Final answer:
When the gain in reproductive success is a decelerating function of allocation to one sex or the other, the fitness of a hermaphrodite is lower than that of a unisexual individual.
Step-by-step explanation:
When the gain in reproductive success is a decelerating function of allocation to one sex or the other, the fitness of a hermaphrodite is lower than that of a unisexual individual. This is because hermaphrodites have to allocate their resources between male and female functions, which reduces the amount of resources available for each function. On the other hand, unisexual individuals can specialize in either male or female functions, allowing them to allocate more resources towards one function and increase their reproductive success.
For example, let's consider a plant that is both male and female. If the plant allocates more resources towards producing seeds (its female function), it may have a higher reproductive success as a female. However, this would come at the cost of allocating fewer resources towards producing pollen (its male function), reducing its reproductive success as a male. On the other hand, if the plant allocates more resources towards producing pollen, it may have higher reproductive success as a male, but lower reproductive success as a female.
Therefore, when the gain in reproductive success is a decelerating function of allocation, unisexual individuals have higher fitness compared to hermaphrodites.