A lousy paper

September 9, 2010 • 6:08 am

Well, it’s actually a good paper, but it’s about lice.  It’s also short and cute: a note by Bush et al. in the new American Naturalist.

Dale Clayton, a former student in my department, a professor at The University of Utah, and inventor of the famous LouseBuster™, has spent his career working on ectoparasites (parasites that live on the outside of their host).  His specialty, however, is feather lice in birds, which eat the feathers and dead skin of their hosts. (Like all lice, these ones are insects in the order Phthiraptera.) There are all kinds of nice evolutionary studies you can do on these beasts. For example, some species of birds harbor up seven species of feather lice, all specializing on different parts of the body.

This raises a phylogenetic (family-tree) question: can a louse form a new species on its host? This goes to the evolutionary controversy about whether a new species can form in a very small geographic area.  But when you make a molecular family tree of the lice on a single bird species, you never see “sister species” of louse (species that are each other’s closest relative) living on a single species of bird. That implies that it’s hard to form a new species on one’s host: the different species on different parts of a bird’s body apparently arise after cross-infection from others species of bird. (See our book Speciation for more details.)

Anyway, Clayton and his colleagues (Sarah Bush was the first author) asked an obvious question that nobody had raised before: can ectoparasites be camouflaged (“cryptic”) on their host?  You might expect this if hosts detect their parasites visually and groom them away.  This would give an obvious evolutionary advantage to those lice having mutations that made them harder to see. (There’s also an obvious advantage to the birds to remove lice, since a bad infestation can severely weaken a bird.)

Bush et al. took 26 pairs of closely related birds (each pair from a different family) that differed strongly in color—one light and one dark species. (Examples:  black swan versus mute swan, glossy ibis versus white ibis, European starling versus chestnut-tailed starling.)  These also harbored closely related species of feather lice—lice in the same genus.

The hypothesis was that if louse color evolved by selection to avoid being groomed to death, you’d find light-colored lice on light birds and dark-colored lice on dark birds.  As a control, the authors also looked at head lice, which are not detected visually since the birds can’t see them.  These are scratched off the head with the bird’s feet.  (The authors call the visually groomed lice “typical” lice.)

The upshot: there was a significant relationship between host color and louse color in typical lice—and it was in the expected direction.  The control showed no relationship between host color and louse color in head lice.  Here’s one of their pairs (two cockatoo species and their resident lice), showing the crypsis and the contrast when you put one host’s lice on the other:

Figure 1: Example of background matching in typical feather lice. The light-colored louse, Neopsittaconirums albus, parasitizes the sulfur-crested cockatoo (Cacatua galerita; A). The dark-colored louse, Neopsittaconirums borgiolii, parasitizes the yellow-tailed black cockatoo (Calyptorhynchus funereus; B). The hosts’ feathers are the natural background for these lice. Both species of lice were photographed on feathers from a sulfur-crested cockatoo (A, inset) and a yellow-tailed black cockatoo (B, inset). Cockatoo photos by Trevor Hampel (A) and Fir0002/Flagstaffotos (GFDL ver. 1.2; B).

You might have noticed one problem here: are the lice colored like the hosts simply because their color comes from eating feathers and skin that are either light or dark?  That is, do the differences in louse color represent evolved, hard-wired genetic differences, or are they simply environmentally induced traits—like the pink color of flamingos—that have the fortuitous benefit of protecting the lice?  If they’re not hard-wired, then the colors wouldn’t reflect natural selection acting on genetic mutations.  The authors consider this unlikely since the color of lice doesn’t reflect their gut contents, and because they’ve done experiments putting lice on differently colored rock pigeons without any effect on louse color.  Also, if color simply came from eating differently-colored skin and feathers, you’d expect to find head lice showing the same color correlation as “typical” lice—but you don’t.

Still, it would be nice to transfer louse species between the differently colored bird species to see if there’s an effect on louse color.  This would be hard, though, since lice often won’t feed well on host species to which they’re not adapted.

Conclusion: If the differences in louse color really are genetic, score one for natural selection.  If there hadn’t been a correlation, I suppose you could claim that color in lice isn’t important in hiding them in the feathers (maybe they’re really detected through touch), and of course the paper would not have been publishable! (People don’t find that kind of negative result very exciting). But the authors weren’t really testing the working of natural selection itself: they were testing whether the variation in color among louse species could be explained by the variation in color among their hosts.

