Ivory poaching and the rapid evolution of tusklessness in African elephants

Understanding the evolutionary consequences of wildlife exploitation is increasingly important as harvesting becomes ever-more efficient. We examined the impacts of ivory poaching during the Mozambican Civil War (1977-1992) on evolution of African elephants (Loxodonta africana) in Gorongosa National Park. Poaching resulted in strong selection favoring tusklessness amidst a rapid population decline. Survey data revealed tusk-inheritance patterns consistent with an X-linked dominant, male-lethal trait. Whole-genome scans implicated two candidate genes with known roles in mammalian tooth development (AMELX and MEP1a), including formation of enamel, dentin, cementum, and the periodontium. One of these loci (AMELX) is associated with an X-linked dominant, male-lethal syndrome that diminishes growth of maxillary lateral incisors (homologous to elephant tusks). This study provides evidence for rapid poaching-mediated selection for the loss of a key anatomical trait in a keystone species.