Bats are the second most species rich mammalian order (after rodents) and occupy a large variety of ecological niches. They are also well-known to be hosts of various highly virulent pathogens, and thus their immune system should be adapted accordingly. While fruit-eating bats are expected to have lower contact rates with pathogens, carnivorous species may have a much higher risk to contract diseases. In a comparative study on the immune system of various Neotropical bat species, we found that frugivorous bats have a lower number of white blood cells than carnivorous species. The lowest white blood cell counts were found in insectivorous bats, probably because frugivory involves sharing food sources that may potentially be contaminated with faeces and saliva of other bats. Insectivorous bats however catch tiny prey that are not expected to transmit diseases by being ingested.
Besides not having to invest as much into the immune system as carnivores, fruigivory may have an other advantage: Fruits contrain high concentrations of antioxidants. These substances can mitigate negative effects of reactive oxygen species, deleterious substances produced by the body as by-products of energy production. Reactive oxygen species cause damages on DNA and other cell structures, which is called oxidative stress and is regarded as the main cause of why animals (including humans) age. We measured oxidative stress in bat species with varying diets and found that frugivores have the lowest level of oxidative stress. They seem to have high concentrations of antioxidants in their blood, probably deriving from a frugivorous diet.
Immunology and ageing
One of the main sources of reactive oxygen species are white blood cells which are produced during immune reactions. During an immune reaction, measures of oxidative stress are elevated, which I showed during an experiment with short-tailed fruit bats (Carollia perspicillata). Thus, being sick comes with more than one disadvantage: It may also excellerate aging. Using a colony of individually marked greater sac-winged bats (Saccopteryx bilineata), I repeatedly measured concentrations of white blood cells over time to see whether elevanted immune components reduce survival. I found that older bats have lower levels of white blood cells, and that individuals with increased concentrations were less likely to be alive in the subsequent year.
Signalling mate quality
In many animals, females are very picky towards males and choose carfully whom to mate with. This is also the case in the greater sac-winged bat, where males court heavily for the females using an odourous liquid which they store in specialised sacs in the wing membrane. The males then hover in front of perching females and fan the scent towards them. Using chemical analysis of the odour, we recently found that the scent may give information about maturity, relatedness and geographical distance of the males and thus may be used by the females to choose the best partner.Furthermore, odour may also signal individual quality, such as immune competence, which I aim at investigating during future projects.
Schneeberger K., Voigt C.C., Müller C., Caspers B. (2016) Multidimensionality of chemical information in male greater sac-winged bats (Saccopteryx bilineata). Frontiers in Ecology and Evolution 4: 83 [pdf]
Schneeberger K., Voigt C.C. (2015) Zoonotic viruses and conservation of bats. In: Bats in the Anthropocene: Conservation of bats in a changing world (eds. Voigt, C.C., Kingston, T.). Springer Verlag. [pdf chapter], [pdf, epub whole book]
Schneeberger K., Courtiol A., Czirják G.Á., Voigt C.C. (2014) Immune profile predicts survival and reflects senescence in a small, long-lived mammal, the greater sac-winged bat (Saccopteryx bilineata). PLoS One 9(9): e108268 [pdf]
Schneeberger K., Czirják G.Á., Voigt C.C. (2014) Fruvigory is associated with low measures of plasma oxidative stress and high antioxidant concentration in free-ranging bat. Naturwissenschaften 101 (4): 285-290 [pdf]
Schneeberger K., Czirják G.Á., Voigt C.C. (2013) Inflammatory challenge increases measures of oxidative stress in a free-ranging, long-lived mammal. Journal of Experimental Biology 216: 4514-4519 [pdf]
Schneeberger K., Czirják G.Á., Voigt C.C. (2013) Measures of the constitutive immune system are linked to diet and roosting habits of neotropical bats. PloS One 8 (1): e54023 [pdf]