Phenotypic divergence associated with genomic changes suggest local adaptation in obligate asexuals

Local adaptation is a key evolutionary process that generates global biodiversity and is promoted by environmental heterogeneity. Most of the existing knowledge on adaptive capacity is focused on sexual organisms, while the adaptation potential of asexually reproducing eukaryotes 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 neighbouring ponds. Similar patterns have been found in obligate parthenogenetic congeners, however studies on their local adaptation potential are rare. Here, we use respiration rate and whole genome sequencing to test the local adaptation of Arctic asexual polyploid Daphnia from lakes with contrasting oxygen environments. The genomic data revealed the presence of two genetic clusters which differed significantly in respiration rates, suggesting molecular evolution as an adaptive mechanism. Functional enrichment pointed to differences in metabolic processes between the two genetic clusters. Our results, combining phenotypic and whole genome sequencing data, suggest that these clones are locally adapted to low oxygen concentrations and provide support for local adaptation by evolution in an obligate parthenogen.