Giraffes are peculiar animals with their unusually long necks and legs. Their height allows them to reach leaves from trees that are inaccessible to other animals such as, zebra, wildebeest and deer, with whom they share their habitat. They are also able to detect predators like lions from far away in the grasslands they live in.
The long necks also pose a physiological problem. The heart has to pump blood at high pressure so that brain is sufficiently supplied. The ligaments supporting their necks need to be stronger. As their bones grow faster than other mammals, their bone density remains more or less similar to other mammals. This is strange because people have found that faster an animal's bones grow, weaker they get. So, what are the factors that enable giraffes evolve the characteristics they have now?
Giraffes belong to larger group of mammals called ruminants. Ruminants are characterized by their special way of digesting their food. They are herbivorous (plant eating) animals that partially ferment their food in specialized stomach compartment and chewing it again. Cattle, sheep, deer, giraffes, okapi and antelopes are some of its members.
With modern DNA sequencing methods and bioinformatics tools, it is possible to compare genomes of several species with another. Doing this, specific differences in genes can be located among different species. Similar approach was used by a group of scientists from China and Denmark to identify mutations (changes in DNA sequences) in giraffe genes that conferred them with tolerance to high blood pressure. They sequenced giraffe genome using three different methods to obtain a high quality sequence. Then they compared the sequence with cattle, goat and okapi. Although they found several differences in giraffe genes, the researchers narrowed down to a single gene, FGFRL1 (Fibroblast growth factor receptor-like protein1). This gene had 7 mutations in its functional domain which was unique to giraffe.
The researchers then modified the DNA of mice so that these mice would have this mutant FGFRL1 gene. Both normal and the mutant mice were then given a drug that causes high blood pressure. Although the blood pressures in normal mice increased dramatically, the blood pressure of mutant mice remained similar to the levels when the drug was not given. The researchers were successful in experimentally elucidating the genetic factor for giraffes high blood pressure tolerance.
The comparison of giraffe's genome also revealed other interesting features. It lost many genes related to olfactory senses (smell) but gained several genes that improved their vision. These genes are generally found in tree dwelling mammals. Improved vision along with tall stature allows them to spot predators easily.
There are several other findings in this paper, but let's stop here. Click here if you are interested in reading the original paper.
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