Cladoceran Daphnia Longispina Research Articles

Combined effects of two abiotic stressors (salinity and temperature) on a laboratory-simulated population of Daphnia longispina

Sea level rise is expected to continue apace, with a concomitant rise in temperature on the globe's surface. Natural populations genetic pool compromised by increased salinity would contribute to decrease resilience under future temperature changes. Therefore, this work aimed to understand the long-term effects of salinization on the genetic diversity of a cladoceran-simulated laboratory population under different temperature regimes. For that, six clonal lineages of the cladoceran Daphnia longispina were chosen based on their reported differential lethal sensitivity (LCx) to salinity. The chronic experiment was initiated when each individual clonal lineage reached the population’s carrying capacity, and then were exposed to the LC70,48 h for the most tolerant clonal lineage of D. longispina (corresponding to 5.91 mS/cm) to 17°C, 20°C and 23°C for at least 30 days. Salinity affected D. longispina survival and reproduction, with the disappearance of salt-tolerant earlier than salt-sensitive lineages after chronic exposures. Different sensitivity ranks were observed for clonal lineages when comparing short-term and chronic survival, most probably due to acclimation-driven population recovery. Non-optimal tested temperatures (17°C and 23°C) enhanced negative effects of salinity through loss of the most sensitive clonal lineages, suggesting a potential future synergistic effect between both abiotic factors.

Sulfate sensitivity of aquatic organism in soft freshwaters explored by toxicity tests and species sensitivity distribution

Elevated concentrations of sulfate in waterways are observed due to various anthropogenic activities. Elevated levels of sulfate can have harmful effects on aquatic life in freshwaters: sulfate can cause osmotic stress or specific ion toxicity in aquatic organisms, especially in soft waters where Ca2+ and Mg2+ concentrations are low. Formerly, chronic toxicity test data in soft water have been scarce. The chronic and acute sulfate toxicity tests conducted with aquatic organisms from 10 families across various trophic levels in this study multiplied the number of tests conducted in soft freshwater conditions and enabled derivation of the species sensitivity distribution (SSD) and sulfate hazardous concentrations for soft freshwaters. The cladoceran Daphnia longispina and freshwater snail Lymnaea stagnalis were the most sensitive to sulfate among the studied species. Harmful effects on the reproduction of D. longispina were observed at 49 mg SO4 /L while growth of L. stagnalis was inhibited at 217 mg SO4 /L. Most studied organisms tolerated high sulfate concentrations: the median of chronic effective concentrations (EC10 or LC10) was 1008 mg/L for all the species tested in this study. Based on the species sensitivity distribution of the studied species the hazardous concentration for 5 % of aquatic organism (HC5) in soft waters was 117–194 mg SO4/L. Different data set combinations were used to demonstrate the data variability in SSD-based HC5 estimates. The lowest values were produced from combining biotest results from the present study and earlier literature, while the highest values were calculated from the present study only. The derived chronic no-effect concentrations (PNEC) varied between 39 and 65 mg SO4/L.

A new microsporidian parasite, Ordospora pajunii sp. nov (Ordosporidae), of Daphnia longispina highlights the value of genomic data for delineating species boundaries.

Speciation is a complex and continuous process that makes the delineation of species boundaries a challenging task in particular in species with little morphological differentiation, such as parasites. In this case, the use of genomic data is often necessary, such as for the intracellular Microsporidian parasites. Here, we characterize the genome of a gut parasite of the cladoceran Daphnia longispina (isolate FI-F-10), which we propose as a new species within the genus Ordospora: Ordospora pajunii sp. nov (Ordosporidae). FI-F-10 closest relative, Ordospora colligata is only found in D. magna. Both microsporidian species share several morphological features. Although it is not possible to estimate divergence times for Microsporidia due to the lack of fossil records and accelerated evolutionary rates, we base our proposal on the phylogenomic and genomic distances between both microsporidian lineages. The phylogenomic reconstruction shows that FI-F-10 forms an early diverging branch basal to the cluster that contains all known O. colligata strains. Whole-genome comparisons show that FI-F-10 presents a greater divergence at the sequence level than observed among O. colligata strains, and its genomic average nucleotide identity (ANI) values against O. colligata are beyond the intraspecific range previously established for yeast and prokaryotes. Our data confirm that the ANI metrics are useful for fine genetic divergence calibration across Microsporidia taxa. In combination with phylogenetic and ecological data, genome-based metrics provide a powerful approach to delimitate species boundaries.

