Resting Eggs Research Articles

A Comparative Study on the Buoyancy of Resting Eggs from Different Artemia Populations, with Emphasis on Its Relationships with Habitat Salinity and Biometric Characters of Resting Eggs

A Comparative Study on the Buoyancy of Resting Eggs from Different Artemia Populations, with Emphasis on Its Relationships with Habitat Salinity and Biometric Characters of Resting Eggs

Rotifer resting eggs: An alternative for rotifer mass cultures in fish farms – Lessons from a comprehensive study on production, storage and hatching of resting eggs

Rotifers of the Brachionus plicatilis complex species serve as the first live food for marine fish larvae. The essential daily supply of rotifers depends on a successful culture of billions of rotifers, as there are no current alternatives for this live food in the large scale production of farmed fish. This problem is not faced with Artemia, the second source of live food, as they are supplied as cysts and hatched according to demand. Rotifers produce resting eggs (RE) that can be stored for long periods of time and hatched when needed, but their use in aquaculture is limited, despite great advantages. Unlike Artemia cysts which are harvested from natural sources or salt works, rotifer RE originate from cultures. A systematic and comprehensive study was carried out to identify the main factors affecting RE production, storage and hatching, with the aim of increasing the efficiency and reducing the costs of production, thus facilitating their wider use in hatcheries.The current study was performed with a clone displaying high propensity towards RE production. RE production was affected by the food type, with a 2–5 fold difference between Nannochlorosis sp. from different sources, at optimal feeding regimes. We uncovered a central role for lipids in promoting RE production. Remarkably, addition of a lipid enriched solution to yeast, increased the number of RE by 10.4-fold, reduced the percent of damaged RE by 5.8-fold and production was similar to one type of algae. The food type did not affect either the length of the obligatory dormant period nor the hatching performance. RE started to hatch at 22–35 days after their formation but the peak was reached after ~44–62 days. RE that were dried close to the time of their formation did not hatch and the hatching potential was gradually obtained towards the end of the obligatory period. Wet RE stored for 2–65 months at 24-26 °C, exhibited a similar hatching performance. Dried RE, however, could be stored for only ~9 months at the same conditions, but for longer periods at 4 °C. Rotifers that hatched from RE can serve for mass production as RE production in these cultures accounted for 4.5% of the total number of females. An automated continuous culture system is proposed and discussed. The current study also provides novel insights into biological attributes on the production and survival of RE, as an important component of the natural food web in the aquatic environment.

High Resistance of Resting Eggs of Cladoceran Moina macrocopa to the Effect of Heavy Metals

The research aimed to determine critical concentrations of heavy metals at which survival of resting eggs of the cladoceran Moina macrocopa is negatively affected. Resting eggs' viability was not affected over a 30-days exposure towards copper, cadmium, zinc or nickel at concentrations up to 60-70g/L. When resting eggs were exposed to sediment contaminated with heavy metals for 8months, the hatching success was affected at 30g copper/kg. Thus, resting eggs of Cladocera can tolerate heavy metals at concentrations that far exceed lethal concentrations of heavy metals to active life stage and exceed low or moderate levels of environmental pollution. Follow up investigation of life table parameters of hatchlings from resting eggs exposed to heavy metals demonstrated that neither lifespan nor fecundity of hatchlings differ from control animals. These results demonstrate that zooplankton may rapidly recover from resting egg bank once aquatic habitat becomes unpolluted.

The Sensitivity of Resting Eggs of the Cladoceran Moina macrocopa to the Effect of Ionizing Radiation during the Reactivation of the Eggs.

We investigated the sensitivity of resting eggs of the cladoceran Moina macrocopa to the effect of ionizing radiation during the reactivation of the eggs. The study showed that the resting eggs during reactivation are more vulnerable to irradiation than the resting eggs in a stage of deep dormancy. The decrease in the efficiency of egg reactivation was observed at high doses, the growth rate of juveniles, fecundity, and the number of produced clutches by females strongly decreased when resting eggs at the reactivation stage absorbed doses of 64 Gy and higher.

