Giraffes are tall. Only their neck is longer than every person walking on Earth… By a quarter of a human… Ok, if you want the actual number, a giraffe’s neck usually stretches to 2,5m! And yes – they do still have as many vertebrae in their neck as the mice, and us – humans. The ecological reasoning behind why giraffes evolved to have such long necks – so to be able to reach the evolving to be ever-taller-to-avoid-them plants – seems obvious nowadays. But that evolution did not affect only the length of their neck, it also included developing incredibly sophisticated cardio-vascular, neural systems and muscles to support the existence of the animal. Now geneticists are able to tell us which genes exactly are responsible for these incredible modifications.
Scientists sequences the genome of the Masai giraffe (the largest species of giraffes) and compared it to its closest relative’s genome – the okapi, and some species which separated from the giraffe lineage earlier in the evolutionary history. Turns out that about 70 genes showed differences which can be contributing to the extraordinary anatomy and physiology of the giraffe compared to its cousins.
Some of these genes code for proteins-regulators of the skeletal growth and differentiation. For example, one of those genes is the FGFRL1, which exists also in okapis, cattle and humans too and is practically exactly the same between them, but in giraffes has seven amino acid substitutions. FGFRL1 stands for Fibroblast Growth Factor receptor-like 1 and as its name shows – is involved in a molecular cascade influencing growth – cell division and cell differentiation. Another gene with yet another 7 giraffe-specific mutations is the FOLR1, which codes for a protein bringing vitamin B9 into the cell. Vitamin B9 is more popular as folic acid and is vital for the production of healthy blood cells among other things. Differences are found also in genes related to cellular metabolism and oxygen consumption/energy production. Other genes have mutated regions very prone to post-transnational modifications in other organisms, basically meaning that the proteins products of these genes are probably very similar to the corresponding proteins in other species, but the “accessories” on these proteins alter their function and interactions with other molecules in the cell, which can significantly alter the outcome of the expression of these genes.
Other genes which are significantly different in giraffes are related to the shape of the heart-muscle cells, to the thickness of the blood-vessel walls and to the ability of the giraffe to maintain blood pressure 2,5 times higher than the human one. And when the trees in the habitats of the giraffes kept evolving taller and more toxic in order to avoid the grazing of the high-reaching animals, the giraffes started evolving metabolic ways to extract more energy from their food and to neutralize the toxicity of the poisonous compounds stored in some of the plants’ leaves.
Most of the mutations found are indeed giraffe-specific as the researchers compared gene sequences from other animals with long necks (camels for example), in which this physical aspect does not relate to a specific feeding advantage in their own environment, and these animals do not posses the specific substitutions or mutations giraffes do.
The article in which these findings are described came out in Nature Communications – “Giraffe genome sequence reveals clues to its unique morphology and physiology” and gave us interesting insight in what makes a giraffe. With the advances of genome sequencing, gene annotation, and comparative and evolutionary biology we are able to better understand the genome-wide differences between species and what are the subtle differences in our genes that make us, in the end, so different organisms from each other.