Long-legged Arachnids Go to Battle

Entomologists from the University of Auckland have found that harvestmen, Pantopsalis cheliferoides, which live in the wet forests of the North Island, are the first animals found to have different types of weapon in a single species.

In the animal world – especially among arthropods like insects and arachnids – evolution has produced a wide array of weaponry, including giant horns and long snouts.

But why evolution should produce this diversity, seen even within same groups of insects, is puzzling.

“One thing that people have been fascinated with is why there are so many different types of weapons in closely related species,” researcher Christina Painting says. “We don’t know what the benefits are to evolving different weapons at all.”

Painting’s unique find, a species with two weapons – and two different fighting tactics – promises to pry the question open.

Some big males have long, slender jaws. They use those like swords, swinging them around wildly. Other large males have short, broader jaws, which they use like a dagger – jabbing viciously at competing males.

Now that she’s found this diversity in a single species, Painting plans to set up fights between the two types and see which wins. But it’s not about sport.

It’s a unique opportunity to explore the question of weapon evolution, Painting says. Since two species of dung beetle, say, won’t generally interact, it’s impossible to compare the costs and benefits of different weapons. But harvestmen of the same species must naturally encounter one another.

“It’s like watching evolution in action,” Painting says.

Original article by Michael Slezak, New Scientist, November 26, 2015.

Photo by Christina Painting.