A gynandromorph moth comes to the light – and tells a story about science

by Matthew Cobb

This tw**t popped up in my feed the other night, from “wildlife illustrator and invertebrate enthusiast” Richard Lewington [Richard has a website showing his art here]. Richard was running a moth trap in the night when he found this beauty:

If you look carefully, you can just see the male’s feathery antenna on the left; the female side presumably had a straighter antenna (these different shapes relate to the different functions – males have to detect female pheromones from far away; females primarily need to be able to detect food plants on which to lay their eggs). You can see this clearly in another example Richard tw**ted:

Gynandromorphs are mixtures of male and female, often occurring because of a developmental problem – we highlighted the potentially gynandromorph cardinal bird here three years ago. There is a link between birds and moths, in that both groups have an unusual form of sex determination. In mammals, females have identical sex chromosomes (XX) while males have one X and one Y chromosome – they can produce two kinds of gametes (X and Y sperm) and so are called the heterogametic sex. For reasons that are unclear, in birds and lepidoptera (moths and butterflies),  females are the heterogametic sex (to avoid confusion, their sex chromosomes are called Z and W; males in both groups are ZZ).

It seems probable that these moths are gynandromorphs because, at a very early stage of development – probably when a fertilised female ZW egg divided into two cells – one of the daughter cells ‘lost’ the W chromosome because of some glitch. The tissues that were produced by that cell were therefore ‘ZO’ – you need the W chromosome to be female, so the tissues became male. The sharp dividing line down the middle of the moths, and the ‘mirroring’ of sexually dimorphic external structures on either side reinforces this intepretration.

There are many examples of gynandromorph lepidoptera on Google, which is probably a combination of people’s interest in these insects and the striking sexual dimorphism that exists in many species, making it easier to spot:

Image taken from here.

Here’s a photo of a gynandromorph gypsy moth, clearly showing the different shaped antennae (the male side is on the right):

Image taken from Jerry’s colleague Greg Dwyer.

As Jerry pointed out in his original cardinal post, those of us who work on the fly Drosophila (which, like us, has XX females and XY males) would occasionally see gynandromorphs in our stocks, although unless you are doing some funky genetics with sex-linked eye- or body-colour, male and female flies are not as different as the examples of the moths seen above. However, I do recall finding an apparently female fly with a male foreleg (male forelegs have ‘sex combs’ that are involved in sexual behaviour). Jerry’s explanation bears repeating:

In flies the sex is determined by the ratio of X chromosome to autosomes.  Flies, like all diploid species, have two copies of every autosome. If you also have two X chromosomes, you’re a female because the ratio of autosomes to Xs is 1:1. If you have one X chromosome and one Y chromosome, your ratio is 2:1 and you’re male.  The Y doesn’t matter here: if you lose a Y chromosome, and hence are XO, you still look like a male, although you’re sterile (the Y carries genes for making sperm).

So to get gynandromorphs in flies, all that has to happen is that one X chromosome gets lost in one cell when the initial cell in a female (XX) zygotes divides in two.  One half of the fly then becomes XX, the other XO, and the fly is split neatly down the middle, looking like the one below.  But gynandromorphs don’t have to be “half and halfs”.  X chromosomes can get lost at almost any stage at development, so flies can be a quarter male, have irregular patches of maleness, have just a few male cells, or even a male patch as small as a single bristle.

Way back in the day (i.e., 1970s), making mosaic flies in which different patches of tissue are either male or female was the only tool we had for identifying which tissues were involved in controlling various behaviours. This was fastidious work pioneered by one of the greats of post-war science, the physicist-turned-molecular-geneticist-turned-behaviour-geneticist, Seymour Benzer. [JAC: see my mini-post at bottom in which I used these methods for another purpose.]

Along with Yoshiki Hotta, Benzer was able not only to show tissue-level genetic control of behaviour, but also to show where in the embryo those tissues were determined, thereby constructing what he called a fate map of the action of a particular mutation. They adapted this technique from one of the founders of genetics, Arthur Sturtevant, who originally proposed it in 1929.

