How and why does this caterpillar whistle?

June 18, 2015 • 9:00 am

A piece in ScienceNews reported some new research (not yet published) that updated an old but good paper on the famous “whistling caterpillar.” I refer to the walnut sphinx caterpillar (Amorpha juglandis), which, when disturbed—as in a predator attack—emits a high-pitched whistle from its spiracles (the body openings used for respiration).

An earlier paper (from 2010) by Veronica Bura et al. in the Journal of Experimental Biology (reference and free link below) studied the whistling behavior, showed how the sound was made, and found that it apparently startles bird predators, who flee and thus allow the whistler to live another day.  Newer work, however, shows that the whistle is even more amazing than thought, for it appears to mimic the sounds that other birds make when they see a predator: an “alarm call.”

But first, let’s look at the magnificent caterpillar. Nice one, eh?

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SAM KIESCHNICK/INATURALIST.ORG (CC BY-NC)

The video below (you can see similar behaviors in the supplementary material to the paper) shows how the caterpillar whistles when it’s disturbed by experimenters, a disturbance designed to mimic a bird attack. (This caterpillar may also be attacked by other vertebrates like bats, snakes, and frogs.) You may notice that the “squeak” sounds like a bird, and that’s important.

In 2010, Bura and her colleagues did a number of studies on this species to locate the source and examine the effect of this sound. The salient results:

  • They measured the characteristics of the sound with sonograms. That needn’t detain us except to note that the median length of the squeak produced by these artificially disturbed larvae was about two seconds.
  • The sound was always accompanied by a contraction of the front of the body that lasted about half a second. I suspect this contraction is what forces air through the spiracles. Here’s what it looks like (figure from the paper), along with a recording of when the sound was produced

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  • The most obvious source of the sound would be the spiracles, the holes in the body wall through which larvae (and adult insects) breathe, taking in oxygen through diffusion (or active body movement) and expelling carbon dioxide. The association of the sound with body contraction makes this hypothesis more credible. The authors then covered up the spiracles with removable make-up latex to see if the spiracles were responsible, and, if so, which ones.  They found that when all spiracles were covered, no sounds were emitted in mock attacks (pinching the beast). When the spiracles were uncovered, one by one, the authors found that only the posterior pair of spiracles (there are eight pairs) were involved, for only this pair, when covered, eliminated no sound. The posterior (“A8”) spiracles are also larger than all the others.
  • The authors also did “laser Doppler vibrometry” to see whether the air and sound emitted during the squeak came out of a specific pair of spiracles.  This involves bouncing a laser beam off of a small piece of tissue paper suspended near a spiracle. Vibrations of the tissue produced by emitted air will be detected by the laser. They found that the laser showed a big signal only when the tissue was by the A8 spiracle rather than a control (A5) spiracle, and that the vibrations disappeared when the spiracle was occluded by latex. Here’s a figure showing the results of the vibrometry. You can see a bit of vibration from A5 (which didn’t disappear when the spiracle was covered), but a a big pulse from A8 (pictures of the spiracles are also shown), which did disappear when the spiracle was covered with latex. Thus, the squeak is produced by air coming out of spiracle A8:

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  • Finally, the big question: does the squeak really deter predators? The authors tested this by exposing caterpillars to three captive (but wild-caught) yellow warblers (Dendroica petechia), who attacked the larvae regularly. In every case, when the bird attacked the caterpillar, the caterpillar produced a squeak (squeaks weren’t made when the larva wasn’t disturbed). And in every case, the bird was deterred by that squeak and fled: every bird hopped or flew away when the sound was made, and one bird even dove down into the vegetation as if it were attacked by a predator”. (That’s important; see below.) No caterpillar was harmed in the least by these attacks, so the sounds seem pretty effective in deterring predation.

Here’s a pretty lousy figure from the paper showing a bird being deterred by the sound and diving for cover:

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But crucial experment wasn’t done. If it is the caterpllar’s squeak that deters the predator, the predator wouldn’t be deterred if the sound were eliminated. In other words, they should have done the same tests using warblers with the A8 spiracles of the caterpillar occluded with latex. If the authors are right, those caterpillars should have been nommed. That would have been an easy experiment to do,  but for some reason it wasn’t. Thus the crucial information—that the sound itself deters predation—is missing.

The update by other investigators was, perhaps, motivated by one sentence in Bura et al.’s paper, which I’ve already alluded to:

In one case, the bird dived away from the caterpillar into thicker vegetation in a manner similar to how it would react to a predator.

