Microprotein
In many species, taste receptors have shown loss of functions. The evolutionary process of which taste receptors lost their function is believed to be adaptive evolution where it is associated with feeding ecology to drive specialization and bifurcation of taste receptors. [1] Out of all the taste receptors, bitter, sweet, and umami are shown to have a correlation between inactivation of taste receptors and feeding behavior. [1] However, there are no strong evidences that support any vertebrates are missing the bitter taste receptor genes. [1]
The sweet taste receptor is one of the taste receptors where the function has been lost. In mammals, the predominant sweet taste receptor is the Type 1 taste receptor Tas1r2/Tas1r3. [2] Some mammalian species such as cats and vampire bats have shown inability to taste sweet. [2] In these species, the cause of loss of function of the sweet receptor is due to the pseudogenization of Tas1r2. [2] The pseudogenization of Tas1r2 is also observed in non-mammalian species such as chickens and tongueless Western clawed frog, and these species also show the inability to taste sweet. [2] The pseudogenization of Tas1r2 is widespread and independent in the order Carnivora. [2] Many studies have shown that the pseduogenization of taste receptors is caused by a deleterious mutation in the open reading frames (ORF). [3] In a study, it was found that in nonfeline carnivorous species, these species showed ORF-disrupting mutations of Tas1r2, and they occurred independently among the species. [2] They also showed high variance in their lineages. [2] It is hypothesized that the pseudogenization of Tas1r2 occurred through convergent evolution where carnivorous species lost their ability to taste sweet because of dietary behavior. [2] Overall, the loss of function of the a taste receptor is a evolutionary process that occurred due to a dietary change in species. [3]
Umami is also a taste receptor where the function has been lost in many species. The predominant umami taste receptors are Tas1r1/Tas1r3 (Jiang). [2] In two lineages of aquatic mammals including dolphins and sea lions, Tas1r1 has been found to be pseudogenized. [2] The pseudogenization of Tas1r1 has also been found in terrestrial, carnivorous species. [2] While the panda belongs to the order Carnivora, it is herbivorous where 99% of its diet is bamboo, and it cannot taste umami (Zhao) Genome sequence of the panda shows that its Tas1r1 gene is pseudogenized. [4] In a study, it was found that in all species in the order Carnivora except the panda, the open reading frame was maintained. In panda, the nonsynonymous to synonymous substitutions ratio was found to be much higher than other species in order Carnivora. [2] This data correlates with fossil records date of the panda to show where panda switched from carnivore to herbivore diet. [2] Therefore, the loss of function of umami in panda is hypothesized to be caused by dietary change where the panda became less dependence on meat. [2] However, these studies do not explain herbivores such as horses and cows that have retained the Tas1r1 receptor. [4]
- ↑ 1.0 1.1 1.2 Feng, Ping; Zhao, HuaBin (2013-6). "Complex evolutionary history of the vertebrate sweet/umami taste receptor genes" (in en). Chinese Science Bulletin 58 (18): 2198–2204. doi:. ISSN 1001-6538. http://link.springer.com/10.1007/s11434-013-5811-5.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 Jiang, P.; Josue, J.; Li, X.; Glaser, D.; Li, W.; Brand, J. G.; Margolskee, R. F.; Reed, D. R.; et al. (2012-03-27). "Major taste loss in carnivorous mammals" (in en). Proceedings of the National Academy of Sciences 109 (13): 4956–4961. doi:. ISSN 0027-8424. PMID 22411809. PMC: PMC3324019. http://www.pnas.org/cgi/doi/10.1073/pnas.1118360109.
- ↑ 3.0 3.1 Antinucci, Marco; Risso, Davide (2017-11-28). "A Matter of Taste: Lineage-Specific Loss of Function of Taste Receptor Genes in Vertebrates". Frontiers in Molecular Biosciences 4. doi:. ISSN 2296-889X. PMID 29234667. PMC: PMC5712339. http://journal.frontiersin.org/article/10.3389/fmolb.2017.00081/full.
- ↑ 4.0 4.1 Zhao, H.; Yang, J.-R.; Xu, H.; Zhang, J. (2010-12-01). "Pseudogenization of the Umami Taste Receptor Gene Tas1r1 in the Giant Panda Coincided with its Dietary Switch to Bamboo" (in en). Molecular Biology and Evolution 27 (12): 2669–2673. doi:. ISSN 0737-4038. PMID 20573776. PMC: PMC3108379. https://academic.oup.com/mbe/article-lookup/doi/10.1093/molbev/msq153.