Ecological Limits and Fitness Consequences of Cross-Gradient Pollen Movement in Lasthenia fremontii

The interaction between gene flow and environmental heterogeneity plays a key role in shaping the distribution patterns that we observe in natural populations. Although a growing body of theoretical work is exploring the effects of gene flow on the evolution of range limits and ecological specialization, explicit empirical tests of model assumptions and predictions in natural populations are almost entirely lacking. This study examines the potential for center-to-edge gene flow to occur and estimates the fitness consequences of cross-gradient gene flow in an annual plant species restricted to California vernal pool wetlands. Phenological differences and highly focused foraging patterns of pollinators reduce the potential for center-to-edge gene flow across populations within pools. Furthermore, controlled crosses simulating different patterns of gene flow across the environmental gradient reveal that center-to-edge gene flow does not reduce plant fitness at the edge but instead yields an increase in emergence rates and a trend toward overall higher fitness.