The Giraffe and its long neck : Gene analysis tells a tall story
At the first instance it sounds like a Rudyard Kipling tale. But actually researchers are dining deep into the giraffe genome.
The study have has uncovered genetic variations that could be behind unusual adaptations to neck length and cardiovascular system
Scientists said that they have discovered new insights into how the creature got its long neck and gangly frame.
The world’s tallest land animal, the giraffe boasts some curious characteristics. Its neck contains seven vertebrae, the same number as humans, but each is elongated. For blood to reach the brain, the heart must pump it to a height of two metres – a feat made possible by an unusual heart structure, blood pressure more than twice that of humans and thick-walled blood vessels.
Now scientists have discovered a host of genetic variations that could be behind such traits.
“Giraffes’ unique stature and turbocharged cardiovascular system did not arise from new genes but instead from genetic modification of a small number of genes that are well-known regulators of development and function,” said Douglas Cavener of Pennsylvania State University, an author of the research.
The international team, which included
scientists from the UK, US and Tanzania, describe how they sequenced the genome of two Masai giraffes.These genomes were then compared to that of the giraffe’s closest relative – a stripy-legged animal known as the okapi – and to cattle, which shared a common ancestor with giraffes and okapi around 28 million years ago. Variations discovered in the giraffe’s protein-coding sequences were then compared to the corresponding genes of 40 other mammals, from camels to mice, and assessed for their influence.
The giraffe genome project has seen scientists from Penn State University and The Nelson Mandela African Institute for Science and Technology team up to sequence and analyse the genomes of the giraffe and okapi.
The upshot was the discovery of 70 genes with variations specific to giraffes that, the researchers believe, could be behind the animal’s unusual adaptations. More than half of these genes were found to code for proteins that are involved in regulating the physiology or development of the cardiovascular system, neural system and skeleton, with some thought to influence factors such as which vertebrae become elongated.
Variations were also found in genes linked to metabolism, which could be involved in the giraffe’s ability to tolerate the toxic leaves and seed pods of the acacia tree.
The authors say that the study also suggests that features such as the giraffe’s long neck and specialised cardiovascular system might have evolved simultaneously, as some of the genes identified influence more than one aspect of development. Among these is FGFRL1, a gene known to be involved in regulating the development of both the skeleton and the cardiovascular system in humans and mice. “The fact that FGFRL1 is critical for the development of both skeletal and cardiovascular system, and these are the two systems that are modified the most in giraffes, makes it a key candidate gene responsible for giraffe’s unique features,” added Cavener.
But Nick Mundy, an evolutionary geneticist at the University of Cambridge, believes there is plenty more to be done before the mystery of how the giraffe got its neck is finally solved. “Describing genetic changes along the evolutionary branch leading to the giraffe is relatively straightforward; what is much harder is interpreting those changes,” he said. While the team have highlighted a collection of mutations, he added, “It is very difficult to say whether any of these are actually relevant to the giraffe’s neck. The genes they have identified are best viewed as candidates for further analysis.”
It’s a point Cavener appears to be probing. While he believes it likely that variations in several of the identified genes are responsible for the giraffe’s lengthy neck, the team, he says, are currently using gene editing techniques to introduce the giraffe’s version of the FGFRL1 gene into mice to see whether it affects their development. “It is quite possible that we will see a mouse with a slightly longer neck,” he said. “If we can show that it is statistically longer, then we will be very happy.”
