Vampire bats might avoid bitter substances to dodge indigestion - New Scientist

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Vampire bats can’t taste sweet foods, but they can taste some bitter substances – and doing so may even be beneficial.

During their evolution, vampire bats lost their receptors for detecting sweet tastes. That is probably because they didn’t need them, says Maik Behrens at the Leibniz-Institute for Food Systems Biology at the Technical University of Munich, Germany. Unlike fruit bats, for example, they don’t eat sweet-tasting foods.

The bats also lost most of their receptors for bitter tastes, but not all of them. Behrens and his colleague Florian Ziegler, also at the Leibniz-Institute for Food Systems Biology, wanted to know why vampire bats still retain some ability to detect bitter-tasting foods. To investigate, they conducted experiments to see exactly which kinds of bitter-tasting chemicals vampire bats could detect.

The common vampire bat (Desmodus rotundus) has three bitter taste receptors; Behrens and Ziegler inserted DNA sequences for producing each one into human kidney cell cultures – which are often used for studying taste – and grew them in the lab.

Then they added small amounts of bitter chemicals to the cultures and measured the cells’ responses to work out which chemicals activated the receptors, as well as to establish their sensitivity to each substance.

Some of the compounds that the bat receptors picked up, like artemisinin and quinine, are found in plants, says Behrens. Since vampire bats don’t eat plants, it is possible that these receptors are just inherited from a bat ancestor that did eat the occasional plant, perhaps as part of a diet comprised largely of insects.

However, Behrens and Ziegler also found that one of the taste receptors detected metal ions, such as those in magnesium sulphate, known commonly as Epsom salt. This chemical can occur in mineral water, like the volcanic springs in Cauca valley, Colombia, where common vampire bats live.

Behrens speculates that this ability to detect what he and Ziegler call “bitter salts” might be adaptive in vampire bats. Magnesium sulphate, in particular, could theoretically encourage the blood that the vampire bats eat to clot more while it is being digested, which might make the bats feel ill. Behrens therefore wonders whether the vampire bats detect magnesium sulphate in water and avoid drinking too much of it.

“It’s like humans with salt; we need a little bit, but not too much,” he says. “I think vampire bats, like most animals, don’t like bitter tastes, and that their receptors tell them when the concentrations of bitter salts are too high because it might not be good for them.”

Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2021.0418