Here are some figures from Hotta and Benzer’s 1972 paper in Nature: ‘Mapping of behavior in Drosophila mosaics’. The first shows the range of mosaics that they produced – they were much more varied than the naturally occurring gynandromorphs because of the way they manipulated a special kind of X-chromosome in these flies, called a ring-X chromosome (known as X-R). This X-R chromosome could be lost at varying times in development, changing tissues from female (XX-R) to male (XO). The later the chromosome was lost, the more specific the tissues that would be male. By using a body-colour mutation on the X-chromosome, Hotta and Benzer could track from the outside of the fly which tissues were male and female, because they had different colours.

The top left fly in the figure apparently lost its X-R chromosome at the earliest stage of development, hence the straight line. As you can see, the effect doesn’t need to be symmetrical – if the chromosome is lost at a later stage, then a very specific part of the fly could be affected, such as the right wing in the top right fly (the left wing is still female).

The second figure shows how they interpreted which parts of the fly embryo were involved in determining the behaviour of a mutation called hyperkinetic in which the fly shakes its legs when anaesthetised (this rather odd behaviour turned out to be of major importance, as it is produced by changes to the activity of ion channels in the fly’s neurons). Unsurprisingly, it appears that the hyperkinetic gene was exerting its influence in three separate regions (one for each of the fly’s pairs of legs), all of which are involved in producing the part of the fly’s nervous system that controls movement.

240527a0The arduous nature of the technique – it was not possible to predict which tissues would lose their X-R chromosome, and often no detectable change occurred – and the problems of identifying which tissues underneath the cuticle had changed sex, meant that it was not not widely adopted. By the late 1980s this method was  overtaken by direct manipulation of genes and the tissues they are expressed in, but for many years it was cutting edge science, available in only a few leading laboratories.


Jerry’s addendum: I used gynandromorphs, and Benzer and Hotta’s ring-X stock, to determine where in the fly the females’s sex pheromone (a waxy substance on her cuticule that incites the males to court her and mate with her) resided.  As Matthew noted, that stock of flies, which still exists, is prone to losing X chromosomes when they’re contributed by a male parent. The male’s XX (female) zygotes often lose the X at different stages of development, producing patches of tissue that are XO and therefore male. You can tell which patches are male because the female’s X carries a recessive gene causing yellow body color, so male bits (XO) are yellow and female bits (XX, with one gene for normal coloration) are normally pigmented.

XX females have very different sex pheromones from XY and XO males, so by correlating which bits of a gynandromorph fly were male vs. female, and then extracting each fly’s sex phreromones with hexane and testing the chemicals’ identities on a gas chromatograph, Ryan Oyama (an undergraduate student) and I were able to determine where in the fly’s body the sex pheromones were produced and/or sequestered. It turned out that this was in the cuticle of the abdomen only: flies with female heads, legs, or thoraxes but male abdomens produced only male pheromones. The amount of female pheromone was proportional to the amount of female tissue in the abdomen, at least as seen in the visible cuticle.

This correlated with behavioral observations, too, for when gynandromorphs were tested with normal males (always horny), those males courted gynandromorphs most vigorously when their abdomens were female.  (This could, of course, have been associated with behavior or morphology of those gynandromorphs rather than pheromones, so we needed to do the pheromone tests as well.) Later workers actually localized the pheromone-producing cells to a layer right below the abdominal cuticle, confirming our results.

We published our results in the Proceedings of the National Academy of Sciences (reference and free download below), and I thought it was a very clever way to use old genetic technology to study behavior and biochemistry. Sadly, the paper didn’t get much notice!


Coyne, J. A. and R. Oyama. 1995. Localization of pheromonal sexual dimorphism in Drosophila melanogaster and its effect on sexual isolation. Proc Nat. Acad. Sci. USA 92:9505-9509.

Another failure to replicate a much-cited study on free will and cheating

There’s been a lot of press about a study just published in Science in which a large consortium of researchers tried to replicate 100 studies published in psychology journals, and managed to get significant results in only 36% of the replications. Further, investigators who repeated the earlier studies judged subjectively that they had replicated the original results only 39% of the time.

