The larger the male lizard, the more likely he is to father sons, suggests a new study on brown anole lizards that also determined smaller males tend to sire daughters. Adult females, however, help to control the process.
Female lizards are always attracted to big males, but when they do mate with smaller males, they somehow manipulate the gender of their offspring to produce daughters, according to a study in the March 4 issue of Science Express, the advance online publication of the journal Science. The authors believe the lizards exert such control to ensure that genes from large fathers are passed on to sons, which stand to benefit from inheriting the genes for large size.
(Image: Bob Cox and Ryan Calsbeek, Dartmouth)
"This species has figured out a clever way to pass on genes with gender-specific effects on fitness," said Bob Cox, the lead author on the paper and a post-doctoral researcher at Dartmouth. "Usually, when natural selection pulls genes in different directions for each gender, the species faces an evolutionary dilemma. But these lizards have solved this puzzle, they've figured out how to get the right genes into the right gender."
Cox and co-author Ryan Calsbeek, an assistant professor of biological sciences at Dartmouth, created opportunities for females to mate with males of different sizes, leading to their findings.The scientists think the genes that make males more fit are often different from the genes that benefit females, even though males and females share most of their DNA. The valuable traits for one gender are not always the same for the other.
"In an evolutionary sense, what's good for the goose is not always good for the gander," as Cox put it.
The gender tweaking benefits survival. To prove this, the researchers documented the survival rates of lizard songs and daughters over eight months after the reptiles were released to their natural habitat in The Bahamas.
"As we predicted, the survival of the male offspring increased if they had large fathers," said Calsbeek. "But, we found that the survival of the daughters was not influenced by the size of the father. This suggests that the genetic benefits of large size are specific to sons."
It's still a big mystery as to how the females control the gender of their progeny.
"That's the big question at this point," said Cox, who, along with his colleagues, hopes to solve the mystery in future.
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