Contents lists available at ScienceDirect Journal of Thermal Biology journal homepage: www.elsevier.com/locate/jtherbio Exploring physiological plasticity and local thermal adaptation in an intertidal crab along a latitudinal cline Juan Diego Gaitán-Espitia a,b , Leonardo D. Bacigalupe b , Tania Opitz c , Nelson A. Lagos d , Sebastián Osores c , Marco A. Lardies c, ⁎ a CSIRO Oceans and Atmosphere, GPO Box 1538, Hobart 7001, TAS, Australia b Instituto de Ciencias Ambientales y Evolutivas, Facultad de Ciencias, Universidad Austral de Chile, Casilla 567, Valdivia, Chile c Departamento de Ciencias, Facultad de Artes Liberales, Universidad Adolfo Ibañez, Diagonal Las Torres 2640, Peñalolen, Santiago, Chile d Centro de Investigación e Innovación para el Cambio Climático, Universidad Santo Tomás, Ejército 146, Santiago, Chile ARTICLE INFO Keywords: Reaction norm Metabolism Heart beat Thermo-tolerance Genotype x environment Geographic variation Physiological flexibility ABSTRACT Intertidal organisms have evolved physiological mechanisms that enable them to maintain performance and survive during periods of severe environmental stress with temperatures close to their tolerance limits. The level of these adaptive responses in thermal physiology can vary among populations of broadly distributed species depending on their particular environmental context and genetic backgrounds. Here we examined thermal performances and reaction norms for metabolic rate (MR) and heart rate (HR) of seven populations of the porcelanid crab Petrolisthes violaceus from markedly different thermal environments across the latitudinal gradient of ~3000 km. Physiological responses of this intertidal crab under common-garden conditions suggest the absence of local thermal adaptation along the geographic gradient (i.e., lack of latitudinal compensation). Moreover, thermal physiological sensitivities and performances in response to increased temperatures evidenced the existence of some level of: i) metabolic rate control or depression during warm temperature exposures; and ii) homeostasis/canalization (i.e., absence or low levels of plasticity) in physiological traits that may reflect some sort of buffering mechanism in most of the populations. Nevertheless, our results indicate that elevated temperatures can reduce cardiac function but not metabolic rate in high latitude crabs. The lack of congruence between HR and MR supports the idea that energy metabolism in marine invertebrates cannot be inferred from HR and different conclusions regarding geographic differentiation in energy metabolism can be obtained from both physiological traits. Integrating thermal physiology and species range extent can contribute to a better understanding of the likely effects of climate change on natural populations of marine ectotherms. 1. Introduction For many marine intertidal organisms, physiological plasticity is a crucial mechanism to cope with natural fluctuations in thermal conditions (Hofmann and Todgham, 2010). This adaptive strategy allows them to maintain performance and survive periods of severe environmental stress (e.g., low tides), with temperatures at or above their heat tolerance limits (Helmuth et al., 2006, 2002; Stillman, 2002). Under these conditions, intertidal organisms adjust their metabolic rates in an attempt to balance tissue oxygenation and energy produc- tion/expenditure (McElroy et al., 2012). The scope for these adjust- ments depends on the functional capacity of ventilation and circula- tion, which is limited to a particular thermal tolerance window for a species or a population and, thus, sets limits to its geographical distribution (Pörtner, 2001). In broadly distributed species, local adaptation to different environmental regimens can lead to spatial differences in thermal tolerance and physiological plasticity among populations (e.g., Fangue et al., 2006; Gaitán-Espitia et al., 2014, 2013; Gardiner et al., 2010; Lardies et al., 2011; Pörtner, 2001). For example, in widely latitudinal distributed ectoherms, populations at high lati- tudes have broader thermal tolerances and live at temperatures under their physiological optima (Addo-Bediako et al., 2000; Deutsch et al., 2008; Janzen, 1967; Sunday et al., 2010), compared with their counterparts at lower latitudes (Gaitán-Espitia et al., 2014, 2013; Gaitán-Espitia and Nespolo, 2014; Naya et al., 2011; Niehaus et al., 2012). This geographic pattern of variation in thermal physiology and plasticity has profound implications in the context of climate change (Kelly et al., 2012), as elevated temperatures are likely to cause localized extinctions of many marine ectothermic species (Helmuth et al., 2002), by affecting their physiological performance and thermal http://dx.doi.org/10.1016/j.jtherbio.2017.02.011 Received 18 August 2016; Received in revised form 9 February 2017; Accepted 9 February 2017 ⁎ Corresponding author. E-mail address: marco.lardies@uai.cl (M.A. Lardies). Journal of Thermal Biology 68 (2017) 14–20 Available online 28 February 2017 0306-4565/ © 2017 Elsevier Ltd. All rights reserved. MARK