The importance of hatching from resting eggs for population dynamics and genetic composition ofDaphniain a deep reservoir

Abstract

Summary1. Cyclical parthenogens, organisms switching between sexual and asexual mode of reproduction, are common in aquatic habitats. In permanent waterbodies with year‐round persistence of populations, the relevance of sexually produced resting eggs for population dynamics and structure is still largely unexplored.2. The aim of this study was to investigate the importance of recruitment from resting eggs toDaphniaspp. in a deep dimictic reservoir with overwintering populations (Saidenbach Reservoir, Germany). We linked field studies onDaphniapopulation dynamics, hatching rates and diapausing egg abundances in the sediment with allozyme analysis of the genetic variability of both the pelagic population and hatchlings from resting eggs.3. We found higher hatching rates at intermediate depths (10–18 m), although highest diapausing egg abundances were found in the deeper parts of the reservoir. From the extensive field data, we calculated a population budget for the main basin of the reservoir, which showed that hatched daphnids accounted for <1% of the total abundance and explained only a tiny fraction of population growth.4. The genetic composition (MultiLocus Genotypes, MLG) of the pelagic population was relatively stable throughout the stratified period with up to five among 39 detected MLGs attaining frequencies >5% per date. From 11 MLGs differentiated among hatched daphnids, three were recovered in the pelagic population in perceptible, albeit low frequencies (1–4%).5. We conclude that the contribution of hatched animals to the spring population dynamics is negligible in situations with an overwintering population present and will only become relevant if densities are extremely low. In this type of system, the significance of the resting egg bank is presumably mainly related to the maintenance of genetic diversity.