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Posts Tagged ‘research blogging’

Hyposmocoma is not the only unusual group of moth caterpillars I failed to observe in Hawai`i. Oh no precious, they are not.

Everyone knows what an inchworm looks like. Inchworms are the caterpillars of a family of moths called, appropriately, geometer moths. They tend to be well-camouflaged, resembling twigs. They eat plants, like most caterpillars, and some are serious agricultural pests.

A handful of Hawaiian species of the genus Eupithecia decided to break with tradition and become carnivores. They take advantage of their camouflage to fool unsuspecting insects into stepping on them. Then they suddenly reach back, grab the interloper with their talon-shaped legs, and eat it.

What’s especially cool is that they are not visual hunters. One species, in fact, hunts in the dark. Instead, they respond to touch: sensitive hairs on their backs tell them when prey is within striking distance. An insect walking on the caterpillar’s head or the front two thirds of its body will be unharmed.

It has been suggested, but not tested, that carnivorous Eupithecia‘s prey capture technique evolved from the “strike response” seen in some herbivorous caterpillars. The behaviour is best studied in the tobacco hornworm (Manduca sexta), the larva of a large sphinx moth. When something brushes against it, it reaches back and sometimes rasps its mouthparts against its skin. This behaviour could serve to startle birds that attempt to eat a hornworm, or to remove parasitoid wasps that would lay their eggs on it (and whose larvae would then eat the caterpillar alive).

By this point you should be dying of curiosity. You want to see these caterpillars in action, don’t you? Well fortunately, the BBC has delivered this nightmarish footage. And io9’s got your animated gif needs covered. Wicked, eh?

I’m going to end this post on a somber note, though. Carnivory by Hawaiian Eupithecia was discovered in the 1970s. The discoverer, Steven Montgomery, described a later foray to the site where he first found a caterpillar chewing on a fly. His report struck a chord with me, calling to mind my own impressions of the Hawaiian rainforest—and this paper is from 1983.

I recently returned to the volcanic cone on the Big Island where I first learned that Hawaii’s caterpillars were insect killers. After 10 years, I was keen to see if the endangered lobelia-like plants still found sanctuary in the steep cinder cone, because a carelessly set fire had destroyed the only other clump of these stately wonders. As I climbed the steep slope, I was stung on the head by a yellowjacket, a recently arrived pest that apparently stole into the Islands with cargo from the mainland. Rounding the top, I searched in vain for the lobelias. With them, half of the native forest plants had disappeared, and signs of rooting by pigs were frequent. Suddenly, a large European boar charged from under the koa tree and fled. I found no caterpillars that day, and heard few native birds. For this place, a conservation opportunity has passed, but on behalf of other Hawaiian forests, it teaches us what is at stake.

These species are not listed as endangered, but their habitat is dwindling; like many endemic Hawaiian species, their days may be numbered.

References
Montgomery, Steven L. (1983). Carnivorous caterpillars: the behavior, biogeography and conservation of Eupithecia (Lepidoptera: Geometridae) in the Hawaiian Islands GeoJournal, 7 (6), 549-556 DOI: 10.1007/BF00218529
van Griethuijsen LI, Banks KM, & Trimmer BA (2013). Spatial accuracy of a rapid defense behavior in caterpillars. Journal of Experimental Biology, 216 (Pt 3), 379-387 PMID: 23325858

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Let me begin by admitting that when I worked in Hawai`i, I didn’t pay much attention to the tiny moths that I sometimes scared out of the moss. So this is a post about what I missed.

Hawai`i, being remote and geologically active, is famous for its endemic, explosive evolutionary radiations: a single founding population, finding itself far from both its natural food sources and its natural predators, diversifies into a flock of functionally diverse new species in a relatively short time. The honeycreepers, descended from a finchlike bird, are well-known for this; the Hawaiian picture-wing Drosophila flies are another oft-cited example.

