Queering ecology

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Eastern bluebird, car. Photo by Automania.

Via Kate Clancy at Context and Variation: Alex Johnson takes a look at the way we think and write about the natural world, and finds it wanting.

Our culture sets Nature as the highest bar for decorum, while simultaneously giving Nature our lowest standard of respect. Nature is at our disposal, not only for our physical consumption, but also for our social construction. We call geese beautiful and elegant and faithful until they are shitting all over the lawn and terrorizing young children. Then we poison their eggs. Or shoot them.

Having popped the naturalistic fallacy with a few pokes, Johnson proposes queering ecology—a deliberate reference to the term’s usage in human sexuality—to better acknowledge the complications of the natural world and humans’ relationships to it. That summary doesn’t do the work justice, though—go read the whole thing.

(Kate linked to this more-or-less alongside my first volley in the old adaptive homophobia kerfuffle, but Johnson’s essay is another order of thought altogether. Also, how cool is it that I can just go to Flickr and find an illustration for Johnson’s point with a simple keyword search? Pretty cool, I think.)

How can you tell if a plant is carnivorous? Feed it!

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A Venus flytrap closes on an unfortunate spider. Photo by cheesy42.

ResearchBlogging.orgPlants that eat animals offend our trophic sensibilities. Those of us who can move independently are supposed to eat those of us who can make sugar from sunlight—that’s just the way the food chain works, right?

Well, not really. From a certain perspective, plants prey on animals all the time, using the sneaky strategy of just waiting us out—when we animals stop moving for good, we’re fertilizer. And there are quite a few plants that aren’t so patient. Venus flytraps, sundews, and pitcher plants have been recognized as carnivores since before Charles Darwin devoted a book to their ecology and anatomy. They all have structures—fly-trapping leaves, or sticky hairs, or deep pitfalls full of water—that are uniquely good at catching wayward insects. All of them also grow in particularly nutrient-poor soils, such as bogs, where the nitrogen from trapped insects makes a big difference.

The vast majority of plants lack either adaptations for trapping, or the same kind of need for nitrogen—they either don’t grow where they can’t get the stuff, or they hire symbiotic bacteria to help fix it. Yet there is a third category of plants, which are not exactly carnivorous, but which might just “eat” the occasional stray fly anyway. Many plants have hairy surfaces that can catch insects, or leaf structures that trap water and create pitfalls—and some of these plants can take advantage of the critters caught in these proto-traps.

Sticky purple geranium can trap insects on its sticky leaves, and seems to get some nutrition out of them. Photo by jby.

One such plant is the sticky purple geranium (Geranium viscosissimum), which grows on dry Palouse hillsides around my current hometown of Moscow, Idaho. As its name implies, sticky purple geranium is sticky—its leaves are velvety with tiny glandular hairs, which leave a gummy residue on your hands if you brush against them. These hairs make it difficult for small insect herbivores to get to the leaves—but they also trap some of those insects.

Back in 1999, a biologist in my department at the University of Idaho, George Spomer (who left the department before my arrival), showed that sticky purple geranium leaves would digest a protein film pressed against them, somewhat like the leaves of a sundew. When Spomer placed protein labeled with carbon-14 on geranium leaves, he found elevated levels of carbon-14 elsewhere in the plant, suggesting that geranium leaves could absorb protein as well as digest it [$a].

Spomer demonstrated that the plants he studied could digest and absorb insects caught on their leaves, but his data can’t tell us whether that ability is of any particular use to a geranium growing in a natural population—whether, that is, geraniums actually need the nutrients they might get from trapped insects. A more recent study of another possibly carnivorous plant gets closer to answering that question.

Water collected in the leaves of a teasel plant forms a death trap for insects, and a source of nitrogen for the plant. Photo by HermannFalkner/sokol.

The plant in this second study is fuller’s teasel, Dipsacus fullonum, a widespread European wildflower that has been introduced into North America. The leaves of many teasel plants form catchments (pictured above) that can collect water and form a makeshift pitfall, which catches and drowns small insects. It has been speculated that, like sticky purple geranium, fuller’s teasel can absorb nutrients from these catchments full of rotting insect corpses. British biologists Peter Shaw and Kyle Shackleton set out to test this hypothesis not by tracking protein from trapped insects, but by determining whether teasel plants benefit from the trapping.

