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, the anthers are high, and self-pollination is easier. Different floral morphs have evolved in many plant species to prevent self-pollination and facilitate cross-pollination by insects. Generally, 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.
According to the study's lead author, Tsipe Aavik, Associate Professor in Macroecology at the University of Tartu, these are very surprising results offering plenty of material for further research. Aavik said that similar results were obtained a few years ago from observations made as part of the citizen science initiative in Estonia, but at the time, the shifts were attributed to Estonia being at the northern edge of the cowslip distribution range. "This study confirmed that the balance of the floral morphs is, in fact, disrupted across Europe, so this change is much more meaningful," said Aavik.
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. According to Aavik, the Europe-wide cowslip observation is only the first step in testing this hypothesis.
During the international cowslip campaign, University of Tartu 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 in Estonia in 2019, observations were made in more than 8,000 locations across Europe, and nearly 900,000 cowslips were examined over four years.
