22. Pesticide Effects on Sex Last Generations in Rats
A lab rat’s life is not a happy one, but for some it’s especially bleak. In March, a team of researchers announced that female rats were spurning males whose great-grandmothers had been exposed to the fungicide vinclozolin. The male rats were fertile and looked healthy; still, something about them—perhaps their smell—was a total turnoff. This suggests that pesticides and other hormone-disrupting chemicals not only may harm those who have close encounters with them, they may also affect mating behavior in later generations.
Reproductive neuroendocrinologist Andrea Gore and her husband, evolutionary biologist David Crews—both at the University of Texas at Austin—examined the sexual inclinations of 12 male and 12 female 90- to 120-day-old rats, great-grandchildren of females injected during pregnancy with vinclozolin by reproductive biologist Michael Skinner. Over the past two years Skinner, of Washington State University, showed that as male descendants of these rats aged, they developed sperm deficiencies, infertility, and various other afflictions, from breast tumors to kidney disease.
To determine the effect the fungicide might have on the brain or on behavior, Gore and Crews timed how long each rat spent sniffing or bumping noses with rats of the opposite sex—studying those descended from injected females as well as controls. (Separated by wire mesh, the animals could not mate.) Male rats spent the same amount of time expressing sexual interest in both test and control females, but females preferred to check out males whose ancestors were fungicide free.
Gore and her colleagues believe these effects are epigenetic; that is, rather than inducing genetic mutations, which would change the sequence of the rats’ DNA, the fungicide is permanently silencing or reprogramming normal genes that control development and behavior. The impact on wild populations could be profound, they say, and because the processes of reproductive development are remarkably well conserved among mammals, these effects are very likely to be occurring among other mammalian species, including humans.
“You could argue, OK, let’s clean up our world, and our world will be pristine. . . . ” Gore says. “Well, here’s the problem: We’re already contaminated, because our epigenetic modifications have already happened to us.”
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