Sexual Selection For Female Mate Choice.

Several mechanisms have been put forward to explain mate choice:

1) Direct phenotypic effects

Female preference for a male attractiveness can evolve as a result of direct phenotypic benefits if the morphology reflects the ability of the male to provide material advantages, such as a high-quality territory, nutrition, parental care or protection.

There is considerable empirical support for this mechanism on some animal taxa. Female choice might also evolve as a result of resistance to direct costs imposed by males.

2) Sensory bias.

Female preference favouring a male ornament can initially evolve under natural selection for other reasons. Males evolving traits that exploit this bias then become favoured by mate choice. There is increasing phenotypic evidence that some male traits initially evolved through female sensory biases, but the evolution of female sensory bias itself requiresmore testing.

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Figure 1. Sensory bias model. Female preference should evolve first, folowed by the evolution of male traits.

3) Fisherian sexy sons

If there are genetic components to variance in female preference and male trait, a female choosing a male with a sexy trait bears daughters and sons that can both carry alleles for a sexy trait, and for the preference for it. This genetic coupling might lead to self-reinforcing coevolution between trait and preference.

Direct critical testing of this mechanism is difficult, but molecular genetics offers new possibilities (see main text).

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Figure 2. Fisher’s Runaway process. If females exhibit preference for a male trait and selection does not act on females, then their sons and daughters will carry genes for both the preference and the trait. This creates a genetic correlation between the preference and trait. And leads to geometric increase until further increase in the male trait is opposed by natural selection.

4) Indicator mechanisms (‘good genes’ or ‘handicap mechanisms’)

It suggest that attractive male traits reflect broad genetic quality. Inherent in such mechanisms is the maintenance of genetic variation, the ‘paradox of the lek’, and parasite- and pathogen-mediated mechanisms have been suggested as potential solutions. In addition, other advantageous genes and relative freedom from deleterious mutations might lead to high male condition and expression of sex traits .

Female preference for such traits can provide genetic benefits to those of her offspring that inherit favourable alleles from their father.  The resolution of the lek paradox remains a crucial area for sexual selection research.

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Figure 3. Good genes models require a mechanism for maintaining heritable variation in offspring viability: Recurrent deleterious mutations, and parasite-host coevolution maintains parasite resistance. Handicap models refer to male traits that can only be displayed by males in good condition. These can be “honest” indicators of male condition.

5) Genetic compatibility mechanisms.

As well as additive genetic benefits reflected by indicator traits, there might be non-additive benefits from choosing a mate with alleles that complement the genome of the chooser. Examples have been found for instance in major histocompatibility complex genes, and compatibility advantages might be one adaptive reason for multiple mating by females.

Conclusions

The evolution of mate choice is based either on direct selection of a preference that gives a fitness advantage (mechanisms 1–2) or on indirect selection of a preference as it becomes genetically correlated with directly selected traits (mechanisms 3-4)

In addition, rather than favouring any particular display trait, mate choice might evolve because it conveys non-additive genetic benefits (mechanism 5).

These mechanisms are mutually compatible and can occur together, rendering the evolution of mating preferences a multiple-causation problem, and calling for estimation of the relative roles of individual mechanisms. Several diagnostic differences among the mechanisms suggest ways in which they can be tested by quantitative genetic analyses.

 

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12 Responses to Sexual Selection For Female Mate Choice.

  1. Norman says:

    What about the evolution of male preferences?

    • sirtyrionlannister says:

      Although mate choice occurs in males and females, for convenience I refer here to female choice of male traits. In most species, females are the choosy sex that discriminate amongst males, therefore selection generally favours female mate choice of males.

      • Norman says:

        Maybe our species is an interesting exception.

        • sirtyrionlannister says:

          Hopefully, but unfortunately is not the case.

          • Norman says:

            How do you know?

            • sirtyrionlannister says:

              Men are under evolutionary pressure to make qualitative concessions and trade-offs. They are compelled to breed more frequently, even to the point of considering less attractive women as an option. Thus, such compromises are a particular male adaptation in pursuit of an optimally high mating rate.

              Women are more choosier than men since it manifests through their role as the rate limiting morph in reproductive success. What you, and most people, seem to have trouble reconciling is that the concept of sexual dimorphism extends far beyond just physical and biological traits (ie. female status as ‘rate-limiting’ necessarily skews male: female prospects accordingly, destroying any notion of symmetry you might otherwise be supposing).

              Which the mating data support (e.g. you could check out all online dating experiments posted on here, or studies outside this blog).

              • Norman says:

                Ancestral men were under pressure to choose long term mates that could provide the most offspring. Ancestral women were dependant on men for survival but a man can only support a limited number of females. Men evolved to be choosy over who they acquired as wives and women evolved to compete with each other for male attention.

  2. thegreatshebang says:

    Thanks for posting this topic. I was just thinking about how preference arises into desires. In other words, what is the mechanism that makes a trait be subjectively experienced as a desire. Not of how subjective desire arises into consciousness, but when does a preference for a trait also trigger the ability and capacity for the female to choose it. The only mechanism I can tell from your 5 part summary is Fisherian Runaway.

    • sirtyrionlannister says:

      Really knowing how mating preferences evolve genetically is harder than showing that they exist, and the problem is aggravated by the possibility that several mechanisms co-occur. For Fisherian sexy son mechanism works, expression of trait and the corresponding preference must be positively correlated ( this has been found in
      several animal species).

  3. Key says:

    I need your business email ASAP!

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