sexual selection

Examples of sexual selection in the following topics:

• Sexual Selection

  • Sexual selection, the selection pressure on males and females to obtain matings, can result in traits designed to maximize sexual success.
  • The selection pressures on males and females to obtain matings is known as sexual selection.
  • Sexual selection takes two major forms: intersexual selection (also known as 'mate choice' or 'female choice') in which males compete with each other to be chosen by females; and intrasexual selection (also known as 'male–male competition') in which members of the less limited sex (typically males) compete aggressively among themselves for access to the limiting sex.
  • Sexual selection can be so strong that it selects for traits that are actually detrimental to the individual's survival, even though they maximize its reproductive success.
  • This is an example of the extreme behaviors that arise from intense sexual selection pressure.

• Nonrandom Mating and Environmental Variance

  • One reason is simple mate choice or sexual selection; for example, female peahens may prefer peacocks with bigger, brighter tails.
  • Traits that lead to more matings for an individual lead to more offspring and through natural selection, eventually lead to a higher frequency of that trait in the population.
  • However, there may also be some sexual selection for more vibrant plumage which indicates health and reproductive performance.

• Mating Systems and Sexual Selection

  • In mating, there are two types of selection (intersexual, intrasexual) and three mating systems (monogamous, polygynous, polyandrous).
  • Not all animals reproduce sexually, but many that do have the same challenge: they need to find a suitable mate and often have to compete with other individuals to obtain one.
  • Two types of selection that occur during the process of choosing a mate may be involved in the evolution of reproductive traits called secondary sexual characteristics.
  • These types are: intersexual selection (the choice of a mate where individuals of one sex choose mates of the other sex) and intrasexual selection (the competition for mates between species members of the same sex).
  • An example of intersexual selection is when female peacocks choose to mate with the male with the brightest plumage .

• Natural Selection and Adaptive Evolution

  • Natural selection drives adaptive evolution by selecting for and increasing the occurrence of beneficial traits in a population.
  • Natural selection only acts on the population's heritable traits: selecting for beneficial alleles and, thus, increasing their frequency in the population, while selecting against deleterious alleles and, thereby, decreasing their frequency.
  • Natural selection does not act on individual alleles, however, but on entire organisms.
  • Natural selection acts at the level of the individual; it selects for individuals with greater contributions to the gene pool of the next generation, known as an organism's evolutionary fitness (or Darwinian fitness).
  • Through natural selection, a population of finches evolved into three separate species by adapting to several difference selection pressures.

• Methods of Reproducing

  • Animal reproduction is essential to the survival of a species; it can occur through either asexual or sexual means.
  • The known methods of reproduction are broadly grouped into two main types: sexual and asexual.
  • Many organisms can reproduce sexually as well as asexually.
  • Sexual reproduction ensures a mixing of the gene pool of the species.
  • The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur.

• Advantages and Disadvantages of Sexual Reproduction

  • The fact that most eukaryotes reproduce sexually is evidence of its evolutionary success.
  • Scientists recognize some real disadvantages to sexual reproduction.
  • In sexual populations, the males are not producing the offspring themselves.
  • Why is sexuality (and meiosis) so common?
  • As one species gains an advantage, this increases selection on the other species; they must also develop an advantage or they will be out-competed.

• Processes and Patterns of Evolution

  • Natural selection can only occur in the presence of genetic variation; environmental conditions determine which traits are selected.
  • Genetic diversity within a population comes from two main mechanisms: mutation and sexual reproduction.
  • Sexual reproduction also leads to genetic diversity: when two parents reproduce, unique combinations of alleles assemble to produce the unique genotypes and thus phenotypes in each of the offspring.
  • However, sexual reproduction can not lead to new genes, but rather provides a new combination of genes in a given individual.
  • Explain why only heritable variation can be acted upon by natural selection

• Genetic Variation

  • Genetic variation is essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population.
  • Because natural selection acts directly only on phenotypes, more genetic variation within a population usually enables more phenotypic variation.
  • Neutral alleles are neither selected for nor against and usually remain in the population.
  • However, existing genes can be arranged in new ways from chromosomal crossing over and recombination in sexual reproduction.
  • Overall, the main sources of genetic variation are the formation of new alleles, the altering of gene number or position, rapid reproduction, and sexual reproduction.

• Defining Population Evolution

  • Just as mutations cause new traits in a population, natural selection acts on the frequency of those traits.
  • In natural selection, those individuals with superior traits will be able to produce more offspring.
  • When selective forces are absent or relatively weak, gene frequencies tend to "drift" due to random events.
  • When recombination occurs during sexual reproduction, genes are usually shuffled so that each parent gives its offspring a random assortment of its genetic variation.
  • As mutations create variation, natural selection affects the frequency of that trait in a population.

• Whole-Genome Duplication

  • This may provide an evolutionary benefit to the organism by supplying it with multiple copies of a gene, thus, creating a greater possibility of functional and selectively favored genes.
  • Gene loss during diploidization is not completely random, but heavily selected.
  • Genome doubling provides organisms with redundant alleles that can evolve freely with little selection pressure.
  • It has been suggested that many polyploidization events created new species, via a gain of adaptive traits, or by sexual incompatibility with their diploid counterparts.