Ever wondered why giraffes has that amazing long neck? For the first time, the genomes of this African rumiant and its closest living relative, the okapi, have been sequenced. They have revealed the first clues about the genetic changes that led to the evolution of the giraffe's exceptionally long neck and its record-holding ranking as the world's tallest land species.
The research, led by Douglas Cevenar of Penn State University and Morris Agaba of Tanzania's Nelson Mandela African Institute for Science and Technology, was published in the scientific journal Nature Communications on May, 2016. They have a great project website called The Giraffe Genome Project.
Okapi and giraffe diverged from a common ancestor only 11 to 12 million years ago. This is a short term in evolutionary terms, but both species are significantly different at a glance, that's why this comparison has been so useful to identify the unique genetic changes on the giraffe.
"The giraffe's stature is dominated by its long neck and legs and an overall height that can reach 19 feet (~ 6 m)" said Cavener. "The evolutionary changes required to build the giraffe's imposing structure and to equip it with the necessary modifications for its high-speed sprinting and powerful cardiovascular functions have remained a source of scientific mystery since the 1800s, when Charles Darwin first puzzled over the giraffe's evolutionary origins," explains the scientist in a press release.
The giraffe's heart must pump blood two meters straight up in order to provide an ample blood supply to its brain. This feat is possible because the giraffe's heart has evolved to have an unusually large left ventricle, and the species also has blood pressure that is twice as high as other mammals.
"The most intriguing of these genes is FGFRL1, which has a cluster of amino acid substitutions unique to giraffe that are located in the part of the protein that binds fibroblast growth factors -- a family of regulators involved in regulating many processes including embryo development," Cavener said. This fibroblast-growth-factor pathway plays a crucial role in controlling development, beginning in early development of the embryo and extending through the bone-growth phase after the giraffe is born. In humans and also in mice, severe skeletal and cardiovascular defects are associated with debilitating mutations in this gene.
The scientists also identified four homeobox genes -- the kind involved in the development of body structures -- which are known to specify the regions of the spine and legs. Cavener speculates, "The combination of changes in these homeobox genes and the FGFRL1 gene might provide two of the required ingredients for the evolution of the giraffe's long neck and legs."
Agaba first noticed a group of genes regulating metabolism and growth that were diverged in giraffe as compared to okapi. One of these genes encodes the receptor for folic acid, which is an essential B vitamin necessary for normal growth and development.
Other metabolic genes that the scientists found to be significantly changed in giraffe are those involved in the metabolism of the volatile fatty acids that are generated by the fermentation of ingested plants, like acacia leaves, that are toxic to other animals.
"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 said. "Giraffe populations have declined by 40 percent over the past 15 years due to poaching and habitat loss. At this rate of decline, the number of giraffes in the wild will fall below 10,000 by the end of this century. Some giraffe subspecies already are teetering on the edge of extinction."
In addition to Agaba and Cavener, other members of the research team include Edson Ishengoma of the Nelson Mandela African Institute for Science and Technology; Webb C. Miller, Barbara C. McGrath, Chelsea Hudson, Oscar C. Bedoya Reina, Aakrosh Ratan, Rico Burhans, Rayan Chikhi, Paul Medvedev, Craig A. Praul, Lan Wu-Cavener, and Brendan Wood of Penn State; Heather Robertson of the Nashville Zoo; and Linda Penfold of the White Oak Conservancy.
This research received financial support from Penn State University, Penn State's Huck Institutes of the Life Sciences, and the Nelson Mandela African Institute for Science and Technology.
The genetic changes occurring in endangered species might increase their extinction probabilities. Low population sizes leads to reduced genetic diversity and increased inbreeding. A low of genetic diversity means a reduced ability to adapt to environmental changes. Inbreeding is often associated to reduced reproduction and survival. Genetic factors might thus play an important role in species extinction -and therefore in their conservation.
Molecular genetic markers are often used to assess the genetic status of endangered species and populations. This information is then used to elaborate conservation plans designed to maximize genetic diversity and minimize inbreeding.