Why the long neck, giraffe? Genetic discovery offers best answer yet

17 May 20168 Shares

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For centuries, we’ve been fascinated by the unique features of the giraffe, particularly its long neck, but we have been at a loss about how it evolved to its current form, until now.

Despite thousands of years of curiosity surrounding how the giraffe with its long neck came to be, the first scientific analysis into the incredible animal began with Charles Darwin in the 1800s, who tried to apply his Theory of Evolution to it.

From a physiological point of view, Darwin and hundreds of biologists who followed in his footsteps questioned the evolutionary benefit a heart that needs to pump blood as high as two metres to the giraffe’s brain.

It was only possible due to the animal evolving to have blood pressure twice as high as other mammals and an abnormally-large ventricle but, in order to find what was responsible for such changes, a team of researchers compared its genetic changes with that of its closest living relative, the okapi.

What is the difference between a giraffe and an okapi?

At first glance, it would be hard to find many similarities between the two, with the okapi appearing to have more in common with a zebra than a giant capable of reaching heights of 6m, with the original divergence believed to have happened between 11 and 12 million years ago.

A paper published in Nature Communications by a research team from Pennsylvania State University compared the gene-coding sequences of the giraffe and the okapi to more than 40 other mammals, including the cow, sheep, goat, camel, and human, to help determine what genetic changes might have been responsible for the divergence.

Using a battery of comparative tests to study the genome sequences of the giraffe and the okapi, the scientists discovered 70 genes that showed multiple signs of adaptations.

And, based on the discoveries that came from these tests, several genes were found to be shared by both, with those that regulate the development of the cardiovascular system and control blood pressure among the genes showing multiple signs of adaptation in the giraffe.

One gene to rule them all

This raises the intriguing possibility that the giraffe’s stature and powerful cardiovascular system evolved in concert through changes in a small number of genes.

“To achieve their extraordinary length, giraffe cervical vertebrae and leg bones have evolved to be greatly extended,” said researcher Douglas Cavener.

“At least two genes are required – one gene to specify the region of the skeleton to grow more and another gene to stimulate increased growth.”

One of these most intriguing genes, Cavener said, was one designated FGFRL1, which has a cluster of amino acid substitutions unique to giraffes that determine the development of the giraffe embryo.

DNA sequencing

DNA sequencing. Image via Shutterstock

Using CRISPR

Both Cavener and his research partner Morris Agaba are now planning on using the latest in gene manipulation technology to take the giraffe’s FGFRL1 gene by introducing its unique changes into mice using the CRISPR gene-editing method.

This does not mean that they will begin growing long-necked mice, but they will see how the gene alters the growth of their spine and legs.

“We hope that the publication of the giraffe genome and clues to its unique biology will draw attention to this species in light of the recent precipitous decline in giraffe populations,” Cavener concluded.

Giraffe image via Shutterstock

Updated 22 June 2016: This article originally stated the giraffe-okapi divergence happened between 11 and 12bn years ago, which was an error.

Colm Gorey is a journalist with Siliconrepublic.com

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