The Correlated Evolution of Dispersal and Mating-System Traits

The existence of an evolutionary syndrome linking dispersal and mating-system traits has been discussed in both plants and animals. In animals, dispersal as a means of inbreeding-avoidance has been cited as an ultimate cause of sex-biased dispersal. In plants, self-compatibility is widespread, which is often cited as a mechanism for reproductive assurance in organisms that have limited control of dispersal. Limited dispersal has also been hypothesized to minimize outbreeding depression and increase local adaptation. Here, we compare and contrast the various evolutionary hypotheses that link dispersal and the mating system in both plants and animals. We conclude that the majority of theoretical evidence supports the existence of two evolutionary syndromes: (1) outcrossing and dispersing; (2) inbreeding and not dispersing. In the light of the evidence compiled, we advocate for a redefinition of Baker's law, which we consider to be an exception rather than the rule. As environmental heterogeneity is common in nature, the role of bet-hedging in the evolution of these strategies is likely to be very strong, albeit difficult to prove empirically. Lastly, we argue that exceptions to these two general syndromes (e.g., inbreeding and dispersing) should not be viewed as contradictory; instead they merit exceptional attention because they represent unusual biological adaptations. Throughout, we refer to specific empirical examples to illustrate these scenarios and conclude by suggesting that a meta-analysis of the available data would be a useful next step.