This ant looks like it’s wearing the insect equivalent of tuxedo shorts. Formal wear and pasty white legs.
If you visit Cape Tribulation, keep an eye out for these little insects. Only 2-3 millimeters long, they are one of the most common ants in that area. I found them nesting in nearly every rotting log I looked at. Insects don’t have to be rare to be beautiful!
With all the recent attention devoted to Pheidole‘s apparently latent ability to produce supermajor workers at the drop of a hormone, now is an opportune time to mention Pheidole fimbriata.
Pheidole fimbriata is, according to Corrie Moreau’s research, the single sister species to the remaining 1000+in the genus. That is, the first thing to happen when Pheidole first head-butted itself into the world some 60 million years ago was that the fimbriata lineage split from the others. Oddly, while the main lineage branched into a diversity insane enough to give taxonomists headaches, the fimbriata lineage contains but a single giant and rather strange Neotropical species*.
This lumbering ant is important. Pheidole fimbriata provides an independent window backwards through time in which to infer how supermajors emerged. Rajakumar et al did not include P. fimbriata in their study, as the logistics of South American research can be difficult, but surely this species is now worth a look.
On the surface, P. fimbriata is a typical Pheidole in that it has, like most of its congeners, just two size classes of worker. It is dimorphic, not trimorphic, and no one thought to include this ant among the supermajor-producing species.
But just look at it. The relative head size is massive compared to most Pheidole. It’s much more like the supermajor of Pheidole rhea than a typical major.
If P. fimbriata turns out with further developmental work to really be a supermajor, I can see a pair of interesting possibilities. First, perhaps the original Pheidole caste structure was dimorphic supermajor/minor. Under this scenario, the major caste as we know it may actually be the more recent innovation. Second, perhaps the Ur-Pheidole was like P. rhea, trimophic, but the fimbriata lineage somehow lost the major caste, leaving it with just supermajors and minors.
This is all just speculation, of course. But someone really ought to start looking at the biology of P. fimbriata. It’s an amazing ant.
*Incidentally, P. fimbriata was one of the more common Pheidole where I was living in Paraguay. They appeared most frequently at night, running in dense columns through my lawn not unlike army ants.
Ant enthusiasts know Pheidole as a common genus where each nest has two distinct worker types: small minors and big majors. But a few odd species add one more: enormous supermajors. You can see all three in the photo above of the Arizona species Pheidole tepicana.
This afternoon, developmental biologists at McGill University and University of Arizona published a clever study in Science suggesting that supermajors, although they emerged independently in the course of evolution, make use of a similar underlying hormonal process. What’s more- and this is what’s really exciting- they found they could induce supermajor-like workers in typical species by adding a juvenile-hormone analog to developing larvae.
What does this mean? Possibly, all Pheidole species have retained an ancestral potential to create supermajors. A few minor tweaks of hormonal regulation and the caste starts to emerge. These induced soldiers don’t to my eye look exactly like the real-world supermajors (not enough head, really), so I suspect supermajors in nature are developmentally fine-tuned more than suggested here. Still, that such a simple developmental change can lead to large differences in colony allometry is intriguing, a clue to how the 1000+ species in the genus managed to produce such a shocking richness in morphology in very short time.
Pheidole is a complicated ant, though, and I’m not sure we’ve defined the terminology of caste clearly enough that Rajakumar et al‘s interpretation can be called uncontroversial. What, really, is a “major”? In light of a conserved supermajor pathway, and the tremendous variation of form among species, it may be that “majors” in some large-headed species are actually supermajors, with the intermediary major caste lost.
Rajakumar et al show that artificial supermajors- defined partly by thoracic development- can be produced in two different dimorphic lineages. Solid evidence, but given the newly apparent fluidity of caste I’m less sure than before that we know what caste even means. Pheidole still has hundreds of untested species, and supermajors in life differ from majors more in head than thoracic allometry. Consider variation of heads among the typical, dimorphic species:
Still, Rajakumar et al is a significant paper. Like all good science, by showing us a little we see how much more we have to learn.
source: Rajendhran Rajakumar, Diego San Mauro, Michiel B. Dijkstra, Ming H. Huang, Diana E. Wheeler, Francois Hiou-Tim, Abderrahman Khila, Michael Cournoyea, and Ehab Abouheif. Science 6 January 2012: 79-82. [DOI:10.1126/science.1211451]
The inimitable Jack Longino published a taxonomic paper today on the Central American Pheidole, including descriptions of some 23 new species. Among these is the marvelously moustached P. bigote. The function of the fantastic facial hair remains unknown.
A South African Sap Beetle (Nitidulidae) reacts to a swarm of Pheidole megacephala by retracting its legs and antennae, leaving little exposed but smooth chitin. The ants have difficulty finding anything their mandibles can grab, even if they have the tank-like beetle surrounded.
photo details: Canon MP-E 65mm 1-5x macro lens on a Canon EOS 20D
ISO 100, 1/250 sec, f13, flash diffused through tracing paper
Pheidole moerens is a small, barely noticeable insect that travels about with human commerce, arriving without announcement and slipping quietly into the leaf litter and potted plants about town. As introduced ants go, P. moerens is timid and innocuous- it’s certainly no fire ant. The species is now present in the southeastern United States, a few places along the west coast, and Hawaii. Conventional wisdom suggests that P. moerens originated in the Greater Antilles, but even though the ant was first described from Puerto Rico a century ago its exact origin remains uncertain.
The Greater Antilles were a major hub in the global trade of the colonial era, receiving slaves from Africa and shipping sugar north to the distilleries. A great number of pests had already been carried to the islands by the time European scientists started to fully describe the fauna, so it’s not unlikely that many animals considered native there may have merely used the archipelago as a way-station between their actual origin and their ultimate global distribution.
Now that scientists are equiped with the tools of molecular genetics, we have the ability to determine more precisely the historical routes of spread. It would not take too much work to pin down the origin of P. moerens. But this ant is just one species of many that are both globally trampy and not particularly troublesome. Elucidating its origin is thus more an academic than an applied matter, so Pheidole moerens will likely remain mysterious for some time yet.
photo details: Canon MP-E 65mm 1-5x macro lens on a Canon EOS 20D
ISO 100, 1/250 sec, f/13, flash diffused through tracing paper
In today’s Zootaxa, Katsuyuki Eguchi has a taxonomic revision of the northern Vietnamese Pheidole, recognizing six new ant species for a genus that is already the world’s most diverse. The revision also contains several nomeclatural changes and a key to the thirty or so species occurring in the region.
As in most tropical taxonomy this research has a comedic/tragic effect of adding several more species, about which nothing is known, to a catalog already overflowing with equally mysterious species. We don’t know what they eat, how long they live, how large their colonies are, or when or how they mate. Many will meet extinction without ever receiving more than a cursory taxonomic registration. Perhaps Pheidole rugithorax has something to teach us; the odds that anyone will get around to learning it are slim indeed.