor the results. This method will be powerful going forward, especially since the test of specificity in this study is weaker than the title would suggest. The researchers only injected a single non-host Camponotus, and they’ll need more for a proper assay of host range. I presume such work is coming, as the Hughes lab is generally thorough and highly productive.

source: de Bekker, C., Quevillon, L., Smith, P.B., Fleming, K., Ghosh, D., Patterson, A.D., Hughes, D.P. 2014. Species-specific ant brain manipulation by a specialized fungal parasite. BMC Evolutionary Biology 2014, 14:166  doi:10.1186/s12862-014-0166-3


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Mycocepurus castrator (photo by Christian Rabeling)

4. A parasite of fungus-growing ants provides convincing evidence for sympatric speciation. Older generations of biologists have been slow to accept that new species can arise while in physical proximity to their parent species, as mating between forms could erase any nascent differences. But Christian Rabeling et al have genetic data in Mycocepurus goeldii and its parasite M. castrator (ouch!) that make any other scenario highly unlikely. From the abstract:

Based on differing patterns of relationship in mitochondrial and individual nuclear genes, we conclude that host and parasite occupy a temporal window in which lineage sorting has taken place in the mitochondrial genes but not yet in the nuclear alleles. We infer that the host originated first and that the parasite originated subsequently from a subset of the host species’ populations, providing empirical support for the hypothesis that inquiline parasites can evolve reproductive isolation while living sympatrically with their hosts.

source: Rabeling, C. Schultz, T.R., Pierce, N.E., Bacci, M. 2014. A Social Parasite Evolved Reproductive Isolation from Its Fungus-Growing Ant Host in Sympatry. Current Biology. doi: http://dx.doi.org/10.1016/j.cub.2014.07.048

What do Tatuidris armadillo ants eat?

Check this out:

It’s the first video of live Tatuidris, among the rarest and least understood of all ants. Until recently, no one had even seen one alive. The video is from a new paper in Insect Science, where a team of Belgian myrmecologists report their observations on a recent collection of live specimens. Here’s the abstract:

Ants of the genus Tatuidris Brown and Kempf (Formicidae: Agroecomyrmecinae) generally occur at low abundances in forests of Central and South America. Their morphological peculiarities, such as mandibular brushes, are presumably linked with specialized predatory habits. Our aims were to (1) assess the Tatuidris abundance in an evergreen premontane forest of Ecuador; (2) detail morphological characteristics and feeding behavior of Tatuidris; and (3) define the position of Tatuidris in the food web. A total of 465 litter samples were collected. For the first time, liveTatuidris individuals were observed. Various potential food sources were offered to them. A nitrogen stable isotope ratio analysis (15N/14N) was conducted on Tatuidris tatusia, other ants, and common organisms from the leaf-litter mesofauna. We found a relatively high abundance of T. tatusia in the site. Live individuals did not feed on any of the food sources offered, as usually observed with diet specialist ants. The isotope analysis revealed that T. tatusia is one of the top predators of the leaf-litter food web.

So Tatuidris is a top micro-predator. But of what?


sources:  Jacquemin J, Delsinne T, Maraun M, Leponce M. 2014. Trophic ecology of the armadillo ant, Tatuidris tatusia, assessed by stable isotopes and behavioral observations. Journal of Insect Science 14(108). Available online: http://www.insectscience.org/14.108.

Greibenow, Z. 2014. Glimpsing Armadillo Ants. Gentle Centipede blog: http://gentlecentipede.blogspot.com/2014/05/glimpsing-armadillo-ants.html

Soil-Nesting Ants Don’t Always Nest Directly In Soil

Most ants live underground, but that doesn’t mean they spend much time in direct contact with the soil. Some nests are worth a detailed look, as not all tunnels through the dirt are as simple as they may first appear:

Polyrhachis (Campomyrma) sp.

This Australian Polyrhachis (Campomyrma) has lined its galleries with a fine wood pulp. I took this photograph last month in southern Australia. In the field, I was far too focused on the ants and their larvae to notice the carton substrate. At least, not right away. But once aware of it, I saw that every nest I uncovered had the pulp wallpaper.

This unusual use of organic matter likely provides the benefit of being better insulated and less prone to flooding or drying out than bare soil. The structure may also be a type of carton, meaning it also holds a connective fungus, but I was unable to find any published literature confirming it. In any case, ant nests themselves can be just as surprising as their hosts.


additional reading: Robson, S. K., & Kohout, R. J. (2007).  A review of the nesting habits and socioecology of the ant genus Polyrhachis Fr. SmithAsian Myrmecology1, 81-99.

The Yellow Crazy Ant, Anoplolepis gracilipes

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A yellow crazy ant, Anoplolepis gracilipes, from an infestation in Cairns, Australia.

I’ve been increasingly self-conscious about not having photographed the yellow crazy ant, Anoplolepis gracilipes. This species is one of the world’s most damaging invasive insects, wiping out entire faunas as it spreads like a formic acid carpet across the south pacific. The famous Christmas Island crabs, for example, are in danger of extinction from the ant menace. For a professional ant photographer to be without photos of this little terror is to be a bookstore without Harry Potter, or a coffee shop without scones.

