Science. 2014 Aug 22;345(6199):929-33. doi: 10.1126/science.1255097.

Sensory biology. Evolution of sweet taste perception in hummingbirds by transformation of the ancestral umami receptor.

Baldwin MW¹, Toda Y², Nakagita T², O'Connell MJ³, Klasing KC⁴, Misaka T², Edwards SV⁵, Liberles SD⁶.

Author information

1: Department of Organismic and Evolutionary Biology, Harvard University, and Museum of Comparative Zoology, Cambridge, MA 02138, USA. maudebaldwin@gmail.com stephen_liberles@hms.harvard.edu.
2: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, Japan.
3: Bioinformatics and Molecular Evolution Group, School of Biotechnology, Dublin City University, Glasnevin, Dublin 9, Ireland.
4: Department of Animal Science, University of California, Davis, Davis, CA 95616, USA.
5: Department of Organismic and Evolutionary Biology, Harvard University, and Museum of Comparative Zoology, Cambridge, MA 02138, USA.
6: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA. maudebaldwin@gmail.com stephen_liberles@hms.harvard.edu.

Abstract

Sensory systems define an animal's capacity for perception and can evolve to promote survival in new environmental niches. We have uncovered a noncanonical mechanism for sweet taste perception that evolved in hummingbirds since their divergence from insectivorous swifts, their closest relatives. We observed the widespread absence in birds of an essential subunit (T1R2) of the only known vertebrate sweet receptor, raising questions about how specialized nectar feeders such as hummingbirds sense sugars. Receptor expression studies revealed that the ancestral umami receptor (the T1R1-T1R3 heterodimer) was repurposed in hummingbirds to function as a carbohydrate receptor. Furthermore, the molecular recognition properties of T1R1-T1R3 guided taste behavior in captive and wild hummingbirds. We propose that changing taste receptor function enabled hummingbirds to perceive and use nectar, facilitating the massive radiation of hummingbird species.