To do this, Shaw and Shackleton experimentally manipulated the number of insects trapped in the catchments formed by teasel plants’ leaves. In one treatment, they watched experimental plants and removed insects as soon as they were trapped; in the other, they “fed” the experimental plants an extra bluebottle maggot at set intervals. They compared both treatments to a group of plants that were left un-manipulated as a control. The “fed” plants didn’t necessarily grow bigger or produce more seeds, but they did produce more seeds as a proportion of their total biomass. That is, fuller’s teasel plants that trap more insects can devote more of their resources to making seeds.

Does this make fuller’s teasel carnivorous? Maybe, but probably not in the same sense that a Venus flytrap is. Teasels tend to grow in better soil than carnivorous plants do in general—they like open fields and stream banks, in my experience. Furthermore, we don’t have any evidence that teasels actively attract insects, as most carnivorous plants do. On balance, it seems far more likely that what Shaw and Shackleton found is not carnivory as we usually know it, but plants making sure that a handy source of nitrogen doesn’t go to waste.

Fuller’s teasel relies on insects for pollination—but does it also rely on them for nutrition? Photo by gynti_46.

References

Darwin, C. (1875.) Insectivorous plants. Google Books link.

Shaw, P., & Shackleton, K. (2011). Carnivory in the teasel Dipsacus fullonum — The effect of experimental feeding on growth and seed set. PLoS ONE, 6 (3) DOI: 10.1371/journal.pone.0017935

Spomer, G. (1999). Evidence of protocarnivorous capabilities in Geranium viscosissimum and Potentilla arguta and other sticky plants. Int. J. Plant Sci., 160 (1), 98-101 DOI: 10.1086/314109

Carnival of Evolution, April 2011

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Tree, sunset. Photo by Voyageur solitaire-mladjenovic_n.

Arriving with the commendable and clocklike regularity of Grendel attacking Hrothgar’s meadhall, the Carnival of Evolution returns for another month, this time hosted by Quintessence of Dust. Check it out for a month’s worth of online writing about all things evolutionary, all in once nice, tidy post.

(naked fisticuffs are always optimal)

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Via Got Medieval: Myths RETOLD does exactly what it says on the tin, with ATTITUDE. For instance, Beowulf. Here’s our hero awaiting the murderous monster Grendel’s highly predictable arrival after the party in Hrothgar’s meadhall:

then the party kind of starts to wind down
so beowulf just goes ahead and strips naked
in the hopes of making this task as needlessly difficult as possible
which actually he fails to do
because it turns out no weapon on earth can harm grendel anyway
so naked fisticuffs are optimal
(naked fisticuffs are always optimal)

anyway Grendel shows up
makes a big show of ripping the doors off
which actually begs the question
do they replace the doors every day?
or does Grendel replace the doors every day
just so he will have something to rip off at night?
either way he immediately eats one of Beowulf’s men
while Beowulf stands there like HMM I SEE
INTERESTING

Even if you haven’t read the original, you will laugh painfully hard. Expect seriously salty language, but nothing that Beowulf himself wouldn’t use if he had a MySpace page.

Science online, “healthy as radium” edition

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Wristwatches have a surprisingly deadly history. Photo by wjhall31.
  • In which a new technology loses its shine. World War I helped create a fashion for wristwatches with radioactive glow-in-the-dark faces—a fashion that turned deadly.
  • Not gay, just confused. Really. Male mice with low serotonin are sexually interested in both males and females, but this is could be because lack of serotonin makes them less sensitive to smell.
  • Wow. A 1987 outbreak of radiation poisoning in central Brazil didn’t actually start with an egg sandwich, but the sandwich is when folks started to notice.
  • Just as nuclear power is starting to look extra scary. A new “artificial leaf” uses sunlight to efficiently generate hydrogen from water.
  • Useless and potentially harmful. Not only does human chorionic gonadotropin not help with weight loss as popularly thought, it can also transmit mad-cow disease.
  • Perfect for reading while in queue. Why do airline passengers jostle for quicker access to reserved seats? Maybe because waiting is territorial.
  • No one is an island, but we might all be lakes. Advances in understanding the immense diversity of microbes every human being carries around may make medicine more like ecology.

