Animal weaponry; an evolutionary arms race from elephants with great imposing tusks and kudu bulls with magnificent spiralling horns, to the array of scorpions with menacing pincers and venomous tails. Examples of animal weaponry and armament abound throughout the natural world. These animals are in a continuous evolutionary arms race, either between predator and prey or between members of the same species competing for food and reproductive rights. Animals with greater armaments will likely have more opportunities to reproduce. They pass on their superior genes to their offspring which fuels the race for bigger and more extensive weaponry.
Doug Emlen, a professor of biology at the University of Montana, describes many of these examples in a recent book “Animal weapons: The Evolution of Battle”. He discusses why certain animals have evolved very elaborate weapons while others have not. One group of animals which really stood out in his research for their extreme weaponry are dung beetles.
Here at Londolozi, and across Southern Africa, the dung beetle is often discussed for its ecological importance and intriguing methods of navigation, but not often for the extensive weaponry that many of the less conspicuous species exhibit. Many species of dung beetles have multiple protruding horns and extensive battle armaments that often grotesquely make up a third of their body size. The extent of these horns when compared proportionately to their body size is completely mind blowing. Two such horned species which occur here at Londolozi are the trident dung beetle and the three horned dung beetle. The more commonly seen ball rolling dung beetles (telecoprids), which often provide guests with hours of great viewing pleasure lack the weaponry of the above mentioned species, which begs the question: “Why”?
Generally with the ball rolling species, battles will occur out in the open. The use of a horn will be of no advantage here against multiple opponents and so they rather spend their energy on being lighter and less encumbered to avoid confrontation. The species which tunnel and burrow in the soil beneath the dung (paracoprids) are the ones which have evolved the greatest arsenal of weaponry. This is because certain conditions are present to promote this arms race. In these tunnels, males will have to face each other one-on–one as there is only space for one beetle at a time. Emlen emphasises that these tunnel duels are consistent and predictable, which is the recipe for the evolution of such extreme armaments. The beetle with the smaller weapons will get pushed out of the burrow and leave, if not severely injured. While the male with the larger weapons is left with all reproductive rights. Their offspring will match their parents in weapon size, if not outdoing them with chance gene mutations, taking the race even further.
Thousands of these one-on-one duels take place every day under the rhino middens and other dung scattered all around the bushveld. There is, however, a great cost to animals for bearing such extensive weaponry which can eventually end the arms race. For the dung beetles above, the horns can make up 30% of a male’s total weight. With these beetles, much of their energy is focused on horn growth at the expense of other organs such as eyes and reproductive parts. Emlen explains that it gets to a point when horns become so costly that only a select few can afford them, and once this happens, the sole option left for the rest of the males is to “cheat”. Many of the same species, who cannot compete due to smaller weaponry, have developed a strategy of their own. They will build their own tunnels to bypass the larger horned males and mate with females undetected. Instead of spending all that extra energy on producing large weapons they can grow bigger testes to produce more sperm. Ultimately this could actually push the heavily armed beetles out of the gene pool which seems counter intuitive.
To quote Doug Emlen, “But much as duels necessarily create arms races, arms races necessarily create cheaters — and cheaters can win, bringing an end to the race.” There is in effect a tipping point where no more advantage is gained from having bigger weapons. I personally don’t see this so much as cheating as I do a mechanism to bring about balance or create a new evolutionary path for these species. It is extraordinary to think how many of these micro stories and battles are playing out around us in the bushveld all the time and yet are seldom noticed. Just one more reason why we should slow down and look for the extraordinary in even the littlest things around us.