Tuskless Elephants: An Evolutionary Response To Poaching
Wildlife exploitation, such as poaching, has obvious consequences. Populations decline, and the exploited animals may become extinct. Changes in an area’s ecology can change the predator-prey balance, food availability, vegetation, and other habitat characteristics. But can external threats such as poaching change the actual biology of the animals themselves? We’re all taught that genetic evolution takes an exceedingly long time, particularly for long-lived animals. But it turns out that, when survival is at stake, evolution can move much faster.
Civil war raged in Mozambique from 1977 to 1992. During this period, ivory poaching decimated the African savannah elephant population. Large herbivore numbers fell by more than 90% as combatants on both sides of the conflict slaughtered animals to buy arms and ammunition. This kind of intensive poaching had been associated with an increase in tuskless female elephants elsewhere in Africa. An increase in tuskless females had also been observed in Mozambique’s Gorongosa National Park. But was this increase in tusklessness random, or did it indicate an evolutionary response to threat?
To answer this question, researchers looked at both phenotypic and genotypic data. They first analyzed survival statistics and concluded that the increased proportion of tuskless females was not a chance event but indeed represented a selection bias. They then conducted whole genome analysis on 18 of the park’s female elephants, seven tusked and 11 tuskless.
Results confirmed that the genetic changes were linked to gender. Approximately two-thirds of tuskless female’s offspring were also female, while normal reproduction patterns would produce a roughly equal number of each gender. In addition, the genomic analysis revealed a plausible genetic driver for these variations. Scientists found an X-chromosome-linked dominant, male-lethal gene that, in humans, diminishes the growth of maxillary lateral incisors. These teeth are homologous to tusks in elephants.
Advocates should view these findings with alarm. In a truly short span of time, human action drove a significant genetic change in a keystone species. The change both distorted the natural gender balance in the population and removed a morphological feature key to both the animal and its habitat. Tusks are multipurpose tools. The elephants use them to find food and minerals. This use also affects their environments. If elephants can no longer perform such ecosystem services, this risks unintended future consequences not only for these magnificent creatures but for untold numbers of other animals that rely on the elephants and their tusks.