There may be more species in the endemic Hawaiian moth genus Hyposmocoma than in the Hawaiian section of Drosophila, and I personally think these moths are way cooler. Consider the many decidedly non-mothlike things these guys do:

  • The caterpillars make cases for themselves out of silk and bits of vegetation, pebbles, and other detritus. Silk-spinning is not unusual for a moth (viz. silkworms), but it’s usually reserved for building a coccoon to protect a pupa. Hyposmocoma caterpillars carry their silk homes on their backs much like a caddisfly larva. This fascinates me because caddisflies are the sister group to butterflies and moths. Is Hyposmocoma case-making an example of reversion to an ancestral state?
  • The cases come in a wide variety of shapes—researchers studying them classify them into such categories as purse-, bugle-, cone-, and burrito-shaped. (Some of them look like oyster shells to me.) You can see some examples of these cases and of the adult moths here. Both moths and cases are quite pretty, but I expect they would be highly cryptic in their natural habitats.
  • Four known species in the genus eat snails; they are the only lepidopterans to do so. I’ll let the researchers who discovered this behaviour describe it:

When [the caterpillars] encounter a resting snail of the native genus Tornatellides, they immediately begin to spin silk webbing attaching the snail shell to the leaf on which it rests, apparently to prevent the snail from sealing itself against the leaf or dropping to the ground once the larva attacks the soft tissue of the living snail. The larva then wedges its case next to or inside the snail shell and stretches much of its body out of its silk case, pursuing the retreating snail to the end of the shell from which there is no escape.

  • Several species have amphibious caterpillars—that is, they can develop successfully either completely submerged in water or on dry land. While many insects, including caddisflies, dragonflies, and stoneflies, have aquatic young that become terrestrial adults, their young are obligately aquatic—they can’t develop out of water. The amphibious Hyposmocoma species are thus unique among insects. This ability has evolved several times independently within the genus. When underwater, the larvae can anchor themselves to the substrate with silk, preventing them from being swept away by strong currents. Scientists suggest that this amphibious lifestyle may be an adaptation to frequent floods in the rainforests in which these species live. Additionally, the limited diversity of insects with aquatic young in Hawai`i compared to such habitats on the mainland may have opened up a niche for these moths to occupy.

So let this be a lesson to me and to all of us who are focused on charismatic macrofauna that we should pay attention to invertebrates once in a while. You never know what they’re up to.

References

 
Rubinoff D, & Haines WP (2005). Web-spinning caterpillar stalks snails. Science (New York, N.Y.), 309 (5734) PMID: 16040699

Rubinoff D, & Schmitz P (2010). Multiple aquatic invasions by an endemic, terrestrial Hawaiian moth radiation. Proceedings of the National Academy of Sciences of the United States of America, 107 (13), 5903-6 PMID: 20308549

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Gratuitous extant collembolan picture.

Fossilized amber famously can preserve insects trapped in it. Sometimes we’re lucky enough to get a glimpse of a bug’s life from these specimens. One such fossil, found in a mine in the Dominican Republic, preserves a tiny springtail piggybacking on a larger fishfly (or mayfly, if you like). Springtails (subclass Collembola – close relatives of insects and teddy bears*) are wingless, but so small that they can easily disperse by hitching a ride on a larger insect. This individual was caught in the act, and in fact represents the first known case of such hitchiking (the technical term is phoresy) on a fishfly (order Ephemeroptera). Here’s part of the figure from the paper that described this fossil, showing the miniscule springtail clinging to the fishfly’s back. There’s also a video in the supplemental section of the paper showing a 3D reconstruction of the bugs.

Figure 1B from Penney et al. 2012: thorax of a fishfly with springtail on the upper edge, just left of where the wing attaches.

 

The second unusual fossil o’the day is one that it never occurred to me could be fossilized: a bird’s nest. And not just any bird’s nest: an ancient flamingo’s! The 18-million-year-old nest consists of leafy twigs and contains five eggs. It is thought that it was abandoned and sank to the bottom of the saline lake in which it was built before becoming fossilized. This sort of habitat is much like the ones flamingos inhabit today. The authors examined the eggshells microscopically to identify them as flamingo eggs, but, interestingly, the nest characteristics and egg number and size resemble those of grebes, the flamingo order’s closest living relatives.

So, two strange fossils that shed a bit of light on prehistoric animals’ behaviour. This is the sort of thing that makes me say “Yay science!”

