Monthly Archives: March 2011

Science online, mnemonic rats edition

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Bat in flight. Photo by tarotastic.

Blah blah blah, Facebook, blah blah blah.

  • When life gives you parasites … Ancient ammonoids—forerunners of modern squid and nautiluses, dealt with parasites by encasing them in pearl.
  • Evolutionary baby pictures. Bats’ evolution from flightless ancestors, illustrated.
  • Note to my students: no human testing planned yet. Enhancing the levels of a particular enzyme in rats’ brains helps them retain memories.
  • Discredited more than a century ago, but you get to use a “cephalometer of Anthelme.” Want to make a living reading people’s personalities by the bumps on their head? Maybe phrenology is for you.
  • Using foremost legs as antennae, even. Spider mimics ant surprisingly well.
  • Sensory metaphor hijinks. People are more likely to identify an ambiguously-gendered face as female when touching something soft.
  • Glass ceilings are durable. Active discrimination may not be preventing women from advancing in the sciences, but institutional biases sure are.
  • Don’t panic. Panic Virus author Seth Mnookin understands the parental worries underlying vaccine denialism, but he still thinks it’s a problem.
  • In case you missed it. Jesse Bering thinks homophobia might be adaptive. He’s wrong.

And now, after a string of weeks without video in my Friday roundup, I give you a slow loris with a tiny umbrella.

An adaptive fairytale with no happy ending

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ResearchBlogging.orgThe evolution of human traits and behaviors is, as I’ve noted before, a contentious and personal subject. This is enough of a problem when there’s some data to inform the contentiousness. In the absence of meaningful data, it’s downright dangerous.

Take, for instance, Jesse Bering’s recent post about the evolution of homophobia, which Steve Silberman just pointed out to me.

A grim fairy tale indeed. Photo by K Wudrich.

When evolutionary biologists say a trait or behavior is “adaptive,” we mean that the trait or behavior is the way we see it now because natural selection has made it that way. That is, the trait or behavior is heritable, or passed down from parent to child more-or-less intact; and having it confers fitness benefits, or some probability of producing more offspring than folks who lack the trait. Lots of people, including some evolutionary biologists, speculate about the adaptive value of all sorts of traits—but in the absence of solid evidence for heritability or fitness benefits, such speculation tends to get derided as “adaptive storytelling.”

Evolutionary biology wasn’t always so rigorous, once upon a time. Then Stephen Jay Gould and Richard Lewontin buried adaptive storytelling under an avalanche of purple prose in their landmark 1979 essay “The Spandrels of San Marco” [PDF]. Norman Ellstrand made a similar point with better humor in a satirical 1983 article for the journal Evolution proposing adaptive explanations for why children always start life smaller than their parents [PDF]. Nowadays, when evolutionary biologists want to, say, argue that horned lizards’ horns are an adaptation for defense against predators, they have to demonstrate the claimed fitness benefit [PDF].

Evolutionary psychologists, however, seem not to have gotten the memo.

Bering’s post focuses on a series of studies by the evolutionary psychologist Gordon Gallup. Gallup was interested in the question of whether there might be an adaptive explanation for homophobia—which, given the fact that many (although far from all) human cultures treat homosexuality as a taboo—is a fair question for research. He hypothesized that treating homosexuality as taboo helped to prevent homosexual adults from contacting a homophobic parent’s children, which would reduce, however slightly, the prospects of those children growing up to be homosexual, and ensure more grandchildren for the homophobe.

Gallup supported this adaptive hypothesis with … evidence that straight people were uncomfortable about homosexuals coming into contact with children [$a]. Here’s the opening sentence of that paper’s abstract:

In a series of four surveys administered either to college students or adults, reactions toward homosexuals were found to vary as a function of (1) the homosexual’s likelihood of having contact with children and (2) the reproductive status (either real or imagined) of the respondent.

If you’ve noticed that this doesn’t mention evidence of heritability or a fitness benefit to homophobia, that’s not because I left it out—that’s because Gallup’s work contains no data to support either.

What this amounts to is arguing that homophobia is an adaptation favored by natural selection because homophobia is a thing that exists.

