Adaptive potential of a Pacific salmon challenged by climate change

Pacific salmon provide critical sustenance for millions of people worldwide and have far-reaching impacts on the productivity of ecosystems. Rising temperatures now threaten the persistence of these important fishes(1,2), yet it remains unknown whether populations can adapt. Here, we provide the first evidence that a Pacific salmon has both physiological and genetic capacities to increase its thermal tolerance in response to rising temperatures. In juvenile chinook salmon (Oncorhynchus tshawytscha), a 4 degrees C increase in developmental temperature was associated with a 2 degrees C increase in key measures of the thermal performance of cardiac function(3,4). Moreover, additive genetic effects significantly influenced several measures of cardiac capacity, indicative of heritable variation on which selection can act. However, a lack of both plasticity and genetic variation was found for the arrhythmic temperature of the heart, constraining this upper thermal limit to a maximum of 24.5 +/- 2.2 degrees C. Linking this constraint on thermal tolerance with present-day river temperatures and projected warming scenarios(5), we predict a 17% chance of catastrophic loss in the population by 2100 based on the average warming projection, with this chance increasing to 98% in the maximum warming scenario. Climate change mitigation is thus necessary to ensure the future viability of Pacific salmon populations.