MHC variation in birds and reptiles

The major histocompatibility complex (MHC) has been studied in a multitude of mammals by now, but much less is known about its organisation and variat ion in other vertebrate species. The mammalian MHC is organised as a single gene cluster, but recent studies on birds suggest that this paradigm of MH C organisation has to be supplemented. The domestic chicken thus possesses two separate gene clusters which both contain MHC class I and class II B ge nes, and we have shown that the ring-necked pheasant Phasianus colchicus al so has two unlinked clusters of class II B genes. We are studying the effec t of the MHC on mate choice, survival and reproductive success in natural p opulations of birds and reptiles. For this reason, we are developing DNA te chniques to determine the animals' MHC genotype. The amplification of the h ypervariable exon 3 of the class I gene from songbirds and reptiles has pro vided us with species specific probes that can be used in Southern blot ana lysis. The first results indicate very extensive variation in all studied s pecies, that is starlings Sturnus vulgaris, great reed warblers Acrocephalu s arundinaceus and water pythons Liasis fuscus. The restriction fragment le ngth polymorphism (RFLP) analysis also suggests that the number of MHC gene s is significantly larger in these species than in pheasants and domestic c hickens.