Morpho-Functional Traits Reveal Differences in Size Fractionated Phytoplankton Communities but Do Not Significantly Affect Zooplankton Grazing.

The recent emergence of approaches based on functional traits allows a more comprehensive evaluation of the role of functions and interactions within communities. As phytoplankton size and shape are the major determinants of its edibility to herbivores, alteration or loss of some morpho-functional phytoplankton traits should affect zooplankton grazing, fitness and population dynamics. Here, we investigated the response of altered phytoplankton morpho-functional trait distribution to grazing by zooplankton with contrasting food size preferences and feeding behaviors. To test this, we performed feeding trials in laboratory microcosms with size-fractionated freshwater phytoplankton (3 size classes, >30 µm; 5–30 µm and <5 µm) and two different consumer types: the cladoceran Daphnia longispina, (generalist unselective filter feeder) and the calanoid copepod Eudiaptomus sp. (selective feeder). We observed no significant changes in traits and composition between the controls and grazed phytoplankton communities. However, community composition and structure varied widely between the small and large size fractions, demonstrating the key role of size in structuring natural phytoplankton communities. Our findings also highlight the necessity to combine taxonomy and trait-based morpho-functional approaches when studying ecological dynamics in phytoplankton-zooplankton interactions.

Multigenerational effects of salinity in six clonal lineages of Daphnia longispina

Sea level rise, as a consequence of climate changes, is already causing seawater intrusion in some freshwater coastal ecosystems worldwide. The increase in salinity at these freshwater coastal ecosystems may occur gradually (through groundwater) or abruptly (through extreme weather events). Moreover, many of them are also being altered and threatened by anthropogenic activities. Accordingly, the present study aimed at assessing the multigenerational lethal and sublethal effects caused by increased salinity in six clonal lineages of the freshwater cladoceran Daphnia longispina differing in their sensitivity to lethal levels of copper. Three specific objectives were delineated: i) to compare the lethal and sublethal toxicity of sodium chloride (NaCl) and natural seawater (SW); ii) to evaluate possible multigenerational effects after exposure to low levels of salinity, and iii) to evaluate if an association exists between tolerance to lethal and sublethal levels of salinity and tolerance to metals. Overall, NaCl was found to elicit sublethal effects at lower or similar concentrations than SW, suggesting its use as a protective surrogate of SW in early phases of ecological risk assessment schemes. Multigenerational exposure to conductivities of 0.73±0.015mScm−1 led to dissimilar responses by the six clonal lineages. Significant associations were found neither between lethal and sublethal endpoints nor between salinity and metals, possibly indicating the absence of common mechanisms responsible to confer metal tolerance and salt stress. However, some clonal lineages presented an inverse sensitivity to lethal levels of NaCl and of copper. These results suggest that natural populations of D. longispina, by exhibiting clonal lineages with differential tolerance to increased salinity, may cope with long-term exposure to small increases of this stressor. However, over time those populations may face the occurrence of genetic erosion due to the loss of the most sensitive genotypes before or after a multigenerational exposure.

