Are mutualists monogamists, while antagonists play the field?

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ResearchBlogging.orgTwo of the most diverse groups of living things on Earth are flowering plants and the insects that make their living from flowering plants. Biologists have long thought that the almost incessant, intimate interactions between plants and plant-eating insects might be the evolutionary cause of each group’s spectacular diversity. On a smaller scale, this means that we’re interested in the reasons that specific insects and plants interact in the first place—what evolutionary trails leads one insect species to specialize on a single host while others eat pretty much any plant they land on.

A new study of one group of plant-eating insects suggests that the kind of interaction between insects and their host plants also determines how specific those interactions are. Examining a group of moths that, like the yucca moths I study, pollinate their host plant and then eat some of its seeds, the authors of the new study find that related, non-pollinating moths use more host plant species than the pollinators [$a]. I think it makes a particularly nice companion piece to my post about the evolutionary origins of yucca moths, because it provides an example of one or two other things biologists can deduce from phylogenies—and, as we’ll see, some things they can’t.

Epicephala: like a yucca moth without the snappy name

The moths in question are in the genus Epicephala, and they have an obligate pollination relationship with trees in the genus Glochidion, a diverse group of plant species found in southern Asia. That is, female moths carry pollen between Glochidion flowers in special mouthparts, deliberately apply pollen to the flower, and then lay eggs in the flower so that, when it develops into a fruit, her larvae can eat some of the seeds inside. Epicephala species are highly specialized, with most species only using one species of Glochidion [$a]. That’s a higher degree of specialization than what’s seen in yucca moths, in fact.

Pollinating moths (genus Ephicephala, left) use fewer host plant species than related non-pollinating moths (genus Caloptilia, right). Photos by CharlesLam and Bettaman.

The family of which Epicephala is a member happens to include other moths that interact with Glochidion, but only as herbivores: species in the genera Caloptilia and Diphtheroptila, whose larvae all eat Glochidion leaves. Do these antagonistic moths use more, or fewer, species of the host plant than the mutualistic Epicephala? Kawakita and his coauthors set out to answer that question by reconstructing the phylogenies of Caloptilia and Diphtheroptila.

Finding species in evolutionary trees

Most biologists agree that two groups of organisms are separate species if there is no gene flow between them. A consequence of genetic isolation between species is that, if they’re isolated long enough, they become monophyletic within phylogenies. That is, all the individuals within each species share a common ancestor that is not shared with any other species. You can see this by contrasting two monophyletic species (on the left in the figure below) with two groups that turn out to be paraphyletic—some individuals of the red species are more closely related to individuals of the blue species than to other individuals of their own species.

Monophyletic and paraphyletic groupings. Image by jby.

The reasoning behind this is a bit subtle. Paraphyletic groups might still be separate species—they just haven’t been isolated long enough to become monophyletic. As a good example, I’m a coauthor on a recent study that did this kind of analysis on non-pollinating “bogus” yucca moths that use three different yucca species. In that case, the moths were paraphyletic with respect to which yucca species they used, but more analysis showed that there is currently very little gene flow between moths using different hosts [PDF].

In the case of the Glochidion-using Caloptilia and Diphtheroptila, Kawakita et al. found something more complicated. Each genus broke up into several monophyletic groupings, or clades of genetically similar individuals—but in most cases each clade included moths collected from at least two different Glochidion species. Kawakita et al. note that the clades also correspond to differences in the moths’ wing coloration, larval feeding behavior, and genitalia, and conclude that each clade is a different species. That would mean that the two antagonist genera tend to use multiple host plants.

Interesting question, but is this the way to answer it?

Except I’m not sure I buy this usage of phylogenies to define species. Kawakita et al. have shown that within the clades they call species, the individuals all have very similar genetics, but only for the two commonly-used genetic markers from which the phylogenies are reconstructed. It’s not impossible that within each clade the moths might be adapted to individual host plant species, and reproductively isolated by that adaptation—and this could have happened recently enough that not many genetic differences would have built up in the two markers.

To really answer the question Kawakita et al. have posed would require a study of each clade in the two antagonist genera at a much finer scale. The question of how specialized Caloptilia and Diphtheroptila are hinges on how many species are in each genus, and that’s better addressed by examining population genetics, not ancient relationships among these genera.

