What is the effect of gene flow origin on the adaptive potential of environmentally marginal populations?

Journal of Ecology has just published a new research article by Morente-López et al. ‘Gene flow effects on populations inhabiting marginal areas: origin matters’. Lead author Javier Morente-López discusses the paper and its implications.

Climate change is causing species to experience new environmental pressures, leading to changes in their distributions and affecting ecological niches. It is well known that populations inhabiting different locations inside the species range may experience environmental variability that causes fundamental demographic, genetic and phenotypic differences among them. The different areas of a species’ range (e.g. central and marginal) can be defined according to the frequency and diversity of environmental conditions experienced. Central areas are those with environmental conditions that are more common; presumably optimal for the species. Marginal areas are sites with environmental conditions that are rarer and probably harsher for the species. With climate change, more species are experiencing marginal climatic conditions inside their distributions. Crucially, the effect of climate change may differ depending on where populations are located.

Figure 1a_Mountain sumits — *Mountain summits located in the Sistema Central of the Iberian Peninsula (Spain), where the* *study was undertaken. Photo: Javier Morente López.*

In this context of environmental variability and climate change, an interesting but still controversial question arises: what is the conservation value of populations already inhabiting environmentally marginal areas? The answer to this question may rely on the adaptive potential of these populations. If marginal populations maintain high enough levels of genetic diversity, they may be able to diverge from optimal populations and adapt to new, harsher environmental conditions.

Gene flow is one of the main factors influencing divergent selection and local adaptation processes since it modulates genetic diversity and the presence of adaptive alleles in populations. The effect of gene flow between marginal populations remains poorly studied, but research into this may be especially beneficial. It could provide information about both the adaptive potential that originates under similar environmental conditions and the genetic diversity necessary for adaptive processes to emerge.

Figure 2_Silene ciliata — *Figure 2: Detail of the flowers of Silene ciliata, the study species for this research. Photo: Javier Morente López.*

In this study, we tested the adaptive potential of marginal populations and assessed the effect that gene flow from different origins has on them. This research is essential – and of great interest – since experimental studies jointly testing gene flow provenance effects and the local adaptation of marginal populations are scarce, despite the importance of these two processes. We experimentally tested the effects of three different types of pollen-mediated gene flow (within marginal populations, and between marginal-marginal and optimal-marginal populations) on Silene ciliata Pourr. (Caryophyllaceae), a Mediterranean alpine plant species (Figure 2). We measured the differential effects of gene flow types on seed germination rate and seedling survival under field conditions, developing in situ common garden experiments (Figure 3).

Morente_converted1 — Figure 3: Diagram representing the gene flow experiment developed in this study and photo showing the pollen mediated gene flow simulated and the plantings made. Photo and diagram: Javier Morente López.

To complement this study, we also carried out a local adaptation test by implementing reciprocal sowing experiments in the field (Figure 4).

Morente_converted2 — *Figure 4: Diagram representing the reciprocal sowing experiment developed in this study and photos showing a Silene ciliata seedling. Photo and diagram: Javier Morente López.*

Our results highlight that, although rarely considered, gene flow between marginal populations provides greater fitness to marginal populations by increasing genetic variation as well as providing favourable alleles and/or genetic combinations that are potentially adaptive. Moreover, our results also emphasise the adaptive potential of marginal populations, suggesting that genetic diversity from marginal areas may provide a fitness advantage to the populations in both optimal and marginal areas. Our results demonstrate the potential adaptive value of marginal populations, increasing their relevance and potential use in conservation management. Marginal populations may be useful through assisted gene flow from these populations to other populations that lack features to deal with harsh environmental conditions, potentially increasing the chances of successfully adapting to climate change.