Copulation order, density cues and variance in fertilization success in a cestode

Area of Science:

• * Evolutionary Biology
• * Parasitology
• * Reproductive Ecology

Background:

• * Simultaneous hermaphrodites balance resource allocation between male and female reproductive functions to maximize fitness.
• * Increased population density is predicted to intensify sperm competition, potentially favoring greater investment in male traits.
• * The cestode Schistocephalus solidus, with an intermediate fish host and definitive bird host, provides a model to study density-dependent reproductive strategies.

Purpose of the Study:

• * To determine if Schistocephalus solidus utilizes cues from intermediate host density to modulate male reproductive investment.
• * To assess the impact of prior infection density (single vs. multiple) on subsequent male fertilization success in the definitive host.

Main Methods:

• * Experimental competition involving two S. solidus worms, one from a single and one from a multiple infection in the intermediate fish host.
• * These competitors sequentially fertilized the eggs of a third worm in the definitive host.
• * Paternity was assessed by comparing fertilization rates of the competing males.

Main Results:

• * Fertilization success rates between competing males frequently deviated from an equal 50-50 distribution, indicating unequal paternity.
• * No significant effect of intermediate host density (single vs. multiple infection) on paternity was detected.
• * Mating order did not significantly influence the fertilization success of either competitor.

Conclusions:

• * While individual male reproductive success in S. solidus exhibits high variance, the tested density cues did not predictably alter paternity.
• * Further research is required to identify the specific traits and environmental factors driving the observed variation in male reproductive success.
• * The adaptive significance of density-dependent reproductive strategies in this species remains to be fully elucidated.