Adaptation is one of the main responses of living organisms to upcoming new environmental conditions. According to the concept of local adaptation (Williams, 1966) the genotypes of a given population will have greater fitness in their local habitat than those coming from other environments. In theory, high genetic diversity and environmental heterogeneity favor the conditions for local adaptation. On the contrary, if population genetic variation is reduced, there is continuous gene flow among populations or there are temporal changes in habitat quality, local adaptation will be diminished. Finally, recent studies have shown that population size directly affects the ability for local adaptation, being it facilitated when population size increases.
The species distribution model known as “center abundance” (Brown, 1984), predicts that species will have greater abundance at the geographic center of the species distribution and that population size will be smaller as populations get farther away from optimal conditions. Consequently, it is expected that peripheral populations will have lower genetic diversity and greater genetic differentiation than central populations.
There is a intense debate on whether populations at the distribution limits should be conserved. Thus, it is necessary to evaluate their evolutionary potential. Depending on their genetic diversity and their demographic patterns, peripheral populations could play an important role in the species response to climate change.
The role of gene flow from central populations to peripheral populations is a hotly debated issue. On one hand, this gene flow can reduce local adaptation and niche expansion due to the introduction of genes maladapted to the environmental conditions of the periphery. Nevertheless, it can also generate an increase of effective population size and fitness contributing to range expansion. On the other hand, gene flow between peripheral populations can provide new adaptive genetic combinations and increase the diversity on which selection can act.
Alpine environments represent a very interesting site for the study of local adaptation for two reasons: 1) the great biodiversity existing in this habitat type and 2) the presence of an elevational gradient that gradually puts an end to the environmental conditions that allow the presence of a species, generating selective pressures in a relatively small scale. Moreover, in the context of climate change it is foreseen that there will be a notable reduction of available habitat for the alpine plant communities. Because of this, alpine plant communities are among those that are the most vulnerable to climate change.
Silene ciliata Pourret (Caryophyllaceae) is a circummediterranean species that is found above 1100m elevation in Spain in the Pyrenees, Cantabrian Range, Iberian System and Central System. It has a mixed mating system and its short seed dispersal range favors local adaptation processes. Because of this it is an excellent study case for the AdAptA project.
Brown JH, 1984. On the relationship between abundance and distribution of species. The American Naturalist 124: 255–279.
Williams GC, 1996: Adaption and Natural Selection. Princeton University Press, New Jersey. 313pp