Spicy foods elicit a pungent or hot and painful sensation that repels most mammals. However, the tree shrew (Tupaia belangeri chinensis), a species closely related to primates, seems to violate this rule of thumb.
Researchers accidentally observed tree shrews directly and actively consuming chili peppers, despite the deep geographic isolation between the animal and the food.
To understand this tolerance for spicy food, a research group led by Prof. LAI Ren from the Kunming Institute of Zoology of the Chinese Academy of Sciences along with researchers from Zhejiang University performed genomic and functional analyses on the tree shrew and its TRPV1.
The research revealed that a single point mutation in the tree shrew's transient receptor potential vanilloid type-1 (TRPV1, a polymodal nociceptor) ion channel (tsV1) lowers its sensitivity to capsaicinoids, thus enabling tree shrews' unique feeding behavior regarding pungent plants.
The experimental evidence suggests that strong selection for this residue in tsV1 might be driven by Piper boehmeriaefolium, a spicy plant that geographically overlaps with the tree shrew and produces Cap2, a capsaicin analog, in abundance.
Therefore, researchers think that feeding adaptation to P. boehmeriaefolium is the most likely explanation for the fixation of this mutation by positive selection, thus allowing the tree shrew's diet to expand.
This study broadens understanding of the evolutionary and molecular mechanisms of pungency tolerance behavior.
This work was supported by funding from the National Science Foundation of China, the Chinese Academy of Sciences and Yunnan Province.