Pw. Hedrick et al., Major histocompatibility complex (MHC) variation in the endangered Mexicanwolf and related canids, HEREDITY, 85(6), 2000, pp. 617-624
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.