That suggests, to the curious and atttentive mind, that the caterpillar’s squeak might imitate the “alarm” calls that birds give when predators nearby. And indeed, a new meeting abstract by Jessica Lindsay and Erik Greene (link and title below), which expands the previous results, suggesting that that the caterpillar noises aren’t just disturbing, but are disturbing because they mimic the “alarm calls” that birds give when predators like hawks are around. The birds react as if they hear the alarm call, leaving the insect alone not because they’re simply startled, but because they need to find cover fast. Here’s part of that abstract; the paper has yet to be published:

Many birds produce “seet” alarm calls in response to high-threat danger (such as flying raptors), and these cause other birds to dive for cover.  Birds also produce more broad-band “mobbing” alarm calls in response to perched or stationary predators.  We noticed that the acoustic structures of some of the caterpillar sounds are similar to bird “seet” and “mobbing” alarm calls.  Using playback experiments, we tested the hypothesis that the caterpillar whistles mimic bird alarm calls.  Many species of birds dove into cover or froze upon hearing bird “seet” calls and two types of caterpillar whistle; they also tended to fly off and orient towards the speaker in response to a third type of caterpillar whistle.  These caterpillar whistles, rather than eliciting a general startle response, may protect caterpillars by mimicking the alarm calls of their avian predators.

This will undoubtedly be published soon as a full paper, but in the meantime it’s a cool suggestion.  I’ve put below what I think is a “seet” call of a chickadee, which resembles the call of the caterpillar above. I may be wrong about the “seet”, so birder/readers who have better examples are welcome to post them below:

h/t: Barry

_________

J. Lindsay and E. Greene. Whistling caterpillars mimic the alarm calls of birds. Presented June 12, 2015, at the 52nd annual conference of the Animal Behavior Society, Anchorage, Alaska.

V. Bura et al. Whistling in caterpillars (Amorpha juglandis, Bombycoidea): Sound-producing mechanism and function. Journal of Experimental Biology. Vol. 214, January 1, 2011, p.  30.  doi:10.1242/jeb.046805.

Readers’ wildlife photographs

June 18, 2015 • 7:45 am

Reader Karen Bartelt sent two sets of photos from the Galápagos; I’ll post the first group today with her notes.

I had been thinking of sending some Galapagos photos anyway. After seeing today’s blog [JAC: I will forgive her], my husband and I realized it was time to go back (armed with better cameras).  These are all from October 2010.
I am not a biologist, so any blatant misidentifications can be attributed to my being a chemist.
 Marine iguana, Amblyrhynchus christatus, North Seymour.  This bothers me a little, because my guidebook does not mention a marine iguana population on N Seymour.  Maybe it was slumming from Santa Cruz.
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Sleeping blue-footed booby, Sula nebouxii excisa, North Seymour:
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Blue-footed booby and chick, North Seymour:
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Man-date.  A bunch of magnificent frigatebirds , Fregata magnificens, (I think), North Seymour.  I can’t tell if they are purplish or greenish on the back, and that’s the only way to tell, unless they are side by side and you can see the size difference.
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Frigatebird over N. Seymour.  Our guide said that if the gular pouch stayed puffed for more than four hours, it was recommended to seek emergency treatment.
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Magnificent frigatebird chick, N Seymour:
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Female magnificent frigatebird, Genovesa:
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Thursday: Hili dialogue

June 18, 2015 • 5:08 am

In a little more than a week I’ll be departing on the Big Road Trip, and hope to see many of you (or some of you, depending on my progress) along the way. It’ll be from about July. 1 (when I’ll be at the Aspen Ideas Festival) to ab out the middle of August.  Posting will probably be almost nonexistent during that time, which will be the longest hiatus this website has ever experienced. But, like Maru, I’ll do my best. Meanwhile in Dobrzyn, Cyrus is threatening to nom Hili!

Hili: Good footwork!
Cyrus: Be careful or I will bite you.
Hili: You wouldn’t dare.

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In Polish:
Hili: Dobra praca nóg!
Cyrus: Uważaj bo cię ugryzę.
Hili: Nie odważysz się.
p.s. I’m pleased to announce that, according to Malgorzata, Hili has lost 300 grams of her winter weight.