After a long stretch of linkfests bereft of moving pictures, here’s video of a wasp deliberately removing ants from its food. Via Ed Yong, who provides more explanation based on the journal article from which this comes.

“Women definitely like heated seats.”

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Savage Car Talk mashes up the Magliozzi Brothers’ Public Radio automotive advice show with questions submitted to Dan Savage’s no-holds-barred sex and relationship advice podcast. The result is not suitable for work, unless you work in an automotive-themed gay bar.

This makes total sense. Dan takes a pretty left-brained, mechanistic approach to the relationship problems brought before him. Click and Clack talk about relationships almost as much as they discuss cars. Many times, I’ve run across relationship and automotive problems of my own that seemed like they would be worthy of a phone call to the appropriate show—only to realize I already knew the answer thanks to long hours of listening to advice given to other people.

Also, I’ve heard that almost a third of Dan’s misanthropic snark is added in post-production.

Via Dan Savage. I’m still waiting to hear what the Car Talk guys think.

You’re a sad man, Charlie Brown

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Via HiLoBrow: 3eanuts removes the fourth panel from “Peanuts” cartoons, and with those fourth panels goes the leavening of humor from Charles M. Schulz’s bleak world. As the AV Club points out, this doesn’t necessarily make “Peanuts” any more depressing than it already was.

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Moths that pass in the night: Reproductive isolation due to pickiness, or just bad timing?

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ResearchBlogging.orgOn a summer night in a Florida corn field, a female armyworm moth emerges from her underground cocoon and spreads her wings to dry in the humid air. Over the next few weeks, she will fly miles away in search of a mate, and a likely-looking patch of host plants on which to lay her eggs.

Her brief adult life will be shaped in many ways by the life she led as a larva, feeding on domestic corn. She could easily find other grasses to feed her offspring, but she’ll probably seek out another cornfield. She may encounter armyworm males who were raised on many other grasses, but the odds are that the males she accepts as mates will also have grown up eating corn. This is so likely to be the case that it has left a mark on the genetics of her species [PDF].

At night in a cornfield, moths mate nonrandomly. Photo by K e v i n.

Yet it isn’t clear how much of this isolation between armyworms from corn (the “corn strain”) and armyworms from other grasses (called the “rice strain”) arises because moths from the different host plants actively prefer mates from their own larval food plant, or because they just don’t encounter moths from the other food plants as frequently. Like many moths, armyworms of both sexes deploy pheromones to attract and woo mates—so maybe armyworms from the same food plant smell better to each other. On the other hand, corn-strain armyworms do more of their mate searching early in the evening (although they’ll keep hunting all night), while rice-strain armyworms wait to search till the last few hours of nighttime.

Disentangling which of these two sources of isolation—preference versus timing—maintains the genetic differences between host plant strains of the armyworm takes some careful experimental work. As in many biological questions, the answer might well be not one or the other, but a little of both [$a].

In a study published in the latest issue of The American Naturalist, a team of entomologists at the Max Planck Institute for Chemical Ecology took on the question of what keeps the armyworm host strains separated. They performed two mating experiments with laboratory-reared moths of both sexes from both strains.

Fall armyworm adult. Photo via Wikimedia Commons.

First was a “no-choice” experiment in which moths were kept in a chamber with a single member of the opposite sex from their own strain, or the other strain. The test was repeated over three nights in a row. On the first night, females from the corn strain were less likely to mate with males of the rice strain than males of their own, and when they did accept rice-strain males, it wasn’t till later in the night. The second and third nights, though, corn-strain females mated about equally with males of both strains. Rice-strain females mated with males of both strains at about equal frequency all three nights, although they did so late in the night.

In the second round of experiments, moths were introduced into flight cages with one member of the opposite sex from each of the two host strains, so they could choose between them. To control for the differences in timing of mate searching between the two strains, the team repeated the experiment twice—in one version, the choosing moth had the entire length of the night to pick a mate, and in the other, the moths were only put into the same cage for the last four hours of the night, when the grass strain prefers to mate.

