The major histocompatibility complex and right whale reproduction

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The North Atlantic right whale is one of the most endangered whales in the world, with a census population of about 350 individuals. I am testing the hypothesis that the low reproductive success of the species is due to the low genetic diversity at Major Histocompatibility Complex (MHC) loci. We have DNA profiles (35 microsatellite loci, the mitochondrial DNA control region sequence and gender - ZfX/ZfY) from 550 samples representing 390 individuals. This represents approximately 70% of the species and includes 150 mother calf pairs, of which 90 calves have been assigned paternity. A preliminary survey of exon 2 variation of the MHC DRß-like gene with 169 samples identified 10 alleles using SSCP analysis, cloning and sequencing. Up to four alleles were present in each individual indicating a duplicated locus. By following inheritance patterns of known family groupings, six alleles were assigned to one locus (DRß-1) and remaining four alleles were assigned to the second locus (DRß-2). Haplotypes were assigned to 28 informative males with assigned paternities and the paternal contribution to the calf determined. We tested the hypothesis that fetuses with MHC haplotypes more like their mother would be more likely to be terminated. In twenty cases the calf received the paternal MHC haplotype that made it less like its mother and in 8 cases the haplotype that made it more like its mother. This transmission bias is highly significant, while the transmission of alleles from the neutral microsatellite loci was essentially Mendelian. This proposal is to characterise more class I and II loci in the MHC and develop haplotypes to increase the number of informative fathers. We presently have 62 fathers that are not informative and are profiling another 100 samples from the recent field seasons that should increase the paternities by at least 20. We will characterise MHC loci for which primers have been developed in other whale species and target homologous loci such as the human HLA-G locus that is directly involved immune tolerance during pregnancy. We will also look at MHC genotypes in mating groups to assess whether mating is random as predicted from the promiscuous sperm competition hypothesis for the species.