In response to heavy poaching by armed forces during the 20-year Mozambican civil war, populations of African savanna elephants (Loxodonta africana) in Gorongosa National Park declined by 90%; as the population recovered after the war, a relatively large proportion of female elephants were born tuskless.
Human-mediated selection for tusklessness in African savanna elephants (Loxodonta africana) during the Mozambican civil war appears to be driven by recent selection on at least one X-linked locus (AMELX) and one autosomal locus (MEP1a). Image credit: Benh Lieu Song / CC BY-SA 2.0.
“The selective killing of species that bear anatomical features such as tusks and horns is the basis of a multibillion-dollar illicit wildlife trade that poses an immediate threat to the survival of ecologically important megafauna worldwide,” said Dr. Shane Campbell-Staton, a researcher at Princeton University and the University of California, Los Angeles and colleagues.
“Megaherbivores are especially vulnerable to overharvesting because of their large habitat requirements, small population sizes, and long generation times.”
“As ecosystem engineers, these species also behaviorally regulate ecological processes; anthropogenic selection on phenotypes that influence these behaviors may, therefore, have cascading effects on ecosystem functioning.”
“However, most work that details human-driven selection has focused on smaller species in which evolutionary change is more readily studied.”
“It remains unclear to what extent, at what rates, and through what mechanisms harvest-induced phenotypic change occurs in the world’s largest land animals.”
In the study, the researchers investigated the impacts of ivory hunting on the evolution of African savanna elephants in Gorongosa National Park, Mozambique, during and after the Mozambican civil war (1977 to 1992).
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, the study authors show that intense poaching during this period resulted in an increase in the frequency of complete tusklessness in female elephants from the region.
The stark lack of tuskless males suggested a sex-linked genetic origin for the pattern.
“Survey data revealed tusk-inheritance patterns consistent with an X chromosome-linked dominant, male-lethal trait,” the scientists said.
“Whole-genome scans implicated two candidate genes with known roles in mammalian tooth development (AMELX and MEP1a), including the formation of enamel, dentin, cementum, and the periodontium.”
“One of these loci (AMELX) is associated with an X-linked dominant, male-lethal syndrome in humans that diminishes the growth of maxillary lateral incisors (homologous to elephant tusks).”
“This study provides evidence for rapid, poaching-mediated selection for the loss of a prominent anatomical trait in a keystone species,” they said.
The findings were published in the journal Science.
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Shane C. Campbell-Staton et al. 2021. Ivory poaching and the rapid evolution of tusklessness in African elephants. Science 374 (6566): 483-487; doi: 10.1126/science.abe7389
Source link: https://www.sci.news/biology/ivory-poaching-tusklessness-african-elephants-10193.html
