Centennial clonal stability of asexual Daphnia in Greenland lakes despite climate variability

Abstract

Climate and environmental condition drive biodiversity at many levels of biological organisation, from populations to ecosystems. Combined with palaeoecological reconstructions, palaeogenetic information on resident populations provides novel insights into evolutionary trajectories and genetic diversity driven by environmental variability. While temporal observations of changing genetic structure are often made of sexual populations, little is known about how environmental change affects the long-term fate of asexual lineages. Here, we provide information on obligately asexual, triploid Daphnia populations from three Arctic lakes in West Greenland through the past 200-300 years to test the impact of a changing environment on the temporal and spatial population genetic structure. The contrasting ecological state of the lakes, specifically regarding salinity and habitat structure may explain the observed lake-specific clonal composition over time. Palaeolimnological reconstructions show considerable environmental fluctuations since 1700 (the end of the Little Ice Age), but the population genetic structure in two lakes was almost unchanged with at most two clones per time period. Their local populations were strongly dominated by a single clone that has persisted for 250-300 years. We discuss three possible explanations for the apparent population genetic stability: (1) the persistent clones are general purpose genotypes that thrive under broad environmental conditions, (2) clonal lineages evolved subtle genotypic differences that are unresolved by microsatellite markers, or (3) epigenetic modifications allow for clonal adaptation to changing environmental conditions. Our results will motivate research into the mechanisms of adaptation in these populations, as well as their evolutionary fate in the light of accelerating climate change in the polar regions.