Theoretical models of animal contests such as the Hawk-Dove game predict that variation
in fighting behaviour will persist due to mixed evolutionarily stable strategies (ESS) under
certain conditions. However, the genetic basis for this variation is poorly understood and
a mixed ESS for fighting can be interpreted in more than ...
Theoretical models of animal contests such as the Hawk-Dove game predict that variation
in fighting behaviour will persist due to mixed evolutionarily stable strategies (ESS) under
certain conditions. However, the genetic basis for this variation is poorly understood and
a mixed ESS for fighting can be interpreted in more than one way. Specifically, we do not
know whether variation in aggression within a population arises from among-individual
differences in fixed strategy (determined by an individual’s genotype – direct genetic
effects (DGEs)), or from within-individual variation in strategy across contests.
Furthermore, as suggested by developments of the original Hawk-Dove model, within individual variation in strategy may be dependent on the phenotype and thus genotype of
the opponent (indirect genetic effects – IGEs). Here we test for the effect of DGEs and
IGEs during fights in the beadlet sea anemone Actinia equina. By exploiting the unusual
reproductive system of sea anemones, combined with new molecular data, we investigate
the role of both additive (DGE + IGE) and non-additive (DGE x IGE) genetic effects on
fighting parameters, the latter of which have been hypothesised but never tested for
explicitly. We find evidence for heritable variation in fighting ability and that fight
duration increases with relatedness. Fighting success is influenced additively by DGEs and
IGEs but we found no evidence for non-additive IGEs. These results indicate that variation
in fighting behaviour is driven by additive indirect genetic effects (DGE + IGE), and support
a core assumption of contest theory that strategies are fixed by DGEs.