The effects of Copper and Zinc on survival, growth and reproduction of the cladoceran Daphnia longispina: introducing new data in an “old” issue

Metal contamination is still a major environmental issue due to their continuous deposition and persistence. In this work we intended to assess the impact that Copper (Cu) and Zinc (Zn) exert in life-history parameters of Daphnia longispina, a common cladoceran in freshwater environments. Thus, we studied the effects of Cu (20-300 µg/L) and Zn (500-4000 µg/L) on the survival, growth, reproduction, feeding rate and population growth rate of D. longispina. Though survival was only reduced for the highest concentration of each metal, other endpoints were strongly affected by lower concentrations. Growth was affected by both metals, especially in the period 0-7 d, being significant for Cu ≥ 40 µg/L and Zn ≥ 500 µg/L. Indeed, growth endpoints at day 7 (body length and growth rate) were equally or more sensitive than the corresponding endpoints at day 21. The size at first reproduction decreased (significant for Cu ≥ 40 µg/L and Zn ≥ 500 µg/L). Reproduction decreased, which was partially explained by the reduced growth, but additional effects were supported by a direct effect of metals on reproduction (based on the relationship body length-brood size). Reduced growth and reproduction are likely a food mediated effect due to feeding inhibition caused by the metals. Globally, the studied endpoints were affected by Cu and Zn differently, supporting a chemical-specificity of the effects, with Zn causing more pronounced effects than Cu. This work presents an innovative approach to the effects of Cu and Zn to D. longispina, giving a general and comprehensive overview of those effects.

Tolerance to Copper and to Salinity in Daphnia longispina: Implications within a Climate Change Scenario

Considering IPPC climate change scenarios, it is pertinent to predict situations where coastal ecosystems already impacted with chemical contamination became exposed to an additional stressor under a future scenario of seawater intrusion. Accordingly, the present study aimed at evaluating if a negative association between tolerance to a metal and to saltwater exists among genotypes of a freshwater organism. For this, five clonal lineages of the cladoceran Daphnia longispina O.F. Müller, exhibiting a differential tolerance to lethal levels of copper, were selected. Each clonal lineage was exposed to lethal and sublethal concentrations of sodium chloride (assumed as a protective surrogate to evaluate the toxicity of increased salinity to freshwater organisms). Mortality, time to release the first brood and total number of neonates per female were monitored and the somatic growth rate and intrinsic rate of natural increase were computed for each clonal lineage. Data here obtained were compared with their lethal responses to copper and significant negative correlations were found. These results suggest that genetically eroded populations of D. longispina, due to copper or salinity, may be particularly susceptible to a later exposure to the other contaminant supporting the multiple stressors differential tolerance.

Could contaminant induced mutations lead to a genetic diversity overestimation?

Contaminant driven genetic erosion reported through the inspection of selectable traits can be underestimated using neutral markers. This divergence was previously reported in the aquatic system of an abandoned pyrite mine. The most sensitive genotypes of the microcrustacean cladoceran Daphnia longispina were found to be lacking in the impacted reservoir near the entrance of the metal rich acid mine drainage (AMD). Since that divergence could be, at least partially, accounted for by mutagenicity and genotoxicity of the AMD, the present study aimed at providing such a characterization. The Allium cepa chromosomal aberration assay, using root meristematic cells, was carried out, by exposing seeds to 100, 10, 1, and 0.1% of the local AMD. Chromosomal aberrations, cell division phases and cell death were quantified after the AMD exposure and after 24 and 48h recovery periods. The AMD revealed to be mutagenic and genotoxic, even after diluting it to 1 and 0.1%. Dilutions within this range were previously found to be below the lethality threshold and to elicit sublethal effects on reproduction of locally collected D. longispina clonal lineages Significant mutagenic effects (micronuclei and chromosomal breaks) were also found at 0.1% AMD, supporting that exposure may induce permanent genetic alterations. Recovery tests showed that AMD genotoxic effects persisted after the exposure.

