Data from: Grow with the flow: a latitudinal cline in physiology is associated with more variable precipitation in Erythranthe cardinalis

Local adaptation is commonly observed in nature: organisms perform well in their natal environment, but poorly outside it. Correlations between traits and latitude, or latitudinal clines, are among the most common pieces of evidence for local adaptation, but identifying the traits under selection and the selective agents is challenging. Here, we investigated a latitudinal cline in growth and photosynthesis across 16 populations of the perennial herb Erythranthe cardinalis (Phrymaceae). Using machine learning methods, we identify interannual variation in precipitation as a likely selective agent: southern populations from more variable environments had higher photosynthetic rates and grew faster. We hypothesize that selection may favour a more annualized life history – grow now rather than save for next year – in environments where severe droughts occur more often. Thus, our study provides insight into how species may adapt if Mediterranean climates become more variable due to climate change.

本地适应（local adaptation）在自然界中普遍存在：生物在其原生栖息环境中表现优异，而在域外环境中生存表现欠佳。性状与纬度之间的相关性（又称纬度梯度，latitudinal clines）是支撑本地适应的最常见证据之一，但甄别受选择的性状及选择压力来源仍颇具挑战。本研究以16个种群的多年生草本红花沟酸浆（Erythranthe cardinalis，透骨草科Phrymaceae）为研究对象，分析其生长与光合特性的纬度梯度特征。通过机器学习方法，本研究将年际降水变率（interannual variation in precipitation）确定为潜在选择压力来源：来自降水变率更高环境的南部种群，其光合速率更高且生长速度更快。我们提出假说：在干旱频发的环境中，自然选择更青睐一年生型生活史——即优先在当下完成生长，而非为次年留存资源。因此，本研究为理解气候变化导致地中海气候（Mediterranean climates）区域环境变异性增强时，物种可能的适应路径提供了新的见解。