Ancestral polymorphism at the major histocompatibility complex (MHCIIß) in the Nesospiza bunting species complex and its sister species (Rowettia goughensis)

A study of the major histocompatibility complex (MHCIIβ) in the Nesospiza bunting species complex and its sister species, Rowettia goughensis, reveals that ancestral polymorphism rather than local selective forces drives population variation. Analysis of 23 unique alleles across 14 Nesospiza and 2 R. goughensis individuals showed no evidence of ongoing selection on the peptide binding region (PBR), with shared alleles between islands and species indicating deep historical divergence. Gene tree analysis further supported preserved ancestral polymorphism, clustering Nesospiza-specific groups distinctively while R. goughensis alleles were interspersed among them. This suggests weak or absent parasite-driven selection, possibly due to low parasite load in these isolated Atlantic islands, and provides rare evidence of extensive ancestral polymorphism in birds.

van Rensburg, A., Bloomer, P., Ryan, P. G., & Hansson, B. (2012). Ancestral polymorphism at the major histocompatibility complex (MHCIIß) in the Nesospiza bunting species complex and its sister species (Rowettia goughensis). BMC Evolutionary Biology, 12(1), 143. https://doi.org/10.1186/1471-2148-12-143