Why do female elephants not have tusks?
|
More than 20,000 African elephants are illegally killed every year for their ivory tusks, leaving behind the animals’ carcasses in their wake. But ivory hunting can impact more than just elephant numbers– a recent study found that previous overhunting has led to the increase of naturally tuskless elephants in Mozambique. During the Mozambique Civil War from 1977 to 1992, armies hunted so many elephants for their highly profitable ivory tusks that the species evolved in the span of a generation. Show In addition to wrecking the natural ecosystem, the war left a scar on local elephant populations. As elephant numbers plummetted, the amount of female African savannah elephants born tuskless rose from just 18% to 51%. (In well-protected areas, tusklessness in elephants is as low as 2%.)  910179134Seized elephant ivory. Photo by: SIA KAMBOU SIA KAMBOU Seized elephant ivory. The decades of poaching and constant killing of tusked elephants made being tuskless more advantageous from an evolutionary standpoint in Mozambique’s Gorongosa National Park. While this mutation may have protected some elephants from ivory hunters, it is not beneficial to the overarching survival and wellbeing of these creatures. Tusks are actually massive teeth deeply rooted in an elephant’s enamel. They have many important functions like digging, lifting objects, gathering food, stripping bark off of trees to eat, and defense– protecting the elephant’s trunk. “[Tusks are] not just ornamental. They serve a purpose,” says Shane Campbell-Staton, an evolutionary biologist at Princeton University, “If an elephant doesn’t have the tool to do those things, then what happens?” 1053558054The tuskless gene mutation is hereditary. Photo by: Peter Chadwick Peter Chadwick The tuskless gene mutation is hereditary. The hereditary trait that causes female elephants to be born without tusks is formed by two tooth genes. In male elephants, the mutation is lethal. Tuskless elephants survived poaching in greater numbers passing down their mutated genes to the next generation– leading to both an increase in female tuskless elephants and a decrease in male elephants overall. The evolutionary change in the African savannah elephant population is so significant, scientists predict the species will continue to experience its impact for generations to come, even as poaching eases. WORLD Science Add Topic Some African elephants are evolving to have no tusks. Is it from years of poaching?Scott Gleeson USA TODAY Female African elephants in Mozambique's Gorongosa National Park have been born without their ever-crucial ivory tusks, and scientists are saying it's an evolutionary result of the brutal poaching and killing of the animals during the country's civil war. According to new research released Thursday in the journal, Science, between the years of 1972 and 2000, elephants born without tusks – almost all female – tripled in number. In Gorongosa in the 1970s, 18.5% of female elephants didn't have tusks. Now that number is 51%. Analysis from the study revealed that tuskless elephants are five times more likely to survive. "Evolution is simply a change in heritable characteristics within a population over successive generations, and based on the results of our study, the shift toward tusklessness among female elephants at Gorongosa fits this definition perfectly," Ryan Long, an author of the study and an associate professor of wildlife sciences at the University of Idaho, told CNN. Fact check::Image of an elephant carrying a lion cub is altered Company:Seeking to resurrect the woolly mammoth, return extinct animal to the Arctic An elephant's tusks help the animal lift heavy branches, topple trees, strip bark, fight, and dig holes for water and minerals. The tuskless elephants started to balloon in numbers shortly after the end of the country's civil war in 1992 (it began in 1977) and analysis revealed they were five times more likely to survive during the war without tusks. "The fact that it occurred so rapidly is rare indeed, and is a direct function of the strength of selection," Long said. "In other words, it happened so quickly because tuskless females had a MUCH higher probability of surviving the war, and thus a MUCH greater potential for passing their genes on to the next generation." One anomaly with the evolutionary development is the fact that almost all of the elephants without tusks are female. Research revealed the trait to be sex-linked and related to specific genes that generated a tuskless phenotype more likely to survive in the face of poaching. “When mothers pass (tusklessness) 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. Why are female elephants tuskless?Driven by the harvest of elephants for ivory, the tuskless trait has become more prevalent in the population as females born without tusks are more likely to survive and reproduce.
Why is Tusklessness only found in females?Campbell-Staton and his colleagues noted that tusklessness is seen only in female elephants. This, and the pattern of inheritance of the trait, suggested that it is caused by a mutation on the X chromosome that is fatal to males and dominant in females — just one copy of a mutation is needed to cause it.
Are female elephants born with tusks?Normally, both male and female African elephants have tusks, which are really a pair of massive teeth. But a few are born without them. Under heavy poaching, those few elephants without ivory are more likely to pass on their genes.
|
