Abstract

Natural dispersal between populations, and resulting immigration, influences population size and genetic diversity and is therefore a key process driving reciprocal interactions between ecological and evolutionary dynamics. Both ecological and evolutionary consequences of dispersal fundamentally depend on the relative fitnesses of immigrants and their various descendants manifested in the context of natural environments. Yet, despite this commonality, recent research advances in predicting immigrants' legacies remain substantially disconnected across disciplines. To bridge resulting divides, we synthesize empirical and theoretical work examining fitness consequences of inter-breeding across the full spectrum of genetic divergence from inbred lines to inter-specific hybridization. We demonstrate how common underlying processes can generate positive or negative fitness consequences of immigration depending on interacting genetic and environmental effects. Impacts of inter-breeding following natural dispersal among sub-populations could consequently vary dramatically, shaping eco-evolutionary outcomes. Yet, our systematic literature review reveals a striking paucity of empirical studies that quantify multi-generational fitness consequences of immigration in natural metapopulations, precluding general inferences on outcomes. Hence, to provide new impetus, we highlight key theoretical and empirical gaps, and outline how cutting-edge statistical and genomic tools could be combined with multi-generational field datasets to advance understanding of dispersal-mediated drivers and constraints on eco-evolutionary dynamics.