The Myth of Promiscuous Males & Choosy Females

January 1, 2013

Biology

A male fruit fly (Drosophila melanogaster) Credit: Jan Polabinski/iStockphoto

A male fruit fly (Drosophila melanogaster) Credit: Jan Polabinski/iStockphoto

Scientists think that a study, which has been a cornerstone in evolutionary biology for the last five decades, could be wrong.

Ecologist and evolutionary biologist Patricia Gowaty and her colleagues Yong-Kyu Kim and Wyatt Anderson published their findings in the journal PNAS¹. The original study was done in 1948 by geneticist A. J. Bateman, who showed that the male fruit fly’s (Drosophila melanogaster) strategy was to mate with as many females as possible, whereas the females’ strategy was to be more discriminating amongst the available males. Male reproductive success correlated positively with the number of mates, but for females, it didn’t.

After the findings, promiscuous males and choosy females, were cited in a 1972 paper, the “Bateman principle” as it became known started turning up everywhere.

In the original experiment, Bateman isolated fruit fly populations and allowed free mating to occur within each of them. The goal was to count the number of mates that males had and compare them to the ones the females had. He didn’t have access to DNA analysis, so he couldn’t link offspring with specific parents. Instead, he reasoned that by using adult flies with mutations, he could trace an offspring back to its parents. The mutations included curvy wings, thick bristles and deformed eyes.

When Gowaty et al. ran the study again, they discovered that a double-dose of mutations seriously impacted the survivability of the offspring. “The crucial assumption of Bateman’s method,” Gowaty et al. wrote, “is that there is no reduction of offspring viability from inheritance of parental markers.” But this turned out to be untrue — and because the non-surviving offspring weren’t counted in the results, the data was skewed.

Bateman’s methods also violated Mendel’s laws of genetics. Bateman’s method over-counted the number of offspring for fathers, because there were more single-mutant offspring that had the father’s mutation than the mom’s mutation. It’s elementary that the number of offspring having fathers must equal the number with mothers.

Bateman didn’t show in any convincing manner that fruit fly males are promiscuous and that females are choosy.

References

  1. Gowaty, P. A., et al., PNAS June 11, 2012 201207851, doi: 10.1073/pnas.1207851109

[via NPR]

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