Conflicting selection on flowering time

Various studies have shown that water stress can influence both the quality and timing of flowering. Generally, dry years or environments are expected to select for early flowering as a drought avoidance strategy. However, for plants that rely on pollinators, these may also be a strong selective pressure, and previous work suggests that pollinators can select for both earlier and later flowering time in different contexts. This raises the potential for conflicting selection on flowering phenology (timing) under ongoing climate change.

To better understand the interaction between water availability and pollinator-mediated selection on flowering phenology, Yun Wu from Sichuan Normal University, China, and colleagues in China and Sweden combined pollination and water manipulation on the flowering herb Primula tibetica. They show that flowering phenology selection was both context-dependent and conflicting: under low water conditions there was pollinator-mediator selection for early flowering, but non-pollinator-mediated selection for later flowering, while under medium water conditions, pollinators and non-pollinator agents selected for shorter and longer flowering duration, respectively. The work highlights the ability for climate to constrain evolutionary responses, and a need to better understand combined abiotic and biotic impacts on selection.