Population histories of reproductive failure and low winter precipitation correlate with risk-averse seed germination in a Mediterranean-climate winter annual

Year-to-year variation in successful reproduction favors risk-averse seed-germination traits, such as dormancy that spreads risk across years and/or germination stimulated by low-risk conditions. Studies of risk-averse germination often consider whether traits vary with suspected climate drivers of failure. Rarely are long-term demographic records of population failure also available.

Supported by nearly two decades of demographic and climate monitoring, we investigated whether germination traits in the California-endemic winter-annual Clarkia xantiana ssp. xantiana can be predicted by populations’ records of reproductive failure and climate. We submitted seeds of 10 populations—4 with histories of failure—to factorial treatments of 12 levels of water potential and 3 of temperature, analyzing variation in the base water potential required for 20% germination, in the proportion of viable seeds remaining ungerminated after 14 d (a dormancy index), and in the time to germinate weighted by water potential above base (hydrotime).

Populations with a history of reproductive failures had higher base water potential, greater dormancy, and marginally shorter hydrotime. With temperature base water potential increased and hydrotime declined. Dormancy was lowest at the intermediate temperature. A multi-trait index of risk-averse germination declined with mean winter rainfall and increased with a history of reproductive failure.

Finding that populations from areas that receive low rainfall and that have experienced reproductive failure exhibit more risk-averse germination suggests local adaptation. Such intraspecific niche variation may contribute to this species’ geographic distribution. Rapid evolution of germination traits may help maintain adaptation during climate change, buffering populations from extinction.

年际间成功繁殖的变异会偏好风险规避型种子萌发性状（risk-averse seed-germination traits），例如能将风险分散至多个年份的休眠（dormancy），以及/或由低风险条件触发的萌发。针对风险规避型萌发的研究往往会考察这些性状是否随被认为会导致繁殖失败的气候驱动因子发生变化，但极少有研究能同时获取种群繁殖失败的长期种群统计记录。
依托近二十年的种群统计与气候监测数据，我们探究了加州特有冬性一年生植物黄克拉克花（Clarkia xantiana ssp. xantiana）的萌发性状是否可通过种群的繁殖失败记录与气候数据进行预测。我们将10个种群的种子（其中4个种群具有繁殖失败历史）置于12个水势（water potential）梯度与3个温度梯度的析因处理（factorial treatments）组合中，分析了20%萌发所需的基础水势、14天后仍未萌发的存活种子占比（休眠指数），以及以基础水势以上的水势加权的萌发时间（水时，hydrotime）的变异情况。
具有繁殖失败历史的种群拥有更高的基础水势、更强的休眠水平，且水时略短。随着温度升高，基础水势上升而水时下降；休眠水平在中等温度下最低。风险规避型萌发的多性状指数随冬季平均降雨量的增加而降低，随种群繁殖失败历史的存在而升高。
研究发现，来自低降雨量区域且经历过繁殖失败的种群表现出更强的风险规避型萌发，这提示该性状存在本地适应（local adaptation）。这类种内生态位分化（intraspecific niche variation）或许有助于解释该物种的地理分布格局。萌发性状的快速演化或可帮助种群在气候变化过程中维持适应性，从而缓冲种群的灭绝风险。