During the Mozambican Civil War, combatants on both sides poached elephants for their ivory to help pay for the costs associated with the conflict. Thirty years later, new research shows how the effects have lingered on, with a larger share of elephants never developing tusks.
In a study published in the journal Science, a team led by researchers from Princeton University investigated the phenomena of tuskless elephants in Mozambique. They say by the end of the civil war – which lasted from 1977 to 1992 – the number of elephants in the country’s Gorongosa National Park declined sharply from more than 2,500 to around 200. At the same time, the share of tuskless females nearly tripled, from 18.5% of the population to 50.9%. While there had been a few anecdotes of males without tusks seen elsewhere, none had been confirmed in the park.
To help understand this change, the team turned to models and analysis of the population. In doing so, they learned that a female without tusks was five times more likely to survive the conflict. That meant that they, in turn, would end up producing a larger portion of the population’s offspring. The researchers say this demonstrates natural selection caused by poachers.
Brian Arnold, co-first author and Schmidt DataX data scientist, says, “Tusks suddenly became a liability, even though in natural circumstances, tusks are very useful organs for elephants. There was intense hunting pressure on tusked females. Specifically targeting tusked females gave tuskless females a huge competitive advantage.”
The researchers wanted to understand the genetics behind this lack of tusks and why it was just observed in females, theorizing that it was a dominant X chromosome-linked trait that may be lethal to males. The hypothesis was that when it’s passed down to males, they die early in development through a miscarriage.
To test the theory, the team did a genetic study of the population’s female elephants and offspring by analyzing blood samples from both tusked and tuskless animals. They learned that about two-thirds of the offspring born to tuskless mothers were female, and they determined that the lack of tusks was related to two genes, including the X chromosome-linked amelogenin. Deletions of this gene cause similar teeth issues in humans and are connected with a syndrome that is X-linked dominant and lethal to males.
Robert Pringle, who also contributed to the research and is a professor of ecology and evolutionary biology at Princeton, says, “It’s fascinating insight into the mystery of how the elephants lost their tusks — a phenomenon that biologists have long been aware of, but that nobody has ever explained.”
The fact that so many of the elephants are now without tusks – roughly a third of tuskless elephants’ offspring still demonstrate this trait – may be problematic for their ecosystem. Researchers say this is because evidence suggests that they behave differently than other elephants.
Ryan Long, co-author and associate professor of wildlife sciences at the University of Idaho, explains, “Tusks are a defining feature of elephants, and they use them for all sort of behaviors, including digging for water and stripping bark from trees. How individual elephants adapt behaviorally to being tuskless is still a mystery that we’re hoping to unravel as we continue working on this project. Some of our preliminary data suggest, however, that tuskless elephants consume different diets than their tusked counterparts. Because elephants are a keystone species, changes in what they eat can affect the entire landscape, so a high rate of tusklessness in an elephant population could very well have ecosystem-wide consequences.”
However, Pringle says if conservation measures remain what they are, they do expect the syndrome to decrease over time. For now, though, some of the changes will likely persist for multiple generations.Whizzco