Phenotypic plasticity at the edge: Contrasting population‐level responses at the overlap of the leading and rear edges of the geographical distribution of two Scurria limpets

Abstract

AbstractAimTo examine the role of ocean temperature and chemistry as drivers of interpopulation differences in multiple phenotypic traits between rear and leading edge populations of two species of limpet.LocationThe coast of north‐central Chile, western South America.TaxonMollusca, Gastropoda (Lottidae).MethodsWe used field and laboratory experiments to study the ecology and physiology of individuals from populations located at the overlap of the rear and leading edges of their respective geographical distributions. At the same time, we characterized local environmental regimes, measuring seawater physical and chemical properties.ResultsTowards the edge of their range, individuals from the leading edge species gradually reduced their shell length, metabolic rate and thermal response capacity, and increased carbonate content in their shells. Individuals of the rear edge species showed dissimilar responses between sites. Contrasting behavioural responses to experimental heating reconciled observations of an unintuitive higher maximal critical temperature and a smaller thermal safety margin for individuals of the rear edge populations. Physical–chemical characterization of seawater properties at the site located on the core of the upwelling centre showed extreme environmental conditions, with low oxygen concentration, high pCO2 and the episodic presence of corrosive seawater. These challenging environmental conditions were reflected in reduced growth for both species.Main conclusionsWe found different spatial patterns of phenotypic plasticity in two sister species around the leading and trailing edges of their distributions. Our results provide evidence that environmental conditions around large upwelling centres can maintain biogeographical breaks through metabolic constraints on the performance of calcifying organisms. Thus, local changes in seawater chemistry associated with coastal upwelling circulation emerge as a previously overlooked driver of marine range edges.