Monthly Archives: October 2009

Video of yucca pollination

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ResearchBlogging.orgWith permission from my doctoral advisor, Olle Pellmyr, I’ve just uploaded a unique video to Vimeo: a yucca moth laying eggs in, then pollinating, a yucca flower. I don’t know why I didn’t think of this earlier — it’s great footage, and deserves to be seen more widely.

A female yucca moth mates, then collects pollen from a yucca flower in specialized mouthparts. She carries it to another flower where, as shown in the video, she drills into the floral pistil with her ovipositor and lays eggs inside, then climbs to the tip of the pistil and applies pollen to fertilize the flower. When the flower develops into a fruit, the eggs hatch and the caterpillars eat some of the seeds inside.

Yuccas and yucca moths are completely dependent on each other [PDF] — nothing else pollinates yuccas, and the moths have no other source of food (they don’t eat as adults). Recently, the Pellmyr lab has shown that this interaction may be leading to speciation in one yucca species, the Joshua tree — Joshua trees pollinated by two different species of yucca moths have differently-shaped flowers [PDF], but these two tree types may not be totally genetically isolated [PDF]. I’ve written about this work before — for more information about the interaction, check out Olle’s publication page.

References

Godsoe, W., Yoder, J., Smith, C., & Pellmyr, O. (2008). Coevolution and Divergence in the Joshua Tree/Yucca Moth Mutualism. The American Naturalist, 171 (6), 816-23 DOI: 10.1086/587757

Pellmyr, O. (2003). Yuccas, yucca moths, and coevolution: A review. Annals of the Missouri Botanical Garden, 90 (1) DOI: 10.2307/3298524

Smith, C., Godsoe, W., Tank, S., Yoder, J., & Pellmyr, O. (2008). Distinguishing coevolution from covicariance in an obligate pollination mutualism: Asynchronous divergence in Joshua tree and its pollinators. Evolution, 62 (10), 2676-87 DOI: 10.1111/j.1558-5646.2008.00500.x

First step to mutualism doesn’t look so friendly

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This post was chosen as an Editor's Selection for ResearchBlogging.orgAnt-plant protection mutualism is a widespread and elegant species interaction. How do species strike bargain like this, requiring specialized behaviors and structures in each partner, in the first place? A new report in The American Naturalist suggests an answer: maybe ants took the initiative [$-a].

In exchange for protection from herbivores and competitors [big PDF], “myrmecophytic” host plants grow hollow structures called domatia and often produce nectar to shelter and feed a colony of ants. This mutualism is really a sort of negotiated settlement between the partners; both ants and plants do what they can to get the most out of the interaction. We have evidence in some cases that host plants cut back support for ants if there aren’t any herbivores around; and, in other cases, that ants prune their host plants to prompt the growth of more domatia.



Domatium diversity: Ant domatia on Acacia (above) and Cordia nodosa (below). Photos by Alastair Rae and Russian_in_Brazil.

So it isn’t entirely surprising that there might be cases where that bargain hasn’t been established yet, and that’s what the new paper reports. The observation turned up in connection with one of the most interesting forms of the ant-plant mutualism: the “devil’s gardens” of the Amazonian rainforest. Devil’s gardens are created by colonies of the ant Myrmelachista schumanni, which attacks possible competitors to its preferred host [$-a], Duroia hirsuta, leaving patches where nothing but D. hirsuta grows.

Clued in by native research assistants, the group studying the devil’s garden interaction discovered that trees growing at the edge of a garden are often afflicted with swollen, distorted trunks. Cutting into the swellings, they found them riddled with passages and populated by M. schumanni. The trees in question are not known as myrmecophytes, and it’s not clear that they receive any benefit from hosting ants. In fact, the authors report that ant-occupied trunks are weakened, and prone to breakage under their own weight or under heavy wind.

The paper doesn’t present direct evidence that the ants create the galls, but as the authors explain, this seems likely — M. schumanni kills its hosts’ competition by injecting them with formic acid, which parallels the irritants other gall-making insects inject into their host plants. It make sense that gall-making might have started as ants’ attempts to kill off trees that are too big to succumb to formic acid outright, but respond to it by growing galls like scar tissue. Furthermore — and this is pure speculation, of course — this looks like a first evolutionary step toward true ant-plant mutualism. Domatia may have originally evolved to redirect ants from more damaging gall-making, and since ants are naturally territorial about their nests, it might not take much behavioral change before they end up protecting their host.

