More Sex Causes Male Burying Beetles To Evolve A Longer Penis

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The shape and sizing of genitals vary dramatically in the different regions of the animal kingdom. From cats with a barbed penis to the spoonlike appendage of the damselfly, there appear to be few limits to their kind. But why is there such range, especially whenconsidering specific elements of biology( such as body shape) remain fairly held? The answer might lie in the evolutionary tug of war that occurs between males andfemales, known as sex conflict.

In an experiment involving the carnivorous burying beetles, researchers found that the frequency at which the insects have sex can physically change the shape of their genitals over a period of only 10 generations. For beetles that were selected to have more sex, the males evolved a longer penis, while females evolved larger claws on their genitalia. The researchers suggest that since these physical changes in genitals were seen in both sexes, they are likely the outcomes of sexual conflict.

It takes two to tango, so when changes in shape in one sexuality leads to corresponding changes in the other sex this is known as co-evolution, explains Dr. Megan Head, co-author ofthe paper published in the publication Evolution, in a statement. There is often a conflict between male and female animals when it comes to how often to mate. For males, who generally put little energy into creating sperms, it is beneficial for them to mate with as many partners as possible, whereas for females it is often better for them to only mate a few times.

They found that the most dramatic changes in the shape of thegenitals forboth sexes were in those that were selected to have the highest mating rate. Although we don’t know the ins and outs of how these genital structures relate to the reproductive success of each sexuality, our results show that sex conflict over mating can lead to co-evolutionary changes in the shape of the genitals of interring beetles, says Dr. Paul Hopwood, another of the co-authors of the study.

Burying beetles ( Nicrophorus ) are unusual among insects as they actually exhibit parental care. They are named after their habit of fighting over and then burying small dead animals, in which they then create their brood. Before interring the dead animal, however, they will first remove fur or featherings and then coat it in antibacterial and antifungal substances secreted from oral and anal glands, in order to mask the decaying reek and keep the meat fresher for longer. When the larvae hatch in the carcass, the adults then feed the larvae regurgitated liquid flesh.

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