A distinguishing characteristic of genes that code for the major histocompatibility complex
(MHC) is that alleles often share more similarity between, rather than within species.
More...A distinguishing characteristic of genes that code for the major histocompatibility complex
(MHC) is that alleles often share more similarity between, rather than within species. There
are two likely mechanisms that can explain this pattern: convergent evolution and transspecies
polymorphism (TSP), in which ancient allelic lineages are maintained by balancing
selection and retained by descendant species. Distinguishing between these two
mechanisms has major implications in how we view adaptation of immune genes. In this
study we analyzed exon 2 of the MHC class IIB in three passerine bird species in the genus
Corvus: jungle crows (Corvus macrorhynchos japonensis) American crows (C.
brachyrhynchos) and carrion crows (C. corone orientalis). Carrion crows and American
crows are recently diverged, but allopatric, sister species, whereas carrion crows and
jungle crows are more distantly related but sympatric species, and possibly share
pathogens linked to MHC IIB polymorphisms. These patterns of evolutionary divergence
and current geographic ranges enabled us to test for trans-species polymorphism and
convergent evolution of the MHC IIB in crows. Phylogenetic reconstructions of MHC IIB
sequences revealed several well supported interspecific clusters containing all three
species, and there was no biased clustering of variants among the sympatric carrion crows
and jungle crows. The topologies of phylogenetic trees constructed from putatively
selected sites were remarkably different than those constructed from putatively neutral
sites. In addition, trees constructed using non-synonymous substitutions from a continuous
fragment of exon 2 had more, and generally more inclusive, supported interspecific MHC
IIB variant clusters than those constructed from the same fragment using synonymous
substitutions. These phylogenetic patterns suggest that recombination, especially gene
conversion, has partially erased the signal of allelic ancestry in these species. While
clustering of positively selected amino acids by supertyping revealed a single supertype
shared by only jungle and carrion crows, a pattern consistent with convergence, the
overall phylogenetic patterns we observed suggest that TSP, rather than convergence,
explains the interspecific allelic similarity of MHC IIB genes in these species of crows.
PeerJ reviewing
Less...Accession | PRJNA277130 |
Data Type | Raw sequence reads |
Scope | Multispecies |
Organism | Corvus[Taxonomy ID: 30420] Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; Archelosauria; Archosauria; Dinosauria; Saurischia; Theropoda; Coelurosauria; Aves; Neognathae; Neoaves; Telluraves; Australaves; Passeriformes; Corvoidea; Corvidae; Corvus |
Submission | Registration date: 4-Mar-2015 Graduate University for Advanced Studies |
Relevance | Evolution |
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