July 26, 2013 | 4
Beware the Giant Paintbrush, Little Insect
Way, way down in the southeast corner of Alaska lies Prince of Wales Island, the fourth largest in the United States. At around 2,500 square miles, it’s some 1,000 square miles larger than Long Island (which ranks a paltry 11th). At the northern end of this sizeable but remote isle lives one of the most obscure insects in the world.
It’s called Caurinus tlagu, and it was just described this month in the journal Zookeys. It lives on a “primitive”, loveable and also somewhat obscure (depending on your geography, vantage point, and botanical training) plant called a liverwort. Here’s what you have to do if you want to catch one (The man conducting the following “sweep” is Loren Russell, who discovered and described the first — and only other — species of Caurinus back in the late 1970s):
It turns out that Caurinus tlagu can perform a neat trick. Here’s what happened next:
Yup. The curious Caurinus tlagu hops like a flea (and is super cute to boot). And as it turns out, there may be a good reason for that.
A Curious Creature
C. tlagu made its debut in the entomology lab of the University of Alaska Museum, which like many natural history museums, accessions thousands of new specimens every year. Student Jill Stockbridge made the discovery, and showed it to Derek Sikes, the Curator of Insects (who shot and narrated the videos above). He was baffled. They posted a plea for expert help online.
It turned out this little unassuming insect is shockingly difficult to identify, even for many experts. Users of the often-tortuous dichotomous keys naturalists use to identify described species would not find either species in the genus in the insect version, according to Sikes and Stockbridge, because they lack the rostrum, or beak, typical of their order: Mecoptera. For extra identification fun, the pair noted, they also lack the features that would put them in any insect order with adults with rudimentary or vestigial wings incapable of flight. Yay.
After many incorrect guesses, Michael Ivie of Montana State eventually produced the correct identification. The only other known species of Caurinus — C. dectes — was described from Oregon and Washington in the late 1970s, as mentioned, by Loren Russsell. He called it “arguably one of the most bizarre and cryptic species of Mecoptera and [larva-producing] insects” .
And yet to look at it, a non-expert probably wouldn’t think so. It looks like a little bug. One small exception is its wings. The females are practically wingless, having only oval flaps or “pads” where they should be. The males sport spiny, “shortened, scissor-like wings” that they use not for flying, but for latching onto their ladies during mating. How they do this is hard for me to envision.
And yet, wings aside, for a remarkably obscure and rare insect, it looks so … well … ordinary. Clearly, there’s something a little odd going on here.
Surviving Glacial Drive-Bys ….
For instance, how C. tlagu ended up on Prince of Wales Island is a bit of a puzzle. It’s 1,059 km from the known host range of the only other known species in its genus, Russell’s C. dectes. What’s more, the island was “mostly” encased in ice during the late Wisconsin glaciation from 26,000 to 13,000 years ago. Before that, it had been repeatedly run over by glaciers during the many other ice ages of the planet’s increasingly schizophrenic last 3 million or so years.
Biological and geological clues seem to indicate that there were small ice-free areas in the midst of the relentless glaciers, and it’s possible the little insects waited out the big chill in these refuges before they re-conquered any ice-liberated land during interglacials (like the one we are currently in).
Sikes and Stockbridge also think it likely based on the great genetic differences between the genus Caurinus and its closest related genus — Boreus, whose earliest putative fossil dates from the Late Jurassic — that the two species are “evolutionary relicts”, that is, the few remaining members of a much larger group that existed 145 million years ago or even earlier.
…. and Dodging Dinosaurs
That would mean that not only is our little leaping bug obscure, it is also quite ancient and has dodged asteroids and dinosaurs as well as glaciers. That wouldn’t be surprising given the pedigree of their order. Mecoptera — the scorpionflies (one family lends the entire group its name because its tail resembles a scorpion’s stinger) — contains just 600 species in nine families.The order seems to be ancient, and not just ancient, but seemingly past its prime. Their fossils are abundant in Lower Permian rocks, and there is no other larva-producing insect order in which extinct families and genera appear to outnumber existing ones by three to one, according to a paper on the taxon in Zoologica Scripta by Michael Whiting.
Caurinus‘s family within that order is the Boreidae, or the snow scorpionflies or snow fleas (not to be confused with the springtails also called “snow fleas”). Found in the Northern Hemisphere, there are just 26 species in the family’s three genera. The adults tend to emerge in winter and like feeding on and generally hanging out with mosses and liverworts, although as Russell pointed out in the first video, Caurinus doesn’t seem to mind going on hopabouts. Indeed, the snow fleas distinguish themselves among the other members of their order in leaping up to 30 cm when so inclined. This not only allows them to leave most predators in the dust, but also to more easily transit freshly fallen, fluffy snow that would otherwise be difficult to navigate. In one genus, Hesperoboreus, the male uses his leaping ability to pounce on his chosen female. Clever boy.
One Giant Leap …
So they leap like fleas. So what? As it turns out, there are a few other boreid features reminiscent of fleas. They secrete the hop-enabling protein resilin in a similar way, and differently from the way locusts and dragonflies do. They both have multiple sex chromosmes and eyes in a “skeletal socket”. And the ovarioles — the egg-producing tubes that make up insect ovaries — of snow fleas differ from the rest of the Mecoptera, but resemble what’s found inside fleas.
Finally, here is a “cleared”(eviscerated) exoseleton of C. tlagu:
And here is Robert Hooke’s engraving of a flea:
You don’t have to squint to see the resemblance.
For a while, scientists thought fleas and flies were each others’ closest kin. Or that the fleas and the whole order Mecoptera had that relationship. But back in the early 2000s, a scientist — Michael Whiting of Brigham Young University, whose paper in Zoologica Scripta I mentioned earlier — conducted a comparative analysis of two genes and two sections of DNA that code for the RNA found in protein-producing structures called ribosomes of all the insects in Mecoptera. He threw the fleas in too.
In contrast to the 26 snow fleas, true fleas comprise an impressive 2,380 species in 15 families and 238 genera. Fleas are almost entirely parasites of mammals. Unlike the snow fleas, they lack compound eyes and have mouthparts specialized for what entomologists are fond of calling “piercing and sucking”. They are found on every continent and terrestrial habitat, and vector some of the most feared human diseases in history: plague, typhus, tularaemia. They’re not fun for other mammals either. In dogs, for instance, they can transmit parasitic worms (Fun fact: They also, according to Whiting, have “extraordinarily complex genitalia”).
… for Parasitekind
When he was finished, Whiting’s work suggested it’s likely that the snow fleas — the tiny, obscure, shy group sub-group of Mecopterans that really digs snow and liverworts and wouldn’t harm a … well, flea — are their closest living relations.
And in his analysis, Caurinus, our obsucre little genus, was the most basal or “primitive” of the snow fleas, which means it branched off first and might — just maybe — most closely resemble the last common ancestor of both groups. Which means, of course, that a feature that developed to aid in navigating snow and escaping predators may have helped some boingy, cute vegetarians become one of the most successful, irritating, and deadly blood-sucking parasites of mammals on Earth.
Sikes D. & Stockbridge J. (2013). Description of Caurinus tlagu, new species, from Prince of Wales Island, Alaska (Mecoptera, Boreidae, Caurininae), ZooKeys, 316 35-53. DOI: 10.3897/zookeys.316.5400
Whiting M.F. (2002). Mecoptera is paraphyletic: multiple genes and phylogeny of Mecoptera and Siphonaptera, Zoologica Scripta, 31 (1) 93-104. DOI: 10.1046/j.0300-3256.2001.00095.x