 

Gratuitous flamingo picture. There are two species here – can you ID them?

*Not intended to be a factual statement.

References

Gerald Grellet-Tinner, Xabier Murelaga, Juan C. Larrasoaña, Luis F. Silveira, Maitane Olivares, Luis A. Ortega, Patrick W. Trimby, Ana Pascual (2012). The First Occurrence in the Fossil Record of an Aquatic Avian Twig-Nest with Phoenicopteriformes Eggs: Evolutionary Implications PLoS ONE, 7 (10) : 10.1371/journal.pone.0046972

David Penney, Andrew McNeil, David I. Green, Robert S. Bradley, James E. Jepson, Philip J. Withers, Richard F. Preziosi (2012). Ancient Ephemeroptera–Collembola Symbiosis Fossilized in Amber Predicts Contemporary Phoretic Associations PLoS ONE, 7 (10) : 10.1371/journal.pone.0047651

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Top left: Cebu hawk owl; bottom right: Camiguin hawk owl. Source: Oriental Bird Club; painting by John Gale.

Did you know that the collective noun for owls is a parliament? Odd, because they tend to be solitary or paired. Anyways: a new parliament of seven owl species from the jungles of the Philippines.

A research team, led by Dr. Pamela Rasmussen of Michigan State University, was documenting the songs of the Philippine hawk owl (Ninox philippensis). This species was known to have geographically variable plumage, and previous taxonomists had split it into a number of subspecies. But plumage was not enough to diagnose

Because owls are nocturnal, they rely heavily on vocalizations to tell each other apart. And since they don’t learn these songs—they are in fact thought to be genetically programmed—owls with distinct enough songs probably belong to separate species. But recording owls at night in remote jungles is no easy task, and it took 15 years before the research team could confirm that they were dealing with seven hawk owls instead of just one.

Five of those seven species had previously been considered subspecies of the Philippine hawk owl on the basis of their plumage. But two—the Cebu and Camiguin hawk owls, named for the islands on which they are found—were completely new. It’s quite rare to discover a new vertebrate, and especially a new bird in this age of fanatical birding. But here were two! It’s nice, I think, to know that there are still mysteries out there to be brought to light.

The full article describing all seven species can be found here in PDF form (see page 12 for pictures of all the owls). And you can hear examples of the song recordings analyzed in this study: here’s the Camiguin hawk owl and the Cebu hawk owl.

Reference: Rasmussen PC, Allen DNS, Collar NJ, DeMeulemeester B, Hutchinson RO, Jakosalem PGC, Kennedy RS, Lambert FR, Paguntalan LM. 2012. Vocal divergence and new species in the Philippine Hawk Owl Ninox philippensis complex. Forktail 28:1-20.

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ResearchBlogging.orgMeet Bolbometopon muricatum—the bumphead parrotfish to its friends. It’s not a Pokemon but the world’s largest parrotfish—a fish that chews up coral with a birdlike beak and poops out sand. It can reach 1.5 metres in length and weigh 75 kilos, and it lives in all those places that make fantastic postcards—the reefs along coastlines of the Indo-Pacific and the Red Sea. Or it did, until humans started chasing it away. Bumphead parrotfish can be pretty tasty (apparently), and big specimens would provide a lot of food. Overfishing and degradation of reefs have made this fish’s populations plummet. Spearfishing, in particular, has been a problem for it, and made it wary of divers and snorkellers in many places. Its scarcity and shyness have made observing its behaviour difficult, and besides, who knows if a solitary fish in an area where fishing is common is acting “naturally”?

