The impressively moustached Pheidole bigote was described from Chiapas by Jack Longino in 2009. What’s up with the bizarrely plush facial adornment? No one knows. Seems like there’s a lot of that going around these days.
The researchers took a large sample of Pheidole- a common, diverse ant genus found in warmer regions worldwide- from a Brazilian forest reserve, sequenced the mitochondrial COI gene, compared morphogical identifications with identifications suggested by the genetics, and then compared the genetics against known, identified Pheidole DNA. Not a single unknown sample came within 4% of matching an identified reference. That’s actually kind of amazing. Ants are tremendously diverse, and a great many species remain to be discovered.
While the notion we can infer species identity from a snippet of DNA seems simple enough, in practice DNA barcoding remains impractical. This is especially true in large understudied groups. Without a well-curated reference database, most mystery samples will fall between the cracks.
I am not making an argument against barcoding. The technique shows great promise when wedded to a strong taxonomic foundation. But that’s just it. The taxonomic foundation- knowing what species look like, where they are found, and which Latin names apply to them- is a prerequisite for all the rest, and it’s still woefully inadequate.
source: Ng’endo RN, Osiemo ZB, Brandl R. 2013. DNA barcodes for species identification in the hyperdiverse ant genus Pheidole (Formicidae: Myrmicinae). Journal of Insect Science 13:27.
Pheidole metallescens, photographed in Gainesville, Florida
Mention a blue ant to any self-respecting myrmecologist and most will think of Australia. The great southern continent hosts an abundance of ants in spectacular metallic hues of blue, purple, and green. As you can see above, though, we Americans aren’t entirely bereft of iridescent formicids. I happened across these adorable little Pheidole in myrmecologist Andrea Lucky’s garden last week.
Not my best photo, unfortunately. But it does show the unusual structural color.
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!
Incidentally, Australian ant expert Steve Shattuck has photos of a major worker here: http://www.flickr.com/photos/steve_shattuck/3822017590/
Canon MP-E 65mm 1-5x macro lens on a Canon EOS 7D
ISO 200, f/13, 1/200 sec
diffuse overhead and back flash
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]
Doesn’t “bigote” mean “moustache” in Spanish?
Why, yes. It does.
Pheidole bigote Longino 2009
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.
source: Longino, J. T. 2009. Additions to the taxonomy of New World Pheidole (Hymenoptera: Formicidae). Zootaxa 2181: 1-90.
A recent study by Gabriela Pirk in Insectes Sociaux provides me with an excuse to share this photo:
Pirk et al examined the diet of both Pheidole species in the Monte desert of Northern Argentina. Why would someone spend time doing this? Ants are important dispersers of seeds, and these Pheidole are two of the most abundant seed-eating ants of the region. What they do with the seeds, which ones they choose to take, and how far they take them has implications for the ecology of the desert.
The interesting bit in my opinion is that the two ant species are rather different, both ecologically and biomechanically. Pheidole spininodis is a dedicated seed harvester. Their majors have enormous blocky heads with blunt mandibles for milling seeds:
In contrast, Pheidole bergi is primarily predatory, taking seeds only opportunistically. Their majors are slender, fast, and with relatively small heads and sharper mandibles better for slicing up the insects that they most commonly feed on:
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
A study out in pre-print by Muscedere, Willey, and Traniello in the journal Animal Behaviour finds little support for a long-held idea that worker ants change specializations to perform different types of work as they age. By creating colonies out of different age classes in the ant Pheidole dentata, the researchers showed that older workers were good at pretty much everything, while younger ants performed only a few tasks, but did those less efficiently. Here is the abstract: Continue reading →