Observed shifts in the floral traits of cowslips
The results of cowslip observations carried out with the help of citizen scientists from 32 countries in over 5,200 locations shed light on the well-being of insect-pollinated plants under changing climate and land use conditions. The study was made possible thanks to the contribution of European science enthusiasts. It revealed some surprising results recently published in the Journal of Ecology, one of the longest-standing top-level journals in this field.
The cowslip (Primula veris) is considered a model species for studying insect-pollinated plants. Cowslips can have two types of flowers: long-styled (L-morph) and short-styled (S-morph). In L-morph flowers, the stamens are at the base of the corolla, and the style is tall, making self-pollination difficult. In S-morph flowers, the style is short, while the anthers are high. Different floral morphs have evolved in many plant species to prevent self-pollination and facilitate cross-pollination by insects. A plant can only be successfully fertilised when it receives pollen from plant with different floral morph than its own. Hence, the proportion of short-styled S-morphs and long-styled L-morphs should be fairly equal in a viable plant population.
However, in many cowslip populations observed across Europe, a significant imbalance and a marked predominance of S-morph flowers were noted. There were 9% more S-morphs than L-morphs. In smaller populations, the imbalance in flower types was more frequent, irrespective of the floral morph. Further analysis of climate and land use data revealed that the higher prevalence of the S-morphs was associated with greater summer precipitation and more intensive land use. Previous studies have shown that the unequal proportion of flower types is one of the risk factors that can lead to species extinction.
“These are very surprising results. Previously, we thought that such changes were only local phenomena, but this study shows that the imbalance is widespread across Europe. This suggests that environmental changes are affecting the pollination system on a larger scale than previously thought”, says Sara Cousins, Professor at the Department of Physical Geography and national coordinator of the project.
The researchers speculate that this may be a step on the evolutionary path helping plants cope with various environmental changes – the loss and fragmentation of suitable habitats, changes in pollinator diversity and composition, and a warmer and wetter climate. The Europe-wide cowslip observation is only the first step in testing this hypothesis.
About the study
During the international cowslip campaign, the Department of Physical Geography researchers invited people across Europe to observe cowslips and share their observation data in the springs of 2021 and 2022. During the citizen science project, which started initiated in Estonia by the University of Tartu in 2019, observations were made in more than 8,000 locations across Europe, and nearly 900,000 cowslips were examined over four years.
The study “A pan-European citizen science study shows population size, climate and land use are related to biased morph ratios in the heterostylous plant Primula veris” was published in Journal of Ecology 22 January 2025.
Last updated: February 5, 2025
Source: Communications Office