An atrazine-induced female frog (a genetic male) is shown (bottom) copulating with an unexposed male sibling. This union produced viable eggs and larvae that survived to metamorphosis and adulthood. Yet, because both animals were genetic males, the offspring were all males. (Tyrone Hayes photo)
BERKELEY —Atrazine, one of the world’s most widely used pesticides, wreaks havoc with the sex lives of adult male frogs, emasculating three-quarters of them and turning one in 10 into females, according to a new study by University of California, Berkeley, biologists.
The 75 percent that are chemically castrated are essentially “dead” because of their inability to reproduce in the wild, reports UC Berkeley’s Tyrone B. Hayes, professor of integrative biology.
“These male frogs are missing testosterone and all the things that testosterone controls, including sperm. So their fertility is as low as 10 percent in some cases, and that is only if we isolate those animals and pair them with females,” he said. “In an environment where they are competing with unexposed animals, they have zero chance of reproducing.”
The 10 percent or more that turn from males into females – something not known to occur under natural conditions in amphibians – can successfully mate with male frogs but, because these females are genetically male, all their offspring are male.
“When we grow these guys up, depending on the family, we will get anywhere from 10 to 50 percent females,” Hayes said. “In a population, the genetically male females can decrease or wipe out a population just because they skew sex ratios so badly.”