Spiny genitalia of seed beetles linked to reproductive success

The spiny genitalia of male seed beetles promote reproductive success and good genes, according to a new study. Despite the risk of potential injury, females who mate with these beetles also have something very important to gain – healthier offspring. 

The new insights will help scientists understand how complex mating interactions have evolved between males and females. 

Study lead author Göran Arnqvist is a professor of Animal Ecology in the Department of Ecology and Genetics at Uppsala University.

“This helps us understand is connected with the evolutionary dance between males and females of all animal species, and the resulting differences between them – sexual dimorphism – that we observe,” said Professor Arnqvist.

“It’s important to understand this evolutionary dance that we’re all caught up in. We can show that this intricate process is influenced and governed by several different processes at the same time.”

The mechanisms that underlie mating interactions are complex, and have developed throughout evolution. 

In the case of insects, it is pretty common for males to develop spiny sex organs for reproductive success. There is a trade-off, however, in that these structures can damage the reproductive tract of the females.  

For the investigation, the researchers bred various strains of the seed beetle, Callosobruchus maculatus. Some of the males had mating organs with large spines, while others had organs with small spines. 

The study revealed that the male beetles with the longest thorns spines had the greatest success with the opposite sex. At the same time, the females suffered severe injuries during mating. 

Despite their injuries, the females had more viable offspring. In other words, there is a genetic link between big spines and good genes.

“Our experiments indicate that the females do pay a high price for mating with successful males -getting injured – but also that the females simultaneously obtain genetic advantages for their offspring,” said Professor Arnqvist.

“Our results provide support for a more nuanced view of mating interactions in the animal world, where behaviors can be shaped by several effects, and seemingly different evolutionary forces, at the same time.”

The study is published in the journal Proceedings of the Royal Society B: Biological Sciences.

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By Chrissy Sexton, Earth.com Staff Writer