Observation on the Embryonic Development of the Resting Eggs of Brine Shrimp Artemia using Artificial Decapsulation

Observation on the Embryonic Development of the Resting Eggs of Brine Shrimp Artemia using Artificial Decapsulation

Whole genome amplification and sequencing of a Daphnia resting egg.

Resting eggs banks are unique windows that allow us to directly observe shifts in population genetics, and phenotypes over time as natural populations evolve. Though a variety of planktonic organisms also produce resting stages, the keystone freshwater consumer, Daphnia, is a well-known model for paleogenetics and resurrection ecology. Nevertheless, paleogenomic investigations are limited largely because resting eggs do not contain enough DNA for genomic sequencing. In fact, genomic studies even on extant populations include a laborious preparatory phase of batch culturing dozens of individuals to generate sufficient genomic DNA. Here, we furnish a protocol to generate whole genomes of single ephippial (resting) eggs and single daphniids. Whole genomes of single ephippial eggs and single adults were amplified using Qiagen REPLI-g Single Cell kit reaction, followed by NEBNext Ultra DNA Library Prep Kit for library construction and Illumina sequencing. We compared the quality of the single-egg and single-individual amplified genomes to the standard batch genomic DNA extraction in the absence of genome amplification. At mean 20× depth, coverage was essentially identical for the amplified single individual relative to the unamplified batch extracted genome (>90% of the genome was covered and callable). Finally, while amplification resulted in the slight loss of heterozygosity for the amplified genomes, estimates were largely comparable and illustrate the utility and limitations of this approach in estimating population genetic parameters over long periods of time in natural populations of Daphnia and also other small species known to produce resting stages.

Morphology of the Resting Eggs of the Australian endemic Fairy Shrimp Australobranchipus (Branchiopoda: Anostraca: Branchipodidae): Similarities and differences from other anostracans

Eggs in large Branchiopoda are often diagnostic of species and may show some phyletic relationships. Those of the two species of Australobranchipus are described and are easily separable from each other and are particularly distinctive among Australian anostracans, all unrelated. Within its family, the Branchiopodidae however, there is some similarity to two African genera, but not Eurasian species, indicative perhaps of a gondwanan connection.

Formation and structure of the ephippium (resting egg case) in relation to molting and egg laying in the water flea Daphnia pulex De Geer (Cladocera: Daphniidae)

Resting eggs produced by daphnid species in response to environmental deterioration play an important role in colonizing new habitats or in re-establishing extinct populations. Females lay resting eggs into the space within the dorsal part of their carapace and form an egg case called the ephippium to protect them. Previous studies mainly reported the morphology of the completely formed ephippium and/or the forming ephippium of an uncertain stage. To understand ephippium formation and to clarify key transitions in the formation of resting eggs, we examined the structure and formation of the ephippium in the water flea Daphnia pulex De Geer (Cladocera: Daphniidae) by stereomicroscopy, histology, and scanning electron microscopy. The females used in this study produced resting eggs by obligate parthenogenesis. We divided ephippium formation into four stages based on two molts and a single ovulation, as follows. Stage I begins 13 min after molting in adult females that do not ovulate. In Stage II, immediately after the first molt, a protuberance appears beneath the neck region and the carapace begins to thicken. In Stage III, the resting eggs ovulate and the carapace in the area of the forming ephippium becomes much thicker than the normal carapace and accumulates dark pigmentation. In Stage IV, following the second molt, the female sheds the ephippium with the enclosed resting eggs and forms a new carapace. These stages will provide a useful reference for future studies on resting egg formation.

