The success of internal fertilization in a post-copulatory context depends on adaptations that protect offspring and ensure specific partner fertilization, leading to higher survival rates despite fewer offspring. In external fertilization, success relies on producing large numbers of sperm to maximize fertilization chances.
The post-copulatory game, with internal fertilization, depends on a variety of factors including sperm competition and cryptic female choice, which can influence the reproductive success of the male. In internal fertilization, adaptations that increase the chance of fertilization with a specific partner and protect offspring from external factors, such as predation or dehydration on land, are significant.
For example, internal fertilization enhances the survival rates of offspring due to the protected environment it offers within the female's body, limiting the predation on the young and helping to ensure that the eggs are fertilized by a specific male. While fewer offspring might be produced through this method, their chances of survival are typically higher compared to external fertilization.
In the context of reproductive success for a male whose species utilizes external fertilization, adaptations might include mechanisms to produce large quantities of sperm to increase the chances of fertilizing eggs in an aquatic environment where eggs and sperm are released into the water.
Whereas, in species where fertilization is internal, adaptations might include, but are not limited to, behaviors that ensure mating rights with females, the development of other structures for direct sperm delivery, and mechanisms to prevent the sperm of rival males from fertilizing the egg.