Sexual Selection Be able to comp are and contrast sexual selection with natural

Question

Sexual Selection Be able to comp are and contrast sexual selection with natural selection. How are the 0 mechanisms similar and how different? Also, be familiar with Fisher's Condition Indication hypothesis, and with West-Eberhards Sensory Exploitation hypothesis. How are they similar? How are they different? re concerning Natural Selection: Chapter 5. Natural selection is not the same as evolution; selection is not the same as evolution by ral selection (diff fitness - selection; diff fitness due to a heritable character- Nat Sel). ures cannot evolve by Nat Sel unless they make a positive contribution to the individual's s. Natural selection may act at a variety of different points during the life cycle of an sm. Both the level of heredity and the strength of selection (selection coefficient) will ine the extent of a population's response to natural selection (measured as the intensity of on: Intensity of selection i ([char after - character before)]/Vp). Absolute fitness (ri for genotype i) versus Relativua fit

Explanation / Answer

Males of monogamous birds often show secondary sexual traits that are conspicuous but considerably less extreme than those of polygynous species. We develop a quantitative-genetic model for the joint evolution of a male secondary sexual trait, a female mating preference, and female breeding date, following a theory proposed by Darwin and Fisher. Good nutritional condition is postulated to cause females to breed early and to have high fecundity. The most-preferred males are mated by early-breeding females and receive a sexual-selection advantage from those females' greater reproductive success. Results show that conspicuous male traits that decrease survival can evolve but suggest that the extent of maladaptive evolution is greatly limited relative to what is possible in a polygynous mating system for two reasons. First, in the absence of direct fitness effects of mate choice on the female, the equilibria for the male trait and female preference form a curve whose shape shows that the maximum possible strength of sexual selection on males (and hence the potential for maladaptive evolution) is constrained. Under certain conditions, a segment of the equilibrium curve may become unstable, leading to two alternative stable states for the male trait. Second, male parental care will often favor the evolution of mating preferences for less conspicuous males. We also find that sexual selection can appear in the absence of the nutritional effects emphasized by Darwin and Fisher. A review of the literature suggests that the assumptions of the Darwin-Fisher mechanism may often be met in monogamous birds and that other mechanisms may often reinforce it by producing additional components of sexual selection.

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