Effects of Demersal Otter Trawls on the Re-suspension of Copepod Resting Eggs and its Potential Effects on Recruitment

Resting eggs are important phases in the life strategy of many coastal and estuarine copepods. The egg mortality in the sediment layers where they are buried, as well as re-suspension from the sediment into the water column where eggs may hatch are factors that affect the success of this life strategy. Considering that fishing effort in some coastal areas is high and trawling leads to re-suspension of the bottom sediments, it is important to understand these effects on the biology of organisms that utilize sediment habitats in part of their life cycle. This study examined the re-suspension and the hatching success of copepod resting eggs in the wake of two different demersal fishing gear components (doors and discs) that are in contact with the seabed, in two areas off the coast of Scotland that are rarely worked by fishermen. Sediment cores were taken and analysed for resting eggs quantity and hatching performance and compared with samples taken in the water column right after re-suspension of sediment by the gear components. This study demonstrated for the first time that although eggs are re-suspended in the water column together with the sediment, providing them with the opportunity to hatch and recruit nauplii to the pelagic, egg viability was reduced by the passage of the gear components. This study also suggests that the viability is dependent on the gear component and accordingly potential effects must be considered for at this level.

Responses in the population growth and reproduction of freshwater rotiferBrachionus calyciflorusto four organochlorine pesticides

In China, although the production and use of organochlorine pesticides (OCPs) have been banned for decades, relatively high levels of OCP residues have still been found in some water bodies, and can result in adverse acute and chronic effects on zooplankton including rotifers, which have caused public concern for many years. Responses in the population growth and reproduction of freshwater rotifer Brachionus calyciflorus to four OCPs including aldrin, dieldrin, β-hexachlorocyclohexane (β-HCH) and chlordecone were studied by 3-day population growth and 4-day resting eggs (RE) production tests. In comparison with control, aldrin at 10 μg.L−1 , β-HCH at 1000 μg.L−1 and chlordecone at 0.05 μg.L−1 significantly increased the population growth rate (r ); but aldrin at 100 μg.L−1 , dieldrin at 0.001 and 0.1 μg.L−1 , β-HCH at 0.1–100 μg.L−1 and chlordecone at 50 μg.L−1 markedly decreased it. Aldrin at concentrations higher than 1 μg.L−1 , dieldrin at 0.01 and 1000 μg.L−1 , β-HCH at concentrations 0.1 and higher than 1 μg.L−1 , and chlordecone at concentrations 0.005 and higher than 0.5 μg.L−1 significantly decreased the ratio of ovigerous females to non-ovigerous females (OF/NOF), but the reverse was true for aldrin at 0.1 μg.L−1 and β-HCH at 0.001 μg.L−1 . Dieldrin at 0.001, 0.01 and 1000 μg.L−1 significantly decreased the ratio of mictic females to amictic females (MF/AF), but β-HCH at 1 and 10 μg.L−1 highly significantly increased it. Dieldrin at 1000 μg.L−1 and β-HCH at concentrations higher than 10 μg.L−1 markedly decreased the fertilization rate (FR). Both aldrin and chlordecone have no significant effect on the MF/AF and FR of rotifers. Aldrin at concentrations higher than 1 μg.L−1 , dieldrin at lower than 0.1 and higher than 10 μg.L−1 , β-HCH at 1000 μg.L−1 and chlordecone at 0.005, 0.05 and 50.0 μg.L−1 significantly decreased the mictic rate (MR) of rotifers, but the reverse was true for β-HCH at 1 μg.L−1 . Aldrin at 10 μg.L−1 , dieldrin at 0.001, 0.1 and 1000 μg.L−1 , β-HCH at concentrations higher than 1 μg.L−1 and chlordecone at concentrations higher than 0.005 μg.L−1 markedly decreased RE production of rotifers, but β-HCH at 0.01 μg.L−1 significantly increased it. A clear dose–response relationship existed between the RE and the concentration of dieldrin, β-HCH and chlordecone, and the OF/NOF and the aldrin concentration. The RE and OF/NOF in rotifer population might be suitable endpoints for monitoring the low concentration of three OCPs (dieldrin, β-HCH and chlordecone) and aldrin, respectively.

