Trans-species polymorphism of the Mhc class II DRB-like gene in banded penguins (genus Spheniscus).

The Major Histocompatibility Complex (Mhc) class II DRB locus of vertebrates is highly polymorphic and some alleles may be shared between closely related species as a result of balancing selection in association with resistance to parasites. In this study, we developed a new set of PCR primers to amplify, clone, and sequence overlapping portions of the Mhc class II DRB-like gene from the 5'UTR end to intron 3, including exons 1, 2, and 3 and introns 1 and 2 in four species (20 Humboldt, six African, five Magellanic, and three Galapagos penguins) of penguin from the genus Spheniscus (Sphe). Analysis of gene sequence variation by the neighbor-joining method of 21 Sphe sequences and 20 previously published sequences from four other penguin species revealed overlapping clades within the Sphe species, but species-specific clades for the other penguin species. The overlap of the DRB-like gene sequence variants between the four Sphe species suggests that, despite their allopatric distribution, the Sphe species are closely related and that some shared DRB1 alleles may have undergone a trans-species inheritance because of balancing selection and/or recent rapid speciation. The new primers and PCR assays that we have developed for the identification of the DRB1 DNA and protein sequence variations appear to be useful for the characterization of the molecular evolution of the gene in closely related Penguin species and might be helpful for the assessment of the genetic health and the management of the conservation and captivity of these endangered species.

Analysis of the sequence variations in the Mhc DRB1-like gene of the endangered Humboldt penguin (Spheniscus humboldti).

The Major Histocompatibility Complex (Mhc) genomic region of many vertebrates is known to contain at least one highly polymorphic class II gene that is homologous in sequence to one or other of the human Mhc DRB1 class II genes. The diversity of the avian Mhc class II gene sequences have been extensively studied in chickens, quails, and some songbirds, but have been largely ignored in the oceanic birds, including the flightless penguins. We have previously reported that several penguin species have a high degree of polymorphism on exon 2 of the Mhc class II DRB1-like gene. In this study, we present for the first time the complete nucleotide sequences of exon 2, intron 2, and exon 3 of the DRB1-like gene of 20 Humboldt penguins, a species that is presently vulnerable to the dangers of extinction. The Humboldt DRB1-like nucleotide and amino acid sequences reveal at least eight unique alleles. Phylogenetic analysis of all the available avian DRB-like sequences showed that, of five penguin species and nine other bird species, the sequences of the Humboldt penguins grouped most closely to the Little penguin and the mallard, respectively. The present analysis confirms that the sequence variations of the Mhc class II gene, DRB1, are useful for discriminating among individuals within the same penguin population as well those within different penguin population groups and species.