Could a complex behavior like homophobia have a genetic basis? Sure. Homosexuality itself is a complex behavior, and it certainly does have some genetic basis. However, the fact that attitudes toward homosexuality have shifted as far and as fast as they have in the last few decades suggests that any genetic effects underlying homophobia are pretty easy to overcome. Behaviors can be inherited culturally, too, since human children learn from their parents. But—note, again, lots of change in the last thirty years or so—cultural inheritance is more fleeting and malleable than biological inheritance.

Careful, Red Riding Hood—that wolf might be gay. Photo by crackdog.

What about Gallup’s proposed fitness benefit for homophobes? Well, that would require homophobia to, you know, actually prevent homosexuality. Gallup’s argument there hangs on two distasteful assertions. First, that gay men are more likely to be pedophiles, and second, that boys sexually abused by gay men are themselves more likely to grow up gay. In spite of Gallup’s assertions otherwise [$a], we have strong evidence from multiple studies that gay men are no more likely to be sexually attracted to children than straight men.

And there is, to my knowledge, no evidence to suggest that abuse can cause homosexuality. Bering cites a recent study that does document an association between childhood abuse and later homosexuality in men. However, the study’s authors point out that, “The reason for the connection between childhood sexual abuse and same-sex partnerships among men is not clear from our findings.”

… gay men tend, on average, to be more gender non-conforming as boys (Bailey & Zucker, 1995). This tendency could increase their appeal or conspicuousness to sexual predators, which might make them more likely to be victims of abuse (B. Mustanski, personal communication, February 11, 2008). Similarly, it is possible that boys who are developing and exploring a same-sex sexual orientation are more likely to enter situations where they are at risk for being sexually abused (Holmes & Slap, 1998). [In-text citations sic]

Why on Earth would Bering dredge up Gallup’s adaptive fairytale a decade and a half after it was published, if it was baseless to begin with and no new evidence supports it? Well, according to Bering, because he’s a hard-nosed scientist who isn’t afraid to consider uncomfortable possibilities.

Sometimes, science can be exceedingly rude—unpalatable, even. The rare batch of data, especially from the psychological sciences, can abruptly expose a society’s hypocrisies and capital delusions, all the ugly little seams in a culturally valued fable. I have always had a special affection for those scientists like Gallup who, in investigating highly charged subject matter, operate without curtseying to the court of public opinion.

Of course, says Bering, Gallup’s work isn’t conclusive, but it sure would be interesting if someone tested it.

Except, when Gallup was forming his hypotheses about the evolutionary benefits of gay-hating—he first proposed the idea in a 1983 article—he was hardly thumbing his nose at public opinion. He was, in fact, giving natural selection’s approval to the prevailing ugly stereotypes about gay men. And, as any competent evolutionary biologist would recognize, he did it without a shred of relevant evidence.

References

Ellstrand, N. (1983). Why are juveniles smaller than their parents? Evolution, 37 (5), 1091-4 DOI: 10.2307/2408423

Gallup GG Jr, & Suarez SD (1983). Homosexuality as a by-product of selection for optimal heterosexual strategies. Perspectives in Biology and Medicine, 26 (2), 315-22 PMID: 6844119

Gallup, G. (1995). Have attitudes toward homosexuals been shaped by natural selection? Ethology and Sociobiology, 16 (1), 53-70 DOI: 10.1016/0162-3095(94)00028-6

Gallup, G. (1996). Attitudes toward homosexuals and evolutionary theory: The role of evidence. Ethology and Sociobiology, 17 (4), 281-284 DOI: 10.1016/0162-3095(96)00042-8

Gould, S., & Lewontin, R. (1979). The Spandrels of San Marco and the Panglossian paradigm: A critique of the adaptationist programme. Proc. Royal Soc. B, 205 (1161), 581-98 DOI: 10.1098/rspb.1979.0086

Wilson, H., & Widom, C. (2010). Does physical abuse, sexual abuse, or neglect in childhood increase the likelihood of same-sex sexual relationships and cohabitation? A prospective 30-year follow-up. Archives of Sexual Behavior, 39 (1), 63-74 DOI: 10.1007/s10508-008-9449-3

Young, K., Brodie, E.D., Jr., & Brodie, E.D., III (2004). How the horned lizard got its horns. Science, 304 (5667) DOI: 10.1126/science.1094790

One snout to rule them all: Does migrating help weevils win the arms race of coevolution?

