Sperm competition intensity affects sperm precedence patterns in a polyandrous gift-giving spider

Area of Science:

• Evolutionary biology
• Behavioral ecology
• Reproductive strategies

Background:

• Sperm competition is a major driver of evolutionary adaptations for fertilization success.
• Understanding how factors like mating order and nuptial gifts influence sperm precedence is crucial, especially in polyandrous species.

Purpose of the Study:

• To investigate the impact of sperm competition intensity on paternity and sperm precedence in the spider Pisaura mirabilis.
• To determine if mating order (first vs. last male advantage) or nuptial gift-mediated copulation duration influences fertilization success.

Main Methods:

• Genotyping of wild spider broods to assess female polyandry (number of sires).
• Experimental manipulation of sexual selection intensity (number of mating partners) to observe fertilization outcomes.
• Correlation analysis between copulation duration, mating order, and paternity share.

Main Results:

• Pisaura mirabilis females exhibit significant polyandry, with a mean of two sires per brood.
• In double matings, paternity was monopolized by one male irrespective of mating order.
• First male priority emerged with four males but disappeared with six males, suggesting sperm mixing overrides order effects.
• Paternity share decreased with an increasing number of competitors.
• Longer copulation durations, often facilitated by nuptial gifts, consistently increased paternity share.

Conclusions:

• Sperm competition intensity significantly impacts paternity outcomes and favors traits that enhance fertilization success, such as prolonged copulation.
• While mating order can play a role, its effect is context-dependent and can be masked by high sperm competition or mixing.
• Nuptial gifts appear to be adaptive by increasing copulation duration and thus paternity share in competitive mating scenarios.