Original Paper

Immunogenetics

, Volume 62, Issue 2, pp 85-100

Major histocompatibility complex variation and evolution at a single, expressed DQA locus in two genera of elephants

  • Elizabeth A. ArchieAffiliated withCenter for Conservation and Evolutionary Genetics, National Zoological Park & National Museum of Natural History, Smithsonian InstitutionDepartment of Biological Sciences, University of Notre Dame Email author 
  • , Tammy HenryAffiliated withCenter for Conservation and Evolutionary Genetics, National Zoological Park & National Museum of Natural History, Smithsonian InstitutionDepartment of Environmental Science and Policy, George Mason University
  • , Jesus E. MaldonadoAffiliated withCenter for Conservation and Evolutionary Genetics, National Zoological Park & National Museum of Natural History, Smithsonian Institution
  • , Cynthia J. MossAffiliated withAmboseli Trust for Elephants
  • , Joyce H. PooleAffiliated withAmboseli Trust for Elephants
  • , Virginia R. PearsonAffiliated withPhiladelphia Zoo
  • , Suzan MurrayAffiliated withAnimal Health, National Zoological Park
  • , Susan C. AlbertsAffiliated withDepartment of Biology, Duke University
  • , Robert C. FleischerAffiliated withCenter for Conservation and Evolutionary Genetics, National Zoological Park & National Museum of Natural History, Smithsonian Institution

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Abstract

Genes of the vertebrate major histocompatibility complex (MHC) are crucial to defense against infectious disease, provide an important measure of functional genetic diversity, and have been implicated in mate choice and kin recognition. As a result, MHC loci have been characterized for a number of vertebrate species, especially mammals; however, elephants are a notable exception. Our study is the first to characterize patterns of genetic diversity and natural selection in the elephant MHC. We did so using DNA sequences from a single, expressed DQA locus in elephants. We characterized six alleles in 30 African elephants (Loxodonta africana) and four alleles in three Asian elephants (Elephas maximus). In addition, for two of the African alleles and three of the Asian alleles, we characterized complete coding sequences (exons 1–5) and nearly complete non-coding sequences (introns 2–4) for the class II DQA loci. Compared to DQA in other wild mammals, we found moderate polymorphism and allelic diversity and similar patterns of selection; patterns of non-synonymous and synonymous substitutions were consistent with balancing selection acting on the peptides involved in antigen binding in the second exon. In addition, balancing selection has led to strong trans-species allelism that has maintained multiple allelic lineages across both genera of extant elephants for at least 6 million years. We discuss our results in the context of MHC diversity in other mammals and patterns of evolution in elephants.

Keywords

African elephant Asian elephant DQA Major histocompatibility complex Coding sequence Molecular evolution