Major histocompatibility complex (MHC) variation in the endangered Mexicanwolf and related canids

We have examined in Mexican wolves and related canids the amount of genetic Variation for a class II gene in the major histocompatibility complex (MHC ), thought to be part of the most important genetic basis for pathogen resi stance in vertebrates. In Mexican wolves, descended from only seven founder s over three lineages, there were five different alleles. These were in thr ee phylogenetic groups? only one of which was shared between lineages. Usin g single stand conformation polymorphism (SSCP), we found that in samples o f animals from the two polymorphic lineages, the observed heterozygosity wa s 0.74 and the genotypes were not different statistically from Hardy-Weinbe rg proportions. The Ghost Ranch lineage of Mexican wolves was monomorphic f or the locus, consistent with the lower level of variation found previously for microsatellite loci and predicted from pedigree analysis. Samples of g rey wolves, red wolves, and coyotes had 16 additional alleles. One Mexican wolf allele was also found in grey wolves and another allele was shared bet ween grey and red wolves. Most of the nucleotide variation resulted in amin o acid variation and there were five different amino acids found at two dif ferent positions. Only two of the 21 variable amino acid positions had sole ly synonymous nucleotide variation. The average heterozygosity for eight in dividual amino acid positions in the Mexican wolves was greater than 0.4. T he estimated rate of nonsynonymous substitution was 2.5 times higher than t hat for synonymous substitution for the putative antigen binding site posit ions, indicative of positive selection acting on these positions. Examinati on of the known dog sequences for this locus showed that one of the Mexican wolf alleles was found in dogs and that the allele found in both grey and red wolves is also found in dogs.