Helena Westerdahl University of Lund, Sweden Title Avian MHC: genetic variation, natural selection and disease resistance in a natural population of great reed warblers Abstract The Major Histocompatibility Complex (MHC) plays a central role in vertebrates’ specific immune defence against various pathogens. Compared with other coding genes the MHC genes exhibit extremely high levels of polymorphism, which most likely is maintained by balancing selection.The importance in immune defence and the polymorphism make these genes essential to study from an ecological and evolutionary perspective, specifically in populations that are subject to natural selection. I am studying MHC genes in a population of wild songbirds, great reed warblers Acrocephalus arundinaceus. Here I have characterized parts of the MHC class I and II genes and I have focused especially on transcribed genes since these are likely to be under selection. In order to be able to study MHC class I diversity in the great reed warblers I developed a PCR-based screening method. I found a large number of MHC loci and also a surprisingly high level of allelic variation in the great reed warblers, in contrast to the limited variation that was detected using neutral markers. The MHC allele frequencies varied significantly between different cohorts (individuals hatched in the same year) in the study population. This implies that there is frequency dependent selection on the MHC class I alleles. Avian malaria could be one such selective force generating the temporal variation in MHC allele frequencies. I found an association between numbers of MHC class I alleles (a measure of level of heterozygosity) and prevalence of a specific avian malaria parasite. There was also an association between a specific MHC allele, previously shown to be under frequency dependent selection, and prevalence of this specific malaria parasite. These associations suggest that individuals carrying either a large number of MHC alleles or a specific MHC allele are protected against lethal malaria infections. So far, associations between certain MHC alleles, or a large number of MHC alleles, and resistance to specific diseases have only been found in a few species. Most of these associations involve humans or are experiments that have been done under controlled conditions. To me it is compelling that the selection pressure from pathogens on MHC genes can be visualised also in a wild bird population.   Biography Helena Westerdahl began her undergraduate studies at Lund University in 1990 and completed a MSc in Animal Ecology in 1995. She started her PhD studies in October 1995 at the Department of Animal Ecology, supervised by Prof Torbjörn von Schantz, Prof Staffan Bensch and Associate Prof Hakan Wittzell. She defended her thesis “Avian MHC: variation and selection in the wild” on 2003.10.10, Opponent Prof. Josephine Pemberton.   International Collaborations Dr David Richardson University of East Anglia, “Comparisons of MHC genes in Seychelles warblers and Great reed warblers” Dr Katharina Foerster, Max Planck Research Centre for Ornithology, Seewiesen “MHC genes in blue tits” PhD Camille Bonneaud, Université Pierre et Marie Curie, Paris “Screening of MHC genes in house sparrows”   Employments Nov. 1998 - Jan 2004: PhD-position at the Department of Animal Ecology, Lund University Jan. 2004 - Oct 2004: Project Assistant at the Department of Animal Ecology, Lund University   Selected recent publications Westerdahl, H., Bensch, S., Hansson, B., Hasselquist, D. and von Schantz, T. (1997) Sex ratio variation among broods of great reed warblers Acrocephalus arundinaceus. Molecular Ecology, 6: 543-548. Bensch, S., Westerdahl, H., Hansson, B. and Hasselquist, D. (1999) Do females adjust the sex-ratio of their offspring in relation to skew in breeding sex ratios? Journal of Evolutionary Biology 12:1104-1109. Westerdahl, H.,Wittzell, H. and von Schantz, T. (1999) RFLP-polymorphism and transcription of Mhc class I sequences in a Passerine bird, the great reed warbler. Immunogenetics 49:158-170. Wittzell, H., Madsen, T., Westerdahl, H., Shine, R. and von Schantz, T. (1999) MHC variation in birds and reptiles. Genetica 104:301-309. Bensch, S., Stjernman, M., Hasselquist, D., Östman, Ö., Hansson, B., Westerdahl, H. and Torres Pinheiro, R. (2000) Host specificity in avian blood parasites: a study of Plasmodium and Haemoproteus mitochondrial DNA amplified from birds. Proceedings of the Royal Society London B 267:1583-1589. Westerdahl, H., Bensch, S., Hansson, B. and Hasselquist, D. (2000) Brood sex ratios, female harem status and resources for nestling provisioning in the great reed warbler Acrocephalus arundinaceus. Behavioural Ecology and Sociobiology 47:312-318. Westerdahl, H., Wittzell, H. and von Schantz, T. (2000) Mhc diversity in two passerine birds: no evidence of a “minimal essential Mhc”. Immunogenetics 52:92-100. Richardson, D and Westerdahl, H. (2003) A comparison of MHC diversity in two Acrocephalus species: the outbred great reed warbler and the inbred Seyshelles warbler. Molecular Ecology 12:3523-3529. Bonneaud C., Sorci, G., Morin, V., Westerdahl, H., Zoorob, R. and Wittzell, H. (2004) Diversity of MHC class I and IIB genes in house sparrows (Passer domesticus. Immunogenetics 55:855-865. Westerdahl, H, Hansson, B, Bensch, S. and Hasselquist D. (2004) Between-year variation of MHC allele frequencies in great reed warblers; selection or drift? Journal of Evolutionary Biology 17:485-492. Arlt, D., Bensch, S., Hansson, B., Hasselquist, D. and Westerdahl H. (2004) Observation of a ZZW-female in a natural population: implications for avian sex determination. Biology Letters 271:S279-S251. Hansson, B., Westerdahl, H., Hasselquist, D., Åkesson M., Bensch, S. (2004) Does linkage disequilibrium generate heterozygosity-fitness correlations in great reed warblers? Evolution 58:870-879. Westerdahl, H., Wittzell, H., von Schantz, T. Bensch, S. (2004) MHC class I typing in a songbird with numerous loci and high polymorphism using motif-specific PCR and DGGE. Heredity 92:534-542. Westerdahl, H. (2004) No evidence of an MHC based mate choice in the great reed warbler. Molecular Ecology 13:2465-2470. Westerdahl H., Waldenström J., Hansson B., Hasselquist D. and Bensch S. (submitted) Associations between malaria and MHC genes in a migratory songbird   Helena Westerdahl Department of Animal Ecology Ecology Building SE -223 62 Lund Sweden http://www.biol.lu.se/zooekologi/forskargrupper_en.htm http://fisher.teorekol.lu.se/ekol_inst/mol_ekol/index.html