Male Harassment of Sexy Female Flies Can Damage the Gene Pool

This is a mating pair of Drosophila serrata. Antoine Morin.

If you're a sexually attractive female fly, then you might think that you've got it made, but the reality couldn't be more different. Instead of being showered with Valentine's chocolates, flowers and messages that say "i heart u," sexy female flies are constantly swarmed with needy male flies desperate to pass on their genes. In fact, these love-struck male flies are so Hell-bent on banging that they are actually damaging the gene pool.

Professor Steve Chenoweth, from The University of Queensland's School of Biological Sciences, lead the study. He commented, "We found that sexually attractive females were overwhelmed by male suitors."

"Female fruit flies with superior genes that allow them to lay more eggs were so attractive to male suitors they spent most of the time fending off male suitors rather than actually laying eggs. The end result was that these supposedly ‘superior’ genes could not be passed on to the next generation."

Chenoweth wanted to see how the transfer of genes through fly generations changed depending on whether males were allowed to harass the females or not. The researchers put the flies into two different groups: they adjusted the number of mates that males and females had in each group, thereby controlling the potential harassment rate.

They then let the flies "do their thing" for 13 generations. By the 13th generation, there was a distinct difference in the flies' genomes. In the group where "sexy" female flies were left alone to birth eggs in peace, without male harassment, the females had offspring in which expression of certain genes was strengthened. The 13th generation females were high-fitness and laid lots of eggs. 

Conversely, these same genes were rare when male flies were allowed to harass the females uncontrolled. This resulted in low-fitness females, which laid fewer eggs, by the 13th generation. Even though it makes genetic sense for male flies to procreate with the females that are the most sexually attractive because it improves the chances of their offspring reproducing, their uncontrolled actions were harming the future of the species. In fact, the females were so bothered by the constant attention that they ended up suffering male-induced harm during courtship. 

"We have known for some time of these harmful interactions between males and females," he said. "However, we hadn’t realized there may be a large number of genes fueling the interactions, or that these types of genes hamper a species’ ability to adapt to new conditions." 

The future of this study will be to see how this persistent behavior in the males effects the genomes of flies in the long term. The findings may even have evolutionary relevance across other species. 

[Via The University of Queensland, Current Biology]

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