Data from: Seasonal genotypic and phenotypic differentiation of a cosmopolitan freshwater diatom

Most ecosystems are characterized by seasonality, which, through biotic
and abiotic changes, influences species biomass dynamics. Recent studies
have shown that ecologically important traits can evolve rapidly in
response to environmental changes, resulting in eco-evolutionary dynamics
with consequences for population and community dynamics. Evidence for
seasonal effects on intraspecific variation is still scarce, and
understanding eco-evolutionary dynamics in the presence of seasonal
fluctuations remains a major challenge. Following the phytoplankton spring
bloom in Lake Constance, we investigated how seasonal changes influence
the intraspecific diversity of Asterionella formosa both at genotypic and
phenotypic levels. We found a moderate degree of genetic and phenotypic
differentiation characterizing the Asterionella population,
explained by a clustering of the isolates into early and late spring
according to lake thermal stratification. Yet, most traits related to
environmental parameters, as well as fitness in different seasonal
environments, did not show a clear response to seasonality (i.e.,
temperature and nutrients). The changes in genetic patterns observed after
a peak in parasite relative abundance suggested that seasonal changes in
biotic interactions (i.e., parasitic chytrids) might be an important
driver of the observed seasonal shift in Asterionella genotypes. Our
results highlight the importance of studying eco-evolutionary processes
for understanding variations in population and community dynamics in
response to seasonal environmental fluctuations.