Rapid evolution and the potential for evolutionary rescue in land snails

Abstract

The role of evolutionary rescue, i.e. adaptive evolution prolonging the persistence of populations declining under environmental stress, has become the focus of intensive research. Sufficiently rapid adaptation is the basis of evolutionary rescue. Recent studies have shown that land snails are capable of adaptive changes within a few decades or an even shorter time. These changes have concerned shell colour, shape and size, and occurred under selective pressures including climatic shifts and impacts of introduced species. Selection coefficients reached up to 0.5 and evolutionary rates up to 0.3 kilodarwin. Land snails are among the most threatened groups of organisms worldwide. Evolutionary changes in response to habitat deterioration might assist efforts to protect their populations. However, threatened species often live in small, isolated populations and the main threats to their persistence, habitat destruction and introductions of alien predators and competitors, are usually drastic and abrupt. Unaided, such species are not likely to be rescued by adaptation. On the other hand, evolutionary change may prevent common species from becoming uncommon; declines in species that until recently were widespread and common are a growing conservation concern. Compared with theoretical models and laboratory studies, little is known about evolutionary rescue in the wild. Practical problems besetting such studies in natural populations might be easier to overcome in land snails than in many other organisms and thus studies on land snails could be relevant to biodiversity as a whole.