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 performed an experimental manipulation of flowering time and ocean exposure in a coastal environment. Flowering plants from twelve yellow monkeyflower populations spanning a coastal-to-inland gradient were placed on a coastal bluff in spring and summer, which differ in average wind speed. A subset of plants were protected from wind and salt spray, and the remaining plants were exposed to these factors. ResultsIn the windier spring cohort, ocean-exposed individuals had severe necrosis and produced few flowers and seeds, while protected plants had little-to-no necrosis, producing more flowers and seeds than exposed plants. In the calmer summer cohort, ocean-exposed individuals had less severe necrosis and produced comparable numbers of flowers as protected plants. 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 contributing to population differences in flowering time.