The Effect of Food Concentration on the Juvenile Somatic Growth Rate of Body Length, Fecundity and the Production of Resting Eggs by Moina brachiata (Crustacea: Cladocera) Single Females

Received 13.12.2012, received in revised form 20.12.2012, accepted 27.12.2012 The study addresses the effect of different food concentrations of green alga Chlorella vulgaris on the life cycle parameters (the body length, specific juvenile somatic growth rate of body length, the number of offspring in the first clutch of parthenogenetic females and the number of females producing resting eggs) of the individually cultivated females of M. brachiata. The lowest food concentration used in the experiment, 100 thousand cells/ml, had a limiting effect on such parameters as the size of females at the first reproduction, juvenile somatic growth rate of body length and fecundity; it also induced the production of resting eggs by females. With food concentration increase, the size of females at the first reproduction, their somatic growth rate of body length and fecundity also increased, and the number of females that produced resting eggs decreased. Under maximal food concentrations (400 and 800 thousand cells/ml) the size of females at the first reproduction, the somatic growth rates of body length and the number of hatched offspring were the largest, and there were no females producing ephippial eggs. We also tested the effect of food concentration under which the maternal generation was kept on the ability of the offspring generation to produce resting eggs. The production of resting eggs failed to occur only at the highest food concentrations for maternal females and their offspring (400 thousand cells/ml). Thus, we concluded that food concentration above 400 thousand cells/ml is favorable concentration for parthenogenetic reproduction of M. brachiata. Since there are no literature data on what food concentration induces the production of resting eggs for this species, the results define the trophic conditions that induce production of resting eggs in M. brachiata.

Bleach Solution Requirement for Hatching of Daphnia magna Resting Eggs

Daphnia (water fleas) belong to the zooplankton group called Cladocerans have sexual reproduction when conditions less favorable that produce diapausing eggs are enclosed in the ephippium. Hatching ephippial eggs in the laboratory is important in ecological, toxicology, genetical, and evolutionary studies. This study aims to improve the current methods of egg hatching from ephippium. Each of 50 ephippium were treated together by placing them in a glass jar and adding 50 mL bleach solution (sodium hypochlorite). Concentrations of sodium hypochlorite used in this experiment were 0%, 0.5%, 1%, 2%, 4% and 8%. These concentration treatments were crossed with the following exposure times (1, 2, 4, 8, 16, and 32 minutes). Culturing was done in 80 mL of artificial Daphnia medium, incubated in constant light and temperatures 20°C for 25 days. There were two repetitions in this experiment that were run at the same time. Result of this experiment showed that pretreatment with 0.5-8% bleach solution significantly increases the yield of total hatch rate of Daphnia magna resting eggs by about 21% over unbleached control. However, there was no significant difference among the bleach treatments. Concentration of bleach solution 0.5%, 1% and 4% significantly accelerated the time period until the first hatching (first day hatching). Difference of exposure time (1 - 32 minutes) at each concentration treatments were not influence the yield of total hatch and the time period until first hatching.

