Tusks are usually a big plus for elephants, as they can use them to dig for water, strip bark for food, and joust with other elephants. But those big incisors can also be a liability amid intense ivory poaching. Now, researchers have found that elephants in Mozambique have evolved towards tusklessness in an area affected by poachers.
Mozambique went through a civil war from the late 1970s to the early 1990s, with both sides of the conflict targeting elephants for ivory to finance their war efforts. As a result, elephant population dropped more than 90% in what’s now the country’s Gorongosa National Park, going from 2,000 animals when the conflict started to about 250.
Many of those who survived shared one key characteristic: over 30% of the females were naturally tuskless, meaning they couldn’t develop tusks, while before the war only 18% lacked tusks. Genes are behind whether elephants inherit tusks from their parents. So after the war the tuskless surviving females passed their genes with surprising results.
“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. In Gorongosa, recovery of both elephant abundance and ancestral tusk morphology may be crucial for ecosystem restoration,” the researchers wrote in the journal Science.
An elephant’s evolution
Researchers from Princeton University worked with colleagues in Mozambique to further understand how ivory trade had tipped the scales of natural selection. They observed over 800 elephants in the Gorongosa national park over several years and created a catalogue of mothers and offspring by collecting blood samples from them.
As tuskless elephants were female, the team decided to focus on the X chromosome. While males have an X and Y chromosome, females have two X. They also believed that the relevant gene was dominant (a female needs only one altered gene to be tuskless) and when passed to male embryos it could alter their development phase.
After sequencing the genomes, the researchers identified a dominant gene that may explain the tusklessness, called AMELX. The gene is passed from mothers to offspring on the X chromosome — remarkably, humans have it too. In people, the gene disruption causes brittle teeth in females. But in human males a disrupted gene usually means death.
For the researchers, this could also be true of African elephants. If a male gets a disrupted AMELX gene, he likely dies. But the mutated gene leads just to tusklessness in a female elephant. Not having tusks might not seem like a critical issue, but this could actually have a snowball effect on the whole ecosystem of the African elephants.
If an elephant doesn’t have tusks, it means that their behavior changes. They don’t push for trees anymore because they can’t strip their bark, for example. This affects other animals too. Once elephants push over tees, this opens new space for other grassland plants, which creates habitats to other species. A decline in tusked elephants alters that process.
Ultimately, while this may allow elephants to survive the poaching crisis, it could have long-term cascading effects for the entire ecosystem.
“A population-wide increase in tusklessness may have downstream impacts such as reduced bioturbation, shifts in plant species composition, reduced spatial heterogeneity, and increased tree cover—any of which could affect myriad other ecosystem properties. Elsewhere, evolution in species that perform key ecological functions has exerted potent effects,” the researchers wrote
The study was published in the journal Science.
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