Fall armyworm larva. Photo by agrilifetoday.

In the all-night experiment, corn-strain males and females were both more likely to choose a mate from their own strain than the other. Rice-strain moths of both sexes mated with moths of both strains about equally—but rice-strain females were less likely to choose any mate at all. On the other hand, when the research team waited till the end of the night to introduce the test moths to their possible mates, rice-strain moths of both sexes mated much more frequently overall, and rice-strain females strongly preferred rice-strain males. Corn-strain males were basically indiscriminate in the late-night experiment, and corn-strain females were also less choosy.

In short, when mating during their usual activity periods, females of both strains were choosy about their mates; but when offered mates at the wrong time, they didn’t discriminate as much. The authors suggest that these mistimed matings were less discriminating because they were more likely to be initiated by the males, who showed relatively weak preferences even during their own usual mating times.

So the genetic differentiation between armyworm host strains is probably due to both timing and mate choice, and the two isolating factors affect males and females differently. Females, particularly rice-strain females, are quite picky about mating with a male of their own strain. Males, on the other hand, seem mainly to be prevented from pursuing females of the other strain by the fact that their respective schedules don’t line up. As the study’s authors conclude, all these individual rejections and missed connections, added up across entire armyworm populations, bring these moths a little bit closer to speciation.

References

Prowell, D., McMichael, M., & Silvain, J. (2004). Multilocus genetic analysis of host use, introgression, and speciation in host strains of fall armyworm (Lepidoptera: Noctuidae). Annals Entomol. Soc. America, 97 (5), 1034-44 DOI: 10.1603/0013-8746(2004)097[1034:MGAOHU]2.0.CO;2

Schöfl, G., Dill, A., Heckel, D., & Groot, A. (2011). Allochronic separation versus mate choice: Nonrandom patterns of mating between fall armyworm host strains. The American Naturalist, 177 (4), 470-85 DOI: 10.1086/658904

In which I try to explain why “heritability” is not quite the same thing as “heritable”

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ResearchBlogging.orgRobert Kurzban responds in the ongoing “adaptive” homophobia kerfuffle (henceforth, the O.A.H.K.) with continued confusion about how biologists identify possible adaptations and test to see whether natural selection is responsible for them. He notes that one effect of natural selection is to remove heritable variation in traits under selection, so that many traits which are probably adaptations—arguably, sometimes the best-adapted traits—actually have zero heritability.

This is true. But it’s important to note that a trait having zero heritability, or no genetic variation, is not the same thing as that trait not being heritable, or having no genetic basis. If the trait has zero heritability, the observed variation in the trait may not be heritable, but the trait still may be. Kurzban’s confusion over this distinction may be a fault of the terminology, as was pointed out to me in a couple independent conversations following the last round of the O.A.H.K.

That aside, reduced heritable variation in a trait—relative to appropriate standards for comparison, like other traits in the same species or the same trait in closely related species—is sometimes used to infer that selection has acted on that trait in the past. This is what my lab has done in the case of Joshua tree and its pollinators, which Kurzban cites. This sort of approach provides only indirect evidence of natural selection’s activity—but it’s often the best you can do when your focal species isn’t amenable to growing in a lab or greenhouse within the span of a single grant cycle.

The two varieties of Joshua tree, because apparently these are part of the discussion now. Photo by jby.

The comparison to other traits or to other species is the critical point here. Without it, you can’t determine whether a lack of genetic variation is due to strong selection, or due to the fact that there is no genetic basis for the trait. In isolation, the observation that there is no heritable variation for a single trait or behavior in a single species doesn’t tell you much except that natural selection cannot currently be acting on the observed range of variation in that trait. If there’s no genetic basis for the trait at all, then it cannot have been under selection in the past, either.

