Among-trait covariance and cross-year repeatability for direct and indirect individual effects in producer-scrounger behaviour in wild house sparrows

Variation in social traits can be attributed to direct individual effects (DIEs) of the focal individual and indirect individual effects (IIEs) due to its social partners eliciting behavioural change, analogous to indirect genetic effects. Indirect effects affect the expressed phenotypic variation upon which selection can act, especially when they covary with direct effects, providing a potential explanation for slower or faster evolution than predicted by classic theory. However, little is known about the among-trait covariance of DIEs and IIEs, or whether IIEs are consistent across time and context and how this can affect evolutionary dynamics. Here we tested game theoretical predictions of producer-scrounger tactic use during social foraging games within a DIE-IIE framework in wild house sparrows (Passer domesticus). We used automated high-throughput phenotyping, where we assayed individuals repeatedly against different social partners. We provide evidence for small IIEs in producer-scrounger behaviour, and show high cross-year consistency. We found tight among-trait covariance, which is expected to impose strong constraints on the evolution of the DIEs and IIEs. Indirect effects decreased the potential heritable variation in producing and scrounging behaviour, which appear temporally stable. Overall, these effects may provide a potential mechanism for the long-term maintenance of stable social foraging strategies.