As global warming accelerates, there is increasing concern about how ecosystems may change as a result of species loss and replacement. Here, we examined the thermal physiology of the European green crab (Carcinus maenas Linnaeus 1758), a globally invasive species, along three parallel thermal gradients in its native and invasive ranges. At each site, we assessed cardiac physiology to determine heat and cold tolerance and acclimatory plasticity. We found that, overall, the species is highly tolerant of both heat and cold, and that it survives higher temperatures than co-occurring native marine crustaceans. Further, we found that both heat and cold tolerance are plastic in response to short-term acclimation (18-31 days at either 5 or 25°C). Comparing patterns within ranges, we found latitudinal gradients in thermal tolerance in the native European range and in the invasive range in eastern North America. This pattern is strongest in the native range, and likely evolved there. Because of a complicated invasion history, the latitudinal pattern in the eastern North American invasive range may be due either to rapid adaptation post-invasion or to adaptive differences between the ancestral populations that founded the invasion. Overall, the broad thermal tolerance ranges of green crabs, which may facilitate invasion of novel habitats, derive from high inherent eurythermality and acclimatory plasticity and potentially adaptive differentiation among populations. The highly flexible physiology that results from these capacities may represent the hallmark of a successful invasive species, and may provide a model for success in a changing world.
KEY WORDS: Acclimatory plasticity, Cardiac physiology, Local adaptation, Species invasion, Thermal tolerance
INTRODUCTIONEnvironmental temperature exerts a pervasive influence on the physiology of ectothermic animals, from the level of molecular processes to that of broad-scale biogeographic patterning (Hochachka and Somero, 2002). As global temperatures rise, there is increasing concern about the ability of ectothermic animals to survive in their warming environments, and considerable effort is being expended to identify the physiological traits that may be of greatest importance in adapting to rising temperatures and to learn how these traits differ among species (Somero, 2010).One aspect of success in a changed thermal environment comprises a combination of broad intrinsic tolerance of acute changes in temperature and a high capacity for acclimatization (phenotypic 'plasticity') during extended exposure to a new thermal regime (Simons, 2011;Healy and Schulte, 2012). These two abilities may largely govern how eurythermal an ectothermic species is, and thus help determine its chances for success in a warming world, particularly over short time scales.
RESEARCH ARTICLEStanfordBecause maintenance of broad thermal tolerance may be metabolically costly and, indeed, unnecessary for animals inhabiting narrow thermal niches, ectothermic species range from extreme eurytherms to na...