Abstracts (first author)

Talk 

In silico peptide-binding predictions of MHC class I reveal similarities across distantly related songbird species, suggesting convergence on the level of protein function

Author(s): Westerdahl H, Follin E, Karlsson M, Drews A, Lundegaard C, Nielsen M, Wallin S, Paulsson K

Summary:

Many songbirds have a large number of transcribed MHC class I genes compared to most mammals. To elucidate the reasons for this large number of genes and to search for non-classical MHC genes in songbirds, we compared songbird MHC class I alleles (α1-α3 domains). By applying phylogenetic analysis, homology modelling and in silico peptide-binding predictions, we could compare both functional and genetic relationships among transcribed genes. We found more pronounced clustering of the MHC class I allomorphs (allele-specific proteins) in regard to their protein function (peptide-binding specificities) compared to their genetic relationships (amino acid sequences), indicating that the high number of alleles is of functional significance.

The MHC class I allomorphs from house sparrow and tree sparrow, species that diverged ten MYA, had overlapping peptide-binding specificities. These similarities across species were also confirmed in phylogenetic analyses, and were similar for genes that we interpret as classical and non-classical. Remarkably, there were also overlapping peptide-binding specificities in the allomorphs from house sparrows and great reed warblers, although these species diverged about 30 MYA. This overlap was not found in a tree based on amino acid sequences. Our interpretation is that convergent evolution on the level of the protein function, possibly driven by selection from shared pathogens, has resulted in allomorphs with similar peptide-binding repertoires, although trans-species evolution in combination with gene conversion cannot be excluded.



Abstracts (coauthor)

Summary:

Over 30 years ago, the first study concerning MHC (major histocompatibility complex)-dependent mate choice was published in which female mice preferred MHC-dissimilar males. Since then, numerous studies about MHC preferences and mate choice in different species were issued. The MHC has a crucial role in the immune system and should therefore be important in mate choice decisions. There is evidence that breeding pairs who do not share the same MHC alleles are more ‘compatible’ in terms of fertility success and offspring survival. Most passer species are socially monogamous, but genetic polyandry is widespread. Females commonly engage in extra-pair matings and therefore it is likely that paternity of offspring is determined by postcopulatory sexual selection mechanisms. In this study we tested the postcopulatory fertility success of similar/dissimilar breeding pairs (respective to their MHC composition) in house sparrows. Additionally we analyzed if ‘compatible’ pairs also produce more chicks. With next generation sequencing technologies (454 sequencing), we sequenced the alleles of MHC class I, exon 3. We used an aviary population of wild house sparrows (61 males and 58 females) and kept them in 14 aviaries with 3-5 breeding pairs/aviary. The obvious benefit of an aviary population is that we could exclude several environmental factors influencing the results. We removed the first clutch of all breeding individuals (52 clutches with 4 eggs on average; 208 eggs total) to count the number of spermatozoa on the inner and outer perivitelline layer of the egg to study the postcopulatory fertility success. Additionally we allowed them to breed a second time to compare the postcopulatory success with the actual breeding success of these pairs (number of eggs, amount of hatching and fledging chicks). This comparison helped us to gain a deeper insight in the principles of MHC-dependent compatibility and fertility success.

Summary:

The major Histocompability Complex (MHC) class I genes have received a considerable of interest from evolutionary biologists. Their role in parasite recognition and extreme polymorphism makes these genes a paradigm for studying genetic effects on survival, mate choice and pathogen resistance. Exon 3 of MHC class I genes encodes a part of the domain that binds and presents peptides from pathogens. Species possessing many highly polymporphic MHC loci are potentially under strong natural selection from parasites. Determining selection acting on MHC in natural population of such species over extended periods of time offers a great opportunity to reveal mechanisms maintaining MHC diversity. Here we present initial characterization of MHC class I genes diversity in a sedge warbler Acrocephalus schoenobaenus from population inhabiting natural wetlands in the Nida valley, SE Poland. We designed primers and determined diversity at MHC class I exon 3 both in cDNA and gDNA of 4 unrelated individuals with use of Next Generation Sequencing methods. We found extreme diversity at the MHC class I exon 3 of the sedge warbler. This data will be used for designing specific primers amplifying functional alleles of MHC class I exon 3 in sedge warbler. Subsequently, we are going to infer long-term selection on MHC class I in the species.

Contacts

Chairman: Octávio S. Paulo
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Address

XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon
Portugal

Website

Computational Biology & Population Genomics Group 
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