Thermal sensitivities of respiration and protein synthesis differ among larval families of the Pacific oyster, Crassostrea gigas.

Understanding the mechanisms of biological responses to environmental change is a central theme in comparative and evolutionary physiology. Here, we analyzed variation in physiological responses to temperature, using 21 full-sibling larval families of the Pacific oyster, Crassostrea gigas. Pedigrees were confirmed with genetic markers for adult broodstock obtained from our breeding program. From these 21 larval families, 41 determinations of thermal sensitivity (Q10 values) were assayed for larvae of different sizes. For respiration, thermal sensitivity was consistent within a larval family during growth, but showed significant differences among families. Different Q10 values were evident among 21 larval families, with family accounting for 87% of variation. Specifically, four larval families maintained an increased thermal sensitivity for respiration (Q10 of 3). This physiology would confer resilience to rising temperature by matching the increased energy demand of protein synthesis (Q10 of 3 previously reported). For protein synthesis, differences in Q10 values were also observed. Notably, a family was identified that had a decreased thermal sensitivity for protein synthesis (Q10 of 1.7 cf. Q10 of 3 for other families), conferring an optimal energy allocation with rising temperature. Different thermal sensitivities across families for respiration (energy supply) and protein synthesis (energy demand) were integrated into models of energy allocation at the whole-organism level. The outcome of these analyses provides insights into the physiological bases of optimal energy allocation with rising temperature. These transgenerational (egg-to-egg) experiments highlight approaches to dissect components of phenotypic variance to address long-standing questions of genetic adaptation and physiological resilience to environmental change.

Increasing Temperature Results in Higher Allocation of Energy to Protein Synthesis in Sea Urchin Larvae (Lytechinus pictus).

AbstractIt is well established that metabolic processes change with temperature and size. Yet the underlying physiological mechanisms are less well understood regarding how such processes covary within a species and particularly so for developmental stages. Physiological analysis of larvae of the sea urchin Lytechinus pictus revealed that protein was the major biochemical substrate supporting metabolism. The complex dynamics of protein synthesis, turnover, and accretion changed during growth, showing a sevenfold decrease in the ratio of protein accretion to protein synthesis (protein depositional efficiency). To test hypotheses of physiological variation with rising temperature, larvae were reared over a temperature range experienced by this species in its ambient habitat. The thermal sensitivity of protein synthesis was greater than respiration (thermal sensitivity values of 3.7 and 2.4, respectively). Bioenergetic calculations revealed a disproportionate increase in energy allocation toward protein synthesis with rising temperature. These differential temperature sensitivities result in metabolic trade-offs of energy acquisition and expenditure, thereby altering physiological homeostasis. Such insights are of value for improving predictions about limits of biological resilience in a warming ocean.