Direct fitness, reciprocity and helping: a perspective from primitively eusocial wasps.

In their review, Bergmüller et al. (2007) examine explanaions for helping based on direct fitness benefits, and suggest arallels with general cooperation theory. Bergmüller et al. 2007) focus on cooperatively breeding vertebrates. Primiively eusocial wasps, in which all individuals have the option f independent reproduction, comprise the vespid subfamilies olistinae (paper wasps) and Stenogastrinae (hover wasps), plus he little-studied lineage of apoid wasps that includes the genus icrostigmus (Ross and Matthews, 1991). These wasps have ife-histories analogous to cooperatively breeding vertebrates. ndeed, Gadagkar (1994) advocates referring to both groups as eusocial’. In this commentary, we first discuss the evidence that irect benefits drive patterns of helping behaviour in primitively usocial wasps. We then consider why cooperation theory has arely been applied to primitively eusocial taxa. Finally, in the ight of the limited empirical data, we discuss which mechaisms in Bergmüller et al.’s (2007) classification are likely to be pplicable to eusocial taxa. As Bergmüller et al. (2007) note, three processes through hich direct benefits have been thought to influence helping ehaviour are known as pay-to-stay, prestige and group augmenation. There are few data with which to evaluate the first two of hese as explanations for helping in primitively eusocial wasps. ay-to-stay is a possibility in that there are significant benefits f group membership, such as resource inheritance, and because ndependent reproduction often has a low payoff (e.g. Queller, 996; Field et al., 1999, 2000). However, although helpers are ccasionally unrelated to breeders, a substantial fraction of unreated helpers has been found in only one or two species of olistes paper wasps (Queller et al., 2000; Liebert et al., 2005). n the majority of species, sample sizes available to examine the ehaviour of unrelated helpers are therefore small. Since paying-