Long-Term Survival of Hydrated Resting Eggs from Brachionus plicatilis

BackgroundSeveral organisms display dormancy and developmental arrest at embryonic stages. Long-term survival in the dormant form is usually associated with desiccation, orthodox plant seeds and Artemia cysts being well documented examples. Several aquatic invertebrates display dormancy during embryonic development and survive for tens or even hundreds of years in a hydrated form, raising the question of whether survival in the non-desiccated form of embryonic development depends on pathways similar to those occurring in desiccation tolerant forms.Methodology/Principal FindingsTo address this question, Illumina short read sequencing was used to generate transcription profiles from the resting and amictic eggs of an aquatic invertebrate, the rotifer, Brachionus plicatilis. These two types of egg have very different life histories, with the dormant or diapausing resting eggs, the result of the sexual cycle and amictic eggs, the non-dormant products of the asexual cycle. Significant transcriptional differences were found between the two types of egg, with amictic eggs rich in genes involved in the morphological development into a juvenile rotifer. In contrast, representatives of classical “stress” proteins: a small heat shock protein, ferritin and Late Embryogenesis Abundant (LEA) proteins were identified in resting eggs. More importantly however, was the identification of transcripts for messenger ribonucleoprotein particles which stabilise RNA. These inhibit translation and provide a valuable source of useful RNAs which can be rapidly activated on the exit from dormancy. Apoptotic genes were also present. Although apoptosis is inconsistent with maintenance of prolonged dormancy, an altered apoptotic pathway has been proposed for Artemia, and this may be the case with the rotifer.ConclusionsThese data represent the first transcriptional profiling of molecular processes associated with dormancy in a non-desiccated form and indicate important similarities in the molecular pathways activated in resting eggs compared with desiccated dormant forms, specifically plant seeds and Artemia.

Abundance, composition and spatial variation in the egg bank of a tropical zooplankton community

Resting eggs have important ecological roles in zooplankton communities, but characterizations of egg banks in tropical systems remain scarce. Here, we describe the abundance, composition and spatial variation in the egg bank of a tropical zooplankton community in a shallow aquatic system (Imboassica lagoon, Brazil). Due to sporadic disturbances by sandbar openings at this system, we hypothesized that the abundance and species richness close to the sandbar is lower when compared to other sites. Sediment samples were collected at four sampling stations, and the egg bank was analyzed using ex situ hatching experiments. Hatchlings from 21 rotifer and five cladoceran species were identified considering all sampling stations. The number of hatchlings at the sampling stations ranged from 14.2 (± 3.8 SE) to 192.8 (± 37.1), whereas species richness ranged from 3.6 (± 0.7) to 12.2 (± 0.5) in 100 g of wet sediment. Abundance and species richness were similar at three of the sampling stations, suggesting low spatial variations in the egg bank of shallow systems. Significantly lower values for abundance and species richness were found close to the sandbar when compared to the other sampling stations, probably as a result of local and recurrent disturbances due to artificial sandbar openings. The presence of an egg bank is a possible mechanism for facilitating the reestablishment of active populations after disturbances by sandbar openings and consequent increases in salinity at Imboassica lagoon. Os ovos de resistência apresentam importantes funções ecológicas para as comunidades zooplanctônicas, mas a caracterização do banco de ovos de sistemas tropicais permanece escassa. Nesse estudo nós descrevemos a abundância, a composição e a variação espacial do banco de ovos de uma comunidade zooplanctônica tropical oriunda de um sistema aquático raso (lagoa Imboassica, Brasil). Devido a eventuais distúrbios ocasionados por aberturas de barra nesse sistema, nós hipotetizamos que a abundância e a riqueza de espécies próximo à barra de areia são menores quando comparadas a outros locais. Amostras de sedimento foram coletadas em quatro estações amostrais, e o banco de ovos foi analisado através de experimentos de eclosão ex situ. Através dos organismos eclodidos dos ovos foram identificadas 21 espécies de rotíferos e cinco de cladóceros, considerando todas as estações amostrais. O número de organismos eclodidos nas estações amostrais variou de 14.2 (± 3.8 EP) a 192.8 (± 37.1), enquanto a riqueza de espécies variou de 3.6 (± 0.7) a 12.2 (± 0.5) em 100 g de sedimento úmido. A abundância e a riqueza de espécies foram similares em três das estações amostrais, sugerindo uma baixa variação espacial no banco de ovos de sistemas rasos. Valores significativamente menores de abundância e riqueza de espécies foram encontrados próximo à barra de areia, quando comparados com as outras estações, provavelmente como resultado de distúrbios locais e recorrentes devido às aberturas artificiais da barra de areia. A presença de um banco de ovos é um possível mecanismo facilitador do restabelecimento das populações ativas após distúrbios ocasionados por aberturas de barra e consequentes aumentos da salinidade na lagoa Imboassica.

