LAUSR

The rise in temperature associated with climate change may threaten the persistence of stenothermal organisms with limited capacities for beneficial thermal acclimation. We investigated the capacity for within-generation and transgenerational thermal responses in brook trout (Salvelinus fontinalis), a cold-adapted salmonid. Adult fish were acclimated to temperatures within (10°C) and above (21°C) their thermal optimum for 6 mo before spawning, then mated in a full factorial breeding design to produce offspring from cold- and warm-acclimated parents and bidirectional crosses between parents from both temperature treatments. Offspring from families were subdivided and reared at two acclimation temperatures representing their current (15°C) and anticipated future (19°C) habitat temperatures. Offspring thermal physiology was measured as the rate of oxygen consumption (Mo2) during an acute change in temperature (increase of 2°C h−1) to observe their Mo2-temperature relationship. We recorded resting Mo2, peak (highest achieved, thermally induced) Mo2, and critical thermal maximum (CTM) as performance metrics. Although limited, within-generation plasticity was greater than transgenerational plasticity, with offspring warm acclimation elevating CTM by 0.5°C but slightly lowering peak thermally induced Mo2. Transgenerational plasticity was evident as a slightly elevated resting Mo2 and a shift of the Mo2-temperature relationship to higher rates overall in offspring from warm-acclimated parents. Furthermore, offspring whose parents were warm acclimated were in worse condition than those whose parents were cold acclimated. Both parents contributed to offspring thermal responses; however, the paternal effect was stronger. Despite the existence of within-generation and transgenerational plasticity in brook trout, it is unlikely that these will be sufficient for coping with long-term changes to environmental temperatures.