The Evolution of Tuskless Elephants due to Human Poaching and Genetic Drift

     Having a “favorite animal” seems to be a hallmark of youth, and most children are more-than-willing to extol the virtues of their chosen animal and explain why it is better than yours. My favorite animal was an elephant: The world’s largest terrestrial animal that is widely represented in popular culture, from children’s movies, such as Dumbo and Tarzan, to short stories, such as Elmer the Patchwork Elephant and Dr. Seuss’s Horton Hears a Who! However, recent studies have revealed that the elephant’s most prominent characteristic, its ivory tusks, may be a thing of the past, as human poaching and genetic drift have led to the prevalence of “tuskless” elephants in both Africa and Asia.
     In the nineteenth century, as the European colonization of Africa reached its zenith, the hunting of large game became incredibly popular, and animal trophies (ranging from elephant tusks to lion pelts) were proudly displayed in aristocratic homes. This hunting frenzy, when combined with extensive poaching, decimated animal populations across Africa. Elephant populations, specifically, experienced drastic declines, with some populations decreasing to as few as 8 individuals. As might be expected, tuskless elephants were highly represented in these remaining populations (due to their lack of ivory). Oddly enough, even as poaching was banned across Africa in the 1950s, the percentage of tuskless elephants continued to increase.
     Anna Whitehouse, a Professor of Terrestrial Ecology at the University of Port Elizabeth, South Africa, has spent years studying the elephant population in Addo Elephant National Park (South Africa), in which the prevalence of tuskless elephants has reached 98%. Poaching was banned in this area in 1954, and the number of elephants on the reserve has since increased from 11 to 324 individuals. The founding population (of 11 individuals) included 4 females and 1 male which were tuskless. As hunting was banned on the reserve, and no migration had since occurred, the prevalence of the tuskless allele could be due to environmental factors (e.g. finding food), sexual selection, or genetic drift. Upon discarding the first two possibilities (tusklessness does not provide advantages in terms of resources and actually decreases an organism’s sexual fitness), she attributed the fixation of the tuskless allele to genetic drift. It is purely by chance, she claims, that this allele has become dominant in the Addo elephant population (as well as in populations across Africa and Asia). The reason for the increasing tusklessness among African and Asian elephant populations, then, might be due to a combination of poaching and genetic drift: Poaching severely reduced elephant populations and resulted in an overrepresentation of tuskless individuals, and genetic drift led to the prevalence of the tuskless allele through chance (the alternative would be that genetic drift led to the loss of this allele).
     The concern with the prevalence of tuskless elephants is not that it will force us to change our childhood ideals of this animal, but that this characteristic seems to affect individual fitness: Elephants use their tusks to search for food and water, for self-defense against their few predators, and for sexual display among males. The dilemma is that individual elephants are capable of surviving without their tusks, but the overall population might not be adapted to do so. Without tusks, how will elephants search for water in droughts, establish social hierarchies, or defend themselves from lions and tigers? As with myriad other organisms, humans have irrevocably altered the course of elephant evolution, and the key question is if elephants will be able to adapt quickly enough to their native environments without the use of tusks? If elephant populations are unable to survive, it is depressing to contemplate that in a few centuries, Dumbo and Horton might be as fantastical to children as T-rexes and velociraptors are today. (623 words)

By: Lauren Lyssy

References

(BBC) British Broadcasting Corporation. 1998. World: Africa Elephants ‘ditch tusks’ to survive.

<http://news.bbc.co.uk/2/hi/africa/180301.stm.>

 

Whitehouse, A.M. 2002. Tusklessness in the elephant population of the Addo Elephant National      Park, South Africa. J. Zool. 257: 249-254.

Steenkamp, G., S.M. Ferreira, and M.N. Bester. 2007. Tusklessness and tusk fractures in free-ranging African savanna elephants (Loxodonta Africana). J. S. Afr. Vet. Assoc. 78: 75-80. 

Image Source 

Girish, Chandra. Evolution of Elephant. 2006. IASZoology.com. Web. 22 Feb 2013.