Bats that eat insects are unable to taste sweet foods, even though they have the genetic ability to do so.
The evolution of taste perception and diet are closely linked for many animals, but in some cases this link is unclear. Different species of bat have highly diverse diets, ranging from nectar to insects and even blood, despite having similar taste receptor genes.
To discover more, Huabin Zhao at Wuhan University in China and his colleagues sequenced two sweet taste receptor genes in 34 bat species. They found that all the bats expressed both genes, meaning their tongues contain the receptor proteins.
Advertisement
They then tested the food preferences of two of the species, the insectivorous Rickett鈥檚 big-footed bat (Myotis ricketti) and the Leschenault鈥檚 rousette fruit bat (Rousettus leschenaultii). This involved placing two bottles in a cage with each bat, one filled with their usual food, the other with a mixture of their food and sugar.
The team found that the fruit bats had a strong preference for the sweet food, but the insectivorous bats didn鈥檛. 鈥淭his is surprising because these two species have similarly conserved sweet taste receptors genes which are expected to show similar sensitivity to sugar,鈥� says Zhao.
The researchers also directly tested the activity of these receptors by expressing them in living cells. They found that in fruit bats, the sweet taste receptors responded to natural sugars, but the same wasn鈥檛 true for insectivorous bats, suggesting a loss of sweet taste.
This makes sense because insects contain little sugar, so insectivorous bats don鈥檛 have much to lose by evolving this sense away. 鈥淭his relaxes the functional constraint on the sweet taste receptor, which eventually resulted in the loss of sweet taste in insectivorous bats,鈥� says Zhao, supporting the idea that taste perception is shaped by an animal鈥檚 feeding preference.
Why these receptor genes are still being passed down and expressed despite the loss of sweet taste in insectivorous bats is unclear. 鈥淥ne possibility is that these receptors have evolved new functions,鈥� says George Zhang at the University of Michigan, but exactly what those functions are is unknown.
PNAS
Sign up for Wild Wild Life, a free monthly newsletter celebrating the diversity and science of animals, plants and Earth鈥檚 other weird and wonderful inhabitants
