A Tadpole Taste Test with Students as “Mock Predators”

Updated: See new addendum at the end of this post.

Last week, as my regular readers know, I wrote the second post in two months that combined the excellent subjects of reptiles and alcohol. That very day, I received an intriguing e-mail:

“Emily — If you’re willing to extend your alcohol and… collection to include amphibian encounters, this study by Richard Wassersug almost recommends itself.”

The first hint that the attached paper was going to be good was the e-mail’s sender: Marc Abrahams, the editor of the Annals of  Improbable Research and the creator of the Ig Nobel Prizes.

The second hint was the title of the attached PDF: “On the Comparative Palatability of Some Dry-Season Tadpoles from Costa Rica.”

I had no choice but to open the attachment. I was not disappointed. The paper, published in American Midland Naturalist in 1971, described a taste test comparing the tadpoles of eight species of frogs native to Costa Rica.

The mock predator in this experiment was a sample of 11 students and faculty of the 1970 Dry Season course, Tropical Biology: An Ecological Approach, offered by the Organization for Tropical Studies. The volunteers were two females and nine males aged 22 to 36 (X= 27.5). The experiment was run at least 2 1/2 hr since the last meal for the volunteer tasters…

The tasters were asked to rate the palatability of each tadpole’s skin, tail and body on a 1 to 5 scale: 1, tastes good; 2, no taste; 3, only slightly disagreeable; 4, moderately disagreeable, and 5, very strongly disagreeable. They were also asked to make comments about the taste as they went along and to note the most and least palatable tadpole at the end of the experiment. The standardized tasting procedure included several steps. A tadpole was rinsed in fresh water. The taster placed the tadpole into his or her mouth and held it for 10-20 sec without biting into it. Then the taster bit into the tail, breaking the skin and chewed lightly for 10-20 sec. For the last 10-20 sec the taster bit firmly and fully into the body of the tadpole. The participants were directed not to swallow the tadpoles but to spit them out and to rinse their mouths out at least twice with fresh water before proceeding to the next tadpole.

The rationale for the study was actually interesting. Richard Wassersug, the paper’s author, had noticed a huge variation in the tadpole species’ vulnerability to predation. While the tadpoles of some species blended in perfectly with their environments or lived hidden under rocks, others were bright, conspicuous and seemed to live right out in the open. Wassersug hypothesized that perhaps these species could get away with being so obvious because they didn’t taste good and predators wouldn’t want to eat them anyway. Perhaps the tastier species had to evolve better disguises to protect themselves, he speculated.

And indeed, that is, by and large, what he found. The more conspicuous tadpoles were, in general, less tasty that the ones who’d learned to hide in their habitats.

My other favorite part of the paper in where Wassersug anticipates perhaps the most obvious objection to his methodology.

In attempting to interpret the ecological significance of the present results, the objection that man is not a natural predator will doubtless be raised. Cott (notably 1951, 1952, 1953, 1954) did massive comparisons of the palatability of birds’ eggs and found a startling amount of agreement between the preferences of natural predators and members of the Egg Panel set up in England to grade the quality of eggs.

He gives, as one example, the “unanimous verdict of unpalatability by animals with such widely differing feeding-habits and diets as spiders, frogs, lizards and various birds, bats and man.” In assessing relative palatability he found broad agreement among the hedgehog, rat, ferret, cat arid man. Man is easy to condition, inquisitive and offers subjective opinions that cannot be obtained from other species. In this sense, it is not unreasonable to use man as an experimental predator.

It’s fascinating, fascinating stuff. More than worthy of a Wonderland post. There was only one thing: Abrahams had, in his e-mail, promised me alcohol. And I didn’t see any mention of it in the paper. So I sent Abrahams a query: Was there alcohol involved in the study?

“Oh, yes,” Abrahams wrote back. “He gave beer to the grad students. At least that’s what he told me.”

Update: I just received the following note from Dr. Wassersug, and it seems like a relevant PSA: “Note: In the old Ig tradition, this was research that ‘shouldn’t be reproduced.’  There is not a chance that such a project could (or should) get past a modern university IRB. Furthermore, now that I know how toxic toad tadpoles are, I would be reluctant to propose such a study.’”

ResearchBlogging.org Reference: Wassersug, R. (1971). On the Comparative Palatability of Some Dry-Season Tadpoles from Costa Rica American Midland Naturalist, 86 (1) DOI: 10.2307/2423690

Image: Wikimedia/Brian Gratwicke

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3 Responses to A Tadpole Taste Test with Students as “Mock Predators”

  1. Felipe says:

    Wow, that was impressive. I´ll certainly talk about this study in class today.

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