There has been a lot of analysis of these results in the press, with conclusions ranging from “psychology can’t be trusted” to “this is just normal science.” I’ll talk more about that, and summarize the Science paper, tomorrow, as it’s complicated and I need to read it for the third time. But in the meantime, and to save space in tomorrow’s post, I’ll cite one study that failed to replicate when redone by the large group of investigators constituting the “Open Science Collaboration” (OSC). That study is of special interest to me because it involves free will and its supposedly salubrious effects on society.

The paper chosen was from Psychological Science, one of the three well-known journals chosen by the OSC as sources of the 100 replicated studies. And this one was Vohs and Schooler’s 2008 paper (reference below) which I discussed in 2014, reproducing its abstract from the journal:

Does moral behavior draw on a belief in free will? Two experiments examined whether inducing participants to believe that human behavior is predetermined would encourage cheating. In Experiment 1, participants read either text that encouraged a belief in determinism (i.e., that portrayed behavior as the consequence of environmental and genetic factors) or neutral text. Exposure to the deterministic message increased cheating on a task in which participants could passively allow a flawed computer program to reveal answers to mathematical problems that they had been instructed to solve themselves. Moreover, increased cheating behavior was mediated by decreased belief in free will. In Experiment 2, participants who read deterministic statements cheated by overpaying themselves for performance on a cognitive task; participants who read statements endorsing free will did not. These findings suggest that the debate over free will has societal, as well as scientific and theoretical, implications.

Since then the study has been touted widely (see below), often as proving that determinism is bad for society. It’s has been used—by Dan Dennett and Eddy Nahmias among others—to show that unless people believe in some form of free will, they’ll behave badly and society will fall apart. I find that argument very odd, for when a similar argument is applied to God (“It’s important for society to be religious, for without religion, the moral glue that keeps us harmonious will dissolve”), it’s rejected by people like Dennett and me. In this way, belief in free will has come to resemble “belief in belief” (as Dan calls it) in a religious sense. But why accept one argument for societal harmony but reject the other?

But as a friend wrote me about this study and how it’s used to promote free-will compatibilism:

A huge proportion of factual statements could, when read immediately prior to an opportunity to act,  nudge the percentage of alternative behaviors up or down by a few points (particularly in experiments where the subjects can infer that the statement was there for a reason and the point of the experiment is to see what they’ll do in response – but let’s put that aside). The response isn’t to disseminate falsehoods that will nudge people to behave better; it’s to disseminate explanations as to why one shouldn’t behave badly even though certain propositions are true.

That last sentence is full of wisdom, and we should remember it whenever we feel tempted to foster “belief in belief”—whether that belief be in God or free will.

At any rate, the New York Times, in a subsection of its blurb on the OSC paper, describes three famous studies that were not replicated but were still widely cited in the press. You can see them all at the piece called “Three popular psychologies studies that did not hold up”. I’ll reproduce only what the Times says about the Vohs and Schooler study.

Free Will and Cheating:

In 2008, a paper in Psychological Science found that people were more likely to cheat on a test after they had read an essay arguing that behavior was predetermined by environmental factors. The authors suggested from their findings that belief in free will had societal implications.

The redone study found an effect pointing in the same direction as the original, but far weaker. One possible reason, the authors suggest, had to do with how subjects’ opinions about free will were manipulated. Participants read an essay, and it’s plausible that they were not as engaged in reading and thinking about it as were those in the first study.

The study was cited 341 times in other journals, the most of any of the 100 studies that the Reproducibility Project tried to replicate. There are 24 citations listed in the PubMed database.

In popular news media at the time, the study was covered with a focus on what it meant for societal belief in free will. A Scientific American report in August 2008 called the study clever and added, “The results were clear: Those who read the anti-free-will text cheated more often!” In Psychology Today in March 2008, a reporter wrote, “Reducing belief in free will might also make people exercise less and drink more.” A New York Times story in February of the same year said that the researchers interpreted their findings to raise, “questions about how human behavior might change if the belief in free will continued to decrease.” However, it added that the researchers, “cautioned against reading too much into the results.”

