Per capita sperm metabolism is density dependent

Area of Science:

• Reproductive Biology
• Metabolic Ecology
• Evolutionary Physiology

Background:

• A negative relationship between population density and metabolic rate is observed across taxa.
• This phenomenon is often attributed to adaptive metabolic plasticity.
• Historically, sperm metabolism studies have overlooked the impact of sperm concentration, assuming no adaptive plasticity.

Purpose of the Study:

• To systematically review and quantify the relationship between sperm aerobic metabolism and sperm concentration.
• To investigate whether sperm exhibit adaptive metabolic plasticity in response to varying concentrations.
• To synthesize evidence across a wide range of species, from protostomes to humans.

Main Methods:

• Conducted a systematic review of 88 studies.
• Analyzed 198 estimates of sperm aerobic metabolism and concentration.
• Included data from 49 diverse species, encompassing protostomes to humans.

Main Results:

• Found strong evidence for concentration-dependent per capita metabolic rates in sperm.
• Sperm exhibited lower metabolic rates at higher concentrations and increased metabolism when diluted.
• A 10-fold decrease in sperm concentration was associated with an average 35% increase in per capita metabolic rate.

Conclusions:

• Sperm metabolic rates are concentration-dependent, demonstrating adaptive metabolic plasticity.
• This plasticity is likely an adaptive strategy to enhance the probability of egg fertilization.
• The findings challenge previous assumptions in sperm metabolism research regarding concentration effects.