1. Studies on adaptive capacity are especially important in ecosystems most vulnerable to rapid environmental change such as Arctic freshwater habitats. Most of the existing knowledge on adaptive capacity is focused on sexual organisms, while the adaptation potential of parthenogens as well as their vulnerability to environmental change remains unclear. Cyclical parthenogens of the keystone freshwater grazer Daphnia are known to be locally adapted with genetic differentiation related to environmental conditions even between neighboring ponds. Similar patterns have been found in obligate parthenogenetic congeners, which typically inhabit higher latitudes and altitudes, however studies on their adaptation potential are rare. 2. Here, we use respiration rate and whole genome sequencing to test microgeographic divergence and physiological adaptation of Arctic asexual triploid Daphnia from lakes with contrasting oxygen environments. 3. The genomic data revealed the presence of two closely related mitochondrial and nuclear genetic clusters which differed significantly in respiration rates. Functional enrichment pointed to differences in metabolic processes between the two genetic clusters. 4. Our results, combining phenotypic and whole genome sequencing data, suggest that these clones are adapted to low oxygen concentrations and indicate that microgeographic divergence has arisen by evolution in an obligate parthenogen.