Four intrepid scientists—Roldan C. Muñoz, Brian J. Zgliczynski, Joseph L. Laughlin, and Bradford Z. Teer, all supported by NOAA, made their way to Wake Island, about halfway between Hawai’i and the Philippines, a protected area where fishing is illegal. This isolated site has a Bolbometopon population that is large, healthy, and, most importantly, unafraid of humans. Here they saw groups of several hundred of these fish looking for mates, and described an extremely unusual and spectacular behaviour. Bumphead parrotfish do indeed have a big bony hump on the front of their head—larger in males than in females. No one was quite sure what it was for: in addition to the obvious sexual selection hypothesis, it was speculated that they might ram coral heads to break them up into easier-to-eat pieces. But in the big breeding schools around Wake, the male parrotfish clearly and repeatedly used their bulging foreheads to ram other males. Like deer, sheep, and possibly pachycephalosaurs, the fish size each other up before rushing straight at each other and meeting with a bang. Check out the supplemental videos to this paper—the head-on collision is loud and painful-sounding.

Muñoz et al.’s findings are more than just a cool natural history story—they’re a reminder that humans can have drastic effects on the environment, not just in terms of numbers of plants and animals but in terms of their behaviour. While it’s important to have areas open to the general public for tourism, education, and fisheries purposes, we need to remember that even healthy, well-managed such areas can be very different from a “pristine” (though I hesitate to use that term) state. Understanding how animal behaviour changes when humans interact with them is hugely important in planning protection and recovery schemes for endangered species. (And if contributing to this knowledge involves diving on coral reefs, allow me to be the first to shamelessly volunteer!)

Muñoz, R., Zgliczynski, B., Laughlin, J., & Teer, B. (2012). Extraordinary Aggressive Behavior from the Giant Coral Reef Fish, Bolbometopon muricatum, in a Remote Marine Reserve PLoS ONE, 7 (6) DOI: 10.1371/journal.pone.0038120

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ResearchBlogging.orgFor those of you who never had a childhood dinosaur obsession, or a dinosaur-obsessed child, Pachycephalosaurus was a “dome-headed” dinosaur: it and its relatives had extremely thick (like, ten inches) skulls, often dome-shaped and fringed with an array of spikes and other protrusions. It is thought—but the idea is controversial—that these dinosaurs engaged in head-butting fights like male goats and sheep do today with their horns. (An alternative is that they head-butted their opponent’s sides, rather than engaging in extremely risky head-on fights.)

A new analysis of a Pachycephalosaurus skull has found evidence of a healed injury or injuries from such a battle. The top of the animal’s cranial dome has two large depressions—and by large, I mean 5 cm across and up to 1.6 cm deep—in addition to a scattering of smaller pits concentrated towards the front end of the skull. The shape of these scars led the authors to rule out postmortem damage by erosion or scavengers as causes. Instead, they believe the dinosaur sustained a skull fracture—and survived, but with a nasty infection. A CT scan showed evidence that the wound had at least partly healed before the animal died.

While there are no modern analogues for skull-bashing dinosaurs, the authors compared the fracture to those sustained by birds flying into windows. They were able to find skeletons of some birds that had survived such a trauma long enough to heal, and they did indeed have large, round depressions on their skulls (though, from the figure, there don’t seem to be any smaller pits—perhaps the bird’s wound wasn’t infected, or perhaps the pits could be attributed to the spikes and nobs also found on Pachycephalosaurus‘s skull).

The authors note that many instances of apparent damage on pachycephalosaur skull fossils have been dismissed as erosion, and that a closer look at many specimens could show similar examples of healed wounds. While such injuries wouldn’t prove whether these dinosaurs were head-butting each other, or just hitting head-to-flank, or for that matter running into things, they would suggest that those thick skulls weren’t just for show.

I note with interest the names of two other pachycephalosaurs mentioned in this study (which may actually be juvenile Pachycephalosaurus, and thus not validly named, unfortunately): Stygimoloch spinifer (the horned devil from the Styx) and Dracorex hogwartsia (the dragon king of Hogwarts).

Peterson, J., & Vittore, C. (2012). Cranial Pathologies in a Specimen of Pachycephalosaurus PLoS ONE, 7 (4) DOI: 10.1371/journal.pone.0036227

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I’m confused. Am I supposed to wear red to attract a mate, or not?

ResearchBlogging.orgThese seemingly contraditory findings (which, as I’ll explain in a moment, aren’t actually contradictory) were amusingly published in the same journal within less than two weeks of each other, so I can’t resist a discussion.

