Genome-wide supermatrix analyses of maples (Acer, Sapindaceae) reveal recurring inter-continental migration, mass extinction, and rapid lineage divergence

Acer (Sapindaceae) is an exceptional study system for understanding the evolutionary history, divergence, and assembly of broad-leaved deciduous forests at higher latitudes. Maples stand out due to their high diversity, disjunct distribution pattern across the northern continents, and rich fossil record dating back to the Paleocene. Using a genome-wide supermatrix combining plastomes and nuclear sequences (~585 kb) for 110 Acer taxa, we built a robust time-calibrated hypothesis investigating the evolution of maples, inferring ancestral ranges, reconstructing diversification rates over time, and exploring the impact of mass-extinction on lineage accumulation. Contrary to fossil evidence, our results indicate Acer first originated in the (north)eastern Palearctic region, which acted as a source for recurring outward migration. Warm conditions favored rapid Eocene-onward divergence, but ranges and diversity declined extensively as a result of the Plio-Pleistocene glacial cycles. These signals in genome-wide sequence data corroborate paleobotanical evidence for other major woody north-temperate groups, highlighting the significant (disparate) impact of climatic changes on the evolution, composition, and distribution of the vegetation in the northern hemisphere.

槭属（Acer，无患子科Sapindaceae）是研究高纬度阔叶落叶林演化历史、物种分化与群落构建的理想研究体系。槭树类群凭借极高的物种多样性、横跨北半球各大陆的间断分布格局，以及可追溯至古新世（Paleocene）的丰富化石记录而独具研究价值。本研究依托涵盖110个槭属类群的质体基因组（plastomes）与核基因组序列（nuclear sequences，总计约585 kb）构建的全基因组超级矩阵（genome-wide supermatrix），搭建了可靠的时间校准演化框架，以此解析槭属的演化历程、推断祖先分布区、重建随时间变化的多样化速率（diversification rates），并探讨大规模灭绝事件（mass-extinction）对谱系积累（lineage accumulation）的影响。与化石记录相悖的是，本研究结果表明槭属最初起源于（北）东古北界区域，并以此作为向外反复迁移的起源源区。温暖的气候条件促进了始新世（Eocene）以来的快速物种分化，但受上新世-更新世（Plio-Pleistocene）冰期循环的影响，槭属的分布范围与物种多样性出现了大幅缩减。全基因组序列数据中的这些演化信号，与北半球其他主要木本北温带类群的古植物学（paleobotanical）证据相吻合，凸显了气候变化对北半球植被演化、组成与分布的显著（差异化）影响。