The world’s most adorable octopus

June 17, 2015 • 3:00 pm

Here, via Science Friday, we have a yet-unnamed deep sea species of octopus, studied and soon to be named by Dr. Stephanie Bush, a postdoctoral fellow at The Monterey Bay Aquarium Research Institute. It looks like a weird Pac-Man character, and barely has tentacles. What astounds me most is the incubation time of the eggs: perhaps 2-3 years! That would make the eggs extremely vulnerable to predators, and is thus puzzling, but perhaps development simply can’t proceed too rapidly in a cold, deep-sea environment. I find the latter hard to accept, for surely other deep-sea invertebrates develop faster. But I don’t know from octopodes.

At least one other deep-sea octopus, however, has been described as producing eggs that take four years to hatch! That’s the longest known incubation period for any animal.

From California Diver:

Opisthoteuthis specimens were first collected in 1990, and live in the deep sea along the California coast at up to 1,500 feet deep. Their body measures about 7 inches in diameter, and its tentacles are webbed, giving it the appearance of an umbrella when spread out along the seafloor. These octopus swim by moving their fins, pulsing their webbed arms, pushing water through their funnel for jet propulsion, or all three at once. The octopus often swim up off the bottom and hover a bit just above the seafloor, looking for small crustaceans, worms, and other food. The thing that makes this octopus especially unique—and cute—is its puppy dog eyes, which Bush says, are unusually large for the size of its small body.

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Opistoteuthis, sp. nov.

Peter Singer disinvited from philosophy meeting in Germany for views on euthanasia of sick or deformed newborns

June 17, 2015 • 12:45 pm

I’m not sure where or when Princeton University philosopher Peter Singer first suggested that it may not be unethical to euthanize newborns if they have a terrible deformity or disease, but that view has caused tremendous controversy.  Apparently, almost all people see the moment of birth as some irrevocable line beyond which “assisted dying” is unethical, both because birth seems to mark some threshhold of “personhood”, and because the infant has no choice in its fate. But of course the concept of “personhood” doesn’t automatically go along with natural exit from the mother (after all, many think it begins when the infant could be viable when removed from the mother by Caesarian), and the concept of “choice” for an infant doomed to a horrible illness or early death is debatable.  At the very least, I think Singer’s suggestion is worthy of rational debate, and shouldn’t be automatically dismissed based on kneejerk reactions about “personhood.”

I for one am able to see some merit in Singer’s suggestion—so long as the infant’s affliction would doom it to either an early death or a horrible, painful life. Infants aren’t aware of death and probably have limited self-consciousness; so both their own well being, and that of their suffering parents, should be taken into consideration. Consequentialist ethics may lead one to agree with Singer. Readers may disagree with him, and if you do please weigh in below, but first read a precis of his views, which you can see in an interview below.

This has come up because, according to Leiter Reports, a popular website run by my Chicago colleague Brian Leiter (a philosopher and legal scholar), Singer has just been disinvited from a philosophy conference in Cologne because of these views.

The details were given by people who translated German articles in the comments sections of Leiter’s page. Apparently Singer was scheduled to speak on “Do vegans save the world?” before his invitation was rescinded. Singer’s previous appearances in Germany have been protested, and one can understand why Germans—the descendants of those who killed not only sick, deformed, and mentally ill infants, but adults as well—would take special umbrage at his views. But I don’t see that as a reason to avoid discussing them.

The disinvitation came when the organizers became aware of an interview Singer just gave to a Swiss newspaper that included some of his “euthanasia of infants” views (among other issue), views which have been known for a long time. As one commenter on Leiter’s site said “There, he is quoted saying: ‘A prematurely born baby of 23 weeks has no morally different status than a 25 week old baby inside the womb’.” Another commenter  added this (I’ve kept the original spelling and capitalization):

Here is how the organizers justify the cancellation on their facebook page:

They say they knew of earlier publications and statements of Singer with regard to PND and disabilities, but had not inticipated that he would put “his questionable claims” in public focus in such a way as he did in the NZZ (the Swiss paper) interview from May 26th. Now, they wirte [sic], a focused discussion on the subject matter that was planned for his talk (veganism) is no longer possible. They also write that they had to balance “the high good of free speech — an essence of philosophy” with the contents of Singer’s position. (The phrase between quatation marks is a literal translation; it sounds no less strange in the German original.)

While the organizers’ estimation that a sober-minded discussion on veganism would not have been possible at the festival may be right (I don’t know the nature and extent of the anticipated protests against the event), one wonders whether it might not have been possible to keep Singer invited and change the topic in order to discuss such things as the controversial nature of his claims, the vigorous reactions to them in the German public, free speech and whether a philosopher ought to be considerate of readers’ sentiments. Here is Singer’s NZZ interview that caused all the ruckus.

