Existence of Two African Elephant Species Declared

Existence of Two African Elephant Species Declared

Rachel Nuwer
Published: 06/10/2011


Forest elephants, a distinct species from their larger savannah counterparts. Credit: Thomas Breuer. 

What is a species?
   
One of the most basic definitions is a group of animals that can breed and produce fertile offspring. Additional frills—like similarity of DNA, the way an animal looks, or how it interacts in its ecosystem—can add clarity, and researchers are constantly updating and tweaking species’ parameters as new scientific findings come to light.
     
Ten years ago, researchers found through genetic analysis that the African elephant, once thought to be a single species dispersed throughout the sub-Saharan continent, is actually two distinct species. Despite this discovery, however, the International Union for Conservation of Nature (IUCN), one of the leading conservation organizations in the world and publisher of the endangered species “Red List,” refuses to acknowledge the reality of two African elephant species.
    
“There is no issue, it has been proven that there are two species,” says Sergios-Orestis Kolokotronis, an evolutionary biologist at the Sackler Institute for Comparative Genomics at the American Museum of Natural History in New York. “The IUCN thinks there’s a disagreement, but there is no disagreement,” says Kolokotronis, who co-authored a paper published in the journal PLoS One in June (lead author Alfred Roca) that further proves the two species conflict isn’t a conflict at all. The IUCN, however, continues to insist that “the taxonomic status of West African elephants remains unsure” and that hastily jumping to conclusions may leave some elephants in “taxonomic limbo.”
    
The story of the two divergent elephant species began about three million years ago, when expansive forests covered a greater area than in present-day Africa and elephants filled these jungles. At some point, the forest-dwelling elephants began to venture into the neighboring savannah. Researchers speculate that evolution began to shape these pioneer populations. They grew larger so they could travel farther for resources in the arid savannah environment. But the newly evolved savannah elephants’ interaction with the forest elephants was far from finished.
    
As it turns out, lady elephants prefer large males. “If you’re a big male, you get the mates,” Kolokotronis explains. When the smaller forest elephant females came into contact with the larger savannah elephants, hybridization—or interbreeding—would inevitably occur. Over time, the hybrid elephants had their own offspring, and their offspring had offspring, and all the while the hybrid females preferred the larger savannah elephant males. In this way, the original hybrid’s genes—once split 50-50 between savannah and forest elephants—eventually stabilized due to the savannah male preference. Their descendents’ genetic fingerprint came to be dominated almost entirely by savannah elephant nuclear DNA, or the hereditary information inherited from parents and stored within the nucleus of a cell.
    
The original forest elephant females, however, left their genetic mark. Some of the savannah elephants still carry the DNA of their great-great-great-great-(…) grandmothers in the form of mitochondrial DNA. Mitochondria, sometimes referred to as the “cell’s power plants,” are remnants of an ancient symbiotic union of our complex cells with helpful bacteria. Because they were once separate organisms, mitochondria maintain their own distinct DNA, which is passed to on to offspring only through the mother. It is this mitochondrial DNA—a remnant of past mating between the two elephant species—that confounded researchers, making it appear that both elephant species shared DNA, and thus were a single species. But as Kolokotronis says, analyzing mitochondrial DNA “only tells half the story.”
   
With Kolokotronis’ study as well as other work published in venues such as Science and Nature Genetics, molecular evidence clearly points towards the existence of two sub-Saharan species of elephant: one occupying isolated forest patches of Western and Central Africa, another living throughout the continent’s open savannahs. “They’re almost as divergent as we are from chimps,” Kolokotronis says of the elephants’ genetics.


A family of savannah elephants. Credit: Ikiwaner

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