This opens up a whole new line of research on camouflage in ectoparasites.  The authors cite previous work suggesting that parasitic flatworms in fish, for example, might be cryptically colored to hinder their detection by cleaner fish.

I suppose a creationist could explain the correlation found by Bush et al. by claiming that God made the lice to match the color of their hosts.  But that presumes that God has an inordinate fondness for lice, and likes to see them torture and kill birds.

UPDATE: I am informed by Professor Clayton that transferring lice between bird species in the same family should not impede their feeding behavior.

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Bush, S. E., D. Kim, M. Reed, and D. H. Clayton. 2010.   Evolution of cryptic coloration in ectoparasites.  Amer. Natur. 176:529-535.

Hitch in Birmingham

September 8, 2010 • 10:49 am

(The title reminds me of Fitzgerald’s original title for The Great Gatsby: Trimalchio in West Egg).  Last night Christopher Hitchens debated the dour David Berlinski in Birmingham, Alabama: the topic was “Atheism poisons everything.”  A short account of the debate has already been published at Al.com.  My friend Leslie Rissler, a professor at the University of Alabama (Tuscaloosa) went to the event and sent me extensive notes: the debate was far more interesting than Al.com reports. I thought of putting her notes here, but now it looks as if the complete debate was taped by CNN and will be online soon.  But I will put up two photos she took at the book signing:

Hitch, looking dapper though less hirsute than usual (is that a silk shirt?):

Her prize!!!

Hitchens is still turning out his weekly column for Slate; the latest explores why religions need to be restrained.

What’s the right way to read the Bible?

September 8, 2010 • 10:27 am

Jason Rosenhouse, who’s writing a book on evolution versus creationism, has been doing a lot of reading about Biblical scholarship.  And he’s gotten pretty sick of all those scholars and theologians who assure us that yes, of course the Bible wasn’t meant to be taken as descriptive truth. It’s not a textbook of science, for crying out loud, but a string of nice stories meant to impart eternal truths about humanity!

Anybody with half a brain knows that this is patent nonsense, meant to protect religion’s authority from the advances of science.  Of course the Bible was meant to be taken literally. And it was—for centuries!*  Over at EvolutionBlog, Jason pricks this apologetic balloon:

For centuries we were told the Bible was an inerrant communication from God, chock-full of facts directly relevant to understanding our plight as humans and our proper relationship with God. Now here comes Borg [Marcus Borg, author of Reading the Bible Again for the First Time: Taking the Bible Seriously but not Literally] to tell us that modern scholarship has shown us the correct way of reading the text. It’s real intention was to embed a handful of vague platitudes into a collection of entirely fictional stories. Charming.

I agree completely that the lights of modern historical scholarship and textual criticism are the proper lenses through which we should read the text. Moreover, I would argue that this view is the only one that leads to a satisfying understanding of the Bible. Any attempt to treat the Bible as an inerrant communication from God, whether we are talking about YEC, OEC, or more liberal interpretations, runs afoul of its innumerable inconsistencies, tensions and contradictions, and the obvious evidence of redactions and revisions by its human editors. Treated as an anthology of ancient documents reflecting the religion, culture and politics of its times and places the Bible has much to teach us. But if you try to treat God as coauthor then the book is just a mess.

Once you take this view, however, it becomes very difficult to maintain any notion of the Bible’s elevated importance relative to other works of literature. If you want literary depth and moral force, you will do much better with Shakespeare, Hugo or Dostoevsky than you will with the Bible.

________

*Please don’t bring up St. Augustine the Hippo as representative of all those millions of people.  Besides, he believed in the literal truth of Noah’s Ark and the Flood.

Does determinism negate moral responsibility?: A survey

September 8, 2010 • 6:13 am

In a Opinionator piece in today’s New York Times, Joshua Knobe, a philosopher/cognitive scientist at Yale, describes the new discipline of “experimental philosophy,” which uses modern scientific methods to address traditional philosophical questions. (Sam Harris’s upcoming book, The Moral Landscape, is a specimen.)

I won’t recount Knobe’s work here, since he does a good job in his piece.  But what he shows is that, if you tell people the world is a deterministic one, then their view about whether such a world allows moral responsibility depends very strongly on whether you pose that question in the abstract or give them a concrete situation in which blame can be affixed.  (Guess which way the answer went!)  Knobe is not of course addressing the question of whether we really have moral responsibility, but rather what makes us think we do:

How can experiments like these possibly help us to answer the more traditional questions of philosophy?