NZZ stands for the Neue Zürcher Zeitung, [roughly, The New Zürich Gazette] “Ein Embryo hat kein Recht auf Leben” (“An embryo has no right to life”). Here is a snippet from that interview—the bit that presumably caused the trouble, again translated by a commenter:

NZZ: Next week, you are due to receive an award for the reduction of animal suffering. This has provoked protests because you, allegedly, want to have disabled children killed. Is that true?

PS: There are circumstances where I would consider that to be justified, yes. For instance, when an extremely premature baby suffers from a cerebral hemorrhage so massive that it will never recognize its mother and smile at her. If such a child requires artificial respiration, almost all doctors would advise to switch the device off and let the child die. The artificial respiration is terminated because they do not want the baby to live. But if the child is already capable of breathing on its own, killing it requires a lethal injection. Why should it be morally relevant whether I switch off a device or give the child an injection? In both cases, I decide over the child’s life. [JAC: People often make a distinction here between a direct action that terminates life and an indirect action that allows life to end, but I consider that a distinction without a difference.]

NZZ: Would you also kill a new-born child with a mild disability?

PS: If the disability is compatible with a good quality of life, it should be possible to find a couple willing to adopt the child if the parents do not want it. Why should it be killed then?

NZZ: So it doesn’t make any difference to you whether a child has already been born or whether it is a case of a terminated pregnancy?

PS: With regards to the status of the child, it doesn’t. The opponents of abortion are right in one respect: birth does not mark a clear-cut boundary. Other factors are more important, like whether the child feels pain or develops self-consciousness. But the moral status of a premature child born after 23 weeks of pregnancy is no different from that of a child still in the womb at 25 weeks.

You can see that Singer doesn’t endorse blanket mercy-killing of all sick or deformed infants. It depends, he says, on their quality of life, something that his opponents seem to ignore. And I’m sensitive to Germans’ awareness of the horrible killings that occurred there (and in Nazi-occupied territory) during the Second World War. But it’s time to get past that, for Germany is no longer a Nazi country, and should be able to engage in philosophical discourse without the taint of Hitler. Singer, as always, raises issues of serious moral import (e.g., Should we kill animals for food? How can we justify living in luxury as well-off Westerners?), and they’re worthy of serious debate. Preventing him from raising the issue, after he’d already been invited to a conference (and has views that have been expressed for years) is a form of censorship.

The Agenda: Science vs. religion

June 17, 2015 • 10:45 am

The Agenda television show broadcast yesterday on TVO is now archived at this site, but you can see the individual segments in order by clicking on the screenshots below. The theme of Steve Paikin’s show was “Science, Religion, and Atheism.”

I went first, with the segment described like this:

Since Galileo’s lifetime house arrest in 1632 for his claim of a sun-centered solar system, the question has remained: are science and religion compatible? Evolutionary biologist Jerry Coyne is unequivocal. “Absolutely not,” he says. He discusses his book, “Faith vs. Fact: Why Science and Religion are Incompatible.”

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I won’t comment on my own statements here; readers will be familiar with them, and I said what I thought.

The second segment featured Andrew Newberg, described as “the Director of Research at the Myrna Brind Center of Integrative Medicine at Thomas Jefferson University Hospital [it’s in Philadelphia]. He is also the author of How God Changes Your Brain.” The segment is described like this:

Why do we believe what we believe? Are the brains of atheists and religious people different? What happens to a person’s brain when they are praying or meditating or communing with God? Andrew Newberg has been studying these questions for years. He calls it Neurotheology, a discipline that “seeks to understand the relationship specifically between the brain and theology.” He joins Steve Paikin to discuss the neuroscience of religion.

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Although he says he disagrees with me about the compatibility of science and religion, Newberg clearly didn’t listen to what I said, for he claims that the existence of religious scientists demonstrates that compatibility, a form of compatibility that I discussed and dismissed. Further, he claims that the compatibility is evidenced by the fact that scientists like him can study the religious beliefs of billions of people. This is a view I find completely bizarre. Science can study beliefs in ESP and Bigfoot, but that doesn’t mean that beliefs in those phenomena are compatible with science.

He then makes a deeply tautological argument, saying that people with brains that reject the supernatural tend not to be religious, and vice versa. This has nothing to do with his claim that there are differences between the faithful and the non-religious in how the brain works.