I’m amazed—and appalled—that the Vohs and Schooler study was not only cited uncritically (doesn’t anybody care if there are long-term effects?), but was even cited improperly, as if denial of fee will would affect exercise and drinking.

I’ve also written that Rolf Zwaan at the University of Rotterdam has failed to replicate the Vohs and Schooler result, so that makes two failures to replicate, even if you accept that some truth is conveyed in the kind of experiment that was done originally. (I have serious doubts about whether cheating immediately after reading a deterministic passage—even if it’s a real effect—says anything about long-term behavior.) All I know is that I haven’t been tempted to cheat more often since I’ve become a hidebound determinist and incompatibilist!

But in the end, these are the words to remember: “The response isn’t to disseminate falsehoods that will nudge people to behave better; it’s to disseminate explanations as to why one shouldn’t behave badly even though certain propositions are true.”


Vohs, K. D., and J. W. Schooler. 2008. The value of believing in free will: encouraging a belief in determinism increases cheating. Psychol. Sci. 19:49-54.

Jesus ‘n’ Mo ‘n’ ableism

The latest Jesus and Mo strip, called “Wow,” takes up the issue of whether religion might gain protection against ‘ableism’ were it to be classified as a mental illness (note Mo’s own ableism in the last panel):


I’ve written recently on the controversy about whether religion should be seen as a mental illness, and decided tentatively that it shouldn’t be, at least not in the same way we see schizophrenia or bipolar disorder as mental illnesses. Still, one can make a case that it is—as Dawkins implied in the title of his famous book—a widespread form of delusion. Jesus and Mo apparently take issue with me, but for tactical rather than scientific reasons.

Readers’ domestic-life photos: a writer’s new kitten

I thought I’d take a break from wildlife today to show some domesticated animals, and that of course means cats. And not just cats, but Bengal cats, one of which I’m contemplating acquiring. (No cracks, please, on acquiring breeder cats rather than shelter ones; I’ve done my share of the latter!). But wait—there’s more! This is not just a Bengal cat, but Joyce Carol Oates’ Bengal cat—her new kitten, Cleopatra.

First, some background. When I was in New York for the ill-fated New Yorker’s Cats versus Dogs Debate (dogs won by cheating; see post here), there was one bright spot amidst our humiliating defeat. And that was the presence of Bengal cat breeder Anthony Hutcherson, who brought two of his cats to be displayed onstage during the debate. Here are some snaps I took in the Green Room, the first of Anthony displaying his cats’ splendor (I’ve shown the following three pictures before).  Aren’t those beautiful animals?


Anthony was a delightful fellow, and you can read about him in Ariel Levy’s profile in a 2013 New Yorker, “Living-room leopards“. Since he was a little boy, Anthony’s goal was always to breed domestic cats that looked like leopards (and now tigers as well). Isn’t that an odd aspiration for a child? But, as you can see, Anthony has both persisted and succeeded.

Everyone fell in love with Anthony’s cats, for they were not only gorgeous but sweet-tempered. One of them was on stage for the full two hours, sitting patiently in Anthony’s lap (and mine, too, for I wanted a turn!).  In the green room beforehand, knowing that Joyce was a cat fan (she wrote a children’s book about her own cat called Naughty Cherie, which I brought to be autographed), I put one of Anthony’s Bengals in her arms. She was a bit wary at first, but soon, like me, was completely smitten. Here she is with “Jungletrax”:


And here’s Ariel, along with Malcolm Gladwell, admiring one of Anthony’s Bengals. Malcolm was on Team D*g, but he has a secret love of felids:


After the talk, and in subsequent emails, Anthony offered both Joyce and me a gratis Bengal kitten from his cattery. I have temporized about this, as I travel a lot and know that Bengals are supposed to need lots of attention and affection.  I need to be sure that I’m around often enough to provide that, but my hankering for a Bengal is keen.

But Joyce went for it, and picked up her marbled Bengal from Anthony in Maryland just yesterday. I hope to learn from her experience whether Anthony’s kittens and cats differ appreciably from “regular” cats in behavior and activity.

