Cofoundress association time affects clutch size contributions in a quasisocial parasitoid

Abstract

One of the key decisions made by parents is determining how many offspring to produce using the available resources. This decision is often made in the presence of other individuals that are also attempting to reproduce. Here, we explored the clutch size response of group-reproducing female parasitoids in the bethylid genus Sclerodermus to the presence of their conspecifics prior to oviposition. We removed excess foundresses before oviposition and focused on the subsequent decisions of individual foundresses. We tested two hypotheses regarding the cues that foundresses may use to attune their reproduction. One was that clutch size decisions are adjusted according to the host handling stage at which cofoundress groups form prior to oviposition. We found no support for this hypothesis, possibly because our experimental groups were unnaturally brief. The other was that cofoundresses assess the time they are together with the host prior to oviposition to adjust their clutch size decisions. We found support for this hypothesis via a decline in the size of clutches produced by individual foundresses as the duration of their association with cofoundresses increased. It appears that smaller clutches were laid in anticipation of concurrent reproduction by the associated cofoundresses and to maintain sufficient per capita resources for the development of offspring that will experience scramble competition. This explanation was supported by further findings that larger offspring were produced when the association with cofoundresses was for longer periods. In Sclerodermus, lengthy associations with cofoundresses, both pre- and postoviposition, mean that the clutch size decisions in this study are just part of a wider set of strategic considerations that affect the success of any given foundress and her offspring within the reproductive group.