26.5:
Mate Choice
In many species one sex, usually the female is choosy selecting a mate from individuals of the opposite sex. Often the sex competing for mates, usually the male, is more colorful and showier such as male peacocks with their bright plumage than the plainer females.
Females in these species tend to have a preference for showier males in part because bright coloration can indicate good health increasing the chance that she will have healthy offspring with her chosen mate.
Because these males are more likely to reproduce their elaborate traits are passed down to future generations increasing the phenotype in the population over time. Although being colorful can raise the risk of predation, this cost is often outweighed by the benefit of increased reproductive success.
Besides appearance females often base their mate choice on male behavior such as the complexity of a male bird's song. Males of some species exhibit complex courtship behaviors such as the male bowerbird that builds a bower, a structure decorated with brightly colored objects to attract a female.
Behaviors such as these may indicate good health or the ability of the male to provide resources. For instance, a well defended territory which would give their offspring an advantage making these males more attractive as mates.
26.5:
Mate Choice
Mate choice—the decision about whom to mate with—is a type of natural selection, since animals must reproduce to pass down their genes. Mate choice is also called intersexual selection because the behavior occurs between the sexes.
In species with mate choice, one sex (usually, but not always, the female) is “choosy,” selecting a mate from individuals of the opposite sex based on appearance or behavioral characteristics. Often, females will choose “showier” males who have brighter coloration, more elaborate ornamentation (such as the peacock’s tail), or more complex songs or courtship displays.
Sexual Dimorphisms
Over time, this has led to the evolution of many sexual dimorphisms—phenotypic differences between males and females. Because males tend to have more reproductive success if they are showier, they typically have more extravagant characteristics than females.
There are several theories about why females tend to choose showier males. Brighter colors and elaborate courtship behaviors may indicate good health, genetic fitness, and the ability to defend a territory and provide resources for the female and her offspring. Females may also have inherent preferences for certain characteristics—such as colors—that give the males displaying those characteristics a reproductive advantage.
Once the animals reproduce, genes for both the preferred traits and the preference for them are passed down from the parents to their offspring—increasing these phenotypes in the population. Although showy characteristics can increase the risk of predation, this cost is often outweighed by the increased reproductive success of these individuals and their offspring.
Suggested Reading
Burley, Nancy Tyler, Elnaz Hamedani, and Cole Symanski. “Mate Choice Decision Rules: Trait Synergisms and Preference Shifts.” Ecology and Evolution 8, no. 5 (January 29, 2018): 2380–94. [Source]
Fitzpatrick, Courtney L., and Maria R. Servedio. “The Evolution of Male Mate Choice and Female Ornamentation: A Review of Mathematical Models.” Current Zoology 64, no. 3 (June 1, 2018): 323–33. [Source]