Friday, February 22, 2013

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.
 

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.

16 comments:

  1. I'm so glad elephants evolved a way to save themselves from poachers! However, the founder effect of the original 11 member tuskless population may reduce genetic diversity and lead to inbreeding, further decreasing the chances of African elephants' long-term survival. I hope scientists introduce new, tusked individuals to this particular national park and diversify the genetic pool.

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  2. Interesting evolution. Given the high rate of poaching especially in Africa, I think the advantages of being tuskless outweigh the fitness advantages of having tusks.

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  3. You mentioned there was concern about the fitness of tuskless elephants, but has it been tested? And also, if there is a shift towards tuskless elephants, perhaps they will find a way to compensate for the lack tusks.

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  4. It is very interesting that the tuskless elephant has been selected towards. While it is understandable because of the poaching, you said the animal's fitness decreases when it has no tusks, so it doesn't make sense why a species would select towards the less fit version. However, this must mean that elephants will have a way to adapt to the change of not having tusks. Before the increase of poaching, do you know the percentage of elephants that were tuskless? Has there also been a change in size of tusks the other elephants? have they become smaller?

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  5. If poaching has been banned in this area it may be a good idea to attempt to introduce tusked elephants back into the population. But with the number of tuskless elephants increasing (11 to 324)it seems as if the absence of tusks hasn't been as detrimental to their fitness as was previously thought.

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  6. From the title, this sounded like a pretty Lamarckian idea, so I was impressed with how it was explained. Also, what a relief that this random allele has been introduced into the population.

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  7. It is comforting that this mutation may ultimately save elephants from poaching. However, it is sad to see an species lose one of its defining features. Now there may be a day in the near future when elephants are no longer associated with large tusks or ivory. This would be incredibly strange to see in another organism such as the rhinoceros which are also constantly poached for ivory

    -Jeff Brown

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  8. The strength of human influence on the evolution of other species is intense. We are constantly forcing other species, like the elephant to evolve and it makes me wonder what current day creatures will look like centuries from now. Very interesting topic!

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  9. I wonder what other notable features of endangered animals could be lost if genetic drift had similar effects on their populations. Rhinos without horns? Tigers without stripes?

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  10. What research has been done to determine what the fitness disadvantage of the tuskless elephants compared to elephant populations that still have their tusks?

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  11. It is sad that we have had such a significant impact on the population of elephants but it also shows nature's resilience. It will be sad to see these changes happen to many species as we move forward. Hopefully, the changes will not make populations more vulnerable to other threats.
    -Jesse Passman

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  12. This is very interesting and yet another example of artificial selection by humans like domestication of pet animals. Tusked elephants must be saved to conserve the biodiversity of these animals.

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  13. I wonder what the prevalence of the tuskless phenotype was before poaching. Also, since having tusks provides an advantage in sexual selection, does that mean the 2% of tusked elephants left who are male enjoy a large mating benefit? I don't know about elephant mating systems, but if they use harems or polygyny then maybe the reproductive success of tusked males is high enough that maybe tusked elephants will start to increase in number.

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  14. This post was depressing yet informative, and definitely brings out the effects that humans have on a species. I don't know much about poaching or the collection of ivory tusks, but is it necessary to kill the entire elephant to retrieve the ivory? Is there a possiblity to only retrieve part of the tusks for ivory, but still leave the elephants alive in order for them to reproduce and continue to pass on the genes for elephants with tusks?

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    1. That's a ? I always wanted to find out about..,I don't think the poachers care enough to dart them and just take the tusks.

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  15. They should breed them to be tuskless- that is the only chance for them to survive since the poachers always win.

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