Some elephants evolve to have no tusks in response to brutal poaching – WSVN 7News | Miami News, Weather, Sports
(CNN) – An elephant’s tusks are one of its features – they help the animal lift heavy branches, knock down trees, bark, fight and dig holes for water and minerals .
But a growing proportion of female elephants in Mozambique’s Gorongosa National Park have been born without these essential tools, and scientists say this is an evolutionary response to the brutal slaughter of elephants for their ivory tusks during the country’s 15-year civil war.
Elephant experts working in the park began to notice the phenomenon after the war ended in 1992. Field data and analysis of old video footage from the park revealed that the proportion of helpless female elephants has increased. more than tripled between 1972 and 2000. It was a period when the elephant population grew from around 2,000 to around 250 individuals, said Ryan Long, associate professor of wildlife science at the ‘University of Idaho.
“During the war, Gorongosa was essentially the geographic center of the conflict,” Long said by email. “As a result, there was a large number of soldiers in the area and a lot of motivation associated… to kill elephants and sell ivory to buy weapons and ammunition. The resulting level of poaching was very intense.
Scientists now have a better understanding of the genetic basis for this lack of tusks and why it only appears to affect female elephants, according to a study published Thursday in the journal Science.
Analysis showed that females without tusks were more than five times more likely to survive over the 28-year period than their female counterparts with tusks, so adaptation is highly unlikely to be a fortuitous event.
Lack of tusk occurs naturally – and only in females – even in the absence of poaching, but usually only in a small minority of elephants. In Gorongosa in the 1970s, 18.5% of female elephants did not have tusks, while three decades later, 51% did.
“Evolution is simply a change in hereditary characteristics within a population over successive generations, and based on the results of our study, the shift to tuskless in female elephants at Gorongosa fits perfectly with this definition, ”said Long, author of the study.
“The fact that this has happened so quickly is indeed rare and is a direct function of the strength of the selection,” he said via email. “In other words, it happened so quickly because the defenseless females had a MUCH higher probability of surviving the war, and therefore a MUCH greater potential to pass their genes on to the next generation.”
But what about male elephants? After taking blood samples from 18 female elephants, with and without tusks, the researchers sequenced their genomes. They found that defenseless females exhibited genetic variation in a very specific region of the X chromosome, which plays a role in the development of defenses.
“Females have 2 X chromosomes. In helpless females, one of these chromosomes is ‘normal’ and the other contains the deleted information. Explain.
“When a defenseless female conceives male offspring, that male has a 50/50 chance of receiving the affected X chromosome from his mother. If it receives the “normal” chromosome, it will survive and be born with the genetic information necessary to produce defenses.
However, if the male elephant fetus receives the chromosome with the genetic variant, it dies in the womb because the variant that produces defenseless females is fatal for males, Long said.
The exact genetic and developmental mechanism that leads to the absence of tusks in females and the loss of male elephants during an elephant’s 22-month pregnancy was not yet understood, according to the study.
Elephant numbers have rebounded in Gorongosa to around 800, Long said. Having no tusks doesn’t seem to bother female elephants significantly, but it’s something researchers want to study further. He said the dietary analysis suggested defenseless females eat a higher proportion of herbs.
“The population is doing well and there are a lot of elephants without tusks. They’ve clearly adapted to life without defenses, but there’s a lot we don’t know.
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