Females from resting eggs and parthenogenetic eggs in the rotifer Brachionus calyciflorus: lipid droplets, starvation resistance and reproduction

Abstract

Summary1. In the heterogonic life cycle of monogonont rotifers, amictic (female‐producing) females develop from two types of eggs: fertilised resting (diapausing) eggs and parthenogenetic subitaneous eggs. Females hatched from resting eggs initiate clonal populations by female parthenogenesis and are called stem females. This study compares females from resting and parthenogenetic eggs that were produced under identical culture conditions and were of similar birth order.2. Newborn stem females had many more lipid droplets in their tissues than similar‐sized, newborn females from parthenogenetic eggs. When neonates were stained with Nile Red and viewed under epifluorescent illumination, these droplets were shown to be sites of neutral‐lipid storage products.3. Stem females had no posterolateral spines and short anterior spines, while their mothers and offspring in subsequent, parthenogenetic generations typically had long posterolateral spines and elongated anterior spines.4. Newborn stem females survived starvation significantly longer than newborn females from parthenogenetic eggs.5. When females from resting and parthenogenetic eggs were cultured from birth to death at a high food concentration, the reproductive potential (r day−1) of the stem females was significantly higher (0.82–0.88 versus 0.70), primarily because of egg production at an earlier age. The mean lifetime fecundity (Ro) of stem females was significantly greater than that of females from parthenogenetic eggs.6. Extensive lipid reserves should increase the ability of stem females to colonise new habitats. Firstly, compared with females from parthenogenetic eggs, stem females are more likely to experience starvation or food limitation. Resting eggs hatch in response to physical and chemical factors that are not directly related to food availability, and from sediments that may be far from food‐rich surface waters. Secondly, when food is abundant, stem females have a greater reproductive potential.