Songbird ancestors evolved a new way to taste sugar

21 October 2021

Bitter, salty, sweet, sour and umami are the five basic tastes humans perceive, but we are naturally drawn to sweet. What about other animals? Do they know sweet from sour?

Dr Simon Sin (Oxford Croucher Scholarship 2008), Assistant Professor of the School of Biological Science at the University of Hong Kong (HKU), was part of an international research team led by Max Planck Institute for Ornithology, which examined whether songbirds can taste sweetness.

Many meat-eating mammals have lost their ability to detect sweetness over the course of evolution. It was thought that birds, descended from dinosaurs, had also lost their ability to taste sweetness.

Sin and the team studied more than 4000 species of songbirds and found that birds’ ability to detect sweetness does not depend on their primary diets. Through behavioural experiments, they noticed both nectar-specialised and grain-eating songbirds preferred sugar water to regular water.

Surprisingly, birds repurpose their umami taste receptors to recognise sugar. This ability has been conserved in the songbird lineage, influencing the diet of nearly half of all birds living today.

The study, published in Science, analysed more than 100 receptor variants to understand the molecular mechanisms underlying the sugar responses. Interestingly, over the course of evolution, distant bird groups converged on the same solution of re-purposing their umami taste receptors to taste sugar. However, each group modified the receptors in distinct ways to achieve the same outcome.

"It is intriguing that hummingbirds and songbirds convergently evolved to taste sugar, but via different ways. This is an important study that shows how different evolutionary pathways can lead to the same adaptation," says Sin.

The team found that songbirds evolved to sense sweetness approximately 30 million years ago, before the early ancestors of songbirds left Australia, their country of origin. Sugary food sources may have had an important role in driving songbirds to spread to other continents and occupy a variety of ecological niches.

Future studies aim to learn how sweetness perception has coevolved with other physiological traits, such as changes in digestion and metabolism, across bird evolution.

Dr Simon Sin is an Assistant Professor at the School of Biological Sciences of the University of Hong Kong. He obtained a BSc degree in Biology with first class honours at the Chinese University of Hong Kong (CUHK) in 2005, and an MPhil degree in Biology at CUHK in 2008. He was awarded a Croucher Scholarship in 2008 and joined the Wildlife Conservation Research Unit in the Zoology Department at the University of Oxford, where he accomplished his DPhil study in 2013.

To view Sin’s Croucher profile, please click here.