Males and females often exhibit differences in behaviour, life histories, and ecology,
many of which are typically reflected in their brains. Neuronal protection and maintenance
include complex processes led by the microglia, which also interacts with metabolites
such as hormones or immune components. Despite increasing interest in sex-specific
brain function in laboratory animals, the significance of sex-specific immune activation
in the brain of wild animals along with the variables that could affect it is widely
lacking. Here, we use the Kentish plover (Charadrius alexandrinus) to study sex differences
in expression of immune genes in the brain of adult males and females, in two wild
populations breeding in contrasting habitats: a coastal sea-level population and a
high-altitude inland population in China. Our analysis yielded 379 genes associated
with immune function. We show a significant male-biased immune gene upregulation.
Immune gene expression in the brain did not differ in upregulation between the coastal
and inland populations. 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 genetic control by the microglia and possible similarities in pathogen
pressures between habitats. We call for further studies on gene expression of males
and females in wild population to understand the implications of immune function for
life-histories and demography in natural systems.
