The ocean is undergoing warming and acidification. Thermal tolerance is affected both by evolutionary adaptation and developmental plasticity. Yet, thermal tolerance in animals adapted to simultaneous warming and acidification is unknown. We experimentally evolved the ubiquitous copepod Acartia tonsa to future combined ocean warming and acidification conditions (OWA approx. 22°C, 2000 µatm CO₂) and then compared its thermal tolerance relative to ambient conditions (AM approx. 18°C, 400 µatm CO₂). The OWA and AM treatments were reciprocally transplanted after 65 generations to assess effects of developmental conditions on thermal tolerance and potential costs of adaptation. Treatments transplanted from OWA to AM conditions were assessed at the F1 and F9 generations following transplant. Adaptation to warming and acidification, paradoxically, reduces both thermal tolerance and phenotypic plasticity. These costs of adaptation to combined warming and acidification may limit future population resilience.

海洋正在变暖和酸化。耐热性受进化适应和发育可塑性的影响。然而，适应同时变暖和酸化的动物的耐热性尚不清楚。我们通过实验将无处不在的桡足类动物 Acartia Tonya 进化为未来的海洋变暖和酸化联合条件（OWA 约 22°C，2000 µatm CO ₂），然后比较其相对于环境条件的耐热性（AM 约 18°C，400 µatm CO ₂）。OWA 和 AM 处理在 65 代后相互移植，以评估发育条件对耐热性和潜在适应成本的影响。在移植后的 F1 和 F9 代评估从 OWA 移植到 AM 条件的治疗。矛盾的是，适应变暖和酸化会降低耐热性和表型可塑性。适应气候变暖和酸化的这些成本可能会限制未来的人口复原力。