doi:10.1038/nindia.2013.140 Published online 21 October 2013
Picture the Asian elephant without its elegant tusks. Ecological scientists filming the pachyderms for months together at the Kaziranga National Park in the north-east Indian state of Assam say this picture might become a reality in a few thousand years from now. The reasons, they figure, are two-fold. One, tusks are merely ornamental, not of much use to the animal and thus dispensable. And two, poaching pressures are rendering more and more elephants toothless.
Analysing over 450 hours of video footage of Asian elephants, Karpagam Chelliah and Raman Sukumar from the Centre for Ecological Sciences at the Indian Institute of Science, Bangalore, conclude that the magnificent beasts might adapt and evolve into becoming tusk-less creatures in times to come .
The duo set out to study the most important factors that determine the winner in a duel between two male elephants. They considered parameters such as body size, tusk and 'musth' (an annual period of heightened aggressiveness and sexual activity in male elephants).
Elephant tusks are elongated upper incisor teeth. In Asian elephants (Elephas maximus), females do not have tusks. Among males, some have tusks and some don't (called makhnas). The number of makhnas vary between populations, from just five per hundred in some to more than 95 per hundred in others. Over three years (2008-2011), the researchers spent 458 days in Kaziranga video-taping and documenting elephant behavior. They then isolated 116 instances where males interacted, and sometimes sparred, with each other.
When they examined who won these jousts, the results were categorical. Musth males always won tussles. The second most important factor for a winning male was his size, just like in African elephants. They found that whether a male had tusks or not was least important.
Out of 86 interactions between males, musth ones won an incredible 84 times (a 98% success rate). On the other hand, out of 82 times when one male had a tusk advantage, the tusker won only 54 times (a 66% success rate). Tuskers lost to both musth males and larger males.
The tensile strength of the Asian elephant tusk is surprisingly low — some species of bamboo have double the tensile strength of such ivory. Elephants can easily snap bamboo with their trunk and body weight, and it is possible they can do the same with an opponent's tusks. "I have seen makhnas grab the tusks of a tusker and push," says Chelliah.
The status of tusks, was therefore, found to be "at the bottom of the hierarchy of male-male signals" and thus could facilitate rapid evolution of tuskless males in the population under artificial selection against tusked elephants increasingly poached for ivory. It may so happen that tusked males are entirely wiped out from the region and replaced with makhnas, the researchers say.
"It would be interesting to examine whether the high proportion of tuskless adult male elephants in northeastern India is a consequence of artificial selection imposed upon a system of signals in male-male combat in which musth and body size override the advantage of possessing tusks," the authors write in their paper.