Hatching and viability of rotifer diapausing eggs collected from pond sediments

Abstract

1. Planktonic rotifers inhabiting variable environments produce diapausing eggs that accumulate in the sediment of lakes and ponds, forming egg banks that may withstand adverse periods. A common assumption in zooplankton diapausing egg bank studies is to count as viable all eggs in the sediment that look healthy. This assumption should be challenged by asking how effectively 'healthy-looking' eggs represent viable eggs. 2. In this study, viability of more than 1100 'healthy-looking' diapausing eggs belonging to the Brachionus plicatilis species complex was assessed in a laboratory hatching experiment. Eggs were collected at different depths from sediment cores obtained from 15 ponds located in coastal and inland areas of Eastern Spain. 3. Only approximately one half of the 'healthy-looking' diapausing eggs hatched after incubation in experimental conditions. Almost all the hatchlings (99.4%) survived to maturity. The proportion of 'healthy-looking' diapausing eggs that hatched varied among areas and among ponds within area, and substantially declined with sediment depth. Most of the hatchlings (88%) were obtained from the uppermost 2 cm of sediment. 'Healthylooking' eggs from upper sediment layers hatched after significantly shorter incubation times than eggs recovered from deeper layers. 4. Both decreased hatching success and increased incubation time for hatching with sediment depth suggest that older 'healthy-looking' eggs are less responsive to hatching stimuli and could become unviable. However, the strong correlation found between the number of 'healthy-looking' eggs and the number of hatchlings indicates that the abundance of 'healthy-looking' eggs is a good index of egg bank viability.

Evaluation of the Egg Bank of Two Small Himalayan Lakes

“…Given the low sedimentation rate of this lake, the deposition time of diapausing eggs spans over three decades, thus the large variation of hatching time we observed (between 4 and 7 days) may reflect differences in age of the eggs. Consistent with our results, viable zooplankton diapausing eggs are recorded in the upper 4-6 cm of sediments [49,92,[96][97][98][99][100][101]. Differences between environments can be related not only to differences in sedimentation rates but also to differences in the mortality rates of dormant stages, that can range between 1% y −1 and 64% y −1 [51,100,102,103].…”

Fire and recovery of resting egg bank: an experimental study in paddy fields in Pathum Thani province, Thailand

“…In addition, the uppermost 2 cm sediment has been indicated as active egg bank (Càceres & Hairston, 1998) and has been demonstrated that this portion obtains the highest success hatching in many zooplankton resting eggs, e.g. rotifer (Brachionus plicatilis complex species), cladocera and copepoda (Hairston et al, 1995;Cousyn & De Meester, 1998;Garcia-Roger et al, 2006).…”

“…Many zooplankton species are reported to be able to survive under adverse conditions through diapauses stage (e.g. Brendonck & De Meester, 2003;Gyllström & Hansson, 2004;Garcia-Roger et al, 2006). Analysis of resting egg banks has been considered as a useful technique to assess the diversity of zooplankton within a habitat (Brendonck & De Meester, 2003;Vandekerkhove et al, 2004).…”

Rotifers in Lake Orta: a potential ecological and evolutionary model system

“…One should check for neonates at least once per day for about two weeks. Viable resting eggs would usually hatch within one week of incubation (García-Roger et al, 2005;García-Roger et al, 2006;Walczyńska and Serra, 2014). During extended hatching trials one can transfer the eggs to new medium every 2-3 days in order to suppress fungal infections (García-Roger et al, 2005).…”