Seasonal variation in wind speed and oceanic salt spray favors delayed reproduction in coastal yellow monkeyflowers.

premiseThe optimal timing of reproduction depends on the relative risk and benefit of continued growth. These risks and benefits depend on the local environment, which varies seasonally. While temperature and water availability are well-studied selective agents on reproductive timing, less is known about other seasonally variable factors.

methodsTo test whether seasonal variation in wind and salt spray influences selection on reproductive timing, we manipulated flowering time and ocean exposure in a coastal environment. Flowering plants from 12 yellow monkeyflower populations that span a coastal-to-inland gradient were placed on a coastal bluff in spring and summer. Inland populations typically flower in spring, which is much windier than the summer months when coastal populations usually flower, other plants were protected from wind and salt spray, and the rest were exposed to wind and salt spray.

resultsIn the windier spring cohort, individuals exposed to the ocean had severe necrosis and produced few flowers and seeds, while protected plants had little to no necrosis, producing more flowers and seeds than ocean-exposed plants. In the calmer summer cohort, individuals exposed to the ocean had less severe necrosis and produced comparable numbers of flowers as plants protected from the ocean. However, only coastal populations produced appreciable numbers of seeds when exposed to the ocean, consistent with prior evidence that coastal ecotypes are locally adapted.

conclusionsOverall, these results suggest that seasonal variation in wind and salt spray is a key selective factor in coastal populations contributing to population differences in flowering time.