Environmental factors have long been presumed to play a prominent role in directing the evolution of genes which regulate the mammalian immune response. Of particular interest in this context are families of genes which are functional in either antigen- specific presentation of foreign antigens or actual recognition of foreign antigens. The overall objective of the proposed research is to evaluate directly the role of environmental factors on the evolution of these "immunoregulatory" gene families. Toward this end, we have developed a new rodent model which utilizes the tassel-eared squirrel, Sciurus aberti, comprised of four subspecies restricted to four geographically isolated but identical environments. Genomic blotting protocols will reveal the number and polymorphism of sequences, exhibited by samples from each subspecies, included in (1) the major histocompatibility complex (TSLA) class I and class II families; (2) immunoglobulin heavy chain region gene families; (3) T cell receptor alpha and beta subunit variable and constant region gene families; and (4) a control group of conserved actin and 7S RNA gene families and mitochondrial DNA. Estimates of average heterozygosity and genetic distance in each family will be calculated for pairwise combinations of subspecies and the relationship between these two values, as determined by linear regression, compared to that predicted by the neutral mutation hypothesis. If environment directs the evolution of a specific gene family, significantly shorter genetic distance should be observed between two subspecies than that predicted by this theory. The effects of variable environmental conditions in delineated habitats on the frequencies of polymorphic sequences included in TSLA and T cell receptor variable region gene families in a single S. aberti subspecies will be investigated by yearly correlations of these sequence frequencies with estimate of food resource and gene swill be investigated by immunoprecipitation with specific reagents and two- dimensional gel electrophoresis to estimate functional polymorphism for comparison with germline polymorphism. In summary, it is believed that the proposed, comprehensive analysis constitutes the first analytical approach to the question of the role of environmental factors in directing the evolution of immunoregulatory gene families.