Modifying the floral microenvironment: elevational divergence in floral thermoregulatory mechanisms

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Highly mobile animals can relocate to microhabitats that suit their thermal requirements when ambient temperatures are either extremely hot or cold, called thermoregulation. Plants however, are subject to ambient temperature conditions which can be detrimental to their reproductive success. This investigation will test whether high elevation populations of a wild perennial plant in the southern Colorado Rockies are locally adapted to cool temperatures, with mechanisms that increase flower temperature, whereas low elevation populations have adaptive mechanisms to lower flower temperatures under high ambient temperatures. The work will pinpoint the mechanisms by which flowers warm and cool their internal floral temperatures and test how variation in thermoregulatory ability impacts plant reproductive fitness and plant-pollinator interactions. This award will involve undergraduates at Clemson University in research in STEM fields through studies on how floral warming in local, charismatic spring ephemeral flowers impacts reproductive performance and pollination at the South Carolina Botanical Garden. As climates are changing globally and flowers continue to emerge earlier, this research will inform how plants will ameliorate thermal stress to maintain reproductive success. This work has important implications for the future of plant reproduction in both wild and economically important crop species. Angiosperms have evolved various mechanisms to achieve floral temperatures that deviate from ambient conditions, ameliorating damage to pollen and ovules and promoting pollinator visitation. Research to date is biased towards examining mechanisms of floral warming in cold environments, limiting the understanding of local adaptation in floral thermoregulation across thermal gradients and providing few examples of floral cooling. Additionally, studies linking variation in thermoregulation with variation in both gamete viability and pollinator-attraction in field conditions are scarce. This study will first test for differences in floral thermoregulation between high and low elevation populations of a widespread perennial distributed across a large altitudinal gradient in the Southern Rocky Mountains. Using growth-chamber experiments, thermal performance curves for pollen and ovule performance will be generated, and mechanisms of floral warming and cooling will be pinpointed using a combination of time-lapse photography and reflectance spectrometry. Finally, geographic variation in selection on thermoregulatory ability will be determined by linking pollen viability, seed set, and pollinator visitation with variation in floral temperature in both high and low elevation populations. This work will elucidate the complex mechanisms of floral thermoregulation and the impacts of thermoregulatory ability on plant fitness. It will shed light on how flowering plants may cope with changing temperatures and advancing phenologies in changing climates.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.