Sperm allocation strategies in a sperm heteromorphic insect

Area of Science:

• Evolutionary biology
• Animal behavior
• Reproductive strategies

Background:

• Polyandrous species face complex mating decisions regarding sperm allocation.
• Empirical data on male responses to rivals and additional mates are inconsistent.
• Copulation duration is often used as a proxy for sperm transfer, but this assumption lacks strong evidence.

Purpose of the Study:

• To investigate how males adjust sperm allocation in response to rivals and additional mates.
• To determine if sperm allocation is correlated with copulation duration.
• To test theoretical predictions in the sperm heteromorphic insect Ephestia kuehniella.

Main Methods:

• Males were exposed to chemical and acoustic cues of rivals or additional mates before and during mating.
• Copulation duration and sperm allocation (eupyrenes and apyrenes) were measured in successive copulations.
• Sperm heteromorphism (fertile eupyrenes, nonfertile apyrenes) was utilized to differentiate sperm types.

Main Results:

• Males significantly increased the transfer of fertile eupyrenes per mate when rivals were detected.
• Sperm allocation patterns remained consistent across successive copulations under rival conditions.
• Nonfertile apyrene allocation was not adjusted in response to rivals.
• Males did not alter sperm allocation in response to additional mates, likely due to the absence of tactile cues.
• Sperm allocation was found to be independent of copulation duration.

Conclusions:

• Males strategically increase fertile sperm allocation to rivals to enhance paternity share.
• Nonfertile sperm may play a limited role in male reproductive success.
• Tactile cues might be crucial for males to adjust mating strategies in response to additional mates.
• Copulation duration is an unreliable indicator of sperm transfer in Ephestia kuehniella.