Developing a transcriptomic framework for testing testosterone-mediated handicap hypotheses.

Area of Science:

• Evolutionary biology
• Animal behavior
• Molecular biology

Background:

• Sexually selected traits signal individual quality, potentially enforced by testosterone.
• Testosterone's role in handicapping is linked to immunity (Immunocompetence Handicap Hypothesis) and oxidative stress (Oxidation Handicap Hypothesis).
• Limited knowledge exists on the molecular pathways testosterone uses to affect immunity and oxidative stress.

Purpose of the Study:

• Investigate the transcriptomic effects of experimentally elevated testosterone.
• Understand the molecular mechanisms behind testosterone-mediated handicaps.
• Test the Immunocompetence Handicap Hypothesis and Oxidation Handicap Hypothesis at a molecular level.

Main Methods:

• Reanalyzed existing RNA-sequencing data from three bird species treated with testosterone or control implants.
• Utilized weighted gene co-expression network analysis to identify molecular pathways.
• Focused on transcriptomic signatures in immune and oxidative stress-related genes.

Main Results:

• Identified significant transcriptomic signatures of immunosuppression in testosterone-treated individuals.
• Found evidence that these immunosuppressive molecular pathways are evolutionarily conserved across the studied species.
• Observed no evidence for testosterone mediating handicaps via oxidative stress pathways.

Conclusions:

• Testosterone enforces the honesty of sexually selected traits by influencing immunocompetence, supporting the Immunocompetence Handicap Hypothesis.
• The molecular pathways underlying testosterone-induced immunosuppression are conserved across species.
• This study provides a framework for future research into the proximate mechanisms of sexual selection.