Reference

Drummond, C., Xue, H., Yoder, J., & Pellmyr, O. (2009). Host-associated divergence and incipient speciation in the yucca moth Prodoxus coloradensis (Lepidoptera: Prodoxidae) on three species of host plants. Heredity, 105 (2), 183-96 DOI: 10.1038/hdy.2009.154

Kawakita, A., & Kato, M. (2006). Assessment of the diversity and species specificity of the mutualistic association between Epicephala moths and Glochidion trees. Molecular Ecology, 15 (12), 3567-81 DOI: 10.1111/j.1365-294X.2006.03037.x

Kawakita, A., Okamoto, T., Goto, R., & Kato, M. (2010). Mutualism favours higher host specificity than does antagonism in plant-herbivore interaction. Proc. Royal Soc. B, 277 (1695), 2765-74 DOI: 10.1098/rspb.2010.0355

Scienceblogging.org will be one-stop shop for, um, exactly what it says on the tin

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And right on the heels of the Carnal Carnival launch, Bora has another big announcement: a new site aggregating online science writing from pretty much everywhere, appropriately located at scienceblogging.org. The site draws from every science blogging collective I follow—ResearchBlogging, Discover Blogs, Wired Science, Field of Science, the still-shiny new Scientopia, and good ol’ ScienceBlogs—along with a lot I don’t run across as often.

Right now there’s a single page listing recent feed results from all these group blogs, and another devoted to science-y blog carnivals, but no independent blogs (ahem), and no particular way of sorting through the contents. It looks more like a starting point than a finished product, and that’s just fine—Bora and his co-founders Anton Zuiker and Dave Munger are still looking for input. Says Dave:

The site is really just an aggregator of aggregators. Everything you see on the front page is a feed from some other bundle of blogs. In a couple cases, we made our own bundles using Friendfeed. The site is flexible enough to add additional bundles as bloggers and publishers form new blogging communities. It’s not ideal — I think the ultimate science blog aggregator will allow users to view blog posts by topic, and perhaps have some way of identifying the best posts. But it’s flexible enough that with some input from the community, we might be able to shape it into something really special. Check it out, and let us know what you think.

As a blogger without a network, I’m naturally interested in seeing independent blogs added to the ScienceBlogging.org stream (although, as Bora points out, we’re already partially accounted for by including the Research Blogging feed). The large number of indy science bloggers would make this challenging, to say the least, but I think many of the issues are the same ones that show up, in smaller scale, on the new ScienceBlogging.org homepage—how to make it easy for a visitor to sift through a large number of posts to find writing by particular people, on particular topics, written in a particular time-frame.

Maybe what’s needed is an analogue to ResearchBlogging that aggregates all posts from member blogs and sifts them into topic-labeled feeds—but that’s a whole different class of infrastructure, and effort from member blogs, than what’s provided at the new site right now. Still, the value of a true one-stop shop for online science writing should be great enough to justify the effort. In the meantime, I’ve added a new bookmark, and I’ll be keeping an eye on ScienceBlogging.org.

Introducing the Carnal Carnival

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A brand-new blog carnival promises to unleash the naughtier impulses of the science blogosphere which, let’s be frank, were never particularly tightly leashed to begin with. Except for the ones that are into that sort of thing.

Ahem.

Anyway, the inaugural edition of the Carnal Carnival is now online at A Blog Around the Clock, where host Bora Zivkovic called for any and all posts relating to poop, feces, dung, and/or excreta. The only shit-related question left unanswered in this fecund roundup is, shouldn’t they have saved this topic for Carnal Carnival #2?

Science online, older than we thought edition

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A little brown bat covered with the white nose fungus. Photo by U.S. Fish and Wildlife Service, Northeast Region.
  • First Ginsu salesman still millions of years away, though. Newly discovered bones bear scratch marks that could have been made by flaked stone cutting tools 3.4 million years ago—more than 800 thousand years earlier than previous evidence of such toolmaking by human ancestors. (Greg Laden’s Blog, Not Exactly Rocket Science)
  • I thought they said it had all magically disappeared? As much as 70% of the oil spilled by the now-plugged Deepwater Horizon well is still out there, somewhere. In fact, it’s probably suspended in the deep ocean, where microbes expected to break down oil may take months to finish it off. (Deep Sea News, Wired Science)
  • Thesis, antithesis. Synthesis! Razib Khan describes how R.A. Fisher united Mendelian genetics and quantitative trait theory into a single mathematical model. (Gene Expression)
  • Really? Life doesn’t look a day over 640 million. New 650-million-year-old fossils may be the oldest examples of animal life. (Science Daily, Highly Allochthonous)
  • Being pecked to death never looked so unpleasant. Stress analysis of terror bird skulls suggest they killed prey by repeatedly stabbing it with the dagger-like tip of their beaks. (Not Exactly Rocket Science)
  • Is there an HVAC engineer in the house? We might be able to save bats from white-nose syndrome by heating their hibernation caves. (Wild Muse)

