Format: ORAL

Andrs Romero-Bravo1, Maria C. Castellanos1, Marko Hyvrinen3, Susanna Koivusaari2,3, Aino Kotilainen2, Martti Levo2, Anniina Mattila3, Charlotte Mller3, ystein Opedal4, Laura Pietikinen3, Maria Hllfors2,5

1 University of Sussex, Brighton, United Kingdom 2 University of Helsinki, Helsinki, Finland 3 Finnish Museum of Natural History, Helsinki, Finland 4 Lund University, Lund, Sweden 5 Finnish Environment Institute (Syke), Helsinki, Finland.

Increasing average temperatures as well as more frequent extreme weather events caused by climate change are likely to affect plant-pollinator interactions around the globe. The ability of plants to adapt their reproductive strategies to new environmental conditions is crucial for their survival. Temperature-induced changes in the floral phenotype might negatively affect visitation rates and potentially hinder plant sexual reproduction and reduce fitness. At the same time, phenotypic plasticity may improve plant fitness under fluctuating environments. We used Hypericum perforatum to assess the effect of temperature on floral and flowering traits using a common garden full factorial setup. Contemporary and historical seed accessions, collected across the native distribution of the species, were grown under four temperature treatments. We tested for differences in population-level floral plasticity between temporal (ancestors vs. descendants) and geographical (trailing, core, and leading part of the distribution) origins to reveal potential changes in plasticity over the last decades and how these vary across space. We compared local adaptation of ancestral and descendant populations in a reciprocal transplant experiment across the European native range of the species. Our results show that higher temperatures are associated with a reduction in flower size and flower display and an earlier onset of flowering. Ancestral and descendant populations differed in flower thermal plasticity, which may have played an adaptive role over the last decades. Additionally, a reduction in fitness linked to a smaller flower size, display or earlier flowering onset could highlight detrimental effects of higher temperatures on plant sexual reproduction. Lastly, in our reciprocal transplant experiment, individuals from descendant populations flowered earlier than their ancestral counterparts, indicating potential rapid adaptive evolution to a warmer climate. Understanding evolution of thermal plasticity and floral adaptation to higher temperatures will improve predictions on how plant-pollinator interactions may respond to climate change.