The two African elephants were thought to be closely related until detailed nuclear DNA studies revealed their differences.
Animals that look very similar have sometimes accumulated so many changes to their genetic makeup over time that they are best described as different species. They might well be able to mate successfully, but if they live in different habitats there is rarely the opportunity to exchange genetic material and each species can evolve independently to suit its environment.
African Elephants
Until recently many experts thought that the two types of elephant currently found in Africa were best considered as races or sub-species of the African Elephant (Loxodonta africana). They were called the Bush Elephant (Loxodonta africana africana) and the Forest Elephant (Loxodonta africana cyclotis). The Forest Elephant lives in the forests of the Congo basin and is half the size of the Bush Elephant which inhabits open savannah country.
Recent DNA studies (Rohland, Reich, Mallick, et al.) suggest that these two populations have been separated for a very long time and most specialists now refer to them as Loxodonta cyclotis (forest) and Loxodonta africana (bush or savanna). In other words they are two different species.
Indian Elephant and Wooly Mammoth
The researchers who showed that the two living African elephants have been evolving independently for thousands of years also looked at the nuclear DNA of the Indian Elephant (Elephas maximus) and the extinct Woolly Mammoth (Mammuthus primigenius).
Their results suggest that the two African elephants are no more closely related to one-another than the Indian Elephant is to the (extinct) Wooly Mammoth.
Nuclear and Mitochondrial DNA
- Animal cells have most of their DNA in the nucleus, and this codes for the genes that males and females pass on (in equal amounts) to their offspring.
- All cells also contain a small amount of DNA in their mitochondria - small cellular structures involved with cellular respiration. Mitochondrial DNA is passed from mother to offspring, males make no contribution.
- Nuclear DNA (thousands of times more complex than mitochondrial DNA) allows a 'broader and more accurate picture of elephants' history' (Nature).
This explains how earlier studies of mitochondrial DNA led scientists to conclude that the two African elephants were closely related, while the more detailed study of their nuclear DNA shows that they are very different.
Elephant Conservation Issues
Now that it is known that Africa has two different elephant species it is important that different strategies are developed to protect and conserve each one.
Forest Elephants have different habitat requirements from Bush Elephants and will need their own conservation programmes if they are to survive.
References:
Rohland N, Reich D, Mallick S, Meyer M, Green RE, et al.'Genomic DNA Sequences from Mastodon and Woolly Mammoth Reveal Deep Speciation of Forest and Savanna Elephants.', PLoS BIOLOGY, December 2010,
and Natasha Gilbert, 'African elephants are two distinct species', NATURE (naturenews), published online 21 December 2010.
