Climate vulnerability of South American freshwater fish: Thermal tolerance and acclimation.Freshwater fish are restricted by their physiology to rivers and lakes, and are generally limited in their capacity to disperse across basins.  Climate change is expected to affect fish diversity and increase extinction, especially in low latitudes, and it has been suggested that species that inhabit low latitude species are more susceptible since they live close to their maximum thermal limits and have low capacity for acclimation.  To understand the mechanisms of variation in thermal tolerance across a broad-scale of South American fishes is fundamental to be able to assess the vulnerability of species and habitat to global warming.  Herein, we present the first attempt to analyze the vulnerability of South American freshwater fish species, based on the review of upper thermal limits of 106 species from a broad range of latitudinal habitats.  Our findings show that upper thermal limits decrease with latitude, while the thermal safety margin (TSM) increase.  Furthermore, the latitude has little effects on the acclimation response ratio, and the TSM decreased with rising temperatures.  These data suggest that thermal phenotypic acclimation has low potential for mitigating global warming. 
THERM