Below are the photos and captions (indented) that Joyce sent Anthony and me, reproduced with permission.  The cat’s name is Cleopatra, and it has not escaped my notice that “Anthony and Cleopatra” go together nicely. (I’m not sure who named the cat.) I think Joyce was too excited to focus the camera, for her excitement was palpable in her emails. When I wrote yesterday, knowing that she was picking up the cat, and loudly demanding photos and information, Joyce wrote this:

Just arrived home with Cleo (Cleopatra).

And then this, with a photo of the cat (Charlie is not a cat but Joyce’s husband):

Cleo is right at home! she is a bundle of energy. (aren’t kitties supposed to sleep 20 hours a day?  oh– not Bengals?)

much affection,
Cherie (outside the door, keenly intrigued)

Bengals supposedly love water, so it’s no surprise that Cleo’s in the sink! Here’s the first photo we got:

ready for my close-up….
Bengal kitten discovers toilet roll!

And so the mischief begins. . .

Almost sleepy-looking– but this is deceptive.  she is not sleepy.
much purring.

I’ll be following Cleo’s life, I hope, as she grows up—also hoping that she’ll not only get along with Cherie, but become a lovely pet. If that’s the case, I’ll get a Bengal, too! (Have a look at this latest litter at the cattery.)

Thanks to Joyce for the photos and commentary, and, as always, to Anthony for breeding such lovely and sweet-tempered cats, and following his childhood dream, which brings happiness to a lot of people.

Wednesday: Hili dialogue

It’s gonna be another scorcher in Chicago today, with temperatures rising into the nineties, and I’m worried about the crayfish, though I haven’t seen any others out of the pond. It’s September, too, and still a month before classes begin at Chicago. Fortunately, things have cooled down in Dobrzyn, with temperatures in the low twenties (Celsius) and the arrival of some much-needed rain.  Meanwhile, the Furry Princess of Poland is preening:

Hili: I will probably look good in this.
A: In what?
Hili: In this landscape.
WednesdayIn Polish:
Hili: Powinno mi być w tym do twarzy.
Ja: W czym?
Hili: W tym krajobrazie.


The sense of style

The title of this post is, of course, also the title of Steve Pinker’s new book on writing, but here I construe “style” as “sartorial style”.

Pinker (who’s always impeccably attired) has just finished lecturing on his book at the University of Manchester, and I begged Matthew Cobb, who attended the talk, to determine whether Steve was wearing cowboy boots. It was, said Matthew, hard to discern, as he talked from behind a lecturn, and his nether half wasn’t visible. But then after the talk there was a discussion with participants sitting at a table.

And so, after much importuning on my part, Matthew sent me this picture with the title, “You’re right!” Voilà: Pinka’s legs and feet (right):

IMG_3025 (3)

Unless I miss my guess, those are Lucchese black caiman boots (see this post). They’re nice, but I keep telling Steve that caiman is a delicate hide, easy to tear, and he should go for either alligator or Nile crocodile.

Cowboy boots: The Official Footwear of Atheism™.

A bigoted religious woman who should be fired

Religion and bigotry don’t always go hand in hand, but when it comes to homosexuality, it’s a natural partnership. Such is the case, for instance, for both Christianity and Islam.  One Christian in particular has acted in such an outrageous way—flouting the Supreme Court’s decision on gay marriage—that she’s not only reprehensible, but deserves to be fired.

The New York Times reports this religiously-based bigotry:

A county clerk in Kentucky who objects to same-sex marriage on religious grounds denied licenses to gay couples on Tuesday, saying she was acting “under God’s authority,” just hours after the Supreme Court refused to support her position.

In a raucous scene in this little town, two same-sex couples walked into the Rowan County Courthouse, trailed by television cameras and chanting protesters on both sides of the issue, only to be turned away by the county clerk, Kim Davis.

As one couple, David Ermold and David Moore, tried to engage her in an argument, Ms. Davis said several times that her office would not issue any marriage licenses. “Under whose authority?” Mr. Ermold asked.

“Under God’s authority,” she replied.

