Does offspring demand affect parental life-history trade-offs?

Abstract

Life-history trade-offs between the number and size of offspring produced, and the costs of reproduction on future reproduction and survival can all be affected by different levels of parental effort. Because of these trade-offs the parents and the offspring have different optima for the amount of care given to the current brood, which leads to a conflict between parents and offspring. The offspring, as well as the parents, have the ability to affect parental effort, and thus changes in offspring traits have the potential to cause reproductive costs on the parents. Here, we used a repeated cross-fostering design to manipulate offspring demand during juvenile development in the burying beetle Nicrophorus vespilloides to examine whether responding to offspring begging incurs reproductive costs to the parent. After a manipulated first reproductive event, we gave each experimental female, that had been exposed to different levels of offspring demand, a chance to breed again, and monitored their survival. We found that larval demand influences the trade-off between the size and number of offspring produced, but has no impact on the reproductive costs through future reproduction or survival of the parent. The parents do, however, pay an overall fecundity cost for the general success of their first broods, but this cost was not related to the changes in the levels of larval begging. Other traits, including survival showed no costs of reproduction. Survival and the number of larvae successfully raised in the second broods correlated positively, indicating differences in the individual quality of the parents.