Balancing selection on allorecognition genes in the colonial ascidian Botryllus schlosseri. (April 2017)

• Record Type: Journal Article
• Authors: Nydam, Marie L.; Stephenson, Emily E.; Waldman, Claire E.; De Tomaso, Anthony W.
• Is Part Of: Developmental and comparative immunology. Volume 69(2017)
• Page Start: 60
• Page End: 74
• Publication Date: 2017-04
• Subjects: Botryllus schlosseri -- Allorecognition -- Balancing selection -- fuhcsec -- fuhctm -- Ascidian; Immunology -- Periodicals; Developmental immunology -- Periodicals; 616.079
• DOI: 10.1016/j.dci.2016.12.006
• Languages: English
• ISSNs: 0145-305X

Abstract

Abstract: Allorecognition is the capability of an organism to recognize its own or related tissues. The colonial ascidian Botryllus schlosseri, which comprises five genetically distinct and divergent species (Clades A-E), contains two adjacent genes that control allorecognition: fuhc sec and fuhc tm . These genes have been characterized extensively in Clade A and are highly polymorphic. Using alleles from 10 populations across the range of Clade A, we investigated the type and strength of selection maintaining this variation. Both fuhc genes exhibit higher within-population variation and lower population differentiation measures (FST ) than neutral loci. The fuhc genes contain a substantial number of codons with >95% posterior probability of dN /dS > 1. fuhc sec and fuhc tm also have polymorphisms shared between Clade A and Clade E that were present prior to speciation (trans-species polymorphisms). These results provide robust evidence that the fuhc genes are evolving under balancing selection. Highlights: fuhc genes exhibit lower population structure than neutral loci. fuhc genes contain a substantial number of codons with >95% probability of ω > 1. fuhc genes have trans -species polymorphisms shared between Clade A and Clade E. fuhc genes are evolving under balancing selection.