Coevolutionary constraints may divide Joshua trees

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Scientists love it when the real world validates our more theoretical predictions. It helps, of course, if those predictions are rooted in the real world to begin with. This is more or less what happened in my own research, with results reported in two just-published scientific papers. In the first, which I discussed last week, my coauthor and I showed that some kinds of species interactions can reduce the diversity of the interacting species [PDF]. Today, I’m turning to the second, in which my coauthors and I found exactly this predicted pattern in one such species interaction, the pollination mutualism between Joshua tree and yucca moths.

The new paper, published this month in the Journal of Evolutionary Biology, examines the phenotypic variation of two forms of Joshua tree and the two different moth species that pollinate it. The data show that although the Joshua trees pollinated by different moths are very different from each other, those pollinated by the same moth species are extremely similar [PDF].

Two forms of Joshua tree pollinated by different moth species, seen here side by side, don’t vary much among themselves. (Flickr: jby)

This is a nice confirmation of the theory paper because it strongly suggests that coevolution between mutualists like Joshua tree and its pollinators works the way the theoretical model assumes it does, with natural selection favoring individuals who best match their partners in the other species.

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Iridescent squid!

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Ran across this charmingly animated and scientifically mind-blowing video in the midst of a search for other purposes, and knew I had to post it.

Science online, yawning opossums edition

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Opossums eat lots of disease-carrying ticks. So that’s one thing they’re good for. Photo by graftedno1.

Remember that story about NASA having discovered bacteria using arsenic in place of phosphorous? UBC microbiologist Rosie Redfield ripped into the data underlying that conclusion on her blog RRResearch. (She’s also writing to the journal.) Redfield’s complaints and others prompted a lot of discussion about the the trouble with over-publicized science—see David Dobbs at Neuron Culture and Carl Zimmer on Slate, as well as Zimmer’s comprehensive roundup of scientific criticism of the study. Slate also took the opportunity to re-post an old piece on problems with peer review, but, as Chris Rowan wisely pointed out at Highly Allochthonous, peer review continues after a paper is published, especially in the case of “cutting edge” results like this one.

Meanwhile, in non-arsenic-based science news:

  • “… like the appendix … only more fun.” Scicurious tackles the question of whether female orgasm is adaptive. (Neurotic Physiology)
  • Save the ‘possums. The relationship between mammal diversity, tick host use, and the risk of Lyme disease spread to humans (previously discussed on D&T), rendered into charming narrative form. (EcoTone)
  • Short answer: cancer isn’t smallpox. Why haven’t we cured breast cancer yet? (White Coat Underground)
  • Ho-hum. I mean, wow. Yawning is measurably “contagious” for adult humans, chimpanzees, and dog—but not for children under the age of five. (The Telegraph)
  • Get out and play. Sitting around all day is worse than simply not exercising. (Obesity Panacea)
  • They’re all legs men. Like many other animal species, deep-sea octopodes practice multiple paternity. (SouthernPlayalisticEvolutionMusic)
  • “It’s not just kids who are bullying. Adults are stacking the deck.” Gay teens—especially openly gay teens—”suffer disproportionate punishments by schools and the criminal-justice system.” (Blogtown, NY Times; original article in the journal Pediatrics)

And now, via Craig McClain of Deep Sea News, video that answers the pressing question of what happens when an alligator attacks an electric eel. Don’t watch this if you don’t want to end up feeling bad for the alligator.

Twelve months of Denim and Tweed

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Following DrugMonkey’s example, here’s the first sentence of the first D&T post in each month of 2010:

  • 1 January—Happy New Year! Link.
  • 3 February—Regular readers of Denim and Tweed know that I’m fascinated by the evolution of species interactions: interactions between plants and nitrogen-fixing bacteria, Joshua trees and yucca moths, parasitoid wasps and butterflies, and between ants and the trees they guard. Link.
  • 4 March—Field Season phase I, in which I play tour guide for my parents through the sights of the California and Nevada desert, is now complete. Link.
  • 9 April—Getting serious mileage out of the new camera! Link.
  • 1 May—Here’s a great American, fretting about immigrants: Link.
  • 2 June—I celebrated the Memorial Day weekend by, among other things, not getting around to writing the final installment of the Big Four series, which was scheduled for sometime this week. Link.
  • 2 July—Between the all-day conferencing of Evolution 2010 and the fact that car trouble stranded me in Kennewick, Washington, almost exactly halfway between Portland and Moscow, I haven’t done enough online reading to justify my usual end-of the week roundup. Link.
  • 3 August—For all living things, information is critical to survival. Link.
  • 1 September—The cover article for last week’s issue of Nature promised to be the last word in a long-running scientific argument over the evolution of cooperation—but it really just rejiggers the terms of the debate. Link.
  • 1 October—Okay, I think I have things back under control. Link.
  • 1 sNovember—Scicurious has officially posted her epic compilation of recipes by and for graduate students, i.e., compiled with budget and preparation time in mind. Link.
  • 2 December—Security expert Bruce Schneier thinks that we should close the Washington Monument. Link.

