Fitness at the Expanding Front: An Exploration-Exploitation Trade-off in Phenotypic Switching

Phenotypic switching is a key bet-hedging strategy for navigating the exploration-exploitation trade-off in fluctuating environments, yet its interplay with spatial population dynamics during range expansions remains poorly understood. We use an individual-based spatial simulation to investigate how switching strategies shape fitness (expansion speed) in heterogeneous landscapes. Maximizing expansion speed requires balancing exploration and exploitation, leading to an optimal intermediate switching rate in these spatial settings. Critically, we incorporate a phenotypic switching lag, representing the biophysical cost of adaptation. We demonstrate this lag imposes a hard fitness constraint, forcing the optimal strategy toward slower switching rates as lag duration increases and reducing maximum expansion speed. Contrasting with models focusing on irreversible mutations, we show reversible switching enhances resilience by allowing recovery from maladaptation, influencing specialist persistence boundaries. Spatial structure also generates emergent phenomena: we find clustering provides collective protection, enhancing the survival of disadvantaged phenotypes. Additionally, our simulations show that conditioning on lineage survival alone is sufficient to generate the apparent stagnancy of deleterious sectors reported experimentally, revealing this observational bias as a crucial factor when characterizing selection effects at expanding fronts. This work integrates bethedging theory with adaptation costs and spatial dynamics, offering a quantitative framework for fitness at expanding fronts.