Insulin Controls Growth of Rhino Beetle's Horn

A new study suggests that the rhinoceros beetles depend on insulin levels for the growth of their horns.

Researchers from Michigan State University, University of Montana and Washington State University studied two Japanese rhinoceros beetles and found that the beetles depend on insulin to increase the growth of their horns in order to attract and mate with females.

The experts revealed that big weapons like horns are very sensitive to nutrient signals through insulin pathway. Insulin levels play a main role in the development of the horns, which is used as a weapon to keep off predators and as an ornament to attract females.

The researchers disturbed the insulin pathway using genetic material that interfered with their insulin receptors of the beetles and analyzed the growth of horns as well as other body parts including the wings and the genitals.

While the wings and horns became smaller in size, the genital grew at a normal rate. "If the horn cells are super sensitive to these nutrition signals, then the same mechanism that makes horns huge in high-quality, good condition males will also make horns especially tiny in low condition, poor-quality males," Dr Douglas Emlen from the University of Montana told BBC.

Insulin level also has an impact on the tissue growth of the animals' reproductive system, meaning that the females get attracted and prefer to mate with males that have large horns as it is always considered that big weapons reflect the quality of the male.

Earlier, researchers debated whether it was possible for all the beetles to cheat and grow horns on their own. But the current study has shown that the beetles' horns are honest and grow based on insulin levels. This may possibly be a big cause of concern for the low quality males as they will not be able to grow such big horns.

The researchers also believe that insulin could possibly play a significant role for the growth of weapons of sexual selection in other animals like elk antlers and the peacock tail feathers.

he study is published in the journal Science.