Age-dependent changes in reproductive behavior and success in a long-lived beetle (Bolitotherus cornutus)

Age-related changes in behaviors often result in shifts in an individual's competitive ability, reproductive success, and fitness. However, how mating behaviors, aggression, and mating success simultaneously change as individuals age in natural populations remains understudied. Investigating these age-dependent effects in wild populations could reveal how age-specific patterns shape social dynamics and influence natural selection. In this study, we ask how behaviors associated with mating and reproductive success vary across age in a wild metapopulation of a long-lived beetle, Bolitotherus cornutus. We used both cross-sectional and longitudinal data from a multiyear field study of individually marked beetles to investigate how aging in the wild influences courtship and mating success. We performed rigorous scan sampling of reproductive behaviors, including courtship, mate guarding, and egg laying. We then observed marked individuals from the same wild metapopulation in male–male competition trials to determine how age influences male aggression. We found that individuals of both sexes increased their mating behaviors and experienced higher mating success as they aged. Males also increased their level of aggression as they aged. The results from our longitudinal analysis support the results from our cross-sectional analysis, showing that the observed increase in reproductive behaviors with age is not a result of survivorship bias. This work has implications for understanding how an individual's competitive ability within a population may change over time and how the age structure of a population could influence variation in sexual selection due to these age-specific reproductive patterns.