He also argues that meditation and other “spiritual” activities affect brain function, but of course, as Diane MacPherson noted yesterday, he doesn’t discuss whether meditating atheists show brain patterns different from those of meditating religionists. The fact that meditating or thinking about matters numinous affects brain activity is not a justification for the existence of the numinous, though Newberg does not make that explicit. Nor does he deal effectively with Paikin’s very good question that perhaps those folks prone to such brain patterns are a priori likely to become more religious.

In the end, Newberg argues that our brain is somehow wired, through either God or evolution, to have a propensity for religious or spiritual experiences. Perhaps he’s right, but if that’s the case, I must have bad wiring. At 15:47, he argues that we all have “faith”, a conflation of different meanings of “faith.”

On the whole, Newberg was articulate and didn’t argue strongly for the truth of religious claims; his main point was apparently that humans seem to be hardwired for some kind of spiritual experiences, and those experiences correlate with brain activity. His main problem, I think, was failing to disentangle the many meanings of the world “spiritual.”

Finally, Paikin interviewed Pamela Klassen, “a professor in the department for the Study of Religion at the University of Toronto” and Amarnath Amarangam, editor of Religion and the New Atheism. The segment is this:

Richard Dawkins, Sam Harris, Daniel Dennett, the late Christopher Hitchens are all known as the “New Atheists,” authors of best-selling anti-God and anti-religion books. But, what exactly is New Atheism? What are its goals? How do they rightly or wrongly view religion? And has it succeeded in selling atheism, or simply angering religious people? The Agenda explores the New Atheism movement.

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Klassen faults New Atheism for being strident and unproductive of thought, largely because, as she says, it is a movement dominanted by white males. In contrast the less strident women “New Atheists”, like Jennifer Hecht and Susan Jacoby, have promoted genuinely thoughtful discussion. (She seems to neglect Ayaan Hirsi Ali, Annie Laurie Gaylor, and the like). Amarangam then agrees with Reza Aslan that New Atheists caricature religion, neglecting faiths like Buddhism and Jainism.

Both panelists, however, completely fail to consider whether religious claims are true. To them, the question, which at least Amarangam sees as the focus of New Atheism, is unimportant. Instead, they concentrate more on the “little people” argument: that religion is, in the main, good regardless of its truth. Klassen also emphasizes the “communal” aspect of religion, further neglecting whether the claims on which religious practices rest are true. Does she think it matters? Amarangam correctly notes that New Atheists ask for evidence for the claims of faith, but argues that such evidence drops into insignificance when one sees religion as a “lived practice.”

Klassen has an obvious aversion to the word “faith,” preferring to discuss practice, yet theologians have no problem with the word “faith.”  She needs to get out more, and to look at the statistics about what religionists really do believe. I am of course biased on this issue, but I saw this segment largely as an exercise in atheist-bashing rather than a discussion of a). are the claims of religion really true?; b). To what extent do believers base their actions and “communality” on those claims?; and c).  If the truth claims are wrong, and yet buttress an entire system of belief, action, and morality, what does that mean for society?

As one commenter noted about this pair:

I can’t help but feel that the people in the program are mainly trying to get their little place in the limelight by vaguely attacking, not what the “New Atheists” say and stand for, but what these people claim the New Atheists say and stand for, i.e. they are pulling out the old straw man.

I fully agree with Amarnath Amarasingam that the New Atheists see the god debate as an intellectual exercise. It is, and it is a simple one at that. The Bible is a fictional book and if you claim otherwise, you have not read it, you are lying, or you are mentally deficient. When a “university” such as Biola *requires* its staff to accept the inerrancy of the Bible, then you know you are dealing with charlatans. It is no more difficult than that.

It is, to some degree, a valid criticism to say that the main god of the Bible is their favourite target, but how would that be wrong? The god of the Bible happens to be a fairly important subject in Western society, since this god (or its promoters) has had some influence on the culture, and still does. I would say that this god is therefore more than just marginally more interesting a topic for our culture than, say, Jainism and Buddishm, which do not have gods.

. . . Pamela Klaassen pulls out the old “I am offended” chestnut, and essentially excludes herself from the debate. “I am offended” is not a valid discussion point in this context.

My final comment is that Paikin is a very good interviewer: he knows what he’s about and asks the right questions. Even when he asks challenging questions, he asks them in a non-confrontational way, i.e., he seems to want to get at the truth, not just create controversy. It was a pleasure to be on his show.