The simple study I have been discussing here can offer at least a rough sense of how such an inquiry works.  The idea is not that we subject philosophical questions to some kind of Gallup poll. (“Well, the vote came out 65 percent to 35 percent, so I guess the answer is … human beings do have free will!”) Rather, the aim is to get a better understanding of the psychological mechanisms at the root of our sense of conflict and then to begin thinking about which of these mechanisms are worthy of our trust and which might simply be leading us astray.

I like these studies since, if you accept their methodology, they give pretty concrete answers—in contrast to a lot of philosophy!  Another study of this type is that of Marc Hauser and his colleagues (I posted about this last December), who asked people to judge the morality of acting in different ways in unusual and contrived situations.  They found that moral judgments seemed to be pretty universal, independent of religious or social background. This suggested that perhaps some of our “morality” is innate and evolved.  Now Hauser, of course, has been found guilty of academic fraud at Harvard, and so this result, like all his other work, remains under a cloud of doubt.  But it’s certainly worth repeating since its results are so interesting.

A marvelously mimetic mollusk

September 8, 2010 • 5:27 am

I’m always glad to see an article by Natalie Angier in the New York Times science section, because I know I’m going to learn about some wonderful new trick of evolution, recounted in Angier’s characteristically lively prose.  Her piece yesterday, “Surviving by disguising: nature’s game of charades,” is about recently discovered and bizarre cases of mimicry in animals.

I’ve already posted about Angier’s first example, involving margays (a neotropical cat) making tamarin calls to lure the monkeys within reach.  (Angier notes that “The scientists published their description of the first official “field observation of margay mimicking behavior” in the journal Neotropical Primates last year, but only now is it circulating among field researchers more widely.” You heard it here first!)  She gives other examples of auditory mimicry in ants and olfactory and tactile mimicry in cockroaches.

But the strangest example is a veritable Proteus of mollusks: the Indo-Pacific octopus Thaumoctopus mimicus.  As an article in this month’s Biological Journal of the Linnaean Society describes, this species has a form of mimicry uncommon in cephalopods: deimatic (conspicuous) mimicy.  In contrast to other types of octopus mimicry, in which the beasts resemble something else to hide themselves (this includes all the wonderful ways that octopuses can change their color to mimic the background), in this instance the creature not only has a deceptive appearance, but one it flaunts before predators to convince them it’s not worth eating.

Thaumoctopus mimicus is named appropriately.  As Angier notes, it can change its appearance to look like a flounder, a lionfish, or seasnake. (It also makes other nonmimetic warning displays.) Here’s Angier’s description, a tad livelier than the one given in the paper:

Like most octopuses, T. mimicus can use its nervous system to instantly change colors into a perfect wallpaper blend. Unlike most other octopuses, the mimic will sometimes choose to make itself more conspicuous to potential predators, rather than less. If it must venture out to forage in dangerous open waters, it assumes a menacing disguise appropriate to context. Before swimming above the seafloor, the octopus gives a shudder, and presto, its flesh becomes boldly striped, its arms and body resolve into a leafy, spiny form: it’s a toxic lionfish. For skating along the sea bottom, the octopus turns its skin bumpy and beige, compresses its body, pulls its limbs to its side: it’s a toxic flatfish, undulating its fins, staring you down with its top-sided eyes.

“When it’s being pestered by a damselfish, it will turn one of its arms into a sea snake, with the contrasting banding pattern of a sea snake, and with the tip of the arm thickened to look like the snake’s head,” said Healy Hamilton, a biodiversity and informatics expert at the California Academy of Sciences and an author on the report. “Sea snakes are voracious predators of damselfish.”

And you can see all three behaviors, and more, in this video:

Here’s the toxic “peacock sole,” Pardachirus pavoninus, that the octopus is thought to mimic. (It may be a general sole mimic, too: Huffard et al. suggest that some predators may avoid eating soles simply because their flat shape makes them hard to nom.)

Two points here.  First, the octopus almost certainly is hard-wired to have these patterns and behaviors rather than making a “conscious” decision to adopt them.  The wiring, of course, would be expressed situationally: if you’re halfway in a crevasse but threatened, do the sea snake; if you’re swimming low to the bottom, do the flounder.  Huffard et al. note that other species which swim like flatfish display the behavior even if raised in isolation, never having a chance to either learn it from other octopuses or to see a flatfish swimming.

