Sexual selection is a mode of natural selection whereby members of a biological sex choose mates from the opposite sex. As a result, there is often competition for mates.
The costs and benefits of sexual selection are discussed. Also discussed is the role of environmental variation in sexual selection. There are many possible outcomes for sexual selection. To understand the benefits and costs of sexual selection, it is helpful to know what sexual traits are advantageous to humans.
Indirect benefits of ‘good genes’
Indirect benefits of ‘good genes’ are a consequence of the evolution of secondary traits that enhance the reproductive success of the bearer. However, this effect has some downsides, as the bearer of the secondary trait may end up with low-quality daughters. Indirect benefits of ‘good genes’ may also result in the emergence of ‘bad’ alleles. This could reduce the reproductive success of the bearer, and thus reduce population viability.
Some evolutionary biologists claim that ‘good genes’ are a result of the evolution of female preference. This hypothesis is based on the ‘runaway’ model, in which females prefer males with traits that enhance their reproductive success. This model predicts that attractive males will have more access to mates, which in turn leads to a genetic correlation between the trait and female preference. However, some researchers have criticized ‘good genes’ models for a lack of a fitness component.
Costs of runaway sexual selection
Runaway sexual selection is a process that makes traits less suitable for survival. In general, this process favors male traits that are more elaborate than the ones chosen by females. This process is harmful for males as it leads to maladaptive evolution. In the long run, the costs of producing these traits outweigh the benefits to reproduction. The costs of runaway sexual selection are often ignored in evolutionary theory. However, these costs may not be so apparent to modern biologists.
Moreover, in many species, a male’s display levels may depend on his mate’s viability. In the case of runaway sexual selection, male displays may have a positive correlation with offspring viability. However, these results cannot be ruled out in other populations. The correlation between paternal display values and offspring viability in runaway sexual selection populations is higher than in control populations. Nonetheless, this relationship is not yet clear.
Influence of environmental variation on sexual selection
Spatial variation in environmental features influences differences in phenotype variance and, hence, in the rate of sexual selection. Environmental variation in reproductive traits and fitness metrics are likely to influence the expression of non-sexual traits as well. Despite this, most studies of sexual selection have focused on males only. The findings, however, suggest that environmental factors have an impact on males in early life stages. For example, females preferred males developed on cacti that bore fruit.
In other words, the degree of train elaboration is an indication of fitness, and the degree to which the females reject males with deleterious mutations suggests fitness. Moreover, in sexually reproducing species, the rate of mutation is higher, revealing a higher fitness. Therefore, sexual selection requires variation in environmental factors. The rate of natural selection depends on the level of environmental variation. Environmental variation may also affect the rate of reproductive reproduction.
Mechanisms of sexual selection
Mechanisms of sexual selection in nature are often considered separate from each other. For example, mating behavior and male-male competition should be taken into account along with post-copulatory equivalents and cryptic female choice. Moreover, the evolutionary theory behind these processes suggests that the number of males evaluated by females can determine the strength of sexual selection. Sexual conflict theory suggests that conflicting male and female interests may lead to multiple mechanisms of sexual selection. The concept is also useful in studying the effects of sexual selection on the shape and evolution of male and female morphology.
It has been suggested that sexual selection can accelerate adaptation. Adaptation to new environments is facilitated by condition dependence. Furthermore, it modulates the selective pressure of sexual selection, thus preventing exaggeration of the sexual display under harsh environmental conditions. Furthermore, a species carrying large signalling traits would not add to the stress caused by the new environment. However, this effect does not work in the absence of environmental variation. Eventually, the population could adapt to the new environment and exaggerate its sexual displays.