drinking blood comes with a cost

The old adage, you are what you eat, also applies to bats. Karin Schneeberger and colleagues discovered that the immune system of bats is strongly affected by their food choices.

Curious about what bats eat?

Bats display a staggering array of eating habits. There are carnivorous bats who eat flesh or drink blood. Omnivores diversify their food portfolio by eating both plants and animals. Insectivores selectively munch on insects. And phytophagous species eschew all other food groups in favour of fruits or flower nectar. Some bats even specialize on particular species of plant.

What are the risks of different diets?

MacConnell's bat_Schneeberger

Being choosey about what to eat might give bats an advantage because they can develop efficient food gathering skills. But there are inherent risks with becoming too specialized when their favourite food becomes scarce, or if it comes with a side of parasites! Carnivorous bats, including the infamous vampire bat, are especially at risk of contracting pathogens from their prey. Schneeberger and colleagues believe that bats have evolved differences in immune system defenses in response to the dangers associated with diet. To test this hypothesis, Schneeberger measured the immune health of 24 neotropical bat species representing different feeding strategies. White blood cell count was used to quantify immune system health because it directly affects the body’s ability to fight infection.

Eating meat is expensive!

While we have to shell out more for meat than veg at the grocery store, bats also pay for a carnivorous diet by investing more in their immune systems. Schneeberger observed that carnivorous bats had significantly higher white blood cell (WBC) counts than insectivorous or phytophagous species, and that, surprisingly, fruit and nectar eating bats had the second highest WBC counts. Schneeberger explained this is likely because fruit and flowers are contaminated with feces and saliva from other animals. Insectivorous bats had the lowest WBC counts because it is rare for insect pathogens to infect mammals, and these bats catch insects in open spaces where there are fewer vertebrate pathogens. This is the first evidence from a comparative study of free-ranging mammals to show a strong link between diet and immune system. These results could have important implications for conservation and studies of disease transmission. They also serve as a helpful reminder to wash your fruit!

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