Gene flow effects on populations inhabiting marginal areas: Origin matters

The evolutionary potential of populations inhabiting marginal areas has been extensively debated and directly affects their conservation value. Gene flow is one of the main factors influencing selection, adaptive potential and thus, local adaptation processes in marginal areas. The effects of differential gene flow provenance are still not well understood, since studies on gene flow between marginal populations have been underrepresented in the literature. This kind of gene flow can be especially beneficial because it can provide both adaptive allelic combinations originated under similar environmental conditions and genetic variation on which selection can act. We conducted a study on the effects of different gene flow provenance on marginal populations of Mediterranean alpineSilene ciliataPourret (Caryophyllaceae) replicated in three mountain ranges of Central Spain. The delineation of optimal and marginal areas of the species distribution was based on environmental differentiation and relied on the ecological definition of centrality and marginality. We experimentally tested the effect of three different types of pollen-mediated gene flow on germination rate, seedling size and survival rate in marginal populations and assessed their effects by establishing in situ common gardens. To further assess the evolutionary potential of marginal populations, we performed a reciprocal sowing experiment and measured the same fitness components to determine the extent of local adaptation. We found that gene flow between marginal populations improved germination rate and seedling survival with regard to gene flow from optimal to marginal populations and within marginal populations. In reciprocal sowing experiments, seedling survival rate was higher when the seed source was from marginal areas than when it was from optimal areas in both marginal and optimal sowing sites. Synthesis. Our results suggest that gene flow between marginal populations from similar environmental conditions increases the fitness of the recipient population by increasing genetic diversity and simultaneously providing adaptive alleles generated under similar selective pressures. Results also highlight the adaptive potential of marginal populations as genetic diversity from marginal areas may provide a fitness advantage to the populations in optimal areas. In this context, the adaptive value of marginal populations increases their relevance and potential use in conservation management.

Automated summary

The study found that gene flow between marginal populations from similar environmental conditions can enhance the fitness of the recipient population by increasing genetic diversity and providing adaptive alleles. These results highlight the adaptive potential and importance of marginal populations.