MHC Polymorphism and the Design of Captive Breeding Programs

Abstract

A goal of captive breeding programs for endangered species and of programs to maintain populations of such species in nature is the preservation of genetic diversity. Here I argue that, although loss of genetic diversity is inevitable in small populations, at most loci loss of diversity should not be a cause for concern because the vast majority of genetic polymorphisms are selectively neutral. Rather, efforts should be concentrated on preserving diversity at the small number of loci on which balancing selection operates in nature. In vertebrates, the primary example of such loci are the loci of the major histocompatibility complex (MHC) (Hughes & Nei 1988, 1989). Therefore, all captive breeding programs for endangered vertebrate species should be designed with the preservation of MHC allelic diversity as their main goal. Currently design of captive breeding programs is based on maintaining an effective population size (Ne) which will minimize loss of heterozygosity (Soule et al. 1986). For an isolated population having an initial average heterozygosity Ho, the expected average heterozygosity after t generations is given by