THE DARWIN-FISHER THEORY OF SEXUAL SELECTION IN MONOGAMOUS BIRDS

Area of Science:

• Evolutionary biology
• Quantitative genetics
• Animal behavior

Background:

• Males in monogamous species often display secondary sexual traits that are less extreme than in polygynous species.
• Darwin and Fisher proposed a theory linking female breeding date, nutritional condition, and sexual selection.
• Understanding the evolution of male traits and female preferences in monogamy is crucial.

Purpose of the Study:

• To develop a quantitative-genetic model for the joint evolution of male secondary sexual traits, female mating preferences, and female breeding date.
• To investigate the constraints on the evolution of conspicuous male traits in monogamous systems.
• To explore the role of female breeding timing and nutritional condition in sexual selection.

Main Methods:

• Development of a quantitative-genetic model.
• Analysis of the interplay between male trait evolution, female preference, and female breeding date.
• Examination of equilibrium conditions for male traits and female preferences.

Main Results:

• Conspicuous male traits that may decrease survival can evolve in monogamous birds, but their evolution is constrained.
• The strength of sexual selection is limited, preventing extreme maladaptive evolution seen in polygynous systems.
• Male parental care can favor preferences for less conspicuous males, further limiting trait exaggeration.
• Sexual selection can occur independently of the nutritional effects proposed by Darwin and Fisher.

Conclusions:

• The Darwin-Fisher mechanism's assumptions are likely met in many monogamous bird species.
• Sexual selection in monogamous birds is constrained by factors limiting trait exaggeration.
• Additional mechanisms likely reinforce sexual selection, contributing to the evolution of male secondary sexual traits.