For instance, if selection for canalization is relatively weak compared to stabilizing selection
on phenotype, then genetic drift can move a population along a contour of equal phenotype.
To calculate how stabilizing selection
acts on individuals that have particular combinations of direct genetic effects, and maternal effects we use the definition of [z.
When females oviposit alone, there is stabilizing selection
on the offspring sex ratio (Green et al.
In this paper, I first develop a model of evolutionary change that incorporates strong stabilizing selection
around an adaptive optimum as the dominant evolutionary force.
When it does so, it should experience stabilizing selection
on glucosinolates but directional selection to minimize trichome density.
For a valley 90% as fit as the starting peak [ILLUSTRATION FOR FIGURE 1B OMITTED], a decrease in the strength of stabilizing selection
of only 16-30% is sufficient to cause the landscape to become unimodal and allow the population to evolve to the higher peak, regardless of the size of the population.
Simple examples include stabilizing selection
on an additive polygenic trait (Wright 1935a; appendix), selection against heterozygous chromosome arrangements, frequency-dependent selection favoring the commoner type (as with Miillerian mimicry; Mallet 1986), and disruptive selection on one or more quantitative traits (e.
We assume that new offspring experience Gaussian stabilizing selection
with fluctuating optimum [[Theta].
Reviews of stabilizing selection
on morphological traits in natural populations report a range of intensities (Johnson 1976; Turelli 1984; Endler 1986).
Specifically, the following questions were addressed: (1) Does stabilizing selection
act on initiation of flowering to promote synchronous flowering within a population?
The forces of directional selection and stabilizing selection
were estimated as the coefficients of the linear and quadratic terms, respectively, from regression analyses between relative feeding rate and bill depth (Lande and Arnold 1983).
We then illustrate the framework by showing how it can be used to determine the covariance pattern expected under several familiar types of gradual phenotypic evolution: (1) mutation and random genetic drift alone; (2) constant or fluctuating directional selection; and (3) stabilizing selection
with random genetic drift or environmental fluctuations.