Inside Doug Emlen’s laboratory opposite a chest-high tank of pitchfork-horned Japanese rhinoceros beetles hangs a framed portrait of Charles Darwin.
The photo is black and white, and in it the father of modern evolutionary thought is gazing off the left edge of the frame, brow furrowed in apparent fixation with an illustration of a large blue beetle a few inches away. Here, in the bio-research building at the University of Montana, the placement of the two pictures hardly seems coincidental.
A third generation evolutionary biologist, Emlen’s laboratory at the University of Montana is covered with beetle specimens and illustrations. There are beetles on coffee mugs, beetle calendars, and a jar full of brightly colored battling beetle toys sits on a bookcase filled with beetle books. Most have horns.
“These things can be longer than the rest of the beetle, so a male will be carrying a horn on its head or on its thorax that literally looks like it ought to make it topple over,” Emlen said.
Emlen and his team of researchers examine exaggerated structures in the animal world to discover new insights into the mechanics of evolution. Much of the group’s work focuses on animal weapons – like the large, pitchfork shaped horns of the Japanese rhinoceros beetles milling around the enclosure in the laboratory’s corner.
Recently, much of Emlen's laboratory's attention has been focused on the influence of nutrition on the growth of the rhinoceros beetle's horns.
Subtle changes in nutrition can raise and lower insulin levels in the beetles, according to Emlen. In the beetles, as in other animals with weapons like caribou and large-clawed fiddler crabs, the growth of such structures is essential in the quest to reproduce as it directly affects mating success through fending off rivals.
“I think that rhinoceros beetles have some of the most elaborate and crazy weapons out there,” said Ph.D. candidate and lab member Erin McCullough. “They’re just fun, really charismatic insects.”
Inside the tank – known to lab members as the “beetle battle box” – two jalapeno pepper-sized male beetles spar over an overripe apple sliver. In bouts between evenly sized males the individual with the largest horn usually wins, using the jet-black fork protruding from their forehead to pry their opponent off tree branches and flip them to the ground, McCullough said.
Tight quarters in the battle box make for near constant skirmishes between its horned inhabitants, McCullough said. Fights between males over food and females can result in serious injury to the combatants, she said. “There’s actually a lot of males in there with pretty bad wounds. Some of their horns have broken tips, and some of the males have puncture wounds.”
“The behavior we see in the beetles is very similar to the behavior we see in lots of other animals with weapons,” Emlen said. “As a structure they’re analogous in every respect to antlers you might see in deer or elk.”
Part of the benefit of working with beetles is the convenience of being able to fit them indoors, Emlen said. The animals can be reared, observed and eventually operated on in the laboratory in a reasonable time frame – a convenience foreign to most researchers studying larger members of the animal kingdom.
With access comes in-depth analysis, according to Emlen. Close examination of such structures allows researchers to tease apart important lessons on the workings of natural selection, the key mechanism in Darwin’s explanation of animal diversity through evolution.
“It’s literally the same genes and the same pathway and the same mechanism in all these systems” Emlen said. “At the end of the day, the processes that we’re studying are universal.”