Final answer:
Mating systems significantly influence sexual selection, with monogamous, polygynous, and polyandrous systems leading to various reproductive strategies and traits. Intersexual selection involves mate choice, often by females, while intrasexual selection involves competition among same-sex individuals.
Step-by-step explanation:
Mating systems play a critical role in the process of sexual selection, which is the differential reproductive success between individuals due to variations in their ability to obtain mates. Mating systems can be categorized as monogamous, polygynous, or polyandrous. In monogamous systems, both males and females often invest heavily in offspring, and mating fidelity is high for at least the duration of a breeding season. Polygyny involves a single male mating with multiple females and is usually associated with a high level of male-male competition and sexual dimorphism. Polyandry, where a female mates with multiple males, is rarer but can lead to intense female-female competition and choosiness.
Intersexual selection, which arises when individuals of one sex, typically females, are choosy in selecting their mates, often drives the evolution of exaggerated male traits, such as the peacock's elaborate tail feathers. In contrast, intrasexual selection involves direct competition between members of the same sex, commonly males, who vie for reproductive opportunities—manifesting in fights, displays, or dominance hierarchies. Various hypotheses explain patterns of monogamy, including mate-guarding, male assistance, and female-enforced monogamy, where females actively reduce the opportunity for males to seek additional mating opportunities.
These mating strategies affect both plants and animals, influencing evolutionary trajectories such as the development of secondary sexual characteristics and influencing what we perceive as 'species.' Sometimes sexual selection can lead to traits that enhance mating success at the cost of survival, demonstrating the potency of reproductive success as an evolutionary force.