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ResearchBlogging.orgNatural selection and gene flow have a sort of love-hate relationship. Natural selection acts, on average, to make a population better fit to its environment. Gene flow, the movement of individuals and their genes, can counter the optimizing effect of selection if it introduces less-fit individuals from somewhere a different environment. On the other hand, not all new immigrants are necessarily less fit—sometimes they’re better suited to their new environment than the locals.

This gets more complicated, and more interesting, when the environment in question is another living species. Then, the question is not just how movement of one species changes its response to natural selection, but how movement of the other species changes the nature of that natural selection. That’s the focus of the latest study of a Japanese weevil species and its favorite food plant. The two species are locked in a coevolutionary arms race—but who wins the arms race in any given location depends on the gene flow each species is receiving from elsewhere [$a].

Male and female camelia weevils, caught at an indelicate moment. Evidently he doesn’t find her much longer rostrum intimidating. Photo from Toju et al. (2011), figure 1.

These are camelia weevils, Curculio camelliae. As their name suggests, they like to eat camelias, at least when they’re young. Specifically, weevil larvae eat camelia seeds, which are protected by a thick layer called a pericarp. To deal with camelia pericarps, the weevils have evolved prodigious proboscises, or rostrums, which female weevils use to drill through the pericarp so they can lay their eggs inside. Note that the female in the picture above is the one with the rostrum longer than the rest of her body.

Camelias can reduce their risk of losing seeds to weevil larvae by evolving thicker pericarps; weevils can make sure they’re able to feed their young by evolving longer rostrums. Both species are constrained by costs, though—the cost of producing more pericarp tissue, or carrying around a Pinocchio-grade snout. These costs vary somewhat with climate—camelias grow thinner pericarps in cooler conditions [$a]. This means the arms race won’t proceed equally far in all camelia populations, and introduces the possibility that the way in which weevils and camelias (well, camelia seeds and pollen) move across the landscape may very well determine which species has the upper hand.

A female weevil drills into a camelia fruit. Photo from Toju et al. (2011), figure 1.

The new study sets out to see whether gene flow among populations of the two species determines how far the arms race proceeds in each population. Rather than directly track weevils and camelia seeds, the authors use genetic markers for each species—the more migrants move between two weevil (or camelia) populations, the more similar those two populations’ genetics will be. The populations in question were seven sites on a small island at the south end of the Japanese archipelago, and presumably relatively free from the influence of immigration from the larger islands.

It looks like the movement of weevils, but not camelias, affects how the arms race proceeds. As the genetic difference between weevils at two different sites increased, the difference in how far the arms race had proceeded—that is, how long the local rostrums were, and how thick the local pericarps—increased too. That suggests weevils may be prevented from evolving rostrums of the optimum length for their local camelias by the arrival of less-than-optimal migrants. On the other hand, there was no statistically significant relationship between the genetic similarity of camelia populations and their place in the arms race.

This is where the relationship between selection and gene flow gets complicated, though. Even given the relationship between weevil gene flow and how far the arms race seems to have proceeded, the genetic differences between weevil populations were consistent with very low actual rates of migration. A female weevil arriving in a population of camelias with pericarps too long for her rostrum isn’t going to contribute many offspring to the next generation of weevils at that site. So it’s not impossible that what we’re seeing is selection constricting gene flow rather than gene flow slowing down selection.

Alternatively, weevils from a population with super-long rostrums should be able to lay eggs in any population of camelias they meet. In fact, an analysis that uses the genetic data to estimate rates of immigration and emigration suggests that one of the weevil populations with the longest snouts contributes more migrants to the other sites than it receives from each of them. In arms-race coevolution, size is all that matters—and so the weevils with the longest snouts may be winners no matter where they go.

