title: Selection for brain size impairs innate, but not adaptive immune responses.
abstract: Both the brain and the immune system are energetically demanding organs, and when natural selection favours increased investment into one, then the size or performance of the other should be reduced. While comparative analyses have attempted to test this potential evolutionary trade-off, the results remain inconclusive. To test this hypothesis, we compared the tissue graft rejection (an assay for measuring innate and acquired immune responses) in guppies (Poecilia reticulata) artificially selected for large and small relative brain size. Individual scales were transplanted between pairs of fish, creating reciprocal allografts, and the rejection reaction was scored over 8 days (before acquired immunity develops). Acquired immune responses were tested two weeks later, when the same pairs of fish received a second set of allografts and were scored again. Compared with large-brained animals, small-brained animals of both sexes mounted a significantly stronger rejection response to the first allograft. The rejection response to the second set of allografts did not differ between large- and small-brained fish. Our results show that selection for large brain size reduced innate immune responses to an allograft, which supports the hypothesis that there is a selective trade-off between investing into brain size and innate immunity.
authors.affiliation: Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, Stockholm 10691, Sweden Konrad Lorenz Institute of Ethology, Department of Integrative Biology and Evolution, University of Veterinary Medicine, Vienna, Savoyenstraße 1a, Vienna 1160, Austria alexander.kotrschal@zoologi.su.se.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kotrschal
authors.affiliation: Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, Stockholm 10691, Sweden.
authors.forename: Niclas
authors.initials: N
authors.lastname: Kolm
authors.affiliation: Konrad Lorenz Institute of Ethology, Department of Integrative Biology and Evolution, University of Veterinary Medicine, Vienna, Savoyenstraße 1a, Vienna 1160, Austria.
authors.forename: Dustin J
authors.initials: DJ
authors.lastname: Penn
mesh_terms: D056704:Adaptive Immunity; D000818:Animals; D001921:Brain / Q000033:anatomy & histology*; D005260:Female; D007113:Immunity, Innate; D008297:Male; D009929:Organ Size; D011036:Poecilia / Q000033:anatomy & histology / Q000235:genetics / Q000276:immunology*; D012641:Selection, Genetic
keywords: brain size; immune response; trade-off