For Australian beetles bigger is better; while American beetles don't care about size
Jeremy Hance, mongabay.com
September 3, 2008
As reported in New Scientist, researchers from Indiana University, Bloomington found that an individual dung beetle in the US and one in Western Australian appear remarkably different. The US beetle has small genitalia and large horns, while the Australian is its opposite: large genitalia and small horns.
The size of the horns and genitalia are inextricably linked. As a developing pupa, the beetles' horns and genitalia compete for the same nutrients. If the beetle's horns require more nutrients then their genitalia remain small. When the horns are stunted the extra nutrients go to the genitalia causing enlargement.
This variation depends on the number of females scuttling about. If the population has more females, the males with large horns have a better chance of mating successfully, since they use the horns to battle outright for mating rights. This is how the American beetle is evolving.
However, when the female population is small—such as in Western Australia—the smaller-horned males prove more successful. Beetles with small horns cannot win battles, so instead they steal females away while their rivals lock horns. By creating cuckolds of their big-horned brethren, they gain the edge in delivering their genes to the next generation.
So far the beetle populations have not diverged far enough to be regarded as separate species, but it may be just a matter of time.
CITATION: David Robson. HOW BEETLES ARE EVOLVING TO TAKE OVER THE PLANET. New Scientist. 6 SEPTEMBER 2008 (Vol. 199 No. 2672)