Invasion risk of active and diapausing invertebrates from residual ballast in ships entering Chesapeake Bay

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 324:57-66 (2006) - doi:10.3354/meps324057 Invasion risk of active and diapausing invertebrates from residual ballast in ships entering Chesapeake Bay Ian C. Duggan1,*, Sarah A. Bailey2, Colin D. A. van Overdijk2, Hugh J. MacIsaac2 1Centre for Biodiversity and Ecology Research, Department of Biological Sciences, The University of Waikato, Private Bag 3105, Hamilton, New Zealand 2Great Lakes Institute for Environmental Research, The University of Windsor, Windsor, Ontario N9B 3P4, Canada *Email: i.duggan@waikato.ac.nz ABSTRACT: We examined the invasion risk posed by active invertebrates and their diapausing stages (e.g. resting eggs, quiescent adults) carried in residual sediment and water of non-ballasted ships to Chesapeake Bay. Many taxa were recorded that are not native to Chesapeake Bay, supporting the contention that residual ballast represents an invasion vector of some risk to marine systems. Composition and propagule supply differed relative to that in ships entering the Laurentian Great Lakes (e.g. marine taxa dominated in Chesapeake Bay ships), indicating that risk varies geographically. Average abundances of active invertebrates in residual sediment (1002.1 ind. kg–1) and water (2.7 ind. l–1), and diapausing eggs in sediments (779.4 eggs kg–1), were typically low relative to those in ships entering the Great Lakes (1322.5 ind. kg–1, 10.9 ind. l–1 and 3650.0 eggs kg–1, respectively). However, due to high variability among ships, differences were not statistically significant. The major cause of composition and abundance differences is dissimilar trade routes between each system, with vessels entering Chesapeake Bay primarily originating from marine rather than freshwater ports, and because diapausing stages are less commonly found among marine invertebrates. Low propagule supplies, predominant intra-continental ship movements, and salinity disparity between the upper (20 to 28‰) and lower (3 to 8‰) regions of Chesapeake Bay (where ballast water is loaded and offloaded) may greatly reduce invasion risk and be a contributing factor to the bay’s low invasion rate: invasion risk from non-ballasted ships here may be low relative to hull fouling or ballast water discharge. Other marine coastal areas may be at greater risk from this vector. KEY WORDS: Ballast sediments · Nonindigenous species · Great Lakes · Resting eggs · NOBOB vessels Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 324. Online publication date: October 23, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Elemental Characterization of Daphnia Resting Eggs by X-ray Analytical Microscopy

Resting eggs of Daphnia, a key crustacean zooplankton of freshwater food chains, can remain viable for more than a century. These eggs are able to withstand freezing and drying, and can survive the harsh environment of a predator's digestive system. Until recently little was known about the chemical composition, microanatomy, and physical properties of the resting eggs. The current study utilized a physical technique, the X-ray analytical microscope, to identify and localize component elements of the Daphnia resting egg. The analysis demonstrated that phosphorus, sulfur, potassium, and calcium were detected as elemental components of the resting egg, and detection intensities of the four elements differed according to the position of the eggs. Phosphorus and calcium were mostly detected in regions of the eggshell that surrounded the two embryos. In addition, sulfur was distributed throughout the eggshell whereas potassium was localized to the areas that corresponded to where the embryos were encased. Through the use of X-ray analytical microscopy, the current study identifies elemental characteristics in relationship to the structure of the Daphnia resting eggs.

