Interacting Phenotypes and the Evolutionary Process: I. Direct and Indirect Genetic Effects of Social Interactions

Abstract

Interacting phenotypes are traits whose expression is affected by interactions with conspecifics. Commonly-studied interacting phenotypes include aggression, courtship, and communication. More extreme examples of interacting phenotypes-traits that exist exclusively as a product of interactions-include social dominance, intraspecific competitive ability, and mating systems. We adopt a quantitative genetic approach to assess genetic influences on interacting phenotypes. We partition genetic and environmental effects so that traits in conspecifics that influence the expression of interacting phenotypes are a component of the environment. When the trait having the effect is heritable, the environmental influence arising from the interaction has a genetic basis and can be incorporated as an indirect genetic effect. However, because it has a genetic basis, this environmental component can evolve. Therefore, to consider the evolution of interacting phenotypes we simultaneously consider changes in the direct genetic contributions to a trait (as a standard quantitative genetic approach would evaluate) as well as changes in the environmental (indirect genetic) contribution to the phenotype. We then explore the ramifications of this model of inheritance on the evolution of interacting phenotypes. The relative rate of evolution in interacting phenotypes can be quite different from that predicted by a standard quantitative genetic analysis. Phenotypic evolution is greatly enhanced or inhibited depending on the nature of the direct and indirect genetic effects. Further, unlike most models of phenotypic evolution, a lack of variation in direct genetic effects does not preclude evolution if there is genetic variance in the indirect genetic contributions. The available empirical evidence regarding the evolution of behavior expressed in interactions, although limited, supports the predictions of our model.

Estimating mechanisms and equilibria for offspring begging and parental provisioning

“…The slope b ESD corresponds to a maternaleffect coefficient (Kirkpatrick & Lande 1989) mediating the indirect genetic effect of provisioning on offspring begging, and b EDS corresponds to an offspring-effect coefficient mediating the indirect genetic effect of begging on provisioning. A quantitative genetic model for general social interactions with reciprocal effects has derived a solution for trait expression that is formally equivalent to equations (2.7) and (2.12) (Moore et al 1997). The formal equivalence of proximate equilibria for begging and provisioning (this model) and indirect-genetic-effect models (Moore et al 1997) highlights the importance of time-scale in the interpretation of model parameters and equilibrium points.…”

“…A quantitative genetic model for general social interactions with reciprocal effects has derived a solution for trait expression that is formally equivalent to equations (2.7) and (2.12) (Moore et al 1997). The formal equivalence of proximate equilibria for begging and provisioning (this model) and indirect-genetic-effect models (Moore et al 1997) highlights the importance of time-scale in the interpretation of model parameters and equilibrium points. It also suggests that the model presented here may apply to general social interactions with reciprocal effects (if there are analogues to the EDS and ESD mechanisms).…”

“…Extending the time-scale towards cross-generational effects, the model converges to a quantitative genetic description of mechanisms regulating parental provisioning and offspring begging through indirect genetic effects (Moore et al 1997). The intercepts of the regression equations, a EDS and a ESD , become genotypic values for parental provisioning and offspring begging, respectively.…”

Parent–offspring conflict and co-adaptation: behavioural ecology meets quantitative genetics

“…Behavioural ecologists have demonstrated that social behaviours in general tend to be flexible in the sense that focal individuals adjust their behaviour to the behaviour of other individual(s) involved in the interaction (Moore et al 1997). Such behavioural flexibility encompasses the whole field of animal communication (Bradbury & Vehrencamp 1998), as well as maternal hormonal effects on offspring behavioural development (e.g.…”

An interaction‐driven cannibalistic reaction norm

“…The social environment created by interactions among individuals also becomes a stage for the evolution of the reaction norm (Moore, Brodie, & Wolf, 1997). There may be social effects on phenotypic evolution whenever interacting phenotypes are present, and the fitness of an individual expressing a certain phenotype will be affected by the phenotypes of the individuals with which it is interacting.…”