References

Edwards, D., Frederickson, M., Shepard, G., & Yu, D. (2009). A plant needs ants like a dog needs fleas: Myrmelachista schumanni ants gall many tree species to create housing. The American Naturalist, 174 (5), 734-40 DOI: 10.1086/606022

Frederickson, M., Greene, M., & Gordon, D. (2005). “Devil’s gardens” bedevilled by ants Nature, 437 (7058), 495-6 DOI: 10.1038/437495a

Janzen, D. (1966). Coevolution of mutualism between ants and acacias in Central America Evolution, 20 (3), 249-75 DOI: 10.2307/2406628

Oh, and by the way …

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I’m gay.

I came out of the closet just a few months ago — but that’s a story I probably won’t recount in any detail on D&T, which has never included much detail about my personal life, and probably never will. I debated whether to write even a brief post like this, and finally decided to do so only because this is a part of my personal experience that colors what I discuss here. And, what the heck, today is National Coming Out Day. Cheers.

PS: For blogging on the politics and personal issues of gay identity, see Dan Savage and Andrew Sullivan, in that order. They’ve strongly shaped my own views in my journey so far, and are much more eloquent and authoritative than I could hope to be. For discussion of homosexuality in an explicitly Mennonite context, see PinkMenno.

Update, added 9 November 2010: Further explanation for my decision to come out online may be found here.

Aiming at a moving target with a shaky pistol: Evolution in a random, changing world

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ResearchBlogging.orgBiologists can become distinctly cranky when we hear evolution described as “random.” This is because evolution isn’t random — it’s undirected. Although it acts on mutations that turn up randomly, natural selection is highly nonrandom, in that (all else being equal) traits that help their owners make more babies are always the ones that spread through a population.

However, even if natural selection predictably aims for the same target, that target is not necessarily fixed. The most obvious case of this is in the coevolution of interacting species, where adaptation by one forces adaptation in the other. This is a field of study in its own right; but one recent innovation is a theory paper by Gandon and Day, which tracks changes in the “fitness landscape” resulting from adaptations and counter-adaptations [$-a]. (For more detail on the paper, see Coevolvers.)


Ground finches (Geospiza fortis) with big beaks might be favored this year, but what about next? Photo by kookr.

Empirical studies have shown that selection’s target can move in unexpected ways, too. One of the best examples of this turned up in the course of the ongoing, decades-long study of finches on the Galapagos Island Daphne Major. As rainfall on the island fluctuated from year to year, the mix of available seeds changed as well, and the finches’ beaks — the size of which determines what seeds are easily cracked and eaten — evolved to keep up [$-a]. The resulting evolutionary path looks like a drunkard’s walk, and the study’s authors, Peter and Rosemary Grant, put the word unpredictable right in the title.

Making things still more complicated, there is actually a random component to the effects of natural selection. That is, in the real world, advantageous traits may not automatically result in greater fitness — they result in greater expected fitness. Last year, Sean Rice published a mathematical model of evolution in which fitness is a random variable. He found that greater variation around the expected fitness can increase the strength of natural selection; that is, more uncertainty about the relationship between fitness and a given trait may actually make that trait adapt more rapidly. In a just-published extension of this work, Rice and Anthony Papadopolous examined the effect of random migration among different populations on adaptive evolution in each population, and found that greater variation in migration rates can reduce the effect of migration on local evolution.

Introducing all this randomness into our view of evolution doesn’t necessarily make evolution unpredictable. As an excellent recent Radiolab episode discusses, there are patterns to be extracted from randomness. It takes more work — larger sample sizes, longer-term studies — for these patterns to become apparent. Yet it’s clear that this is work we’ll have to do in order to understand biological systems.

