Sperm competition promotes the exploitation of rival ejaculates

Area of Science:

• Reproductive biology
• Evolutionary ecology
• Animal behavior

Background:

• Polyandrous species often exhibit second male fertilization priority.
• This pattern is typically attributed to males increasing ejaculate size.
• Female insemination sites can be hostile to sperm, with seminal fluid components aiding survival.

Purpose of the Study:

• To propose a novel mechanism for second male sperm precedence in internal fertilizers.
• To explore how female tract conditions influence sperm competition.
• To challenge classical predictions regarding ejaculate investment and paternity advantage.

Main Methods:

• Theoretical modeling of sperm competition dynamics.
• Analysis of existing literature on polyandry and ejaculate composition.
• Comparative study of reproductive strategies in species with rapid female remating.

Main Results:

• Second male sperm precedence may arise from the female tract being pre-conditioned by previous ejaculates.
• This pre-conditioning can reduce second male ejaculate costs by lowering sperm mortality.
• Second males may achieve higher paternity with reduced ejaculate investment.

Conclusions:

• The buffering effect of prior ejaculates offers a new explanation for second male precedence.
• This mechanism suggests that ejaculate investment is not always directly proportional to paternity success.
• Female remating frequency and tract physiology are key factors in sperm competition outcomes.