A new study published in Science has uncovered how birds have evolved to tolerate the high acidity of many fruits-revealing a key sensory adaptation that may have helped fuel their explosive diversification and ecological dominance.
While frugivory plays a crucial role in avian ecology, with most bird species relying on fruits as essential energy sources particularly during periods of food scarcity or migration. However, the high concentrations of organic acids in many fruits pose a physiological challenge. For most mammals, sour taste acts as a deterrent, signaling potentially harmful substances. Yet, birds not only tolerate sour fruits but often consume them in large quantities. Until now, the biological basis for this tolerance remained unclear.
Led by Prof. LAI Ren from the Kunming Institute of Zoology of the Chinese Academy of Sciences, a research team focused on organismal survival strategies and environmental adaptations has discovered that birds' sour taste perception is modulated by a key molecular mechanism. Their findings show that the avian sour taste receptor OTOP1 is inhibited under low pH conditions, reducing the neural signals associated with sour taste and mitigating the aversive response to acidic foods.
When the researchers introduced the OTOP1 gene from songbirds (canaries) into mice, the mice exhibited a marked reduction in sour taste-related neural activity. Conversely, the pharmacological inhibition of OTOP1 in birds (pigeons and canaries) significantly impaired their sour tolerance, confirming the critical role of this receptor in avian sour taste perception and sour tolerance.
Further analysis showed that songbirds, carrying an additional G378 mutation, exhibit even higher sour tolerance than other birds. Analysis of reconstructed ancestral avian sour taste receptors indicates that enhanced sour tolerance in songbirds likely co-evolved alongside the acquisition of sweet taste perception, potentially enabling dietary diversification, environmental adaptation, and the occupation of broader ecological niches.
This study demonstrates that the functional evolution of avian sour taste receptor played a key role in driving the adaptive radiation of both birds as a taxonomic class, as well as the highly diverse songbird lineage specifically.
By proposing a novel hypothesis of co-evolution dynamics between sour tolerance and sweet taste perception in songbirds, this work significantly deepens our understanding of avian radiative evolution and provides new insights into how sensory receptor functional evolution drives avian adaptation and ecological success.
Although the interaction between birds and fruits spans vast evolutionary time, how birds perceive and tolerate the high concentrations of organic acids in fruits remained unexplained.
The mechanism of environmental adaptation mediated by the evolution of the sour taste perception function in birds. (Image by ZHANG Hao)
