Sex allocation in a simultaneously hermaphroditic marine shrimp

Area of Science:

• Evolutionary Biology
• Reproductive Strategies
• Sex Allocation Theory

Background:

• Simultaneous hermaphrodites face fundamental questions regarding optimal resource allocation between male and female functions.
• Understanding shifts in optimal sex allocation with age or size is crucial for evolutionary success.
• Fitness gain curves illustrate the relationship between sex-specific investment and fitness outcomes.

Purpose of the Study:

• To explore factors influencing fitness gain curves and predict sex allocation in simultaneous hermaphrodites.
• To test overall and size-dependent sex allocation strategies in the brooding shrimp Lysmata wurdemanni.
• To investigate how age and size impact resource allocation to male and female reproductive functions.

Main Methods:

• Theoretical modeling of fitness gain curves based on empirical data.
• Analysis of mating behavior, male mating ability, and population structure in Lysmata wurdemanni.
• Quantification of ovarian and testicular mass to determine gonad allocation in dissected shrimp.

Main Results:

• Lysmata wurdemanni exhibits absent sperm competition and unconstrained brooding, leading to saturating, but distinct, male and female fitness gain curves.
• The female fitness gain curve shows a greater absolute gain than the male curve, with the male curve leveling off more rapidly.
• Hermaphrodites allocated significantly more resources to female function (118:1 ratio) and showed a higher proportion of male investment in smaller individuals.

Conclusions:

• Overall sex allocation is female-biased in Lysmata wurdemanni, maximizing fitness returns from the more profitable female function.
• Size-dependent sex allocation favors higher male investment in smaller individuals, capitalizing on greater mating opportunities at smaller body sizes.
• Observed sex allocation patterns are consistent with adjustments to improve size-specific reproductive success, despite the absence of a trade-off between male and female investment.