Age-dependent trajectories differ between within-pair and extra-pair paternity success.

Area of Science:

• Evolutionary biology
• Behavioral ecology
• Animal reproduction

Background:

• Reproductive success often varies with age, increasing initially and then declining (reproductive senescence).
• In socially monogamous species with genetic polygamy, male mating strategies (within-pair vs. extra-pair) may have distinct age-related trajectories.
• Understanding these age-specific patterns is crucial for explaining mating system evolution.

Purpose of the Study:

• To investigate the age-dependent patterns of both within-pair and extra-pair paternity success in male house sparrows.
• To compare the trajectories of these two mating tactics across a male's lifespan.
• To determine if age influences the pay-offs of alternative mating strategies.

Main Methods:

• Utilized 13 years of longitudinal data from an insular house sparrow (Passer domesticus) population.
• Employed within-individual analyses to track changes in reproductive success with age.
• Simultaneously analyzed both within-pair and extra-pair paternity success.

Main Results:

• Both within-pair and extra-pair paternity success increased with age, followed by a decline indicative of senescence.
• The age trajectories of within-pair and extra-pair paternity success differed significantly.
• Extra-pair paternity success showed a faster early-life increase and a delayed decline compared to within-pair success.

Conclusions:

• Male house sparrows exhibit age-dependent shifts in reproductive effort between within-pair and extra-pair mating tactics.
• These differential trajectories suggest age-specific optimal strategies for maximizing combined reproductive benefits.
• The interplay of mating strategies and age-related mortality may explain variation in extra-pair paternity.