Data from: Limited scope for plasticity to increase upper thermal limits

Increases in average temperature and the frequency of extreme temperature events are likely to pose a major risk to species already close to their upper physiological thermal limits. The extent to which thermal phenotypic plasticity can buffer these changes and whether plasticity is constrained by basal tolerance levels, remains unknown. We examined the effect of developmental temperature under both constant and fluctuating thermal regimes (developmental acclimation), as well as short-term heat hardening on upper thermal limits (CTmax) in a tropical and temperate population of Drosophila melanogaster. We found evidence for thermal plasticity in response to both developmental acclimation and hardening treatments; CTmax increased at warmer developmental temperatures and with a prior heat hardening treatment. However, hardening and acclimation responses were small, improving CTmax by a maximum of 1.01° C. These results imply that overheating risk will only be minimally reduced by plasticity. We observed significant associations between developmental temperature and both basal CTmax and hardening capacity (a measure of the extent of the plastic response). Basal CTmax increased, while hardening capacity decreased, with increasing developmental acclimation temperature. This indicates that increases in basal heat resistance at warmer temperatures may come at the cost of a reduced capacity to harden. While plasticity in CTmax is evident in both populations of D. melanogaster we studied, plastic increases in upper thermal limits, particularly at warmer temperatures, may not be sufficient to keep pace with temperature increases predicted under climate change.平均气温升高与极端高温事件频次增加，或已对那些已接近自身生理热耐受上限的物种构成重大威胁。热表型可塑性（thermal phenotypic plasticity）能否缓冲此类变化带来的影响，以及可塑性是否受基础耐受水平约束，目前仍未明确。本研究以热带与温带种群的黑腹果蝇（Drosophila melanogaster）为研究对象，探究了恒温与变温热环境下发育温度（即发育驯化）以及短期热硬化处理对其临界高温上限（CTmax）的影响。研究发现，发育驯化与热硬化处理均可诱导热可塑性响应：较高的发育温度与前置热硬化处理均能提升果蝇的CTmax，但此类可塑性响应的幅度较小，最多仅能使CTmax提升1.01℃。上述结果表明，热可塑性仅能极小程度降低物种面临的过热风险。我们还观察到，发育温度与基础CTmax以及硬化能力（即衡量可塑性响应程度的指标）均存在显著关联：随着发育驯化温度升高，基础CTmax上升，而硬化能力下降，这意味着较高温度下基础耐热性的提升，或许会以硬化能力受损为代价。尽管本研究所涉及的两个黑腹果蝇种群均表现出CTmax可塑性，但临界高温上限的提升幅度，尤其是在高温环境下，或不足以跟上气候变化预测的温度增速。