Why do males and females of some species look so different?

Dec 04, 2006
Why do males and females of some species look so different?
Examples of the diversity and magnitude of horn development among horned beetles. Surprisingly, the growth of horns is quite uniform across sexes. Instead, female beetles reabsorb massive amounts of horn tissue grown just a few days earlier. Credit: Courtesy Armin Moczek

Why and how do males and females of the same species often look so different? Armin Mocsek (Indiana University) has shown that in a certain group of insects, sex-differences in appearance are not the product of growing structures in a sex-specific manner, as previously assumed, but rather are generated by the sex-specific loss, or removal, of structures initially grown alike by both males and females.

Studying a group of beetles famous for their dramatic diversity in the development of male-specific horns (which are used in fights over females), Moczek discovered that growth of horns is surprisingly uniform across sexes.

Instead, both sexes undergo a second developmental period during which the female beetles reabsorb massive amounts of horn tissue that they had grown just a few days earlier. The males retain all of their horn tissue into adulthood. As a consequence, fully horned females molt into completely hornless adults.

"From an engineering perspective this seems very inefficient," Moczek says, "especially given that it takes a lot of energy to grow these structures in the first place."

He speculates that growing horns might serve multiple, hidden functions not apparent in the adult, or that the ancestor to the present-day representatives of these beetles actually had horns in both sexes, and that evolution somehow favored the loss of horns in females but not males.

"If this is correct," he argues, "then it seems to have been easier for females to lose their horns by evolving a way to 'ungrow' them, rather than not growing them in the first place. This is yet another example of the quirky paths that evolution has taken to generate the diversity of biological shapes and forms around us."

Source: University of Chicago

Explore further: First structural insights into how plant immune receptors interact

add to favorites email to friend print save as pdf

Related Stories

Death, tumors harm efforts to save rare rhinos

Apr 04, 2014

Efforts to save critically endangered Sumatran rhinoceroses were dealt a double blow this week with the death of one animal in a US zoo and the discovery of reproductive tumors in another.

Helping to save the rhino

Jan 14, 2014

Research from Victoria University has revealed a way to help secure the future of an endangered species of black rhinoceros in South Africa. Rosalynn Anderson-Lederer, who spent six months working with black ...

Recommended for you

Orchid named after UC Riverside researcher

2 hours ago

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

For resetting circadian rhythms, neural cooperation is key

3 hours ago

Fruit flies are pretty predictable when it comes to scheduling their days, with peaks of activity at dawn and dusk and rest times in between. Now, researchers reporting in the Cell Press journal Cell Reports on April 17th h ...

User comments : 0

More news stories

Fear of the cuckoo mafia

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

Turning off depression in the brain

Scientists have traced vulnerability to depression-like behaviors in mice to out-of-balance electrical activity inside neurons of the brain's reward circuit and experimentally reversed it – but there's ...

Is Parkinson's an autoimmune disease?

The cause of neuronal death in Parkinson's disease is still unknown, but a new study proposes that neurons may be mistaken for foreign invaders and killed by the person's own immune system, similar to the ...