Abstract
Few theoretical and experimental studies have analyzed the genetic basis of body size dimorphism. Since the evolutionary response to selection depends of the genetic variance in a population it is to be expected that traits under selection would have smaller genetic variance than traits not affected by selection. The evolution of sexual size dimorphism is affected by the genetic correlation between females and males, with the most dimorphic traits showing smaller genetic correlations between the sexes. As result of the differences in the intensity of sexual selection between the sexes, it is expected that the levels of genetic variance would be larger in females than males. I analyzed the genetic additive variance underlying six traits of Acheta domesticus, and the genetic correlations between females and males. The most dimorphic trait with the smallest genetic correlation between the sexes was forewing length, this trait showing genetic variance only in females. It may be that sexual selection acting on male traits has depleted the genetic variance not only in male traits but also for those female traits that have a large genetic correlation with male traits. It is also possible that the evolution of sexual dimorphism in A. domesticus could be constrained as a result of the large genetic correlation between the sexes.
Highlights
Falconer (1989) has pointed out that the evolutionary response to selection depends on the quantitative genetic variance in the population and that the amount of genetic variance present in a population can reflect the historical consequences of natural selection, because of which it is to be expected that genetic variance would be depleted by natural selection
If the correlation between the sexes is large there are two alternative scenarios; the genetic variance in females can decrease in a correlated response to selection pressure on males, or, if natural selection is operating in a different way on females than on males, it is possible that the genetic variance will be maintained in the population due to an equilibrium between female and male selective pressures (Simmons and Ward, 1991)
Only a few experimental studies have analyzed the genetic basis of body size dimorphism (Simmons and Ward, 1991; Reeve and Fairbairn, 1996; Merila et al, 1998; Badyaev and Hill, 2000)
Summary
Phenotypic differences between sexes can arise as result of sexual differences in the intensity or mode of selection (Badyaev et al, 2000; Krausaar and Blanckernhorn, 2002). Falconer (1989) has pointed out that the evolutionary response to selection depends on the quantitative genetic variance in the population and that the amount of genetic variance present in a population can reflect the historical consequences of natural selection, because of which it is to be expected that genetic variance would be depleted by natural selection.Since sexual selection is generally stronger on males than females (Andersson, 1994), it is to be expected that the levels of genetic variance underlying sexually-selected traits would be larger in females than males because of the differences in the intensity of sexual selection between the sexes. If the correlation between the sexes is large there are two alternative scenarios; the genetic variance in females can decrease in a correlated response to selection pressure on males, or, if natural selection is operating in a different way on females than on males, it is possible that the genetic variance will be maintained in the population due to an equilibrium between female and male selective pressures (Simmons and Ward, 1991) Despite these evolutionary implications, only a few experimental studies have analyzed the genetic basis of body size dimorphism (Simmons and Ward, 1991; Reeve and Fairbairn, 1996; Merila et al, 1998; Badyaev and Hill, 2000)
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