Age interactions influence biparental care behavior and reproductive success

Prolonged reproductive interactions can lead to social plasticity and fitness differences for a focal individual in response to their partner’s characteristics. Age can provide a way to manipulate the influence of a social partner due to its predictable consequences for mate quality and reproductive effort. Here, we use a full factorial design to examine the interactions between male and female age on behavior and reproductive performance in the obligately caring, frequently biparental burying beetle Nicrophorus orbicollis. We found that both males and females increased their reproductive effort with age. However, this response was weaker than that of a related, more uniparental species that provides facultative care, indicating that details of age-related behavior are predictable based on species differences. We also found that male and female behavior depended on both their own and their partner’s age, as well as their partner’s behavior. Lastly, we found that mismatched age pairs had the highest levels of reproductive success. These results indicate that reproductive senescence does occur but that it can be mitigated by having a young social partner. This also suggests a rarely found pattern wherein age-mismatching may have beneficial consequences for both parental and offspring fitness.