By Karen Griffiths
Broadly put sexual selection is an explanation for the way traits may vary or be restricted to one sex. These differences can be in shape and size (dimorphism), colour (dichromatism). Sexually dimorphic traits evolve as a result of sexual selection. Fitness, as defined by the number of offspring that survive and reproduce in the next generation, differs in individuals, and is selected for by the ability of an individual to find a mate. There may be trade-offs between different components of fitness, such as a brightly coloured male lizard attracting more mates (sexual selection), but being more vulnerable to predation because of bright colour (natural selection).
The mechanisms of sexual selection are intrasexual selection and intersexual selection.
Intra sexual selection is the competition for mates among members of the same sex. For example, males may fight with the victor mating with the female. Thus weapons such as horns and the better fighters will be selected for. But fighting can be extremely costly, especially to the loser. So some species use colour, as a badge of status to indicate who is more likely to be the victor, and thus avoid a fight altogether. For example some species of frogs have chest patches which indicate the amount of testosterone circulation, and thus the likely winner of the fight. The larger the chest patch, the more testosterone circulating.
Inter sexual selection is essentially the mate choice among members of the opposite sex. This can be an estimate of sexual selection, for example the choice the females are making. Females constantly selecting for certain characteristics leads to selection gradients for those particular traits.
Unfortunately, the need for parental care is a constraint on male reproductive success. In species where the male is crucial to the survival of the off spring, such as having an important role in care and foraging, and the female cannot care for the young on her own, then their maximum lifetime reproductive success will be lower
The mechanisms of sexual selection are intrasexual selection and intersexual selection.
Intra sexual selection is the competition for mates among members of the same sex. For example, males may fight with the victor mating with the female. Thus weapons such as horns and the better fighters will be selected for. But fighting can be extremely costly, especially to the loser. So some species use colour, as a badge of status to indicate who is more likely to be the victor, and thus avoid a fight altogether. For example some species of frogs have chest patches which indicate the amount of testosterone circulation, and thus the likely winner of the fight. The larger the chest patch, the more testosterone circulating.
Inter sexual selection is essentially the mate choice among members of the opposite sex. This can be an estimate of sexual selection, for example the choice the females are making. Females constantly selecting for certain characteristics leads to selection gradients for those particular traits.
Unfortunately, the need for parental care is a constraint on male reproductive success. In species where the male is crucial to the survival of the off spring, such as having an important role in care and foraging, and the female cannot care for the young on her own, then their maximum lifetime reproductive success will be lower