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Posts Tagged ‘Evolution’

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…)

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A short clip from the BBC program “Ant Attack

Driver ant males are astoundingly strange creatures. They are larger, more muscular, more exaggerated than most other male ants. The reason is likely linked to the behavior shown in the above video: males must first be accepted by a gauntlet of choosy workers.

A classic paper by Franks and Hoelldobler (1987) describes the theory. This preference of workers for bulkier males- and a corresponding slaughter of smaller or otherwise unsuitable ones- drives an evolutionary trajectory towards increasing monstrosity. It’s an ant version of the peacock’s tail.

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The online early section of Molecular Phylogenetics and Evolution this week has the first comprehensive phylogeny of a rather important genus of ants: Myrmica.

Myrmica is ubiquitous in the colder climates of North America and Eurasia, with a few seemingly incongruous species inhabiting the mountains of tropical southeast Asia. The genus contains about 200 species, many that are common soil-nesting ants in lawns and gardens, and at least one damaging invasive species, M. rubra. The taxonomy ranks among the most difficult of any ant genus, as workers of different species tend to be numbingly similar to each other. And there are a lot of species.

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Tapinoma sessile, the odorous house ant, with larvae

Last summer I replaced the old covering on our porch roof. When I peeled back the rotting shingles, I was greeted by a frenzy of frenetic brown ants- thousands of them- running about every which way. Dozens of fat queens scurried for cover. It was an impressive display of formicid infestation, reminiscent of the swarms of invasive Argentine ants in California.

But these weren’t exotic pests. This was a native species, Tapinoma sessile, whose pleasant blue-cheese odor lends it the name  “odorous house ant”.

Tapinoma sessile is found nearly everywhere in North America. I’ve seen it in alpine meadows near Lake Tahoe, in parking lots in rural Missouri, in desert canyons in Arizona, and along sidewalks in suburban New York. Native meadows and urban jungles alike host populations- it’s perhaps the most consistently present ant in North American ecosystems.

In spite of its ubiquity, little is known about the origins of Tapinoma sessile. There are two likely hypotheses for the source of persistently pesty urban populations, though. One is that T. sessile is like many invasive ants- a single lineage particularly well-suited to urban conditions could have spread with human commerce across the continent. If this is true, genetic analyses should show a single clade of urban ants. The second is that T. sessile is naturally pesty and the pest populations are simply local ants thriving in the human landscape. In this case, urban populations should be intermingled among their local counterparts.

Fortunately, we don’t have to wait to solve this question. A paper out today in PLoS One by Sean Menke and colleagues provides an answer:

relationships of mtDNA from Tapinoma sessile collected across North America, based on the gene COI (from Figure 3 of Menke et al)

Urban T. sessile is overwhelmingly local, insofar as its mtDNA is concerned. The urban populations are not a single pesty lineage tramping around with trade but are natives doing well in the human-modified landscape. Furthermore, the authors found that the colony structure of urban and rural populations were similar. So the pest colonies may not actually be behaving differently than their rural counterparts. They just live in places where people take notice. Like porch roofs, for instance.

One caveat, though (and there’s always a caveat!). This study looked at a single genetic locus, and it’s possible that the phylogenetic pattern seen here is a result of repeated introgression of local mitochondria into invasive pest lineages as a result of interbreeding. I don’t think it likely, though, considering the persistence of the pattern.


source: Menke SB, Booth W, Dunn RR, Schal C, Vargo EL, et al. (2010) Is It Easy to Be Urban? Convergent Success in Urban Habitats among Lineages of a Widespread Native Ant. PLoS ONE 5(2): e9194. doi:10.1371/journal.pone.0009194

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click to enlarge

The top-tier journal Nature doesn’t often deal in purely phylogenetic research. So when such a study graces their pages we know it’s big stuff.

Yesterday, Nature published a 62 gene, 75 species analysis of the evolutionary history of the arthropods. Arthropods, as readers of this blog likely know, are animals with a chitinous exoskeleton and jointed legs. They include the insects, arachnids, crustaceans, centipedes, and others. This is a staggeringly diverse group, and one found just about everywhere on the planet. Most animals are arthropods.

This study has been in the works for many years. Jerry Regier’s lab at the University of Maryland has been diligently developing protocols for extracting single-copy nuclear DNA from across the arthropods, and the work has paid off handsomely. They have created the largest and most relevant data set yet assembled for addressing the hard questions in arthropod evolution. This is exciting! Today is like Christmas for arthropod systematists.

There’s a lot to digest here, but below are my first impressions: (more…)

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I did not expect everyone to nearly instantaneously solve yesterday’s termite ball mystery.  I’m either going to have to post more difficult challenges (from now on, nothing will be in focus!) or attract a slower class of reader.

Cuckoo fungus grows in a termite nest.

As you surmised, those little orange balls are an egg-mimicking fungus. It is related to free-living soil fungi, but this one has adopted a novel growth form that is similar in diameter, texture, and surface chemistry to the eggs of Reticulitermes termites. These hardened sclerotia are carried about the termite nest as if they were the termite’s own offspring, earning them the title “Cuckoo fungus”. Since termites are blind there is no advantage to the fungus in visually looking like an egg, though, so we sighted creatures can tell the difference at a glance.

For more about the Cuckoo fungus, check out the publications of Kenji Matsuura. Matsuura first identified the balls as a fungus ten years ago, as a graduate student, and has been working on them ever since.

Termites can't tell the difference between their own eggs (white) and the fungal sclerotia (orange).

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Amblyopone australis: a primitive ant?

Earlier I chastised Christian Peeters and Mathieu Molet for misinterpreting the term “basal” in a phylogenetic context.  What was that about?

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