CONSEQUENCES OF VARIATION IN FLOWERING TIME WITHIN AND AMONG INDIVIDUALS OF MERTENSIA FUSIFORMIS (BORAGINACEAE), AN EARLY SPRING WILDFLOWER

Climate change is causing many plants to flower earlier in spring, exposing them to novel selection pressures, including-potentially-pollinator shortages. Over 2 years that contrasted in timing of flowering onset, we studied reproductive strategies, pollen limitation, and selection on flowering time in Mertensia fusiformis, a self-incompatible, spring-flowering perennial. Plants opened most of their flowers early in the flowering period, especially in 2007, the early year; but selection favored early-flowering individuals only in 2008. However, resource allocation to early vs. late seed production was flexible: In 2008, but not 2007, early flowers on a plant produced more and heavier seeds. Late flowers were capable of equal seed production if fertilization of early ovules was prevented, suggesting that late flowers serve a bet-hedging function. Evidence for pollen limitation was weak, although there was a tendency for early flowers to be pollen-limited in 2007 and for late flowers to be pollen-limited in 2008. Poor reproductive success in 2007 was likely attributable less to pollen limitation than to frost damage to flowers. We suggest that plasticity in floral longevity and resource allocation among flowers will make this species resilient to short-term pollinator deficits; whether this will help or hinder future adaptation is unclear.