Oxidative stress affects sperm performance and ejaculate redox status in subordinate house sparrows

Area of Science:

• Reproductive biology
• Environmental toxicology
• Animal behavior

Background:

• Oxidative stress, caused by reactive oxygen species, damages cells and is linked to aging, illness, and infertility.
• Male reproductive success in promiscuous species depends partly on ejaculate fertilizing ability.
• Dominance hierarchies suggest subordinate males may invest more in ejaculate quality to compete for mates.

Purpose of the Study:

• To test the hypothesis that subordinate male house sparrows prioritize antioxidant protection of ejaculates against oxidative stress.
• To investigate the physiological mechanisms linking oxidative stress, resource access, and ejaculate quality in wild house sparrows.

Main Methods:

• Wild house sparrows were chronically dosed with diquat, a herbicide that induces pro-oxidant generation.
• Ejaculate antioxidant levels and sperm velocity were measured in treated and control males.
• Sperm velocity was analyzed in relation to social hierarchy rank and diquat treatment.

Main Results:

• Diquat treatment increased ejaculate antioxidant levels but reduced sperm velocity.
• Males lower in the social hierarchy experienced the greatest reduction in sperm velocity.
• Contrary to the hypothesis, subordinate males did not show enhanced ejaculate protection.

Conclusions:

• Oxidative stress is a likely physiological factor affecting ejaculate quality.
• Resource access appears to limit an individual's ability to cope with environmental hazards.
• Social status and resource availability may constrain the allocation of resources to ejaculate quality.