Data from: Very high MHC Class IIB diversity without spatial differentiation in the Mediterranean population of Greater Flamingos

Background: Selective pressure from pathogens is thought to shape the
allelic diversity of major histocompatibility complex (MHC) genes in
vertebrates. In particular, both local adaptation to pathogens and gene
flow are thought to explain a large part of the intraspecific variation
observed in MHC allelic diversity. To date, however, evidence that
adaptation to locally prevalent pathogens maintains MHC variation is
limited to species with limited dispersal and, hence, reduced gene flow.
On the one hand high gene flow can disrupt local adaptation in species
with high dispersal rates, on the other hand such species are much more
likely to experience spatial variation in pathogen pressure, suggesting
that there may be intense pathogen mediated selection pressure operating
across breeding sites in panmictic species. Such pathogen mediated
selection pressure operating across breeding sites should therefore be
sufficient to maintain high MHC diversity in high dispersing species in
the absence of local adaptation mechanisms. We used the Greater Flamingo,
Phoenicopterus roseus, a long-lived colonial bird showing a homogeneous
genetic structure of neutral markers at the scale of the Mediterranean
region, to test the prediction that higher MHC allelic diversity with no
population structure should occur in large panmictic populations of
long-distance dispersing birds than in other resident species. Results: We
assessed the level of allelic diversity at the MHC Class IIB exon 2 from
116 individuals born in four different breeding colonies of Greater
Flamingo in the Mediterranean region. We found one of the highest allelic
diversity (109 alleles, 2 loci) of any non-passerine avian species
investigated so far relative to the number of individuals and loci
genotyped. There was no evidence of population structure between the four
major Mediterranean breeding colonies. Conclusion: Our results suggest
that local adaptation at MHC Class IIB in Greater Flamingos is constrained
by high gene flow and high MHC diversity appears to be maintained by
population wide pathogen-mediated selection rather than local
pathogen-mediated selection. Further understanding of how pathogens vary
across space and time will be crucial to further elucidate the mechanisms
maintaining MHC diversity in species with large panmictic populations and
high dispersal rates.