This plate is in Anthropogenie by Ernst Haeckel
September 2010 Archives
A researcher: Tyrone Hayes at the University of California Berkeley was doing research on the environmental impact of herbicides
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.
Now that I am finding myself entering into the upper division biology classes I often find that things I was told in 1000 and 2000 level courses are contradicted in later courses. I keep coming across misconceptions that are an artifact of how biology is taught both in coursework and textbooks.
For example I was told thorough the most memorable mnemonic ever made the "ABC's" of animal behavior according to Tinbergen. Under this scheme of thinking there are two divisions of biological thought of what sorts of questions can be asked.
Animal
Behavior
equals=
Causation (What are the physiological causes?)
Development (How does the behavior unfold given the environment?)
Evolution. ( when did the behavior enter a given clade and how is it distributed or modified?)
Function (How does the behavior lead to increases in reproductive success?)
It is said that C and D are proximate which deal with individuals and populations and such.
It was also said that E and F are ultimate causes that deal with populations through time and things like selective pressure. In the lab sections when writing up those lab reports we were asked for sections relating to these four questions(above) in such a way that
the evolution section could only relate to comparing sister taxa and that causation had to just talk about the physiology that say causes a refrigerated nerve to generate an action potential. It was so tightly
Classically there was little attempt to try to explain either C or D in terms of E and F. But I always thought that was a mistake to ignore the middle ground. Now much of this was due to the limitations in technology.
Evo-devo is interesting in that it tries to explain how "evolution is the control of development through ecology". I can see why evo-devo is resented. For the longest time biology was about
naming things, shoving frogs in pickle jars, and just creating volumes upon volumes of facts. From my understanding; that's the point of a synthesis-- to create a new explanatory framework form which things in one field can be applied to others.
I really can't see why there's so much pushback.
