Sexual dimorphism in immunity across animals: a meta-analysis

Area of Science:

• Zoology
• Immunology
• Evolutionary Biology

Background:

• Sex differences in immunity are proposed to influence infection dynamics within animal populations.
• Females are often expected to have superior immunity due to life-history trade-offs related to reproduction.

Purpose of the Study:

• To systematically analyze the magnitude and direction of sex differences in animal immunity.
• To identify factors influencing sex-biased immunocompetence, including age, taxonomy, and methodology.

Main Methods:

• A systematic meta-analysis was conducted, synthesizing data from 124 studies comprising 584 effect sizes.
• Phylogenetic, taxonomic, methodological, and age-related effects were assessed as potential moderators.

Main Results:

• Females exhibited a significantly stronger immune response than males, though the overall effect size was small.
• This female advantage became non-significant after controlling for phylogenetic relationships.
• Immunity bias towards females was more pronounced in adult animals and notably large in insects.

Conclusions:

• The pervasive notion of female-biased immunity is challenged, with effect sizes being smaller than often assumed.
• Testosterone is unlikely to be the sole driver of sex differences in immunity, as indicated by findings in insects.