Second, the mimicry is not perfect. You can see that the “flatfish display” is, to us at least, easily distinguishable from a swimming flatfish.  But mimicry need not be perfect to give an advantage, favoring the genes promoting the behavior. Angier has this covered:

None of the octopus’s imitations are perfect, and they don’t need to be. “If the predator just takes pause,” said Dr. Healy, “the octopus can ink and jet propulse away.”

A word more about the paper.  The authors wanted to see if the flatfish-swimming display was an “adaptation,” evolved de novo in this species and its relatives, or was an “exaptation,” that is, a trait for which some of the parts were already present, evolved for other ends in an ancestor, and which were later cöopted and elaborated in this lineage to assume a new adaptive function.  They made an octopus phylogeny using mitochondrial DNA, and concluded that swimming like a flatfish was a genuine adaptation, evolved in conjunction with the long arms that can be dragged behind, resembling a fish body and fins.  They concluded this because we don’t see any of these traits in the “outgroup” species to which T. mimicus and its close relatives—all of which swim like flounders—are related.  Less closely related species don’t seem to have even the rudiments of a “flatfish display.”

Now we’re not sure that mimicry evolved because it promoted a protective resemblance to a flounder.  We don’t have evidence that you survive better if you can mimic a flounder, a sea snake, or a lionfish.  Proving that would take a lot of hard experimentation—probably in the open ocean or large tanks.  Nevertheless, the discovery of such a weird trait is the first step in trying to understand its significance.  And even if we never know for sure, we can at least marvel at evolution’s ingenuity.

Angier also mentions recent work suggesting that we humans may mimic each other for “adaptive” ends:

Yet psychologists are coming to appreciate the profound importance of nonconscious mimicry in making us feel loved and appreciated, or simply smoothing the edges of our everyday affairs. Without realizing it, when we’re conversing with friends, we match our tone of voice and speech rhythms to theirs, adopt similar body posture and even imitate their tics. Studies have shown that, when students are instructed to work cooperatively with somebody who engages in either repeated hair touching or foot shaking, the students soon start fiddling with their hair or waggling a foot. Waiters who repeat their customers’ orders word for word, or who subtly mimic a customer’s body language, earn higher tips than do waiters who paraphrase the order or forgo the gestural mirroring.

_____________

Huffard, C. L., N. Saarman, H. Hamilton and W. B. Simison.  2010.  The evolution of conspicuous facultative mimicry in octopuses: an example of secondary adaptation? Biological Journal of the Linnean Society, 2010, 101, 68–77.

NY Times pans Hawking’s book

September 7, 2010 • 5:55 pm

In today’s NY Times, Dwight Garner reviews Stephen Hawking’s new book, The Grand Design. It’s a thumbs-down:

The real news about “The Grand Design,” however, isn’t Mr. Hawking’s supposed jettisoning of God, information that will surprise no one who has followed his work closely. The real news about “The Grand Design” is how disappointingly tinny and inelegant it is. The spare and earnest voice that Mr. Hawking employed with such appeal in “A Brief History of Time” has been replaced here by one that is alternately condescending, as if he were Mr. Rogers explaining rain clouds to toddlers, and impenetrable.

Meanwhile, over at the Daily Telegraph, Tom Chivers talks about the boom in science books, with physics replacing evolutionary biology as the flavor du jour. He recommends five of them, including Hawking’s.  John Gribbin’s In Search of the Multiverse looks interesting.

America is going to hell

September 7, 2010 • 9:27 am

From today’s New York Times:

BALTIMORE (AP) — Call it Zombies 101.

The University of Baltimore is offering a new class on the undead.

The course is being taught by Arnold Blumberg, the author of a book on zombie movies, ”Zombiemania,” and the curator of Geppi’s Entertainment Museum, which focuses on American pop culture.

Students taking English 333 will watch 16 classic zombie films and read zombie comics. As an alternative to a final research paper they may write scripts or draw storyboards for their ideal zombie flicks.

The university isn’t the first to have a class on the undead. Columbia College in Chicago has offered a course on Zombies in popular media for years, and at Simpson College in Iowa students spent the spring semester writing a book on ”The History of the Great Zombie War.”

I’m sure someone will defend this debasement of education and explain why watching zombie flicks and reading zombie comics makes you a better-educated person.