Elephants in Mozambique are evolving away from having tusks due to pressure from rampant poaching over decades, according to a daunting new study.
Published in the journal Science on Friday, the report from researchers across departments at Princeton University, the non-profit ElephantVoices, Gorongosa National Park in Mozambique, and the University of Idaho, analyzed survey data that suggests natural selection has favored tusklessness in female elephants—a rare genetic trait that has become more common—amid high rates of poaching and population decline.
The researchers took scans of the entire elephant genome and located two genes associated with tooth development in mammals, both of which guide the formation of enamel, dentin, and other materials necessary for tooth and tusk development. One of the genes—AMELX, which provides instructions for the creation of a protein called amelogenin—was found to be associated with selection pressure due to poaching.
The team undertook the study after observing both growing rates of tusklessness among female elephants and severe population declines (2,542 elephants in 1972 whittled down to 242 in 2000) among both sexes in Gorongosa National Park. A civil war in Mozambique from 1977 to 1992 killed off some 90 percent of the country’s elephant population, the paper notes, as armies on both sides of conflict targeted the animals for ivory. Though tusklessness is currently considered a rare genetic trait in female African elephants, they’re significantly less attractive to poachers. Tuskless elephants are therefore much more likely to survive, passing on the tuskless gene to their offspring, who pass it onto their offspring, and so on. The paper notes that as the population of elephants took a nosedive, there was a threefold increase in the frequency of tuskless females.
Today, poaching remains a multi-billion dollar trade worldwide, one that is primarily responsible for diminishing elephant numbers, the authors say.
“Intensive poaching in Africa has been associated with an increase in the frequency of tuskless elephants,” the study reads. “Our study shows how a sudden pulse of civil unrest can cause abrupt and persistent evolutionary shifts in long-lived animals even amid extreme population decline.”
The team used mathematical models to test whether the increased numbers of tuskless females could have occurred without natural selection, and concluded that this was unlikely. They found that tuskless female elephants were more than five times as likely to survive over the 28-year period studied as their tusked counterparts. Somewhat curiously, no tuskless males were located in the data collection process. The researchers think the trait may be tied to a mutation on the x-chromosome that is fatal to male elephants and dominant in females.
“When mothers pass it on, we think the sons likely die early in development, a miscarriage,” Brian Arnold, a co-author of the study and evolutionary biologist at Princeton, told the Associated Press.
The research serves as a wakeup call to ecologists and policymakers alike about the long-term threat of poaching, Chris Darimont, a conservation scientist at the University of Victoria in British Columbia who was not involved in the work, told Nature.
“They have this very compelling genomic data,” he says. “This is a wake-up call in terms of coming to grips with humans as a dominant evolutionary force on the planet.”
A widespread reduction in the prevalence of tusks can have far-reaching implications for ecosystems, the paper notes. Tusks are crucial for excavating food and minerals from underground, gouging and peeling bark, killing trees and creating habitat for other species. A disruption to elephant genetics could cause a ripple effect for other species.
“A population-wide increase in tusklessness may have downstream impacts,” the paper says. “Elsewhere, evolution in species that perform key ecological functions has exerted potent effects.”
“Understanding the dynamics of rapid evolution in the Anthropocene is therefore essential, not only for revealing the biological impacts of contemporary human activities,” it continues, “but for designing strategies to mitigate them.”