Landscape-Enhanced Mutant Survival

Evolutionary signatures of past range expansions are encoded into a population's genetic composition. These signatures can arise from demographic heterogeneity, and spatial environmental fluctuations when populations expand into new territory with complex structure. Our recent computational study has demonstrated that, in the context of neutral evolution, environmental quenched-random noise can dominate the growth dynamics and lead to deterministic evolutionary outcomes despite generating statistics reminiscent of growth driven by genetic drift. In particular, a landscape of many hotspots, localized regions of enhanced reproduction, gives rise to population boundaries, which are composed predominately by genealogical lineages that are pinned to a small number of optimal paths through the landscape. While we can describe these optimal paths through geometrical optics, how such optimal paths influence the survival of deleterious mutations remains unknown. Using an Eden model, we simulate population spatial expansion through a landscape of hotspots with deleterious mutations arising at a fixed rate. By investigating the role of environmental noise in the survival of these emerging mutants, we show that deleterious mutations can establish when they emerge near an optimal path.