A world revolving around manure may seem uninteresting, but come time to breed and the dung beetle males show some tactics that can’t be ignored. Existing somewhere between two forms, big horned ‘fighters’ and hornless ‘sneakers’, the reason for these alternative appearances may surprise you.
It’s all about the females.
Photo courtesy of Bruno Buzatto.
While the larger males can use their horns to fight off competition, the sneakers build small tunnels, reaching females as the fighters stay unaware. Having two alternative breeding tactics like this, is a phenomenon known as male dimorphism and it was this concept that UWA PhD student Bruno Buzatto studied with the help of these unusual animals.
The European Dung beetle was introduced to Western Australia in the 70s to help eliminate excess cow dung, and they were introduced into America for the same reason. Despite their similar purpose, the two populations are arranged differently, with beetles in WA living in large dense populations and those in America having much more space between them.
This difference in population density has caused a difference in the male fighters they include, and oddly enough, it’s because of the mothers.
Bruno and his colleagues found that female dung beetles raised in high densities, like those in Australian populations, invested more energy into their fighter sons than those raised in low densities. Living in a more dense population their sons would fight more often and needed to be more competitive to win a female. This maternal care meant that the Australian males had on average, horns that were 8% larger than those raised in populations with small densities similar to American ones.
“This is significant as a horn difference over 5% guarantees the bigger will win. A percentage less than that and the outcome of the fight is hard to predict” Bruno describes.
Dung beetle juveniles do all their growing inside a dung ball, so they have no concept of the population density around them. It is therefore up to the mother to decide how large her fighter male should be and the UWA team believes this could be happening through the composition of the egg she lays.
While the thought of working with dung beetles may have some people turning up their noses, Bruno says “they’re extremely easy to work with in the lab” and looks forward to more study with these colourful critters sometime in the future. Sneakers and fighters included.
This was a media release I wrote for a university assignment, on the work of scientist Bruno Buzatto. Thanks for reading!