Low MHC variation in the endangered Galápagos penguin (Spheniscus mendiculus)

• Published in: Immunogenetics (New York) Vol. 59; no. 7; pp. 593 - 602
• Main Authors: Bollmer, Jennifer L, Vargas, F. Hernán, Parker, Patricia G
• Format: Journal Article
• Language: English
• Published: United States Berlin/Heidelberg : Springer-Verlag 01-07-2007; Springer Nature B.V
• Subjects: Alleles; Amino Acid Sequence; Animals; Aptenodytes patagonicus; Birds; Divergence; Drb1 protein; Ecuador; El Nino; Evolution; Evolution, Molecular; Galápagos penguin; Genetic bottleneck; Genetic diversity; Genetic drift; Genetic Variation - immunology; Genomes; Histocompatibility Antigens Class II - genetics; Major histocompatibility complex; Molecular Sequence Data; Mutation; Ocean temperature; Phylogeny; Population decline; Population genetics; Random Allocation; Sibling species; Species diversity; Spheniscidae - genetics; Spheniscidae - immunology; Spheniscus humboldti; Spheniscus mendiculus; Trans-species evolution; Ecuador
• ISSN: 0093-7711; 1432-1211
• DOI: 10.1007/s00251-007-0221-y

The major histocompatibility complex (MHC) is one of the most polymorphic regions of the genome, likely due to balancing selection acting to maintain alleles over time. Lack of MHC variability has been attributed to factors such as genetic drift in small populations and relaxed selection pressure. The Galápagos penguin (Spheniscus mendiculus), endemic to the Galápagos Islands, is the only penguin that occurs on the equator. It relies upon cold, nutrient-rich upwellings and experiences severe population declines when ocean temperatures rise during El Niño events. These bottlenecks, occurring in an already small population, have likely resulted in reduced genetic diversity in this species. In this study, we used MHC class II exon 2 sequence data from a DRB1-like gene to characterize the amount of genetic variation at the MHC in 30 Galápagos penguins, as well as one Magellanic penguin (S. magellanicus) and two king penguins (Aptenodytes patagonicus), and compared it to that in five other penguin species for which published data exist. We found that the Galápagos penguin had the lowest MHC diversity (as measured by number of polymorphic sites and average divergence among alleles) of the eight penguin species studied. A phylogenetic analysis showed that Galápagos penguin MHC sequences are most closely related to Humboldt penguin (Spheniscus humboldti) sequences, its putative sister species based on other loci. An excess of non-synonymous mutations and a pattern of trans-specific evolution in the neighbor-joining tree suggest that selection is acting on the penguin MHC.