10.5061/DRYAD.9V2362D
Slade, Joel W. G.
Western University
Watson, Matthew J.
Western University
MacDougall-Shackleton, Elizabeth A.
Western University
Data from: “Balancing” balancing selection? Assortative mating at the
major histocompatibility complex despite molecular signatures of balancing
selection
Dryad
dataset
2019
assortative mating
Melospiza melodia
positive selection
trans-species polymorphism
Major histocompatibility complex
Balancing selection
2019-05-01T11:38:35Z
2019-05-01T11:38:35Z
en
https://doi.org/10.1002/ece3.5087
94522 bytes
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
In vertebrate animals, genes of the major histocompatibility complex (MHC)
determine the set of pathogens to which an individual's adaptive
immune system can respond. MHC genes are extraordinarily polymorphic,
often showing elevated nonsynonymous relative to synonymous sequence
variation and sharing presumably ancient polymorphisms between lineages.
These patterns likely reflect pathogen‐mediated balancing selection, for
example, rare‐allele or heterozygote advantage. Such selection is often
reinforced by disassortative mating at MHC. We characterized exon 2 of MHC
class II, corresponding to the hypervariable peptide‐binding region, in
song sparrows (Melospiza melodia). We compared nonsynonymous to synonymous
sequence variation in order to identify positively selected sites;
assessed evidence for trans‐species polymorphisms indicating ancient
balancing selection; and compared MHC similarity of socially mated pairs
to expectations under random mating. Six codons showed elevated ratios of
nonsynonymous to synonymous variation, consistent with balancing
selection, and we characterized several alleles similar to those occurring
in at least four other avian families. Despite this evidence for
historical balancing selection, mated pairs were significantly more
similar at MHC than were randomly generated pairings. Nonrandom mating at
MHC thus appears to partially counteract, not reinforce, pathogen‐mediated
balancing selection in this system. We suggest that in systems where
individual fitness does not increase monotonically with MHC diversity,
assortative mating may help to avoid excessive offspring heterozygosity
that could otherwise arise from long‐standing balancing selection.
Sequences analyzed in Figure 3Fasta file of sequences analyzed in Figure
3similar_sequences.fasUniFrac DataFiles and code used to compute UniFrac
in RUniFrac_Data.zip
Newboro
Canada
Ontario