House sparrows with high epigenetic potential in the Toll-like receptor
4 promoter are better able to resist a pathogenic Salmonella
enterica infection
Abstract
Animals encounter many novel and unpredictable challenges when moving
into new areas including pathogen exposure. Because effective immune
defenses against such threats can be costly, plastic immune responses
could be particularly advantageous, as such defenses can be engaged only
when context warrants activation. DNA methylation is a key regulator of
plasticity via its effects on gene expression. In vertebrates, DNA
methylation occurs exclusively at CpG dinucleotides, and typically, high
DNA methylation decreases gene expression. The CpG content of gene
regulatory regions may therefore represent one form of epigenetic
potential (EP), a genomic means to capacitate gene expression.
Non-native populations of house sparrows (Passer domesticus) - one of
the world’s most cosmopolitan species – have high EP in the promoter of
a key microbial surveillance gene, Toll-like receptor 4 (TLR4), compared
to native populations. We previously hypothesized that high EP may
enable sparrows to balance the costs and benefits of immune responses
well, a trait critical to success in novel environments. In the present
study, we found support for this hypothesis. House sparrows with high EP
in TLR4 were better able to resist a pathogenic Salmonella enterica
infection than sparrows with low EP. These results support the premise
that high EP contributes to adaptation in novel environments.