CONCLUSION
Our theoretical review highlights that short- and longer-term impacts of
natural immigration on local population demography and evolutionary
dynamics will depend on the relative fitness and frequencies of existing
natives, F1s, F2s and various potential
backcrosses that emerge across generations. In turn, these fitnesses
will depend on underlying genetic effects, their interaction with the
environment, as well as the relative contribution of adaptive and
non-adaptive mechanisms to the evolutionary history of population
differentiation. Quantifying the relative fitness of parents and filial
generations in principle allows estimation of multiple components of
dominance and epistasis impacting fitness, with the potential to reveal
underlying genetic architectures of fitness and of population
differentiation, or even complement population genetic and local
adaptation studies aiming to understand the role of adaptive and
non-adaptive divergence. By corollary, quantifying such
multi-generational effects, and hence resulting time-courses and
manifestations of realized migration rates and effective gene flow, is
necessary to predict population and micro-evolutionary dynamics in
spatially structured populations. Our literature review indicates this
resource remains almost entirely untapped within the context of natural
dispersal and resulting immigration in wild populations and yet, spatial
structure has the potential to generate a multitude of hybrid fitness
effects across demes in a metapopulation. Therefore, studies of hybrid
offspring at the metapopulation level may not only prove some of the
most interesting and rich fields of research, but will be of fundamental
importance to understanding eco-evolutionary dynamics in a world where
fragmentation of populations is an ever-growing threat to biodiversity.