It’s an old canard of pop evolutionary psychology that the colour red denotes sex. It had been hypothesized that red ornamentation—especially lipstick—mimics the colour of receptive female genitalia, and therefore advertised (perhaps falsely) fertility or sexual receptivity. A study which I described several weeks ago laid this particular hypothesis to rest by showing that straight men were less sexually interested in pictures of redder female genitals. But still, the colour red has strong cultural connotations, perhaps with evolutionary significance. The newer study was intended to show that red denotes (female) sexual availability—particularly for casual sex.

This study had three parts. First, the researchers recruited women and asked them to pretend they were creating an online dating profile. Half of these women were asked specifically to imagine that they were creating this profile to find casual sex partners. They were asked questions about what their profile picture would look like, including whether they would wear jewelry, and what colour they would wear. Interestingly, they were given only four options: green, blue, black, and red. Women in the “casual sex” group were indeed more likely to say they’d wear red, but by only a small margin (it was just barely statistically significant, at p=.047).

The next part of the study looked at whether this stated preference existed on real online dating sites. The researchers selected profiles of 500 women who were looking for casual sex and 500 who weren’t (must resist urge to make snide remarks about this methodology!). They had three people classify the predominant clothing colour in these profile pictures (again, only red, black, blue, and green were considered). And, indeed, women who were interested in casual sex were more likely to wear red prominently than those who weren’t*.

The third and final part of this study was similar to the second, except that it compared women on websites specifically dedicated to casual relationships to women on sites that emphasized more long-term relationships. A similar result was found: red was more common on the casual sex-focused website.

Now, what can and can’t we conclude from these results, assuming they’re sound? We can say for sure that women (more specifically, women who fit the online dating demographic) who are looking for casual sexual relationships tend to display red clothing more often in the context of looking for those relationships. We cannot say whether this tendency is learned or instinctive, or whether it has an evolutionary “purpose”, or even whether it has anything to do with fertility (=fitness). The authors of this study do a great job of pointing out these limitations. For example, they note that their findings may not hold for face-to-face interactions or for all personalities.

I want to discuss why these results say little about evolution, though, because this is the sort of study that tends to be spun into an evolutionary psych fairy tale. First, it does not distinguish learned from genetically entrained behaviour (and, of course, there may be a little bit of both genes and memes at play). But if this red=casual sex link has a weak genetic basis, it’s probably not something that arose in our species as a result of natural selection in the traditional sense. Second, there’s an underlying assumption that red=casual sex=increased fitness (i.e. more babies). I have a feeling that the average woman these days is not pursuing casual sex in order to get pregnant. Perhaps this was the case in our evolutionary past, but it’s a pretty big assumption.**

Nevertheless, this study is not bad in terms of making wild claims about evolution. I do have some problems with its methods, though. Only four colour options? (None of which include, say, orange or pink—something closer to red.) And no mention of whether shades of pink, orange, or purple could be classified as red. On top of that, having people score what they thought was the “most prominent” colour in the profile pictures seems like not the best method, even though it was repeatable between scorers. (I’m thinking you could come up with a Photoshop manipulation to determine redness of a selected area of clothing. I think it’s been done with stickleback! (That is, with their red throats, not their clothing.))

What you can take away from this paper is that red is associated in women’s minds with sexuality in certain contexts. This is probably not surprising to anyone, but having data to back up the conventional wisdom is always good. However, it’s a huge stretch to ascribe evolutionary significance to this observation. Whether it’s as far a stretch to use it to choose your lipstick colour, though, is entirely up to you.

This study has also been covered eloquently at Scicurious. (Special bonus points to this set of comments.)

*For both of the online dating site studies, most photos had people wearing black, which is interesting if red is really that important a signal. Also, why were so few people wearing green? It’s clearly the best colour. (But not a real green dress, that’s cruel.)

**Also, and this is a question I could probably answer easily with a bit of Google Scholar-ing but I’m too lazy, what about red-green colour blindness, which occurs in 10% of men?

Elliot, A., & Pazda, A. (2012). Dressed for Sex: Red as a Female Sexual Signal in Humans PLoS ONE, 7 (4) DOI: 10.1371/journal.pone.0034607

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