Forming hypotheses versus testing them

Regarding Kurzban’s broader point about how biologists identify adaptations:

Futuyama’s textbook, which Yoder cites for the discussion of heritability, indicates the following: “Several methods are used to infer that a feature is an adaption for some particular function” (p. 261), and lists the criteria that evolutionary psychologists rely on, including complexity, evidence of design, experiments, and so on. From the material I quoted in my prior post, it seems to me that by indicating the two kinds of evidence that are necessary for inferring a feature is an adaptation, Yoder is rejecting Futuyama’s claim that one can infer adaptation from its form, complexity, and so on.

Here Kurzban is confusing how we initially infer that a trait or behavior might be an adaptation with how we actually demonstrate that a trait or behavior is an adaptation. Forming a hypothesis is not the same thing as testing it, as Jon Wilkins explained so well. If Kurzban is accurately representing evolutionary psychology’s standards of evidence, then he’s confirmed Wilkins’s accusation that evo psych usually doesn’t go beyond the step of forming a plausible hypothesis to collecting the data that can test it.

Demonstrating that an adaptive hypothesis is well supported by data is, as I’ve previously said, a lot of work—usually enough for more than one scientific article. Depending on what is easiest to do, building the case that a trait is an adaptation might start with a paper that merely demonstrates a trait’s function—but that trait has not been conclusively shown to be an adaptation until we know that its demonstrated function is selectively important, and that the trait itself has a genetic basis.

While familiar to anyone who reads the evolutionary biology literature, this maybe isn’t so obvious to non-biologists. This may be because popular science accounts don’t always differentiate between hypotheses with good scientific support and those with none. Walk through a zoo or a natural history museum, and you’ll read nothing but adaptive hypotheses all day—but you’ll rarely see good, deep discussion of how well they’re supported.

This is why, since I started graduate school, I’ve became rather tiresome company on trips to museums and zoos. But one of the great things about popular writing by working scientists (from my perspective as a scientist) is that it lets specialists explain exactly such finicky details of our fields directly to the public. Doing so clearly and accessibly is challenging, to be sure, but naïve, uncritical endorsements of unsupported hypotheses—about the adaptive values of human behavior, or anything else—are available in just about every major media outlet. If scientists don’t do better than that in our own science communication, what value do we have to add to the discussion?

And now something new: relevant data

Your reaction to this image might be in your genes, but the evidence is that it can change, too. Photo source unknown, presumed public domain.

Which brings us back to evaluating Gordon Gallup’s “adaptive” homophobia hypothesis. Kurzban also points to evidence (ye gads! data!) that natural selection actually could have something to work with in the case of attitudes towards homosexuals. A 2008 Australian twin study, which finds a genetic component of variation in responses to a questionnaire about attitudes towards homosexuality.

This is indeed, as Kurzban suggests, preliminary data in support of the idea that natural selection could operate on homophobia. As Neuroskeptic pointed out in the comments on my last O.A.H.K. post, it also means that natural selection could be operating on tolerance of homosexuals. It’s an interesting and important question, actually, why the authors of that study chose to frame their results as showing the heritability of intolerance, rather than the heritability of tolerance.

However, as I noted all the way back at the beginning of the O.A.H.K., we also know that homophobic attitudes can change considerably over the course of an individual’s lifetime. It’s hard to say how survey responses taken at a single point in time relate to what natural selection would actually have to work with, if homophobic attitudes or lack thereof somehow shape an individual human being’s expected reproductive fitness. Even if there is some solid genetic basis to homophobia, we still don’t have data that can rigorously determine whether or how natural selection might act on that variation.

References

Godsoe, W., Yoder, J.B., Smith, C.I., Drummond, C., & Pellmyr, O. (2010). Absence of population-level phenotype matching in an obligate pollination mutualism Journal of Evolutionary Biology, 23 (12), 2739-2746 DOI: 10.1111/j.1420-9101.2010.02120.x

Verweij, K., Shekar, S., Zietsch, B., Eaves, L., Bailey, J., Boomsma, D., & Martin, N. (2008). Genetic and environmental influences on individual differences in attitudes toward homosexuality: An Australian twin study. Behavior Genetics, 38 (3), 257-265 DOI: 10.1007/s10519-008-9200-9

Science online, “I tawt I taw a puddy tat” edition

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Rawr! Photo by pasma.

Wink wink, nudge nudge, Facebook. Say no more.