Yukta Kulkarni ’22
Poaching is defined as the illegal hunting of animals, especially when some part of an animal is profitable. This type of wildlife exploitation has been occurring for years, harming multiple species and causing unforeseen evolutionary consequences. A prominent example of this is habitual ivory poaching, or the killing of both male and female elephants for their extremely valuable ivory tusks. In fact, some elephant populations in Africa have declined 90% after years of heavy poaching. This has led to large percentages of African elephants being without tusks, specifically females. Campbell-station et al. sought to determine the genetic reasons as to why this phenomenon is occurring. They hypothesized that tusks are an X-linked dominant, male-lethal trait, meaning that tusks are passed down via the X-chromosome (females have XX chromosomes and males have XY chromosomes). One affected X-chromosome will lead to tusklessness in females (because there’s an unaffected chromosome), and death in males.
To test this, the researchers used elephants already in an African database, thus the age, sex, and physical attributes for multiple elephants were already on file. Once the elephants were correctly identified outdoors, 18 female elephants (7 tusked, 11 tuskless) were injected with an immobilizer to draw blood for DNA samples. The elephants were taken care of during the entire process with heart rate, respiratory rate, and temperature monitoring. After DNA analysis, it was discovered that 87.1% of mother-child pairs followed the hypothesis of tusks being X-chromosome linked and that the X-chromosome had lethal effects on males. The specific selection of humans hunting and killing elephants with tusks has been shown to decrease the number of tusked elephants that are available to pass down their genes to their offspring.
This has considerable consequences on the population and ecosystem of elephants. Since they use their tusks for a variety of purposes, some corresponding to survival, elephants are becoming evolutionarily disadvantaged. Another worrying factor is the size of the male elephant population as this tusklessness X-chromosome has been seen to be lethal in males, causing females to overpower the population. This can lead to many issues with finding partners for reproduction and may lead to female-dominant populations. Even though further research is needed to study the tusklessness X-chromosome, poaching of elephants for their tusks needs to stop before this physical trait is permanently erased.
 S. Campbell-Station, et al., Ivory poaching and the rapid evolution of tusklessness in African elephants. Science 374, 483-487 (2021). doi: https://doi.org/10.1126/science.abe7389
 Image retrieved from: https://www.flickr.com/photos/paulshaffner/282428428