See for yourself:

Davis has defied the Supreme Court (a recent order directed specifically at her); one of the people denied a marriage license has filed a contempt of court suit; and Davis is defying lower court rulings, and the state governor’s own directive. She’s exhausted all her appeals (except to God):

On Monday, a stay granted by the District Court expired, and the Supreme Court rejected without comment Ms. Davis’s emergency application for a new stay, pending the outcome of her appeal. That left her no legal grounds to refuse to grant licenses to same-sex couples.

“She’s certainly in contempt of court by any definition of the term, so the District Court has an array of sanctions it can resort to, to deal with that,” said Daniel J. Canon, a lawyer for some of the same-sex couples seeking licenses.

It hardly needs noting that Davis is a Christian—an Apostolic Christian—and is whining about the fact that her “rights” have been violated by the court orders. But legal rights are determined by the courts, and she has none. She can be fired, but only after being convicted of a misdemeanor; they can’t just remove her outright. And of course some God-fearing folk of Kentucky are demonstrating on her behalf, asserting their “right” to discriminate.

I end with two statements in the Times piece. The good one:

“It really just blows my mind that people can be so closed-minded,” said Shaina Cercone, a 22-year-old student at nearby Morehead State University. “We’re out here trying to support love. Christianity supposedly supports love in all ways, so it seems kind of contradictory that they’re out here, I guess, discriminating.”

It was Cercone’s mistake to think that all Christians actually practice Christian values.

And the dumb one:

But [Flavis McKinney, a Davis supporter] also said he was confident that with God’s help, Ms. Davis would ultimately prevail, even though her odds appeared to be narrowing.

“He delivered Daniel from the lion’s den,” Mr. McKinney said. “So I trust he will deliver her.”

I hope He delivers her from her job. I have no patience for bigots like Davis. And while I don’t readily call for people to be fired, an extreme act, in her case it’s well deserved.  If she can’t learn to accept equality, at least she can be forced to practice it in her job—or leave her job.

h/t: Randy

Two babies playing – one is human

By Matthew Cobb

Now this looks to me as though the baby gorilla is playing peekaboo. Any hard-noses out there want to come up with a different interpretation?

Video filmed in the Columbus Zoo.

h/t Ziya Tong


Decoy calls unexpectedly change a frog’s mate preference

Behavioral work on many animals, ranging from insects to mammals, has shown that females prefer a certain type of male call: perhaps one that is longer, louder, or has certain combinations of sounds. We’re not sure why these preferences have evolved, though there are many theories. Those include hypotheses that males with, say, louder calls are healthier, and would confer better genes on their offspring, or that the calls are species-specific and a narrower “call window” prevents you from mating with another species and producing maladaptive offspring. The phenomenon of mate preference in females is well documented, but its evolutionary basis is poorly understood—such studies are very difficult. How can we learn what a female gains by mating with one kind of male versus another? Those studies must be done in the lab, and involve tricky preference tests combined with accurate measurements of female offspring number and quality.

Mike Ryan’s group at the University of Texas in Austin has spent years studying mating behavior (and how it relates to male calls) in túngara frogs (Engystomops pustulosus), a species found in Mexico and Central and South America. Males sit in or near streams and croak for hours, hoping to attract females with the beauty of their calls.

In most cases, female túngara frogs prefer male calls that are more complex, louder, and have lower frequencies and faster call rates, though the situation is complex. (One possibility for the louder-call preference is that those calls are producer by larger males, who not only can fertilize more eggs but may have better genes. They thus could confer a non-genetic benefit on the female (more sperm means more offspring) or a genetic one (offspring carry their father’s genes that make the sons bigger and themselves more likely to get mates).  Both advantages could, over time, impose natural selection on females to prefer certain kinds of calls.

