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.