| Summary: | Abstract Hosts and pathogens are involved in a continuous evolutionary arms race, where pathogens attack and hosts defend themselves. The main tools for winning the race are natural selection and the genetic diversity that selection acts on. However, in small populations natural selection may be ineffective. Therefore, the genes taking part in immune defense may lack adaptability to new or changing pathogens. Major histocompatibility complex (MHC) is an important genomic region that includes highly polymorphic immune defense genes. In this doctoral thesis, I studied the natural selection and genetic diversity of MHC class II genes in dogs and Finnish wolves. I also used dog MHC diversity to estimate the number of founding wolves in dog domestication. The Finnish wolf population declined rapidly in size due to excessive hunting from the late 19th century until the early 20th century. After decades of a very small population size, the population started recovering in the mid-1990s. This study shows that, despite the fluctuations in population size, the diversity of the MHC loci in the Finnish wolf has remained high and comparable to the larger neighboring Russian Karelian wolf population. Unlike the neutral genetic markers, the MHC loci of the Finnish and Russian Karelian populations have not differentiated. These results indicate similar balancing selection acting on the MHC loci of the two wolf populations. In dogs, the strength of natural selection is likely weakened by artificial selection and veterinary care. The potential phases of natural selection would be during embryogenesis and fetal development. However, no strong signs of prenatal selection were found in this study. MHC diversity was estimated to be higher in Asian dogs than in dogs from Europe. A simulation study indicated a minimum of 500 founding wolves for the modern dog population. Dog MHC diversity implies an Asian origin for domestication from a large and diverse wolf population. Both natural selection and demography have an influence on the ...
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