Sexual selection is a mode of natural selection in which members of one biological sex select mates of the opposite sex. As a result, they compete with each other for survival and reproduce. This process allows for rapid evolution. In nature, sexual selection has led to many adaptations. For example, some mammals have evolved large antlers or colored feathers, while others lack these characteristics.
Dysmorphism
Dimorphism in sexual selection reflects the different selection pressures on males and females. This may be due to the different ecological niches of the sexes, which reduce intersexual competition for food. It may also be due to the specific nutritional requirements of each sex.
Sexual dimorphism may evolve into three fates: the species may become monomorphic, the sex-specific traits become mutually ornamented, or the dimorphic characters evolve into the non-ornamented sex. In some instances, sexual dimorphism might even lead to a transition from a single-sex expression to a dual-sex expression. However, the mechanism behind mutual ornamentation is largely unknown.
Colored feathers
Female robins use colored feathers in mating decisions to avoid being cheated by males that are brightly colored. This condition-dependent trait is expensive, but protects mates from cheating if it indicates fitness. Biological fitness is a biological trait that is genetically fixed and only expressed when a bearer is in good condition.
Although most studies have focused on male plumage and dichromatism, it is not always possible to exclude the role of sexual selection. Many species of birds have colorful plumage in both sexes, and evolutionary transitions toward color-coordinated plumage in males and females have been attributed to sexual selection.
Large antlers
It’s not clear exactly how large antlers affect a buck’s sexual selection. The researchers looked at the physiological mechanism behind the selection process as well as the relationship between body size and antler size. The results suggested that large antlers increase a male’s sexual attraction and therefore his ability to control and monopolize females.
In mid-century America, an essay by evolutionary biologist Stephen Gould argued that antlers were an indicator of quality, and that large antlers in a living buck meant he was superior in attracting females. But more recent studies are supporting the idea that antler size is driven by sexual selection. Irish elk, for instance, shrunk their antlers if they were unable to find enough food. Some research has even found evidence that red deer on predator-free islands shrunk their antlers to half their original size.
Mating differential
The concept of mating differential in sexual selection is based on the notion that sexual traits are selected to increase the probability of achieving reproductive success. In other words, males are selected for traits that will improve their chances of copulating with their mates. A study of mating success should include details on the proxy used to determine mating success and the components of sexual selection that might affect the result.
The study of mating preferences involves examining mate choice evolution within and among taxa. In some cases, more than one model may be working in concert to produce selection on mating preferences. A comparative phylogenetic approach is necessary to evaluate the relative contributions of these different models.
Fecundity benefit
Fecundity benefit of sexual selection is a benefit to females with traits that increase egg production. Because females compete with males for sperm, females with these traits are more likely to produce offspring. Fecundity benefit of sexual selection can also be seen in the early breeding pairs of certain species. These females mate with preferred males and tend to produce more eggs.
Sexual selection is different from other types of selection because the fitness of one sex depends on that of the opposite sex. The process of sexual selection is influenced by the frequency of the genotype and the fecundity of the focal individual. In addition, social interactions and population composition can influence fecundity selection.
Female reproductive competition
In many systems, females do not compete for mates. But in some systems, females experience intense competition for resources, including resources that facilitate reproduction. This competition affects the intensity of selection on females, and is often a key factor in reproductive success. But it can also result in reversed sexual dimorphism, with females exhibiting more elaborate secondary sexual characters than males.
The role of male mate choice in female reproductive competition has been examined extensively, but the exact mechanisms are still unknown. However, it has been suggested that males prefer females with high expression of secondary sexual traits, as opposed to those with low expression. It is unclear whether these preferences are adaptive, but they are likely important targets of sexual selection in these species.