Exceptional anatomy of the giraffe and a series of evolving adaptations

Giraffes are generally very alert and use their advantage in height to scan the horizon thanks to their excellent eyesight. Credit: Mogens Trolle

The giraffe is a really confusing animal. With its exceptional anatomy and its series of evolutionary adaptations, the giraffe is an exceptional case of animal evolution and physiology. Today, an international team of researchers from the University of Copenhagen and Northwestern Polytechnical University in China produced a high-quality genome from the giraffe and studied the genes that may be responsible for its unique biological characteristics. .

The extraordinary stature of the giraffe has led to a long list of physiological co-adaptations. Giraffe’s blood pressure, for example, is twice as high as in humans and most other mammals to provide a constant blood supply to the head held high. How does the giraffe avoid the usual side effects of high blood pressure, such as severe damage to the cardiovascular system or stroke?

Testing giraffe mutations / genes in mice

The team discovered a particular gene – known as FGFRL1 – that underwent many changes in giraffes compared to all other animals. Using sophisticated gene editing techniques, they introduced giraffe-specific FGFRL1 mutations into laboratory mice. Interestingly, giraffe-type mice differed from normal mice in two important ways: they suffered less cardiovascular and organ damage when treated with a blood pressure-increasing drug, and they had more compact bones and more dense.

“Both of these changes are directly related to the giraffe’s unique physiological characteristics – coping with high blood pressure and maintaining compact and strong bones, despite growing faster than any other mammal, to form the elongated neck and legs,” explains Rasmus Heller. from the Department of Biology at the University of Copenhagen, one of the main authors of the study.

The giraffe can’t sleep

While jumping out of bed for (some) humans can be an effortless and elegant affair, the giraffe certainly isn’t. Just getting up is a long and delicate procedure, let alone getting up and running away from a fierce predator. As a result, giraffes have evolved and spend much less time sleeping than most other mammals.

Rasmus Heller explains: “We found that key genes regulating circadian rhythm and sleep were highly selected in giraffes, possibly allowing giraffes to have a more interrupted sleep-wake cycle than other mammals. “

Consistent with research on other animals, an evolutionary compromise also appears to determine their sensory perception, Rasmus continues:

“Giraffes are generally very alert and use their advantage in height to scan the horizon thanks to their excellent eyesight. Conversely, they have lost many genes linked to smell, which is probably linked to the presence of odors radically diluted at 5m above ground level.

A model of evolutionary mechanisms – and perhaps even of human medicine?

These results give an overview of the basic evolutionary modes. The double effects of the highly selected FGFRL1 gene are consistent with the phenomenon that one gene can affect several different aspects of the phenotype, which is called progressive pleiotropy. Pleiotropy is particularly relevant in explaining unusually large phenotypic changes, as such changes often require that a series of traits be altered within a short period of evolutionary time. Therefore, pleiotropy could provide a solution to the conundrum of how evolution could effect the many co-dependent changes needed to form an animal as extreme as a giraffe. In addition, the results even identify FGFRL1 as a possible target for research into human cardiovascular disease.

“These results show that animals are interesting models, not only for understanding the basic principles of evolution, but also for helping us understand which genes influence some of the phenotypes that really interest us, such as those related to disease. However, it should be noted that genetic variants do not necessarily have the same phenotypic effect in different species, and that phenotypes are affected by many factors other than variation in coding regions, ”explains Qiang Qiu of Northwestern Polytechnical. University, another senior author on the study.

The results have just been published in the prestigious scientific journal, Scientists progress.

Reference: “An Imposing Genome: Experimentally Validated Adaptations to High Blood Pressure and Extreme Stature in Giraffes” by Chang Liu, Jianbo Gao, Xinxin Cui, Zhipeng Li, Lei Chen, Yuan Yuan, Yaolei Zhang, Liangwei Mei, Lan Zhao, Dan Cai, Mingliang Hu, Botong Zhou, Zihe Li, Tao Qin, Huazhe Si, Guangyu Li, Zeshan Lin, Yicheng Xu, Chenglong Zhu, Yuan Yin, Chenzhou Zhang, Wenjie Xu, Qingjie Li, Kun Wang, Mr. Thomas P. Gilbert, Rasmus Heller, Wen Wang, Jinghui Huang and Qiang Qiu, March 17, 2021, Scientists progress.
DOI: 10.1126 / sciadv.abe9459

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