Dispersal asymmetries and deleterious mutations influence metapopulation persistence and range dynamics

Asymmetric dispersal within and between populations is more often the norm than the exception. For example, prevailing winds and currents can result in directional dispersal of many passively dispersed species and inter-individual variability in physical condition can generate asymmetric dispersal rates between individuals and populations. Despite this, very little theory incorporates asymmetric dispersal into spatial ecological or genetic models. We therefore present three illustrative scenarios incorporating asymmetric dispersal into spatially and genetically explicit individual based models. In the first, asymmetric dispersal due to environmental forces, such as wind or currents, interacts with the accumulation of mutation load across an environmental gradient, with consequences for range dynamics. In the second, asymmetric dispersal rates arise as individuals disperse according to their physical condition, such that individuals carrying more mutation load disperse less. We demonstrate that this condition-dependent asymmetric dispersal substantially reduces metapopulation persistence. Finally, we turn to the potential implications of condition-dependent dispersal for range expansions. Simulations demonstrate that asymmetric dispersal of individuals according to their load status can substantially slow the rate of range expansion. Taken together, these results highlight that overlooking asymmetric dispersal can result in major biases of our estimates of species persistence and range expansion dynamics.