Sex Differences in Immune Gene Expression in the Brain of a Small Shorebird

Abstract Background: Males and females often exhibit different behaviour, life histories and ecology, and sex differences are typically reflected in their brains. Neuronal protection and maintenance include complex processes led by the microglia that also interact with metabolites such as hormones or immune components. Despite increasing interest in sex-specific brain activation in laboratory animals, the crucial significance of immune function protecting in the brain of wildlife is widely lacking. Here, we study sex-specific expression of immune genes in the brain of a small shorebird, the Kentish plover (Charadrius alexandrinus), that is an emerging model of mating system evolution and speciation. We compare immune gene expression patterns between adult males and adult females in two wild breeding populations in contrasting habitats: a coastal sea-level population and a high-altitude inland population in China.Results: Our analysis yielded 379 genes associated with immune function. We show a significant male-biased immune gene upregulation, which is in line with ecological studies that showed higher survival in males than in females. Immune gene expression in the brain did not differ in upregulation between the coastal and inland populations.Conclusions: We discuss the role of dosage compensation in our findings and their evolutionary significance mediated by sex-specific survival and neuronal deterioration. Similar expression profiles in the coastal and inland populations suggest comparable pathogen pressures between the habitats. We call for further studies on gene expressions of males and females in wild population to understand the implications of immune function for life-histories and demography in natural systems.