Asymmetry in Sexual SelectionEdit
It might be thought that sexual selection is close to even or symmetrical between sexes or choices, but this is quite the opposite. The level of investment determines a great deal about how sexual selection continues the behavioral consequences of these asymmetries.
Parental investment is the energy and time invested by a parent in regards to caring for the offspring, as well as making the offspring. The parent who is giving the investment may have a negative effect on its fitness since it is spending time with the current offspring. While the offspring receiving the investment is having an increased fitness (Freeman & Herron, 2007).
In some species there is not much of an investment by either parent, while mammalian species have the greatest difference between the two parents level of investment. There is a level of investment in both copulation and rearing/caring.
Eggs are many times considered to be more expensive than ejaculates, meaning the female would have more investment from the start, compared to the males (Freeman & Herron, 2007). There is also a limit to amount of
eggs that females can produce, comparing to the amount of a male. As well, a female must go through the gestation and delivery stage, which means she is reproductively inactive, compared to a male who can still be active.
Sexual Selection: Strong for One Sex, Weak for Another SexEdit
Sexual selection will act differently, because of asymmetries and limits by many factors, on sexes, being stronger or weaker for different sexes (Freeman & Herron, 2007).
The sex that is subject to strong sexual selection is the sex that has the least investment in reproduction. These individuals will be competitive.
The sex that is is subject to weak sexual selection is the sex that has the greatest investment in reproduction. These individuals will be choosy.
Dimorpishm indicates that there is two forms and in this case it means that each sex can take a different form, where this species can be visually seen in two different ways. In most cases, sexual dimorphism displays itself through males having specialized body decorations, colors, larger body size and canine size.
Sexual Dimophism is something that rose from the competition for mates by the sex that is subjected to strong sexual selection (Freeman & Herron, 2007). Since males do not tend to have as great of an investment as females, males usually exhibit the enhanced or exaggerated traits compared to the usually less elaborate females.
Freeman, S. & Herron, J. (2007). Evolutionary Analysis 4th Ed. Sexual Selection, pp 401-441.