Data from: 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

The distylous plant Primula veris has long served as a model
species for studying heterostyly, i.e., the occurrence of multiple floral
morphs within a population to ensure outcrossing. Habitat loss, reduced
plant population sizes, and climate change have raised concerns about the
impact of these factors on morph ratios and the related consequences on
fitness of heterostylous species. We studied the deviation of
floral morphs of P. veris from isoplethy (i.e., equal frequency)
in response to plant population size, landscape context and climatic
factors, based on a pan-European citizen science campaign involving
observations from 28 countries. In addition, we examined the relative
frequency of morphs to determine whether landscape and climatic factors
disrupt morph frequencies or whether a specific morph has an advantage
over the other. Theory predicts equal frequencies of short-styled S-morphs
and long-styled L-morphs in populations at equilibrium. However, data from
> 3000 populations showed a substantial morph deviation from
isoplethy and a significant excess (9%) of S-morphs compared to L-morphs.
Deviation of morph frequency from equilibrium was substantially stronger
in smaller populations and was not affected by morph identity. Higher
summer precipitation and land use intensity were associated with an
increased prevalence of S-morphs. Five populations containing individuals
exhibiting short homostyle phenotypes (with the style and anthers in low
positions) were found. Genotyping of the individuals at CYP734A50 gene of
the S locus, which determines the length of the style and the position of
anthers of P. veris, revealed no mutations in this region. Our
results based on an unprecedented geographic sampling suggest that changes
in land use and climate may be responsible for non-equilibrium morph
frequencies. This large-scale citizen science initiative sets foundations
for future studies to clarify whether the unexpected excess of S-morphs is
due to partial intra-morph compatibility, disruption of heterostyly or
survival advantage of S-morphs. Synthesis. Human-induced environmental
change may affect biodiversity indirectly through altering reproductive
traits, which can also lead to reduced fitness and genetic diversity.
Further research should consider the possible role of pollinators in
mediating the ecological and evolutionary consequences of recent landscape
and climatic shifts on plant reproductive traits.