"Weed Killer Makes Male Frogs Lay Eggs" is the understated headline for this National Geographic article about a study of atrazine. I'll start with the data.
1. They raised 40 genetically male frogs in water that was 0.003% atrazine
2. Four frogs matured into normal looking females (females have cloacal extensions on the end of their abdomen)
3. They dissected two and found they had ovaries, but still male DNA
4. The other two female look-alikes mated with male frogs and laid eggs, and most importantly THE EGGS HATCHED AND A WHOLE CREW OF MALE FROGS GREW TO ADULTHOOD!
I get that because both the mother and the father were genetically male it's impossible to have a genetic female. This is kind of an important point though. Because while the idea that an animal can change sex isn't really that big a deal on its own, it is a big deal that you can MAKE them do it in just one generation and then skew the whole ratio of males to females.
There are 23 families of fish that change sex naturally. Most common is for the dominant female to turn into a male, called protogyny. Usually it's triggered by their social structure. For example harems of Indo-Pacific cleaner wrasses with one large male and up to 10 females. If you take away the male the largest female starts courting the next largest female within two hours. She develops functional male parts in two weeks. Females that turn into males are called supermales. This type of life cycle is common in fish that compete for mates. Physical size is an advantage for males.
So it's possible for a species to survive just fine only producing male babies as long as some of them make the switch to being females. But if they didn't evolve that way gradually but instead were pushed into that state in a single generation by anthropomorphic doping what happens? Hard to say. If you got them all "hooked" on atrazine then took it out of the system would all the African clawed frogs die off? Could be. Considering they are a terrible invasive species outside their native habitat that might not be a big deal. But in general I am uncomfortable with messing with balances we don't understand. Invasions of African clawed frogs with immunity to a certain fungus are already blamed for spreading that fungus to native frogs in North America. Those African clawed frogs have no tongues and just eat any old rotting garbage they can cram down their throat, but native frogs are linked closely with insects, and insects with spreading disease. Messing with anything in this cycle is a bad idea. Please keep these African clawed frogs in the lab and the weed killer out of the water is what I say.
my fish book and had to include this because it amuses me. I can't help think of bad horror movie plots where they make the shift from fish to humans. Corydora catfish, like in aquariums, breed like this -- the female places her mouth over the genital opening of the male and drinks his sperm. She then passes the sperm rapidly through her digestive system, extrudes eggs that are held between her pelvic fins and releases the male's sperm to fertilize the eggs. They call it sperm drinking and it's in bold in my book. Farther down the column they talk about spawning stupor. Species that are normally difficult to approach or are very active instead move like they're in a trance. Spawning stupor has been observed in suckers.
Tuesday, March 2, 2010
Atrazine Creates Male Baby Mamas
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