Predation by the mysid shrimps Mysis mixta and M. relicta on benthic eggs of Bosmina longispina maritima (Cladocera) in the northern Baltic Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 281:155-163 (2004) - doi:10.3354/meps281155 Predation by the mysid shrimps Mysis mixta and M. relicta on benthic eggs of Bosmina longispina maritima (Cladocera) in the northern Baltic Sea Satu Viitasalo1,2,*, Markku Viitasalo3 1Department of Biological and Environmental Sciences, University of Helsinki, PO Box 65, 00014 Helsinki, Finland 2Tvärminne Zoological Station, 10900 Hanko, Finland 3Finnish Institute of Marine Research, PO Box 33, 00931 Helsinki, Finland *Email: stmviita@mappi.helsinki.fi ABSTRACT: The abundance of Bosmina longispina maritima (Cladocera), the most common water flea in the Baltic Sea, shows considerable interannual fluctuations.The number of Bosmina resting eggs (ephippia) in the sediment also fluctuates from year to year. Biotic as well as abiotic factors have been suggested to contribute to these fluctuations, but the impact of benthic predation by pelagic mysids has not yet been considered. The objective of this study was to investigate the effect of benthic predation and bioturbation by Mysis mixta and M. relicta on the ephippia of B. longispina maritima on the SW coast of Finland. The results show that mysids can significantly affect the number of Bosmina eggs in the sediment. All size groups of both mysid species preyed upon ephippia of B. longispina maritima both in the water column and directly from the top layer of sediment, whereas they rejected the eggs of another cladoceran species, Pleopsis polyphemoides. The predation rate on B. longispina maritima ephippia was significantly lower when the eggs were buried under a sediment layer of ca. 1 cm. This suggests that factors affecting the vertical distribution of ephippia in the sediment determine the magnitude of the impact that mysids have on B. longispina maritima benthic eggs. KEY WORDS: Bosmina longispina maritima · Resting eggs · Mysis mixta · M. relicta · Benthic predation · Baltic Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 281. Online publication date: November 01, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

A comparison of egg‐bank and long‐term plankton dynamics of two Daphnia species, D. hyalina and D. galeata: Potentials and limits of reconstruction

Resting eggs of planktonic organisms from datable sediment cores are increasingly used to reconstruct historical information on the abundance, size, genetic composition, and microevolution of planktonic organisms. All of these studies have relied on the (up to now) mostly untested assumption that the resting egg bank in sediment will indeed allow an accurate reconstruction of past populations. Here we test the performance of the egg bank to reconstruct historical data of the Daphnia population of Lake Constance, which was thoroughly investigated throughout the past century. We show that it is possible to reproduce the variability in the abundance, size, and genetic composition of Daphnia galeata within a period of ~2 decades. Furthermore, resting egg data allowed us to reconstruct the timing of the invasion of D. galeata into Lake Constance. However, the egg bank did not reconstruct (1) the dynamics of the native Daphnia species of Lake Constance, D. hyalina, and (2) the relative importance of the two Daphnia species. We present evidence that the latter is caused by differences in the sexually reproductive activity between the two species. The failure to reconstruct the long‐term dynamics of D. hyalina in the lake is most probably due to a change in the frequency and timing of sexual activity during the course of eutrophication.

Chronic responses of different clones of Daphnia longispina (field and ephippia) to different food levels

Abstract Resting eggs are a fundamental reproductive strategy among freshwater cladocerans. Under adverse environmental conditions, whole Daphnia populations can disappear from a lake and a new community will arise from ephippial eggs. Since these new populations are subjected to genetic variation, their responses to environmental stress or contaminants can be different from the “original” population. In the present study, life history responses (reproduction and growth) of Daphnia longispina to different food concentrations was studied. Two Daphnia populations were tested: (a) field clones and (b) ephippial clones. Food ( Selenastrum capricornutum ) concentration was the stressor tested (absence of food, and low to high food concentrations). The results showed that reproductive responses of D. longispina to the tested food concentrations varied among clones, independently from their origin.

Risk of Predation and Hatching of Resting Eggs in the Ostracod Heterocypris Incongruens

Risk of Predation and Hatching of Resting Eggs in the Ostracod Heterocypris Incongruens