Extra-pair paternity and sexual dimorphism in birds

Area of Science:

• Evolutionary biology
• Behavioral ecology
• Ornithology

Background:

• Sexual dimorphism arises from differing sexual selection strengths between sexes.
• Extra-pair paternity (EPP) intensifies sexual selection, particularly in males, potentially driving dimorphism in traits like plumage and size.
• Previous studies indicate EPP's role in avian dimorphism.

Purpose of the Study:

• To investigate the relationship between EPP frequency and sexual dimorphism in wing length and plumage color across 401 bird species.
• To determine if EPP influences dimorphism differently based on which sex is more exaggerated.
• To control for confounding factors like social mating systems and life-history traits.

Main Methods:

• Statistical analysis of covariation between EPP frequency and dimorphism metrics (wing length, plumage color).
• Inclusion of 401 bird species in the dataset.
• Controlling for variables such as social polygamy, parental care bias, body size, and migration distance.

Main Results:

• EPP frequency positively correlated with wing length dimorphism, alongside social polygamy, sex bias in parental behavior, and body size.
• EPP was the sole predictor of plumage color dimorphism.
• High EPP was linked to increased sexual dichromatism when males were more colorful, but decreased it when females were more colorful.
• Contrary to predictions, EPP increased wing length dimorphism regardless of whether males or females were larger.

Conclusions:

• EPP plays a significant role in the evolution of both size and plumage dimorphism in birds.
• Wing length and plumage color dimorphism appear to evolve independently, influenced by distinct reproductive, social, and life-history factors.
• The study highlights the complex interplay between mating systems and the evolution of sexual dimorphism.