Below are some videos, audio clips, and photos of male túngara frogs calling. As you see, males put a lot of energy into attracting mates, using both their bellies and inflated vocal sacs:


Males calling:

(See also the video at the bottom of the Science News blurb.) If you click on the screenshot below, you’ll go to a page where you can listen to a typical call: a loud squawk followed by a series of “chuks,” which increase its complexity:

Screen Shot 2015-09-01 at 7.26.32 AM

Calling has its dangers, too. Males who emit more elaborate calls are subject to more predation by fringe-lipped bats, who presumably can detect the frogs more easily. That counterselection may prevent males from evolving even more elaborate calls, for there might be a point beyond which the higher predation outweighs the advantage of attracting females. Here’s a calling male meeting a sad fate (photo by Christian Ziegler from Smithsonian.com):


One thing that’s tacitly assumed in studies of mate preference is that there is a continuum of call characteristics that is fixed and transitive. That is, if call A is preferred over call B, and call B over call C, then call A should be preferred over call C.  And the order of preference shouldn’t change if other calls are present in the population. But a new paper in Science by Amanda Lea and Mike Ryan (reference and free download below) shows that this might not be the case, at least in this frog.

Their hypothesis was that “decoy” calls could actually change the order of preferences between two calls, making the least preferred call the most preferred. They tested this by making three artificial calls of differing attractiveness to females, and then testing the females’ preferences by playing these calls through speakers in the lab, seeing which speaker a female hopped toward.  (Directional hopping towards a sound source is a common way to estimate female preferences in frogs.)

Lea and Ryan based their experiment on a human analogy: psychological preferences can change direction when a decoy preference is thrown into the system. Here’s how their paper describes the “decoy effect”:

One well-known violation of regularity is the “decoy effect”. For example, while shopping for a used vehicle, the buyer may value both low price and fuel efficiency. Of the two vehicles considered, one has a higher price tag but also better efficiency (A), whereas the second has a lower price but also lower efficiency (B). The buyer decides that he or she values lower prices over higher efficiency and so chooses B. At this point, the salesperson mentions that there is a third vehicle (C), which also has good fuel efficiency but a much higher price than both A and B. This causes the buyer to reconsider, despite no interest in the higher-priced vehicle. To the salesperson’s delight, the buyer ultimately chooses A, spending more money for better fuel efficiency. This irrational behavior has been produced by the decoy effect.

Do frogs do the same thing with calls? Lea and Ryan made three artificial calls differing in “type” (presumably complexity) and rate. The call most preferred in choice tests was call B, with call A significantly less preferred. Then they made a really lousy call, call C, which served as the decoy call, When pairs of calls were tested, B was more preferred than A, and both were preferred more than C.

The twist was then giving individual females a choice of all three calls presented simultaneously. And they did this in two ways. First, they put speakers on the floor emitting all three calls at the same time, and seeing which one the females chose (A below). Then they put the decoy call (C) on a ceiling-mounted speaker, so the female could hear it but not “choose” it, as she couldn’t hop to the ceiling! That’s design B below.

Screen Shot 2015-08-30 at 7.28.36 AM

And here are the results, shown as the proportion of frogs choosing either A (light gray) calls or B (dark gray calls) in two situations: the “binary” (the decoy call not broadcast), and “trinary” (decoy call broadcast).  The top plot below is from design A above, when the “trinary” situation involves females being able to hop toward the decoy speaker (those preferences aren’t given). The bottom plot is from design B, where females could hear the decoy call but not “prefer” it by moving toward it. Again, the data are just the relative preferences for A and B.

Screen Shot 2015-08-30 at 7.28.47 AM

Let’s look at the top figure first (C; it’s a bit confusing because the figures are given designations that use the same letters as call type). When calls A and B are tested against each other without the decoy call, B is slightly preferred (as it was in the preliminary experiments), but the difference is not significant. However, things change when the decoy call is played: all of a sudden call A becomes strongly and significantly preferred (asterisk shows statistical significance, with a p less than 0.05). The decoy has altered the preference, but not reversed it since there was no significant preference between calls A and B in the “binary” experiment. The alteration, as shown by the comparison with three asterisks between the binary and trinary experiments, is highly significant (p < 0.001).

The results are similar, but even more striking, in experiment B, when the decoy call was played from the ceiling. In this case when only A and B were played, there’s a strong and significant (p < 0.05) preference for B, as in the preliminary experiments. But when the decoy was played from the ceiling, all of a sudden females significantly preferred call A (p < 0.05), a reversal that was significant when binary and trinary tests were compared (three asterisks: p < 0.001).

