Abstract
1. Introduction Ongoing climate change poses an increasing threat to
biodiversity. To avoid decline or extinction, species need to either
adjust or adapt to new environmental conditions or track their climatic
niches across space. In sessile organisms such as plants, phenotypic
plasticity can help maintain fitness in variable and even novel
environmental conditions and is therefore likely to play an important
role in allowing them to survive climate change, particularly in the
short term. Understanding a species’ response to rising temperature is
crucial for planning well-targeted and cost-effective conservation
measures. 2. Methods We sampled seeds of three Hypericum species (H.
maculatum, H. montanum, and H. perforatum), from a total of 23
populations originating from different parts of their native
distribution areas in Europe. We grew them under four different
temperature regimes in a greenhouse to simulate current and predicted
future climatic conditions in the distribution areas. We measured
flowering start, flower count, and subsequent seed weight, allowing us
to study variations in the thermal plasticity of flowering phenology and
its relation to fitness. 3. Results Our results show that individuals
flowered earlier with increasing temperature, while the degree of
phenological plasticity varied among species. More specifically, the
plasticity of H. maculatum varied depending on population origin, with
individuals from the leading range edge being less plastic. Importantly,
we show a positive relationship between higher plasticity and increased
flower production, indicating adaptive phenological plasticity. 4.
Synthesis The observed connection between plasticity and fitness
supports the idea that plasticity itself may be adaptive. This study
underlines the need for information on plasticity for predicting
species’ potential to thrive under global change and the need for
studies on whether higher phenotypic plasticity is currently being
selected for as natural populations experience a rapidly changing
climate.