And now, via Ed Yong and BoingBoing, Humbolt penguins chasing a butterfly:

Pakistan

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I would hope you don’t have to be as much of a news junkie as I am to know that, right now, tens of millions of people have just watched their lives—fields, homes, entire villages—wash away in Pakistan. (NASA has some astonishing
before-and-after images.) For reasons political and logistical, aid is not arriving very fast where it’s most needed. So let me take this opportunity to suggest that my readers direct a contribution to Doctors Without Borders/Médicins Sans Frontières, which was on the scene pretty much from the start. I make a (very small) monthly contribution to MSF, which they like because it’s income they can count on—if you can, I’d suggest going that route.

Satellite image of flooding in Nowshera, taken 5 August. Photo by DigitalGlobe-Imagery.

Re: Cite more papers, get more citations?

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Courtesy Zen Faulkes’s Twitter feed: Philip Davis of the Scholarly Kitchen shows that the study I discussed earlier, purporting to show that journal articles that cite more sources are themselves more likely to be cited is, um, quite probably bunk. Davis was skeptical of the cite-more-be-cited-more (henceforth, CMBCM) correlation, so he did what any good scientist would, on reading a result he didn’t believe: he tried to replicate it, collecting his own data set from articles published in the journal Science in 2007.

Davis replicated the CMBCM result with his own dataset, but then he started looking for other correlations in the data. It turns out that longer papers are also more likely to be cited—and, when Davis statistically controlled for that effect, the CMBCM result not only disappeared, it reversed. That is, long Science papers with more citations are slightly less likely to be cited than long Science papers with fewer citations. Building a still more complicated statistical model that incorporates the paper’s length, subject area, and number of authors, Davis totally eradicated the effect of variation in the length of the Works Cited list.

Controlling now for pages, authors, and section, reference list length is no longer statistically significant. In fact, it looks pretty much like a random variable (p=0.77) and adds no information to the rest of the regression model.

Davis’s analysis looks convincing to me. It’s hard to say, however, whether it conclusively refutes the result reported in Nature News. That’s partly because the CMBCM analysis is derived from a much larger data set than Davis’s; but more importantly, it was presented at a conference, not in a published article.

Conference papers often present preliminary results, and in the absence of a published Methods section, the News article doesn’t tell us whether the coauthors controlled for the effects of the confounding factors Davis identifies or not. (Although it seems logical to conclude from the News piece that they didn’t.) If the CMBCM data set is going to make it through peer review at a journal, however, its authors will have to account for confounding factors.

If your idea of a fun time might include snarky dissection of illuminated manuscripts,

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Then you should definitely be following Got Medieval. You might also consider checking out Carl Pyrdum’s blog if your idea of a good time might include being told another way in which Newt Gingrich is an ass. If your idea of a good time does not involve such things, consider following those links anyway; you many rapidly change your mind.

Turning up the alarms makes aphids careless

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ResearchBlogging.orgThe oven in my apartment needs a serious deep-cleaning. A really serious deep-cleaning. To the point that, when I want to do some baking, smoke is more or less inevitable. As a result, I’ve developed the habit of responding to the apartment’s smoke alarm by reaching up and un-mounting it from the ceiling, which completely disables it. If a fire were to start somewhere else in the apartment while I’m baking, I’d probably be in trouble.

That’s more or less the idea behind an approach to agricultural pest control proposed in a paper just released online at PNAS: if you saturate insect pests with a predator warning signal, they become used to the signal, and more vulnerable to predators [$a]. Aphids are the target pest—they form huge, clonal swarms to literally suck the life out of plants, as described very nicely in this BBC Nature video.