In both cases, then, throwing a third “decoy” call into the mix makes female prefer a call that was either neutral or less preferred when tested against one alternative call. In other words, the direction of mate preference was not fixed, but altered by a third call—a call that was the least attractive!

What’s the upshot? Clearly, in this experiment (and we’re not sure if the same results would occur in nature rather than the lab), mate preferences are not fixed but malleable: they change depending on what other calls abound in the environment. What we see is similar to the “decoy” effect described by Lea and Ryan for car-buying, with call C playing the role of the more expensive, gas-efficient car.

But what does that mean? First of all, we don’t know whether the result is a general one: is this intransitivity typical of animal mating systems? The authors cite one or two papers suggesting this may be the case in some other species (I haven’t read them), but we’d need a lot more experiments like this to see how general the “decoy” effect is in nature.

But why does this happen at all? Does it make any evolutionary sense, or does it simply reflect confusion on the part of the females, who are thrown off by the decoy call? But if that were the case, why would their preference all of a sudden switch to the suboptimal call A?

We don’t know, but at the end Lea and Ryan suggest some hypotheses:

In socially complex situations such as frog choruses, rational decisions could be time-consuming, potentially resulting in lost mating opportunities or the risk of further exposure to predators. Decision rules might evolve to include loss aversion, mitigating the risk of costly errors, which are more likely when there are extreme alternatives and in uncertain environments. Such heuristics could lead to stabilizing selection on male traits and maintenance of genetic variation. Moreover, as human consumers are susceptible to manipulation by salespeople, context-dependent choice rules may make female frogs vulnerable to behavioral exploitation by competing males; for instance, if males are selective of their nearest neighbors.

Although it is clear that female choice patterns do not coincide with the consistent valuation predicted by traditional models in sexual selection, it is far from clear whether perfect formal rationality is mutually compatible with optimal evolutionary fitness. Closer inspection is required to determine whether inconsistencies revealed by decoy effects are, in fact, suboptimal in the context of fitness maximization. Variation of female mate choice in different social contexts might reflect adaptations for using additional sources of information, resulting in the expression of more complex but predictable choice patterns.

What they’re saying here, in scientific jargon, is that this might just be an irrational mess without adaptive significance. (Perhaps call B just comes through more clearly than does call A when the decoy call is played.) But they also propose alternative scenarios, involving spatial proximity, predators, and loss aversion—all of them adaptive. That is, the changes in preference in the presence of a third call could be an evolutionary phenomenon that gives the female higher offspring number.

Such adaptive hypotheses might make sense, but not necessarily in light of the decoy results. For example, if females want to avoid long-distance hopping, or predators, by mating with the nearest caller rather than the most attractive, that does make adaptive sense, but doesn’t seem to relate at all to Lea and Ryan’s result that the presence of a decoy call makes the female reverse her preference. Why the reversal? And perhaps it’s adaptive to just mate with any male when the acoustic environment is confusing, but again that fails to explain the switch in preference rather than just a loss of preference.

In the end, I find the experimental results intriguing, but their meaning unclear. That’s not the experimenter’s fault, for although they expected decoy effects, their significance, and whether the explanation involves adaptation, would be very hard to disentangle. The only problem I have with the paper, and it’s a minor one, is that the adaptive hypotheses don’t seem to relate very well to the experimental findings of a reversal of preference. What is sound (pardon the pun) is the finding that relative preferences between two call types can be dramatically altered by the presence of a third call.


Lea, A. M. and M. J. Ryan. 2015. Irrationality in mate choice revealed by túngara frogs. Science 349:964-966.

A Twi**er exchange about woo

Grania sent me this Tw**er exchange with Jim Al-Khalili, a physicist and popular science writer/broadcaster in the UK, and one other person. Al-Khalili recounts a phenomenon that I’m well familiar with: kooks sending us crazy papers and asking for our opinion. I get several of these a month, all in manila envelopes with scrawled handwriting. I can tell from the envelope alone that it contains some wacky theory.

The tw**ts (read from the bottom up):


That paper’s title is not too far from the kind of thing that Deepak Chopra writes.


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