Using DNA from formaldehyde-preserved Daphnia to reconstruct past populations

We compared taxon composition of the Daphnia longispina hybrid community, as reconstructed from dormant eggs (retrieved from sediment samples) and the pelagic population (retrieved from formaldehyde-preserved zooplankton samples), from the same lake and of the same time period. As microsatellite markers do not work on largely fragmented DNA, such as of formaldehyde-preserved samples, both types of samples (dormant eggs and pelagic Daphnia) were screened with single-nucleotide polymorphism (SNP) markers. Here, we designed a genotyping panel of short SNP-bearing amplicons and, to facilitate screening, we developed a multiplex genotyping protocol. The results of this comparison confirmed differences between dormant and pelagic samples. Specifically, D. galeata was overrepresented in the sedimentary egg bank in comparison to the pelagic population, indicating that this taxon is more involved in sexual reproduction than other taxa. In addition to being successfully applied on formaldehyde-preserved samples, SNP-genotyping was more efficient than microsatellites on sedimentary eggs, and was more sensitive for hybrid detection. In conclusion, the SNP-based genotyping panel presented here enables to study the genetic structure of past populations from common formaldehyde-preserved collections. It is also promising for genotyping old dormant eggs, which can extend the temporal range of Daphnia community reconstructions.