Plasticity of Sex in Frogs

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A researcher: Tyrone Hayes at the University of California Berkeley was doing research on the environmental impact of herbicides

http://www.pbs.org/wnet/nature/episodes/frogs-the-thin-green-line/video-agricultures-effect-on-frogs/4848/

The video shows how experimentally genetic male frogs can be changed into females by exposure to a commonly used herbicide.

That this is possible probably seems very strange to those who don't know volumes about biology but this is not without precedent. There is the charnov-bull principle of sex determination that shows that some reptiles change sex while in the egg due to the ambient temperature because the physiology of the different sexes have different survival rates dependent on temperature Amphibans have long been known to be very sensitive to chemicals. I have heard it said that this is due to their thin and porous skin.

In fact back in the days before instant pregnancy tests they would take blood or urine from a woman and inject it into an african clawed frog Xenopus laevis and if it developed eggs then that means the human woman had these reproductive hormones at high levels and was likely pregnant.

Still, this is very striking because we usually think of sex as something set in stone.

This brings up some ecological questions such as what ecological effects this will have.
It is generally said that females are the limiting sex and that as long as there are a few males around the population can continue to survive. This probably does matter on the mating style. Amphibians for example often use the "big bang" method where there are just a few nights where actual mating takes place. Since it takes a while for sperm to mature it might not be possible for one male to fertilize more than one female's clutch of eggs.This will is just the sort of thing that produces interesting population genetic scenarios.

Also, maybe this could illustrate the Baldwin effect. Perhaps if males are largely turning into females that there could be a selective advantage to decreased sensitivity to whatever environmental factors are affecting sex ratios.

It should be said though that if you search for information on atrazine you will find astroturf, google bombed links and such sponsored by agribusiness-- reminiscent of big tobacco and climate deniers so be advised.

9 Comments

You mean African clawed frogs, not African crawled. I used to raise those guys -- in addition to being popular research animals, they're interesting (if incredibly messy) little frogs.

My understanding is that atrazine-induced female frogs, when fertile, only produce male offspring (since both parents are genetic males). It raises some interesting questions about the survival of the population, because it seems to me that after enough generations of atrazine exposure the population would become dependent on atrazine. Withdraw the atrazine and wham, you're left with a population of males.

I agree with the critiques above.

My biggest question was going to be if there is was or could be research done to find out if the populations could be examined to see if the population was demonstrating a resistance to this, you mentioned the Baldwin effect, but it seemed like you just kind of left that and moved on to being done. Is there any demonstration of the Baldwin effect?

Amphibians are amazing, there's a ton of incredibly unique aspects of their reproduction, I would like to know if the chemical sensitivity is absolute or not, or if we still lack that knowledge and why. If any of the questions I'm asking were covered in the link I apologize :)

Wow, you are stepping straight into the quagmire. The whole topic of environmental estrogens and their various feminizing effects is huge and has been an active (and controversial - because of major vested political and industrial interests) area of research for several decades. This field includes developmental issues in fish and amphibians as well as larger animals including alligators (I seem to remember a penis length study) and mammals (cryptorchidism in panthers in the everglades). There are large studies on any number of compounds and species. While you identify problems in females here there are clearly male phenotypes too. One major question is whether and to what extent these issues affect human fertility and disease profiles.

For a historical perspective you might want to go back to Rachel Carson and read Silent Spring - which was about the effects of DDT and environmental toxins. Then move forwards into the more recent realization that things can be toxic in less obvious ways. That's a lot of reading that you might want to spread over a few years.

Anyhow, the statement that struck me was the one about sex being fixed in stone (by the way I appreciate that you correctly used the word sex - rather than the incorrect but commonly abused "gender"). Being too indolent to get a MN login earlier today my point has now been taken by whomever it was that you chopped in half above. I was going to use the example of the california sheepshead wrasse which all start off as female with a single dominant local male. If that fish dies a female becomes a male and replaces him. So it's important to bear in mind in biology that just because your species happens to do something a particular way, it doesn't mean everything else will be doing the same.

Stick with the writing - practice and edit, you'll get better and you'll still look back and wonder how mistakes can slip through. Point 7 from the critique above is important - the story is what people remember - but good style allows it to emerge and gives them the inclination to look for it - rather than moving on to something else.

I hardly ever read blogs to the end. I don't know what it is... I hate "chatty style", and too much attention to try and make it "easier" to read?
I read this blog entry right to the end.
So I don't know, somehow I like it.

I am not a scientist, merely a person fascinated with science. I read several science blogs daily, and my primary criterion when choosing which blogs to read is that I learn something from them. I also prefer writers that are somewhat entertaining. I very much enjoyed this first entry, and I know more now than I did before reading it. I look forward to seeing more from you.

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This page contains a single entry by gonza275 published on September 25, 2010 2:05 PM.

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