Bateman's principle is reversed in a cooperatively breeding bird

Area of Science:

• Evolutionary biology
• Behavioral ecology
• Animal behavior

Background:

• Bateman's principle explains sex differences in mating behavior and sexual selection.
• It predicts a stronger relationship between mating success and offspring for males than females.
• Its applicability in cooperatively breeding systems with strong sexual selection in both sexes is unclear.

Purpose of the Study:

• To test Bateman's principle in the cooperatively breeding superb starling (Lamprotornis superbus).
• To investigate the role of sexual selection in sex differences in mating behavior within this species.

Main Methods:

• Empirical testing of Bateman's principle using mating and reproductive data from superb starlings.
• Analysis of the Bateman gradient (relationship between mating success and reproductive success) for both sexes.
• Assessment of the opportunity for sexual selection in both males and females over time.

Main Results:

• Only female superb starlings showed a significant, positive Bateman gradient.
• The opportunity for sexual selection was, on average, higher in females.
• The strength and direction of the opportunity for selection in females oscillated over time.

Conclusions:

• The findings support the hypothesis that sexual selection drives female trait elaboration in superb starlings and other cooperative breeders.
• Despite a steeper Bateman gradient in females, temporal oscillations in sexual selection opportunity may prevent sexual role reversal.
• Bateman's principle may not apply to cooperative breeders where both sexes experience strong sexual selection.