Abstract
BackgroundIn the arms race between hosts and parasites, genes involved in the immune response are targets for natural selection. Toll-Like Receptor (TLR) genes play a role in parasite detection as part of the innate immune system whereas Major Histocompatibility Complex (MHC) genes encode proteins that display antigens as part of the vertebrate adaptive immune system. Thus, both gene families are under selection pressure from pathogens. The bananaquit (Coereba flaveola) is a passerine bird that is a common host of avian malarial parasites (Plasmodium sp. and Haemoproteus sp.). We assessed molecular variation of TLR and MHC genes in a wild population of bananaquits and identified allelic associations with resistance/susceptibility to parasitic infection to address hypotheses of avian immune response to haemosporidian parasites.ResultsWe found that allele frequencies are associated with infection status at the immune loci studied. A consistent general trend showed the infected groups possessed more alleles at lower frequencies, and exhibited unique alleles, compared to the uninfected group.ConclusionsOur results support the theory of natural selection favoring particular alleles for resistance while maintaining overall genetic diversity in the population, a mechanism which has been demonstrated in some systems in MHC previously but understudied in TLRs.
Highlights
In the arms race between hosts and parasites, genes involved in the immune response are targets for natural selection
Pooled Sequencing & Sequence Processing we successfully amplified, indexed, equimolarly pooled, sequenced, and called alleles for 5 immune loci in the same 99 bananaquit individuals:45 in the uninfected group 41 in the group infected with host-specialist LA07, and 13 in the group infected with either OZ02 or OZ21. (UNI = uninfected, LA07 = infected with host-specialist LA07 strain, or INF = infected with OZ02 and OZ21)
We found that the allele frequencies at the three Toll-Like Receptor (TLR) and two Major Histocompatibility Complex (MHC) loci sequenced in this study, as well as the expected heterozygosities, are associated with infection status in the bananaquit
Summary
In the arms race between hosts and parasites, genes involved in the immune response are targets for natural selection. Toll-Like Receptor (TLR) genes play a role in parasite detection as part of the innate immune system whereas Major Histocompatibility Complex (MHC) genes encode proteins that display antigens as part of the vertebrate adaptive immune system. Both gene families are under selection pressure from pathogens. Two major immune gene families in the vertebrate immune system are the Major Histocompatibility Complex (MHC) of the adaptive immune system and the Toll-like Receptor (TLR) family of the innate immune system.
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