Climatic adaptation in an isolated and genetically impoverished amphibian population Germa ´n Orizaola, Marı ´a Quintela and Anssi Laurila G. Orizaola (german.orizaola@ebc.uu.se) and A. Laurila, Population and Conservation Biology/Dept of Ecology and Evolution, Evolutionary Biology Centre, Uppsala Univ., Norbyva¨gen 18D, SE-75236 Uppsala, Sweden.  M. Quintela, Population and Conservation Biology/Dept of Ecology and Evolution, Evolutionary Biology Centre, Uppsala Univ., Norbyva ˜gen 18D, SE-752 36 Uppsala, Sweden and A ´ rea de Ecologı ´a, Fac. de Ciencias, Univ. de la Corun ˜a, Campus A Zapateira s/n, ES-15071 La Corun ˜a, Spain. The capacity of populations to respond adaptively to environmental change is essential for their persistence. Isolated populations often harbour reduced genetic variation, which is predicted to decrease adaptive potential, and can be detrimental under the current scenarios of global change. In this study, we examined climatic adaptation in larval life history traits in the pool frog Rana lessonae along a latitudinal gradient across the northern distribution area of the species, paying special attention to the isolated and genetically impoverished fringe populations in central Sweden. Larvae from eight populations within three geographic areas (Poland, Latvia and Sweden) were reared under three temperatures (19, 22 and 268C) in a common garden laboratory experiment. We found clear evidence for latitudinal adaptation in R. lessonae populations, larvae from higher latitudes growing and developing faster than low-latitude ones. Larvae from the Swedish populations were able to compensate for the effects of cooler temperatures and a shorter growth season with genetically higher growth and development rates (i.e. countergradient variation) in the two higher temperature treatments, but there was no difference among the populations at the lowest temperature treatment, which is likely to be close to the temperature limiting growth in R. lessonae. Our results demonstrate that isolated and genetically impoverished populations can be locally adapted, and identify the Swedish fringe populations as a significant conservation unit adapted to the northern environmental conditions. The potential of populations to adapt to changes in the environmental conditions is essential for their long-term persistence. Given anticipated global changes, knowledge on the adaptive potential of populations is becoming increasingly relevant (Hoffmann et al. 2003, Thomas et al. 2004, Kellermann et al. 2006). As isolated populations are expected to harbour limited adaptive potential, studies on adaptive variation in these populations are especially relevant for understanding the limits of evolution in nature (Frankham 1995, Willi et al. 2006). Populations isolated from the species’ main distribution area receive very little or no immigration and they can be strongly affected by genetic drift and by inbreeding depression, both of which processes reduce genetic diversity (Frankham 2005, Smith and Keller 2006, Willi et al. 2006, Allendorf and Luikart 2007). Consequently, these populations may lack the genetic variation necessary for adaptive change, which is likely to increase their risk of extinction if the environment changes (Burger and Lynch 1995, Frankham 2005, Allendorf and Luikart 2007). On the other hand, isolated populations are not constrained by gene flow from core populations and, consequently, may be better able to adapt to local environmental conditions (Bridle and Vines 2007). Indeed, several studies on plants have demonstrated that isolated, marginal populations can be exposed to a different selective environment than core populations, and that this divergent selection has lead to increased adaptive, among-population variation (McKay et al. 2001, Jakobsson and Dinnetz 2005, Willi et al. 2007). However, studies on adaptive variation in small and isolated populations are scarce in animals and especially in vertebrates. Large-scale climatic variation often selects for clinal adaptation along latitudinal and altitudinal gradients (Conover and Schultz 1995, Ashton 2004, Blanckenhorn and Demont 2004). In ectotherms, temperature is the major abiotic factor affecting physiological rates, including growth rate (Atkinson 1996, Angilletta et al. 2004). Organisms living at higher latitudes or altitudes are exposed to lower temperatures and a shorter growing season. Due to the cooler climate, they are expected to experience reduced growth and development rates in the wild, so these traits should be under strong selection pressure. There are two adaptive strategies by which ectotherms can mitigate these environmental constraints. First, according to the tempera- ture adaptation model, organisms should show the highest growth and/or development at the temperatures they most Ecography 33: 730737, 2010 doi: 10.1111/j.1600-0587.2009.06033.x # 2010 The Authors. Journal compilation # 2010 Ecography Subject Editor: Jeremy T. Kerr. Accepted 7 September 2009 730