第49回生態適応セミナー (Bセミナー)

     
  日時:10月29日(金曜日)17:00から  
  場所:生物地学共通講義室(青葉山キャンパス)  
     

講師:
Dr. Cock van Oosterhout
Evolutionary Biology Group, Department of Biological Sciences,
University of Hull, UK

     
  MHC evolution: beyond selection on the immune genes  
     
 

The Major Histocompatibility Complex (MHC) is a large multigene family that harbours many of the vertebrate immune genes. The MHC contains the most polymorphic genes in the entire genome, and besides playing a critical role in immune-defence, these genes are also implicated in female mate-choice. The MHC is a text-book example of a gene under balancing selection, i.e. a type of selection that maintains genetic variation by favouring heterozygotes or rare alleles. The traditional models of balancing selection were developed to understand the evolution of a single immune gene. However, the MHC is a large multigene family, and these models ignore the role of other evolutionary forces acting in this region. For example, the MHC genes in humans (the HLA) are surrounded by linked genetic variation that is associated with more diseases than any other part of the human genome. This genetic variation is non-neutral, which suggests that the entire MHC region is under strong selection, and that it could play an important role in MHC evolution. Here I will discuss the advances made in studies on the MHC, highlighting some of the population genetic puzzles that cannot be explained by the traditional theories of MHC evolution. I will discuss how the interaction between selection, drift, recombination and mutationcan explain the fascinating complexity of multigene evolution, and I will set-out some promising new avenues in MHC research.

 
     
  18:00から  

講師:
Dr. Mark McMullan
Evolutionary Biology Group, Department of Biological Sciences,
University of Hull, UK

     
  Spatial and temporal Major Histocompatibility Complex (MHC) variation in the Trinidadian guppy  
     
 

The MHC has become a paradigm for biologists to study evolution by natural selection in vertebrates. MHC molecules bind to amino acid fragments (antigens) from invading pathogens, and these antigens become the target for the adaptive immune system. Variation at the MHC is often higher than can be explained by neutral evolution (e.g. migration and genetic drift), and selection by a diverse parasite fauna is thought to maintain the high level of polymorphism at the MHC. Here, I study the MHC and parasites of the Trinidadian guppy (Poecilia reticulata). Specifically I analyse MHC and parasite diversity at three locations within a river system and interpret my results under the established dogma that parasite diversity maintains MHC diversity. I show that the guppy populations differ diametrically in parasite fauna, and I predict that low MHC diversity should be found in low-parasite populations due to relaxed parasite-mediated selection. In addition, I analyse temporal variation in MHC diversity, showing that MHC alleles are rapidly replaced over time by alternative alleles. This is consistent with the Red Queen hypothesis, which predicts that parasites change over time in order to escape recognition by the MHC, and visa versa. However, alternative explanations are possible, and I use a computer simulation to analyse whether such rapid evolution of the MHC can also be explained by the large spatial/temporal variation in population size and migration rates observed in guppy metapopulation in Trinidad.