The mystery of the disappearing elephant tusk
Give it a few thousand years, and tusks could completely disappear from the Asian elephant (Elephas maximus). The beautifully smooth, elongated ivory incisors neatly bordering a long trunk are iconic in the public mind. The reigning hypothesis is that tusks evolved to help male elephants fight one another, as demonstrated when males compete over females in estrus. However, a recent study published in the journal Animal Behaviour has shown that tusks may not be key factors in tussles, at least as far as elephants are concerned.
Size seems to matter. Studies of African savannah elephants (Loxodonta Africana) in Amboseli, Kenya, have shown that larger males tend to win jousts, as do those in "musth." Musth is an intense but temporary sexual state during which a male's testosterone level shoots up, he starts dribbling pungent urine and secreting a tar-like substance from either side of his head. But the role of tusks during interactions between male elephants has not been determined until this study.
Karpagam Chelliah and Raman Sukumar from the Centre for Ecological Sciences at the Indian Institute of Science, Bangalore, decided to study which factor - tusks, musth or body size - gives fighting male elephants the biggest competitive edge. They needed a population that had all three variables: both tusked and tuskless males, males that come into musth and come out of it, and males of varying sizes.
They found just the population they needed at Kaziranga National Park in the state of Assam in eastern India. In Asian elephants, females do not have tusks and males can be either tusked or tuskless (called "makhnas"). This is unlike the African elephant species, in which all individuals have tusks. The number of makhnas in a population varies from place to place; in Kaziranga, there are approximately equal numbers of tuskers and makhnas among the males.
Situated in the floodplains of the majestic Brahmaputra River and crisscrossed by her tributaries, Kaziranga is rightly called the Serengeti of India. Its large swathes of grassland, patches of tall elephant grass, tropical semi-evergreen forest and water bodies laced with riverine vegetation are home to approximately 1,165 elephants. Come the monsoon, most of the park vanishes underwater.
The researchers spent 458 days at Kaziranga during the dry season over three years, observing elephant activities. They documented the behavior they saw, capturing more than 450 hours of video. Using these videos, they created a photographic database of 132 adult male elephants, differentiating individuals primarily through ear morphology - degree of folding, cuts in the ear margin, holes in the ear and the vein pattern.
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Elephant image via Shutterstock.