Reference

Toju, H. (2008). Fine-scale local adaptation of weevil mouthpart length and camellia pericarp thickness: Altitudinal gradient of a putative arms race. Evolution, 62 (5), 1086-102 DOI: 10.1111/j.1558-5646.2008.00341.x

Toju, H., Ueno, S., Taniguchi, F., & Sota, T. (2011). Metapopulation structure of a seed-predator weevil and its host plant in arms race coevolution. Evolution DOI: 10.1111/j.1558-5646.2011.01243.x

Science online, falling coconuts edition

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Waiting for the next one to drop? Photo by KhayaL.

What? You still haven’t told Facebook you like Denim and Tweed? But then how else will it know to send you ads for, um, obligate pollination mutualism?

  • Gotta start somewhere. The simplest possible biological eye—and the starting point for the evolution of more complex models—may have been found in brachiopod larvae.
  • Look out below! In Palmyra Atoll National Wildlife Refuge, introduced coconut palms are literally bombing the natives into extinction.
  • In case you missed it. The Carnival of Evolution is out at Genome Engineering.
  • Herpetologist porn. Anolis osa has just been differentiated from Anolis polylepis based on what a leading Anole scholar calls their “man parts.”
  • Big cats, but no longer the top dogs. With population declines of more than 90 percent since 1960, lions are in danger of extinction in the wild.
  • But wait, there’s more. It’s not looking so great for every other known species, either.

Testimony from the front lines, Exhibit B.

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Via the Hairpin’s sister site The Awl this time: Queer students at the very Christian Harding University have published a ‘zine trying to explain themselves to the rest of the student body. It’s pretty damn’ hard to read, although maybe just because it sounds pretty damn’ familiar to me:

Our voices are muted, our stories go unheard, and we are forced into hiding. We are threatened with re-orientation therapy, social isolation, and expulsion. We are told stories and lies that we are disgusting sinnners who are dammed [sic] to hell, that we are broken individuals and child abusers. We are told we will live miserable lives and are responsible for the collapse of civilization. …. We are good people who are finished being treated as second-class citizens at Harding. We have done nothing wrong and we did not choose this suppression.

From the vantage point of someone for whom it got better, it’s hard not to see a certain amount of cognitive dissonance underlying the attempts to engage the intended audience with Biblical exegesis. But you know what, Harding University queers? Whether or not God hears your “cries for liberation from harsh oppression,” the rest of us do.

Naturally, Harding University has blocked access to the ‘zine website on its campus.

Testimony from the front lines, Exhibit A.

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Over at The Hairpin, which is rapidly becoming one of my favorite blogs, Dolores P. explains why she is training to become an abortion provider. And, wow. It’s incredible from start to finish, but her accounts of specific patients’ stories will blow you away:

Couple days later one of our patients was a soldier from Afghanistan. Hey, I was just reading about you guys.

No contraception around (she was stationed pretty far out) meant that she got pregnant. “Regulations require that a woman be flown home within two weeks of the time she finds out she’s pregnant, a particular stigma for unmarried women that ends any future career advancement.” Ends any future career advancement. For my patient, that meant that she had to figure out how to make it back to the states on her own. Even if she had chosen to “go straight,” it wouldn’tve been much better: “Servicewomen who make the decision to have an abortion must first seek approval from their commanding officer to take leave from their military duty and return to the United States or a country where abortion is legal.” (Guttmacher.) Ask your boss if you can please take off a while for your abortion. And no matter what, she had to pay for it all herself. So even though she knew she was pregnant almost immediately, it took eight weeks to make arrangements, travel plans and raise all the money. That means by the time she walked in our door, she was beginning her second trimester, which is a way more expensive and invasive procedure. She also had to spend eight more weeks than she had to miserably pregnant. In Afghanistan. [Hyperlink sic.]

Meanwhile, the House of Representatives is trying to eliminate Federal funding for Planned Parenthood, 100 percent of which goes towards services that help avoid abortions. You should go do something about that right now.

Carnival of Evolution No. 32

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Barnacles, one of Darwin’s first study organisms. Photo by Minette Layne.

The 32nd Carnival of Evolution, collecting online writing about exactly what it says on the tin, went live yesterday at Genome Engineering, with contributions from yours truly, Zen Faulkes, Bite Sized Biology, Dr. Bik, and Kevin Zelnio. Go have a look!

