Ricerc@Sapienza

Divergence among species can start as a subtle variation of phenotypic traits among populations of the same species, triggered by different ecological conditions. From this point of view, more and more attention is focused on the particular eco-evolutionary conditions of peripheral populations, found at the margin of species range. These populations are supposed to live in low suitable environments, under a strong selective regime. So that, we can talk for many of these cases of a "natural experiment", which can be used to better understand how the species react to extreme environments, close to their adaptive potential limit. Unfortunately, a clear methodological and theoretical framework to study this phenomenon is still lacking. The main problem is that the definition of "center" and "margin" of a population is not uniform across the scientific literature and often just reflects a geographic gradient. However, geographically peripheral habitats are not always unsuitable areas and, at the same time, central populations could not live in optimal ecological conditions. Alternatively to a pure spatial definition of central and marginal population, Species Distribution Models (SDM) can be a useful tool to face this question from an ecological perspective. These models provide a good proxy of the realized ecological niche and, as a consequence, of the environmental suitability of a specific area for the species. In my PhD project I'm investigating the existence of a "marginal effect" on Podarcis siculus pheripheral populations phenotype (head shape and size), using both a spatial (from the geographical center to the margin) and an environmental (from high to low suitable areas, as defined by the SDM model) gradient.