Division of Biological Sciences, University of Montana, Missoula, MT, 59802, USA.
Department of Biology, Grinnell College, Grinnell, IA, 50112, USA.
Am J Bot. 2021 Feb;108(2):309-319. doi: 10.1002/ajb2.1607. Epub 2021 Feb 1.
Whether drought-adaptation mechanisms tend to evolve together, evolve independently, or evolve constrained by genetic architecture is incompletely resolved, particularly for water-relations traits besides gas exchange. We addressed this issue in two subspecies of Clarkia xantiana (Onagraceae), California winter annuals that separated approximately 65,000 years ago and are adapted, partly by differences in flowering time, to native ranges differing in precipitation.
In these subspecies and in recombinant inbred lines (RILs) from a cross between them, we scored traits related to drought adaptation (timing of seed germination and of flowering, succulence, pressure-volume curve variables) in common environments.
The subspecies native to more arid environments (parviflora) exhibited slower seed germination in saturated conditions, earlier flowering, and greater succulence, likely indicating superior drought avoidance, drought escape, and dehydration resistance via water storage. The other subspecies (xantiana) had lower osmotic potential at full turgor and lower water potential at turgor loss, implying superior dehydration tolerance. Genetic correlations among RILs suggest facilitated evolution of some trait combinations and independence of others. Where genetic correlations exist, subspecies differences fell along them, with the exception of differences in succulence and turgor loss point. In that case, subspecies difference overcame genetic correlations, possibly reflecting strong selection and/or antagonistic genetic correlations with other traits.
Clarkia xantiana subspecies' differ in multiple mechanisms of drought adaptation. Genetic architecture generally does not seem to have constrained the evolution of these mechanisms, and it may have facilitated the evolution of some of trait combinations.
干旱适应机制是否倾向于共同进化、独立进化，还是受遗传结构的限制进化尚不完全清楚，特别是除气体交换外的水分关系特征。我们在两个加利福尼亚冬季一年生的黄花紫露草亚种（柳叶菜科）中解决了这个问题，这两个亚种大约在 65000 年前分离，部分通过开花时间的差异，适应于降水不同的原生范围。
在这两个亚种和它们之间的杂交重组自交系（RIL）中，我们在共同环境中对与干旱适应相关的特征（种子萌发和开花时间、多汁性、压力-体积曲线变量）进行评分。
在更干旱环境中（parviflora）的亚种表现出在饱和条件下较慢的种子萌发、较早的开花和更大的多汁性，可能表明具有优越的耐旱性、耐旱性和通过储水来抵抗脱水。另一个亚种（xantiana）在完全膨压下具有较低的渗透压和在膨压损失下较低的水势，这意味着具有优越的脱水耐受性。RIL 之间的遗传相关性表明某些特征组合的进化得到了促进，而其他特征组合则独立进化。在存在遗传相关性的地方，亚种差异沿着它们存在，除了多汁性和膨压损失点的差异外。在后一种情况下，亚种差异克服了遗传相关性，这可能反映了强烈的选择和/或与其他特征的拮抗遗传相关性。
黄花紫露草亚种在多种干旱适应机制上存在差异。遗传结构似乎并没有限制这些机制的进化，并且可能促进了某些特征组合的进化。
