HLA-DQ8 - DQ8 and Selection

DQ8 and Selection

Like DQ2.5, DQ8 might have been under selection for maritime, coastal foraging peoples and in particular for peoples adapted to the climate/habitat situation on the northern end of the habitable west pacific rim at the Last Glacial Maximum. Triticeae cultivation may apply negative selection on DQ8. While there were numerous members of Triticeae species similar to Mid-Eastern wild Triticeae in the Americas, and a great number of domesticated plants in the new world, no single species of Triticeae appears to have been domesticated in the New World, and no clear examples in closely related tribes of grasses. Among new world grass species in post Columbian times, one species of Elymus has been domesticated for human consumption and another as a pastoral cultivar. This could be interpreted in 2 ways. First, that levels of DQ8, negatively, inhibited the domestication of Triticeae strains. Second, that the absence of such cultivars more suitable than already developed cultivars allowed DQ8 to rise or remain high, while DQ2.5 levels in NW under much longer term selection have fallen, or a little of both. Most of American cultivars were domesticated south of the Rio Grande river (exceptions are Caddo rice and Texas varigated squash, etc.). Wheat, particularly Barley and Rye are preferential cultivars in cooler climate, whereas Zea is more adaptive in tropical climates and some cultivars are relatively drought-tolerant, Zea however lacks certain amino acids that must be supplemented by other foods to prevent malnutrition. The proximity of neolithization to the Equator in the New World may have much to do with the unapparent negative selection of DQ8 relative to the neolithization of Western Eurasia.