As the video notes, those clonal swarms are vulnerable to all sorts of predators, most famously ladybird beetles. So when attacked, the aphids emit an alarm pheromone to warn the rest of the clone. But it’s possible to habituate aphids to the alarm pheromone—if they’re surrounded by it long enough, they won’t respond to it by running away. The new study’s authors proposed genetically engineering crop plants to produce the alarm pheromone, to automatically produce that habituation.

To see if this would work, they raised aphids on a line of Arabidopsis thaliana (the white lab mouse of the plant world) that had been engineered to produce the alarm pheromone. And, indeed, habituated aphids were much less likely to be repelled by the alarm pheromone—and were even in some cases attracted to it. Perhaps the most telling test involved leaving habituated and non-habituated aphids on an experimental plant with ladybird beetles introduced—habituated aphids were less likely to survive 24 hours with the beetles.

This is a pretty clever approach to pest control, but there’s an obvious caveat. I don’t see any reason why aphids couldn’t evolve a way around this attempt to swamp out their own alarm signals—the paper notes that different aphid species have different responses to the particular alarm pheromone tested, so engineering one pheromone into crop plants doesn’t leave the aphids without evolutionary options. Unless it’s very cleverly designed, any pest-control strategy creates strong natural selection—and the better the strategy is, the stronger the selection is—to evolve resistance. Alarm-pheromone-producing crops might be another tool for pest control, but they won’t be the last one we need.


A ladybird beetle makes short work of some aphids. Photo by kenjonbro.

See also this press release from Cornell University, which discusses the paper’s results.

Corrected, 17 Aug 2010, 2305h: Fixed the photo of the ladybird with aphids, which was meant to be full-width, and added a jump. Why do I keep forgetting those?

Reference

de Vos, M., Cheng, W., Summers, H., Raguso, R., & Jander, G. (2010). Alarm pheromone habituation in Myzus persicae has fitness consequences and causes extensive gene expression changes. Proc. Nat. Acad. Sci. USA DOI: 10.1073/pnas.1001539107

Giants Shoulders #26 online at Neurotic Physiology

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Host Scicurious has just posted the 26th edition of the Giant’s Shoulders history of science blog carnival, and wow, it’s a doozy. The “Fools, Frauds, and Failures” theme drew a huge list of contributions in all three categories (including my own piece on Sewall Wright and Linanthus parryae). And Sci introduces it all with a lovely olde-worlde flourish.

Greetinges, all ye who enter here.
Beholde, before you doth appear
A moste unusual carnivale!
And this one hath a grand moral.
This speakes of fools, failures and fraudes.
Those findings no longer we applaude.

I may very well spend the rest of the month until the next edition reading it all.

Cite more papers, get more citations?

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Update, 18 August 2010: An attempt to replicate the result discussed here finds serious issues with the statistics.

ResearchBlogging.orgNature News is reporting some interesting results presented as a paper at a meeting of the International Society for the Psychology of Science & Technology last week: articles published in the journal Science with longer “Works Cited” sections are themselves more frequently cited.

A plot of the number of references listed in each article against the number of citations it eventually received reveal that almost half of the variation in citation rates among the Science papers can be attributed to the number of references that they include. And — contrary to what people might predict — the relationship is not driven by review articles, which could be expected, on average, to be heavier on references and to garner more citations than standard papers.

The same authors did a similar analysis of papers published in the journal Evolution and Human Behavior over 30 years, and found similar results [PDF]. Here’s the relevant figure from that paper:

Cite more, be cited more. Figure 2 from Webster et al. (2009) [PDF].

The lack of a “review effect” is surprising, but I don’t think this overall result is. Academia, as much as we might describe it as cutthroat, also runs on reciprocal altruism. Authors notice when their papers are cited, and are more likely to cite papers that build on or relate to their own work. I’d be interested to see the network of citation underlying the pattern Webster et al. have found—I suspect that there’s a lot of clustering around disciplines and sub-disciplines and sub-sub-sub-disciplines that contributes to all this mutual back-scratching citing.

Updated, 15 August 2010, 2126h: Fixed the link to the original Nature News article, which turns out not to be access-restricted.

Reference

Webster, G.D., Jonason, P.K., & Schember, T.O. (2009). Hot topics and popular papers in evolutionary psychology: Analyses of title words and citation counts in Evolution and Human Behavior, 1979-2008. Evolutionary Psychology, 7 (3), 348-348 Other: http://www.epjournal.net/filestore/ep07348362.pdf