References

Gandon, S., & Day, T. (2009). Evolutionary epidemiology and the dynamics of adaptation Evolution, 63 (4), 826-38 DOI: 10.1111/j.1558-5646.2009.00609.x

Grant, P., & Grant, R. (2002). Unpredictable evolution in a 30-year study of Darwin’s finches Science, 296 (5568), 707-11 DOI: 10.1126/science.1070315

Rice, S. (2008). A stochastic version of the Price equation reveals the interplay of deterministic and stochastic processes in evolution BMC Evolutionary Biology, 8 (1) DOI: 10.1186/1471-2148-8-262

Rice, S., & Papadopoulos, A. (2009). Evolution with stochastic fitness and stochastic migration PLoS ONE, 4 (10) DOI: 10.1371/journal.pone.0007130

Wait, let me get this straight …

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The compromise that might actually get us a nationwide, publicly-financed insurance plan — what many are calling a “public option” — is to make it optional? Well, at least the crazy is flowing the way I’d prefer, for once.

Snark aside, the compromise is to make the public option “optional” at the state level — states can opt out if they want, presumably through legislative action. Sounds fine to me. The point of a public option is to make it big, and the big blue states — California, New York, &c — won’t opt out. It’ll be (mostly) smaller, hyperconservative states that — Mississippi, Alabama, Idaho — are most likely to do so. That’s unfortunate, because these are also poor states, with lots of citizens who would benefit from public health insurance — but at least their legislatures can be crazy on their own, and not derail it for the rest of the country.

This is also one more reason I’d better find a postdoc somewhere outside of Idaho.

Empirical pacifism?

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ResearchBlogging.orgSlogger Charles Mudede points to a new epidemiological study on the effectiveness of carrying a gun for self defense [$-a]. Not only does packing heat fail to help in the event of an armed robbery,

… individuals in possession of a gun were 4.46 (P < 0.05) times more likely to be shot in an assault than those not in possession. Among gun assaults where the victim had at least some chance to resist, this adjusted odds ratio increased to 5.45 (P < 0.05).

That’s right, carrying a gun increases the odds that you’ll be shot by an armed assailant. It also increases the odds that you’ll be shot fatally, by about 4.23 times. The authors interviewed 677 gun assault victims in Philadelphia, from between 2003 and 2006, with 648 interviews drawn from the general population in the same period as a control. (If you can’t get to the paper on the journal website, Mudede links to a ScienceDaily article about the result that gives more detail.)

Here’s empirical evidence that returning violence with violence (or having the ability to do so) doesn’t lead to better outcomes — unless, of course, you’re of the school of thought that it’s better to be shot than to lose your wallet or your pride. I doubt this will have much impact on the U.S. political conversation about guns and gun control, because as I’ve noted before, this is not a subject about which people think rationally. Nevertheless, it’s a statistic I intend to remember for the next time I’m asked to defend the ethics of nonresistance.

Reference

Branas, C., Richmond, T., Culhane, D., Ten Have, T., & Wiebe, D. (2009). Investigating the link between gun possession and gun assault American Journal of Public Health DOI: 10.2105/AJPH.2008.143099

A radical idea

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Responding to Nature‘s review [$-a] of his new book about evolution, The Tangled Bank, Carl Zimmer objects to the reviewer’s justaposition of his work with the more, shall we say, combative book Richard Dawkins has just released. Zimmer has the audacity to assume that his readers aren’t hostile:

I envisioned my potential readers as curious people who didn’t know much about evolution–what the idea actually is and how scientists study it. I envisioned people who might be interested in learning the nuts and bolts of processes like selection and drift, and who might be intrigued by sexually deceptive wasps, whales with legs, the viruses that dominate our genome, and other features of life that evolution allows us to understand.

With all due respect for those who want to take the fight to the wingnuts in the war on science — I enjoy Pharyngula as much as the next grad student — this seems so much more, well, hopeful. Ultimately, it might even be more productive.

Growing up in a science-friendly household surrounded by creationists, I didn’t come to the conclusion that evolution was true because I read a diatribe about the idiocy of biblical literalism. I came to that conclusion because I thought dinosaurs were pretty cool, and it turned out that you could learn a lot more about dinosaurs in the context of their evolutionary history than if you just assumed they all died in Noah’s flood. I think that people in a similar state — “curious people who didn’t know much about evolution” are much more likely converts to the cause of science than the wingnuts. Certainly there must be a lot of them out there; otherwise who’s keeping the Discovery Channel afloat?