Data from: Phylogeographic differentiation versus transcriptomic adaptation to warm temperatures in Zostera marina, a globally important seagrass

Populations distributed across a broad thermal cline are instrumental in addressing adaptation to increasing temperatures under global warming. Using a space-for-time substitution design, we tested for parallel adaptation to warm temperatures along two independent thermal clines in Zostera marina, the most widely distributed seagrass in the temperate Northern Hemisphere. A North–South pair of populations was sampled along the European and North American coasts and exposed to a simulated heatwave in a common-garden mesocosm. Transcriptomic responses under control, heat stress and recovery were recorded in 99 RNAseq libraries with ~13 000 uniquely annotated, expressed genes. We corrected for phylogenetic differentiation among populations to discriminate neutral from adaptive differentiation. The two southern populations recovered faster from heat stress and showed parallel transcriptomic differentiation, as compared with northern populations. Among 2389 differentially expressed genes, 21 exceeded neutral expectations and were likely involved in parallel adaptation to warm temperatures. However, the strongest differentiation following phylogenetic correction was between the three Atlantic populations and the Mediterranean population with 128 of 4711 differentially expressed genes exceeding neutral expectations. Although adaptation to warm temperatures is expected to reduce sensitivity to heatwaves, the continued resistance of seagrass to further anthropogenic stresses may be impaired by heat-induced downregulation of genes related to photosynthesis, pathogen defence and stress tolerance.

沿宽泛温度梯度分布的种群，是解析全球变暖背景下生物对升温适应性机制的关键研究材料。本研究采用空间替代时间实验设计（space-for-time substitution design），以北半球温带分布最广的海草——大叶藻（Zostera marina）为研究对象，沿两条独立的温度梯度检验其对高温的平行适应性演化。我们沿欧洲和北美海岸选取了一对南北分布的种群，于通用花园中型实验生态系统（common-garden mesocosm）中开展模拟热浪暴露实验。在对照、热应激及恢复三种条件下，我们对99个RNA测序（RNAseq）文库进行了转录组分析，共鉴定到约13000个经唯一注释的表达基因。本研究通过校正种群间的系统发育分化，以区分中性分化与适应性分化。相较于北方种群，两个南方种群的热应激恢复速度更快，且表现出平行的转录组分化特征。在2389个差异表达基因中，有21个超出中性分化预期，推测其参与了对高温的平行适应性演化。然而，经系统发育校正后，最强的遗传分化出现在3个大西洋种群与地中海种群之间：在4711个差异表达基因中，有128个超出中性分化预期。尽管对高温的适应性演化被认为可降低物种对热浪的敏感性，但热应激诱导的光合作用、病原体防御及应激耐受相关基因的下调，可能会削弱海草对后续人为胁迫的持续抗性。