Daily, repeating fluctuations in embryonic incubation temperature alter metabolism and growth of Lake whitefish (Coregonus clupeaformis)
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abstract
Lake whitefish (Coregonus clupeaformis) utilize overwintering embryonic development (up to 180 days), and such stenothermic, cold-water embryos may be particularly susceptible to thermal shifts. We incubated whitefish embryos in temperature treatments that were constant temperature (2.0 ± 0.1 °C, 5.0 ± 0.1 °C, and 8.0 ± 0.1 °C; mean ± SD) or variable temperature (VT, mean = 5.0 ± 0.3 °C). In the VT, a daily 2 °C temperature change followed a continuous pattern throughout development: 2-4-6-8-6-4-2 °C. Hatchling survival proportion from fertilization to hatch was significantly impacted by incubation temperature (P < 0.001): 2 °C (0.88 ± 0.01) and 5 °C (0.91 ± 0.01) showed higher survival than both the VT (0.83 ± 0.02) and 8 °C groups (0.15 ± 0.06), which were statistically distinct from each other. Time to hatch (dpf) was significantly different across all treatments (P < 0.001): 8 °C (68 ± 2 dpf), VT (111 ± 4 dpf), 5 °C (116 ± 4 dpf), 2 °C (170 ± 3 dpf). Likewise, hatchling yolk-free dry mass (mg) and total body length (mm) were significantly different across all treatments (P < 0.001): 8 °C (0.66 ± 0.08 mg; 11.1 ± 0.08 mm), VT (0.97 ± 0.06 mg; 11.7 ± 0.05 mm), 5 °C (1.07 ± 0.03 mg; 12.0 ± 0.02 mm), 2 °C (1.36 ± 0.04 mg; 12.8 ± 0.05 mm). Oxygen consumption rate (V̇o2) was significantly affected by the interaction between treatment and measurement temperature (P < 0.001). Hatchling VT whitefish showed mean V̇o2 that was higher compared to the 2 °C group measured at 2 °C, and lower compared to the 2 °C and 5 °C group measured at 8 °C. This study demonstrates that the VT incubation treatment produced fewer (increased mortality), smaller embryos that hatched earlier than 2 °C and 5 °C embryos. The plasticity of V̇o2 for this stenothermic-incubating fish species under variable incubation conditions reveals a metabolic cost to cycling thermal incubation conditions.