There’s one or two instances of genuine unintentional out-of-context humor there. Also, I write some long-ass sentences, don’t I?

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Not all species interactions are (co)evolved equal

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Biologists have long thought that coevolutionary interactions between species help to generate greater biological diversity. This idea goes all the way back to The Origin of Species, in which Darwin proposed that natural selection generated by competition for resources helped cause species to diverge over time:

Natural selection, also, leads to divergence of character; for more living beings can be supported on the same area the more they diverge in structure, habits, and constitution, of which we see proof by looking at the inhabitants of any small spot or at naturalised productions.
—Darwin (1859), page 128.

In the twentieth century, this idea was extended into suggestions that coevolution between plants and herbivores or flowers and pollinators helped to generate the tremendous diversity of flowering plants we see today. In general, biologists have found that strong coevolutionary interactions are indeed associated with greater diversity.

Yet although there is a well-established association between coevolution and evolutionary diversification, correlation isn’t causation. Furthermore, every species may coevolve with many others, and diversification that seems to be driven by one type of interaction might actually be better explained by another. It has even been suggested that coevolution rarely causes speciation at all.




Species interact in a lot of different ways, as antagonists, competitors, and mutualists. Do all these interactions shape diversity the same way? (Flickr: jby)

One step toward determining how often coevolution promotes diversification would be to identify what kinds of coevolutionary interaction are more likely to generate diversity. This is precisely the goal of a paper I’ve just published with Scott Nuismer in this month’s issue of The American Naturalist. In it, we present a single mathematical model that compares a wide range of species interactions to see how they shape diversification, and that model shows that coevolution doesn’t always promote diversity [PDF].

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Pardon the dust

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I’ve been fiddling with D&T’s formatting yesterday and today, mainly because I want to use a more up-to-date version of Blogger’s template system, including slightly shinier integration of stand-alone pages and the native post-sharing buttons. I think I’ve finally got things about the way I want them.

Getting into the spirit

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There’s nothing like purchasing a grocery bag full of sugar and butter and dark rum and downloading a new Pink Martini holiday album to put me in that Saturnalian spirit. Happy holidays.

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Science online, inhospitable conditions edition

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Precarious, yes, but he’s protecting his sperm count. Photo by Ed Yourdon.
  • Don’t roast your junk, dude. Scicurious takes on the recent study showing that laptop computers can raise dudes’ scrotal temperatures, putting their sperm at risk. (Neurotic Physiology)
  • In case you needed another reason to hate them. A grad student specializing in mutation repair mechanisms considers the risk of the TSA’s new X-ray backscatter body scanners. (My Helical Tryst)
  • Too late to change the name to Phoenix? The neuroscience blog carnival Encephalon is back, in spades. (A Blog Around the Clock)
  • It’s that time of year again. Bora kicks off the lead-up to ScienceOnline 2011 with a series of posts introducing registered participants. (A Blog Around the Clock)
  • More than cat videos. Jonathan Eisen lists the ways blogging and microblogging have contributed to his scientific career. (The Tree of Life)
  • Actually, it’s just an eternal dissertation defense. Neuroskeptic imagines what scientific Hell would be like. (Neuroskeptic)
  • Waterproof sunscreen, anyone? Depletion of the ozone layer may mean whales are at greater risk of sunburn—and skin cancer. (Mental Floss, original article in Proc. Royal Soc. B)
  • Preadaptation for the win. One of the few Australian predators that can tolerate invasive cane toads is a snake that may have evolved the tolerance in response to selection from toxic prey in its ancestral range. (Oh, For the Love of Science)
  • NASA has not found extraterrestrial life. But it has found bacteria that use arsenic in place of phosphorous, which means there’s one more form extraterrestrial life could take. (Nature News, NY Times, Not Exactly Rocket Science; original article in Science [$a])

Regarding that last item, I’ll give the final word to good ol’ xkcd.

Comic by xkcd.

Carnival of Evolution No. 30

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Photo by ricmcarthur.

Or maybe it should be Carnival of Evolution XXX? Anyway, it’s online at This Scientific Life, and full of good posts from all over the evolution-inclined science blogosphere. Go check it out!

Close the Washington Monument

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Security expert Bruce Schneier thinks that we should close the Washington Monument. The most distinctive part of the D.C. skyline has been a challenge to secure, but that’s not Schneier’s reason.

An empty Washington Monument would serve as a constant reminder to those on Capitol Hill that they are afraid of the terrorists and what they could do. They’re afraid that by speaking honestly about the impossibility of attaining absolute security or the inevitability of terrorism — or that some American ideals are worth maintaining even in the face of adversity — they will be branded as “soft on terror.” And they’re afraid that Americans would vote them out of office if another attack occurred. Perhaps they’re right, but what has happened to leaders who aren’t afraid? What has happened to “the only thing we have to fear is fear itself”?

An empty Washington Monument would symbolize our lawmakers’ inability to take that kind of stand — and their inability to truly lead.

Go read the whole thing.

Photo by Scott Ableman.