Thanks to ant researcher Lori Lach, though, I was able to remedy this oversight. Lori took me to one of the infested sites near Cairns earlier this month. It was like a horror movie:

Lori Lach in an invaded riparian forest, with media commentary.

Well, not *exactly* like a horror movie. But still. I had never seen anything like it.

A trail of yellow crazy ants covers a tree trunk.

The ants are big. Most invasive ant species have large colonies of rather small ants, but Anoplolepis has large colonies of large ants. Viscerally, that makes a difference. Especially since they are also fast. Much more of the ground and foliage seems to be moving. Even for an ant guy, the effect is unnerving.

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A worker collects honeydew from a sugarcane whitefly.
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Grass aphids were another source of honeydew.

I was told not to be impressed, though, because that particular site had been treated recently and the infestation was “light”. It didn’t look light to me. I saw hardly any other ants and very few insects apart from the honeydew-producing bugs the ants were guarding. A heavy infestation must be… crazy.

Anoplolepis gracilipes

Anyway. Check out the new photographs:

Yellow Crazy Ant Photos

And, if you’d like a yellow crazy ant explainer Minute Earth has a short video.

A Myrmicine Phylogeny Shakes Things Up

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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. 

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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.

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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.

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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.

Everything Old Is New Again – Ponerine Taxonomy Returns To Its Roots

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Pachycondyla striata, from Brazil, is one of the few names to remain stable after Schmidt & Shattuck fragmented Pachycondyla.

A monumental day for ant taxonomy! The mythical Schmidt & Shattuck ponerine revision, long rumored to be in the works, has emerged from the mists of legend and lore. It’s real! All 242 pages are in Zootaxa:

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I don’t wish to speak for the entire myrmecological community, but I think it is safe to say that Chris Schmidt and Steve Shattuck’s ponerine revision has been the most awaited taxonomic paper of the past decade. Ponerine ants comprise one of the greatest subfamilies in terms of abundance and species diversity, particularly in the tropics. Ant people know ponerines. The group is the most purely predatory of the large subfamilies and contains some spectacular insects: trap-jaw ants, matabele ants, various and sundry predators and huntress ants.

Schmidt & Shattuck’s paper is significant for two reasons. First, nearly all ant researchers will be affected by the taxonomic changes. And second, the changes themselves are large, especially for the hundreds of species that used to belong to the sprawling polyphyletic genus Pachycondyla. Under the Schmidt & Shattuck hammer, Pachycondyla in the strict sense remains just a shadow. All but a handful of Neotropical species move to 19 different genera, some new, most revived from older literature. There are about a third more ponerine genera to learn than there were yesterday. That’s a lot to digest.

You might think such large changes would invite controversy, but I anticipate that the new scheme will be widely accepted and largely stable.

1. The work itself is thorough, involving morphology and several different genetic markers. There is good reason this paper was years in the making.
2. Many of the newly valid names are resurrected from the older literature, and as such they already reflect gross morphological groupings as seen by earlier generations of myrmecologists.
3. Ant taxonomists are more uniformly phylogenetic in their outlook than the preceding cohort. The polyphyly of Pachycondyla was not an accident born of ineptitude; rather, it was designed that way by Bill Brown, who was operating under a different philosophy of systematics more popular in the middle of the last century. Since Brown’s school has faded from prominence, most biologists are uncomfortable with polyphyly. As Schmidt & Shattuck are dragging ponerine taxonomy back into the comfort zone of most evolutionary biologists, I expect the new scheme will be popular.

In the big picture, Schmidt & Shattuck have put this important group of ants on a stronger taxonomic foundation. In the small picture, we are faced with the mundane realities of re-memorization.

Pachyondyla apicalis? No longer. Get used to Neoponera apicalisPachycondyla stigma? Nope. It’s Pseudoponera stigma. Plus, there’s Brachyponera, PseudoneoponeraMesoponera…


source: Schmidt, CA, Shattuck, SO (2014) The Higher Classification of the Ant Subfamily Ponerinae (Hymenoptera: Formicidae), with a Review of Ponerine Ecology and Behavior. Zootaxa 3817 (1): 001–242.

 

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.)

Nestmate Transport

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Nestmate transport in Myrmica. Raven Run Nature Sanctuary, Lexington, Kentucky.

If you spend time watching ants, you may sometimes notice that one ant appears to be carrying the body of a second, motionless ant. The second individual isn’t dead; rather, she’s just tucked away into EZ-carry mode. What’s going on?

It’s thought ants carry each other around for two reasons. The first is that the carrying ant knows the destination, and transport is a more reliable way than, say, leading, to get the second ant to location. The second reason is that the small size of ants makes carrying a more energy efficient way to move two ants than were both walking individually.

I photographed these Myrmica in Kentucky last week while out with the graduate students at Raven Run Nature Sanctuary.


photo details:
Canon MP-E 65mm 1-5x macro lens on a Canon EOS 6D
ISO 200, f/6.3, 1/180th second
diffuse twin flash