Vampire bats feed exclusively on blood, a mode of feeding unique amongst mammals. It has therefore been long suspected that vampire bats have highly specific evolutionary adaptations, which would be documented in their genome, and most likely also have an unusual microbiome, the community of micro-organisms assembled in their digestive tract which may help with the digestion of blood. An international group of scientists including several from the German Leibniz Institute for Zoo and Wildlife Research (IZW) analysed the genome of vampire bats and the microorganisms that live in their gut and asked the question how much the viruses contained in the blood may affect the vampire bats. The results demonstrate that the microbiome plays an essential part in tackling nutritional and non-nutritional challenges posed by blood meals and improving resistance to viral infections. Because vampire bats carry rabies, they are often considered as a threat to livestock. As it turns out, vampire bats carry fewer infectious viruses than previously thought. These findings have now been published in Nature Ecology & Evolution and EcoHealth.
Specialisation to a unique food source often requires specific adaptations in a genomic context. The common vampire bat (Desmodus rotundus) belongs to a small group of bat species that are adapted to a blood-based diet (sanguivory). Feeding only on blood poses a big challenge, as this diet is low in vitamins, lipids and glucose and has a high salt content. A blood diet also exposes these animals to a large variety of blood-borne pathogens, including viruses.
An international group of scientists, including several researchers from the Leibniz Institute for Zoo and Wildlife Research (IZW), sequenced and analysed both the vampire bat genome and its microbiome -- the micro-organisms that live inside the gut -- to investigate specific adaptations of vampire bats to sanguivory. The scientists discovered that the vampire bat microbiome is very different from other carnivorous, insectivorous or frugivorous bats. The adaptations to feeding on blood conferred by both the genome and the microbiome include the ability to tackle nitrogen waste and increased osmotic pressure, iron assimilation and changes in immunity, including a high number of protective bacteria capable of producing antiviral substances. In a second study, researchers from the Leibniz-IZW and colleagues from Mexico examined the presence of viruses in populations of vampire bats and cattle from the same geographic region. The surprising insight was that bats and cattle did not share pathogenic viruses. In general, vampire bats carried far fewer retroviruses, for example, than other bats or other mammals.
"To understand an animal's specific evolutionary adaptations it is essential to examine it from what we now call a "hologenomic" perspective, which includes the interactions of an animal with its environment and its microbiome," says Dr Marina Escalera-Zamudio, a former PhD student at the Leibniz-IZW and currently a postdoctoral fellow at Oxford University.
The concept of hologenomic evolution argues that both an animal and its microbiome are subject to natural selection and experience changes because of the specific environmental circumstances of the animal. Dietary specialisation may therefore require evolutionary changes in both the genome and the microbiome, which in turn have an influence on digestion, kidney function and the immune system. "In vampire bats, the microbiome not only helps to process a nutrient-poor diet, which is difficult to digest by the host, it also contributes to host defense against blood borne viruses. This is a really good example of the interdependency between the host and its bacterial community during the evolutionary process," says Escalera-Zamudio.
Both studies suggest that host ecology and species-specific adaptations must be taken into consideration to determine the risk that a bat species poses in transmitting viruses.