Patterns of variability at the major histocompatibility class I and class II loci in populations of the endangered cyprinid Ladigesocypris ghigii

The patterns of MHC diversity were studied at UAA and DAB1 loci and the two domains involved in the recognition of antigenic peptides (α2 and β1, respectively) in eight Ladigesocypris ghigii populations inhabiting streams and a concrete reservoir, in order to understand the significance of these genes in bottlenecked populations of an endemic species and develop conservation rationale. In agreement with previous study employing RAPD and mtDNA markers (Mamuris et al., Freshw Biol 50:1441–1453, 2005), both loci exhibited a very low level of polymorphism with only two and four alleles detected for UAA and DAB1, respectively. The functional MHC diversity was even lower since UAA alleles were distinguished by a single synonymous substitution. The type of habitat did not affect the level of polymorphism. Our data suggest that DAB1 polymorphism might be the outcome of the positive selection, imposed by the temporal and spatial variation of pathogen load, and the genetic drift as a result of successive habitat shrinkage and deterioration by water abstraction year after year. The populations studied were significantly less diverged at MHC loci than expected based on nuclear and mtDNA markers, suggesting that common parasites might act as causative factors to homogenize selection. Sufficient epidemiological data are required for the interpretation of the results and decision-making on suitable conservation actions.