Hybrid evolution repeats itself across environmental contexts in Texas sunflowers (Helianthus)

AbstractTo what extent is evolution repeatable? Little is known about whether the evolution of hybrids is more (or less) repeatable than non-hybrids. We used field experimental evolution in annual sunflowers (Helianthus) in Texas to ask the extent to which hybrid evolution is repeatable across environments compared to non-hybrid controls. We created hybrids between Helianthus annuus (L.) and H. debilis (Nutt.) and grew plots of both hybrids and non-hybrid controls through eight generations at three sites in Texas. We collected seeds from each generation and grew each generation × treatment × home site combination at two final common gardens. We estimated the strength and direction of evolution in terms of fitness and 24 traits, tested for repeated versus non-repeated evolution, and assessed overall phenotypic evolution across lineages and in relation to a locally adapted phenotype. Hybrids consistently evolved higher fitness over time while controls did not, though trait evolution varied in strength across home sites. Repeated evolution was more evident in hybrids versus non-hybrid controls, and hybrid evolution was often in the direction of the locally adapted phenotype. Our findings have implications for both the nature of repeatability in evolution and the contribution of hybridization to evolution across environmental contexts., MethodsData were collected from common gardens in 2017 and 2019. Data were collected on paper, transcribed to Microsoft Excel, then processed using R.

摘要：演化的可重复性究竟能达到何种程度？目前学界对于杂交类群的演化是否比非杂交类群更（或更不）具有可重复性仍知之甚少。本研究以美国德克萨斯州向日葵属（Helianthus）的一年生向日葵为研究对象，开展野外实验演化研究，旨在对比杂交类群与非杂交对照类群在不同环境下的演化可重复性。我们以普通向日葵（Helianthus annuus L.）与海滩向日葵（Helianthus debilis Nutt.）为亲本构建杂交群体，在德克萨斯州的3个试验位点分别种植杂交组与非杂交对照组，并连续培育8个世代。每一代均收集种子，随后在2个最终同质园（common garden）中，针对每一世代×处理组×原试验位点的组合开展种植试验。我们以适合度与24个性状为指标，估算演化的强度与方向，检验演化的重复性与非重复性，并评估不同谱系间的整体表型演化特征及其与本地适应表型的关联。结果显示，杂交类群的适合度随时间推移持续提升，而非杂交对照组则未出现这一趋势；不过不同原试验位点间的性状演化强度存在差异。相较于非杂交对照组，杂交类群的演化重复性更为显著，且其演化方向往往朝向本地适应表型。本研究结果对理解演化可重复性的本质，以及杂交在不同环境背景下对演化的贡献均具有启示意义。
方法：数据采集于2017年与2019年的同质园试验。数据先以纸质记录，后转录至Microsoft Excel，再通过R语言完成数据处理。