Pollinating birds leave plants in the lurch

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ResearchBlogging.orgPlants’ ancient relationship with animal pollinators is pretty crazy, when you think about it. On the one hand, it gives plants access to mates they can’t go find on their own, and it’s more efficient than making scads of pollen and hoping the wind blows some onto another member of your species. On the other hand, it can leave a plant totally dependent upon another species for its reproduction.

This catch is probably why lots of plants still use wind pollination strategies, or reserve the option to pollinate themselves if animals don’t do the job for them. Avoiding complete dependence on animal pollinators is likely to become more important in the modern era, as human disruption of the environment amplifies the inherent risk of entrusting your reproduction to another species [$a], a study in the latest issue of Science shows.

A flower of Rhabdothamnus solandri, waiting for pollinators who may never show up. Photo by Tonyfoster.

Sandra Anderson and her coauthors examined the health of populations of Rhabdothamnus solandri, a forest shrub native to the North Island of New Zealand. The flowers of R. solandri are classic examples of the pollination syndrome associated with birds—bright red-orange, with long nectar tubes. Rhabdothamnus solandri is incapable of self-pollinating, because its The flowers attract three native bird species, the tui, the bellbird, and the stitchbird. Thanks to human activity, all three of these birds “functionally extinct” in most of the range where R. solandri grows.

The bellbird and the stitchbird were eliminated from much of the North Island in the Nineteenth Century as European colonists cleared forests for farmland and introduced cats, rats, and dogs that preyed on the native fauna. Tuis have persisted, but tend to stay in the upper forest canopy—possibly to avoid rat predation—and don’t visit lower-growing shrubs. However, all three birds are still living as they did before Europeans arrived on two island nature preserves just a few kilometers off the North Island’s shores. This creates an inadvertent experiment in pollinator loss, allowing Anderson et al. to compare R. solandri populations on the mainland with those on the preserve islands to see how the plant gets on without its pollinators.

The short answer is: not well.

The three principle pollinators of R. solandri, the tui, the bellbird, and the stitchbird. Only the Tui is still common in most R. solandri habitat. Photos by kookr, angrysunbird, and digitaltrails.

To test whether R. solandri‘s reproduction is limited by pollen supply (as opposed to water or nutrients), the authors compared flowers that were either enclosed to prevent pollinator access, left open to natural pollination, or pollinated artificially. On the islands, plants left open set about as much fruit as plants pollinated by hand—but on the mainland, plants pollinated by hand set much more fruit than those left open. Mainland plants also produced smaller fruits, with fewer seeds per fruit, than island plants. The enclosed flowers set very little fruit, so it seems clear that pollen is the limiting factor for island and mainland R. solandri populations, and mainland populations aren’t getting enough.

The age structure of island and mainland R. solandri populations bears this out. Anderson et al. surveyed the island and mainland sites and counted the number of “adult” shrubs in a given area relative to recently sprouted seedlings. Island and mainland sites had similar densities of adult shrubs, but mainland sites had much lower densities of seedlings. It looks very likely that R. solandri populations on the North Island mainland are in decline as a direct result of losing pollinator services.

As Cagan Sekercioglu points out in an invited commentary [$a], this study demonstrates that species’ ecological roles can be strongly compromised even if they don’t go extinct. Tuis and bellbirds are not considered particularly endangered, and the stitchbird is classified as “vulnerable,” the lowest level of “threatened” under the system used by the International Union for the Conservation of Nature. Yet these birds’ local losses and adaptation to human activity have left R. solandri without adequate pollination services. Conserving biodiversity requires more than preventing extinction—but it can be quite a bit harder to preserve important relationships between species such as this one.

References

Anderson, S., Kelly, D., Ladley, J., Molloy, S., & Terry, J. (2011). Cascading effects of bird functional extinction reduce pollination and plant density. Science, 331 (6020), 1068-1071 DOI: 10.1126/science.1199092

Sekercioglu, C. (2011). Functional extinctions of bird pollinators cause plant declines. Science, 331 (6020), 1019-20 DOI: 10.1126/science.1202389