Abstract
Evolutionary branching occurs when a population with a unimodal phenotype distribution diversifies into a multimodally distributed population consisting of two or more strains. Branching results from frequency-dependent selection, which is caused by interactions between individuals. For example, a population performing a social task may diversify into a cooperator strain and a defector strain. Branching can also occur in multi-dimensional phenotype spaces, such as when two tasks are performed simultaneously. In such cases, the strains may diverge in different directions: possible outcomes include division of labor (with each population performing one of the tasks) or the diversification into a strain that performs both tasks and another that performs neither. Here we show that the shape of the population’s phenotypic distribution plays a role in determining the direction of branching. Furthermore, we show that the shape of the distribution is, in turn, contingent on the direction of approach to the evolutionary branching point. This results in a distribution–selection feedback that is not captured in analytical models of evolutionary branching, which assume monomorphic populations. Finally, we show that this feedback can influence long-term evolutionary dynamics and promote the evolution of division of labor.
Highlights
Natural selection can act on multiple traits at the same time
Evolutionary branching is the phenomenon by which frequency-dependent selection causes a population with a unimodal phenotype distribution to diversify into multiple modes
Employing different numerical techniques we demonstrate that this is due to changes in the shape of the population’s phenotypic distribution as it approaches the branching point: the population accumulates variance orthogonally to the selection gradient, which results in a predictable branching direction
Summary
Natural selection can act on multiple traits at the same time. When this is the case, the population’s response to selection depends on the strength and direction of selection and on the shape of its phenotypic distribution [1]. Selection changes the shape of this distribution, which in turn may affect future dynamics. This creates the potential for a distribution–selection feedback that could render the outcome of evolutionary processes contingent on initial conditions and more generally on past evolutionary dynamics. Most analytical models of evolutionary branching disregard the phenotypic distribution; we show that, in multidimensional phenotype spaces, the direction of branching can be influenced by the population’s phenotypic distribution, which in turn is affected by the direction of approach to the branching point
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