Ivory poaching leads to rapid evolution of tuskless African elephants

Intense ivory poaching during the Mozambican Civil War (1977-1992) resulted in the rapid evolution of tusklessness in female African elephants amid a precipitous population decline, researchers report, resulting in a phenotype far more likely to survive in the face of poaching. The findings shed new light on the powerful selective forces human harvesting can exert on wild animal populations. The selective killing of species – whether for food, safety, or profit – has only become more common and intense as human populations and technology have grown. So much so, it's suggested that wildlife exploitation by humans has become a powerful selective driver in the evolution of targeted species. However, the resulting evolutionary signatures remain unclear. In this study, Shane Campbell-Staton and colleagues investigated the impacts of ivory hunting on the evolution of African elephants in Gorongosa National Park, Mozambique, during and after the Mozambican Civil War. During this conflict, armed forces on both sides heavily relied on the ivory trade to finance war efforts, which led to a rapid population decline of more than 90%. Using historical field data and population modeling, Campbell-Staton et al. show that intense poaching during this period resulted in an increase in the frequency of complete tusklessness in female elephants from the region. According to the authors, the stark lack of tuskless males suggested a sex-linked genetic origin for the pattern. Whole-genome analysis revealed a pair of candidate genes, including AMELX, a loci with known roles in mammalian tooth development. In humans, these genes are associated with an X-linked dominant, male-lethal syndrome that diminishes the growth of lateral incisors, which are homologous to elephant tusks. “Campbell-Staton et al.’s elegant approach is among the rare studies that document a genetic response to harvest selection, informing debate about the potential for selective harvests to lead to evolutionary responses,” write Chris Darimont and Fanie Pelletier in a related Perspective.