Birds, nutrients, and climate change: mtDNA haplotype diversity of Arctic Daphnia on Svalbard revisited

Abstract

Ecosystems in the high Arctic are in transition due to climate change and species shifts. On the Svalbard archipelago, the average annual temperature has increased by more than 2 °C over the past 30 years, and there has been a striking increase in breeding populations of geese. Birds serve as a dominant source of nutrients (via faeces) and may also serve as vectors of dispersal of many small aquatic organisms. We compared samples of species and haplotype composition of the dominant freshwater crustacean Daphnia spp., from 1992, and those resampled in 2014 to see if these major impacts on Arctic freshwater ecosystems may also have affected this key grazer over the past three decades. The study covers tundra ponds that vary in levels of nutrients, abundance, and diversity of birds. Comparison of genetic mitochondrial DNA sequences revealed little change in haplotype and nucleotide diversity between 1992 and 2014, but higher species and haplotype diversity were found in nutrient-rich ponds that hosted large migratory bird populations. This could either reflect that high nutrient levels allow for the maintenance of higher levels of genetic diversity (i.e. haplotypes, lineages), that birds serve as vectors for the dispersal of clones, or likely a combination of both mechanisms.