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Posts Tagged ‘PLoS ONE’

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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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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ResearchBlogging.orgThere’s a tired pop evolutionary psych idea that gets repeated by scientist and nonscientists alike—I think I heard it most recently in the movie “Hanna”—that red lipstick is meant to be a symbol of engorged female genitalia, and thus that lipstick is meant to signal sexual receptivity and possibly fertility. This idea apparently dates back to a chapter called “Sexual selection and human ornamentation” by one B. S. Low in a book called Evolutionary Biology and Human Social Behaviour. It’s called the “sexually salient” hypothesis—the idea that the colour red is attractive because of its resemblance to naughty bits. Supporting evidence (“evidence”?) for this idea included various studies indicating effects of the colour red on people’s perceived attractiveness, performance in sports, and perceived social dominance, as well as the fact that numerous primate species, especially baboons, have exaggerated, red female genitals and a corresponding male preference for red. Not surprisingly, the idea wasn’t properly tested but was picked up and repeated. Let me toss out a few objections to it before we even get to scientific hypothesis-testing. First, those primates with red genital displays have lots of body hair but hairless genitals and are quadrupedal. Humans are kind of the inverse, having pubic hair but little body hair, plus we walk on two legs, so chances are that female genitalia weren’t constantly on display in our australopithecine ancestors. Furthermore, redder lips could simply be a signal of better overall health or fertility, regardless of whether lip colour correlated with aroused genital colour.

If human females use red ornamentation to attract males by coopting a male preference for redder “sexual skin” as an indicator of fertility, we’d expect the following: male preference for redder female genital skin, male preference for redder lips (this relationship seems to be somewhat validated), and a correlation between female genital colour and health and/or fertility. The latter two predications would be tricky to measure properly—are we talking about a between-person correlation between a woman’s lip colour, labia colour, and health/fertility, or one that occurs within an individual woman over the course of her menstrual cycle? On top of that, we’d have to be careful to rule out a preference for red lips because they indicate health/fertility, as opposed to a preference for red lips because they look like more fertile genitalia. It would be easier to test—and easier to disprove—the first hypothesis, that men prefer redder female genitalia.

A new PLoS ONE study has done just that, using pictures of female genitalia digitally manipulated to be different shades of pink/red within the normal human range. They asked forty straight men to rate these pictures on a 1 to 100 scale of attractiveness. Interestingly, they rated the darkest red images as least attractive. Nor was there a correlation between attractiveness and the shade of pink. Hypothesis effectively rejected. Well, let me throw in some caveats about sample size (40 isn’t that many participants) and demographics (while the authors didn’t report anything about the age or race of their test subjects, perhaps their sample was too uniform to show anything*). Regardless, the preference for pinker genitals stands in sharp contrast to data on preference for red lipstick, clothes, and other ornamentation, making the “sexually salient” hypothesis highly unlikely.

This study does something I’m fully in favour of—testing a widely-repeated but unsupported idea—and disproves the hypothesis pretty soundly. It doesn’t, however, manage to break away from the assumption that a male mate preference must be universal and adaptive. It is entirely possible that strong evolutionary pressure shaped human male preference for a certain genital colour, and the authors list some quite plausible such pressures: menstrual blood (which indicates that a woman is not ovulating at that time) and diseases like yeast infections and trichomoniasis (which can cause reddening of the labia, and would put a mate at risk of infection). They don’t raise the point that a lower preference for red could also be cultural, though they do cite a study that found no change in the redness of Playboy centrefolds’ labia since the late fifties, suggesting at least that no recent cultural trend explains the preference for pink. But this preference doesn’t have to be adaptive at all—especially if vulva colour was never an important part of mate choice in our recent ancestors. Indeed, preference for red ornaments needn’t be adaptive or even genetically based either—just look through the archives of Sociological Images for examples of how the meaning attached to different colours changes over time and between cultures. Take-home message: test your hypotheses, but make sure you don’t limit your alternative hypotheses as well.

*But let me just say that, since many pop evo psych ideas come from observations of Western cultural expectations, if we can disprove it for a sample that fits those expectations, that’s a pretty strong sign.

Johns, S., Hargrave, L., & Newton-Fisher, N. (2012). Red Is Not a Proxy Signal for Female Genitalia in Humans PLoS ONE, 7 (4) DOI: 10.1371/journal.pone.0034669

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I just got back from my most recent field excursion and am completely exhausted. But look, I am nevertheless providing you with things to read! The new species announcements have been piling up for a few months, so here is another roundup of recently discovered or described life forms on this lovely planet of ours.

  • A plethora of colourful, strange-looking creatures from Suriname
  • A tiny deep-water shark from around the Galapagos
  • The littlest chameleons! (Highlights: figures 6, 8, and 10.)
  • One that deserves a lot more publicity: an Amazonian fungus that can eat plastic, potentially helping to break down garbage in landfills
  • A keen-eared herpetologist discovers a new species of leopard frog right smack in NYC
  • Also re: urban New York wildlife, this post is an enjoyable read about engaging non-biologists in nature. There’s not an undescribed species found, but they do discover ants that, though widespread and abundant there, had not previously been documented in New York.

Enjoy! I will tell you all about the Hawaiian rainforest in a few days!

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(or at least the first to make headlines; I don’t actually pay that close attention)

The world’s smallest frogs—in fact, the world’s smallest vertebrates—are two newly described species from New Guinea, Paedophryne amauensis and P. swiftorum. What makes them particularly cool is that they are terrestrial, while the previous holders of the smallest vertebrate title were fish. It was thought that aquatic vertebrates could reach smaller size extremes because of buoyancy-related release from constraints. Apparently this is not so. Here’s the original article describing these two species and one of many media accounts.

Not a new species, but a new discovery about a known species: a Brazilian plant called Philcoxia minensis turns out to be carnivorous. It is unique in that it has underground leaves in addition to its normal leaves that capture and digest small nematode worms.

In cutesy scientific name news, just in time for the arrival of a certain baby of famous parents, entomologists named a species of horsefly Scaptia beyonceae, because its shiny golden abdomen is, as we like to say in the technical literature, “bootylicious”.

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