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Sour foods are often avoided by mammals, but many birds regularly feed on highly acidic fruits. Evolution has provided them with a clever strategy to eat extremely acidic fruit. A new study that birds' sour receptors shut down when exposed to acidic food, reducing the transmission of sour signals and thus influencing their perception and tolerance. The findings suggest that the molecular evolution of sour receptors in birds may have played a key role in their evolution and diversification. Interestingly, in songbirds, this appears to have occurred at the same time as the evolution of sweet taste perception, suggesting a possible coevolution of sour and sweet taste.
Birds are one of the most diverse and charismatic groups of terrestrial vertebrates. A critical factor that has shaped their evolutionary history is the ability to adapt flexibly to food resources and exploit new dietary niches. Fruit, in particular, is an important food source for most bird species, providing an important source of energy, especially during migration or periods of food scarcity.
In a new study, scientists at the Kunming Institute of Zoology, the Chinese Academy of Sciences and the Max Planck Institute for Biological Intelligence found that birds have evolved a strong tolerance to acidic food thanks to molecular changes in their sour taste receptors, an evolutionary trait that may have helped them expand their ranges and occupy diverse ecological niches. This provides a new perspective for understanding the evolution of animal senses and ecological adaptations.
Sour foods are often avoided by mammals, but many birds can frequently feed on fruits that are extremely acidic – including some wild fruits with a pH as low as 2.5. The team identified a key player in this tolerance: the sour taste receptor otopetrin 1 (OTOP1), which actively shuts down in low pH environments in some birds, reducing the transmission of sour signals and thus reducing their aversive response to acidic foods.
Through gene editing technology, the researchers introduced the OTOP1 gene from a canary (a songbird) into mice. They found that the modified mice showed a significant reduction in neuronal responses to sour stimuli. In addition, they found that inhibiting the sour taste receptor OTOP1 significantly weakened the ability of pigeons and canaries to tolerate acids, confirming the central role of this receptor in sour taste perception and sour tolerance in birds.
Further analysis pinpointed four key amino acid sites (H239, L306, H314, G378) that contribute to the receptor’s acid-inhibiting properties. Unlike other birds, songbirds (such as canaries) possess the final mutation on this list – G378 – which confers an even higher acid tolerance.
Insights into taste receptor evolution
By reconstructing ancestral taste receptors at different locations on the songbird evolutionary tree, the researchers also found that the enhanced acid tolerance in these birds co-occurred with the emergence of sweetness perception, raising the possibility that sour and sweet taste perception in songbirds evolved in parallel. This coordinated shift in sweet and sour sensing may have enabled them to expand their dietary preferences to not only include highly acidic fruits, but also sugary resources such as nectar- and may have impacted the songbirds, a group of birds containing nearly half of all bird species alive today.
This study suggests that the functional evolution of sour taste receptors may have played a key role in shaping avian evolution, providing new insights into the molecular mechanisms of animals’ sensory adaptation to their environment.
(This text has been adapted from a press release by the Kunming Institute of Zoology, Chinese Academy of Sciences.)
Dr. Maude Baldwin
Director
Max Planck Institute for Biological Intelligence
maude.baldwin@bi.mpg.de
Molecular evolution of sour tolerance in birds
Hao Zhang †, Lei Luo†, Qiaoyi Liang †, Lifeng Tian †, Yong Shao †, Xiuping Zhang, Kaixun Cao, Anna Luo, Chengsan Wang, Peter Muiruri Kamau, Dong-Dong Wu, Maude W. Baldwin, Ren Lai
† These authors contribute equally to this work
Science, online June 19, 2025
http://www.bi.mpg.de/baldwin - Website of Maude Baldwin's department
http://www.bi.mpg.de - Website of the Max Planck Institute for Biological Intelligence
https://www.science.org/doi/10.1126/science.adr7946 - Original publication
Unlike mammals, birds often feed on sour fruits. A new study shows how this tolerance developed.
Copyright: © Gabriel Weijie Low
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Unlike mammals, birds often feed on sour fruits. A new study shows how this tolerance developed.
Copyright: © Gabriel Weijie Low
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