Fatty acid profiling reveals seasonal and spatial shifts in zooplankton diet in a temperate estuary

Fatty acids composition of copepod and cladoceran species and their possible food sources was investigated in the Mondego estuary (southern Europe) in order to explain the seasonal variation of the small copepods Acartia clausi, Acartia tonsa, Copidodiaptomus numidicus, Temora longicornis and the freshwater cladoceran Daphnia longispina. A total of 12 zooplankton species (7 marine, 2 estuarine and 3 freshwater species) were studied. A multivariate analysis revealed a clear seasonal distribution of zooplankton species in terms of fatty acids composition and abundance, with winter and spring zooplankton species showing maximal concentrations and diversity of total fatty acids. These findings underline the role of lipids as storage during the colder seasons in a highly variable environment like an estuary. Estuarine and freshwater species showed a more diverse array of saturated and unsaturated fatty acids rather than marine species, except for Centropages typicus. Fatty acids markers of trophic position indicated the presence of two trophic levels: copepod species were primarily omnivorous, whereas cladocerans showed to be herbivorous. Our results suggest that feeding patterns of plankton change spatially and temporally, reflecting the shifts in dominance between diatoms and flagellates as well as between dinoflagellates/diatoms and small animals.

Genetic erosion and population resilience in Daphnia longispina O.F. Müller under simulated predation and metal pressures

This study investigated the effects of nonselective predation (culling) and metal toxicity on the genetic diversity of laboratory populations of the cladoceran Daphnia longispina. Populations, comprising five clones differing in their sensitivity to lethal concentrations of a metal-rich mine drainage effluent, were subjected to all possible combinations of three levels (absent, weak, and strong) of each stressor. Observed population densities were compared to those expected from a life history experiment, and clone frequencies were determined by allozyme profiling. Culling did not affect population density, although clonal diversity was higher than the control. Populations stressed by mine drainage recovered to their initial densities within 12 days, though the most sensitive genotypes disappeared under both weak and strong metal stress levels. Because the surviving resistant clones were shown to be the most sensitive ones to other chemicals (Cd and H+), it is suggested that successive inputs of partially lethal concentrations of different chemicals can lead to the disappearance of the population, even if the time between inputs is large enough to allow density recovery. These results suggest that changes in abundance are not enough to evaluate ecological effects of chemicals on the environment and information on co-tolerance and multiple tolerance within populations is highly valuable to prevent their extinction. Moreover, populations exposed to low levels of both stressors showed clonal diversity levels identical to controls, highlighting the importance of low level effects of nonselective stressors in the maintenance of high clonal diversity levels in Daphnia populations, and thus further supporting the intermediate disturbance hypothesis.

Coupling of the Biochemical Composition and Calorific Content of Zooplankters with the Microcystis aeruginosa Proliferation in a Highly Eutrophic Reservoir

The impact of the Cyanobacteria Microcystis aeruginosa on zooplankton dynamics was studied in the hypertrophic Villerest Reservoir (France). Samples were collected and their biochemical composition and calorific content examined. Three most abundant zooplankton species in the reservoir were considered: the cladoceran Daphnia longispina and the copepods Cyclops vicinus and Eudiaptomus gracilis. The three species were differently affected by the Microcystis aeruginosa blooms. Daphnia longispina did not seem to suffer from the proliferation of the M. aeruginosa, although its biomass decreased concomitantly to the bloom. This collapse would be attributable to the lack of nutritional value of algae. Cyclops vicinus seemed to move away when Microcystis invaded the superficial layers of the reservoir. Because this zooplankter had migratory abilities, it reached the littoral zone where food was available. The energetic costs linked to this migration were clearly pointed out when the species recovered the pelagial zone in early fall. The behaviour of Eudiaptomus gracilis was not clear. This species underwent diapause as M. aeruginosa proliferated. This suggests that Eudiaptomus gracilis moved away from the pelagial zone over the cyanobacterial blooms. In most cases, the cyanobacterial toxins affected the growth of zooplankton and the potential to use herbivorous zooplankton as a means to combat Microcystis proliferation in the Villerest reservoir seems limited.

Impacts of a submerged plant (Elodea canadensis) on interactions between roach (Rutilus rutilus) and its invertebrate prey communities in a lake littoral zone

Summary1. Using 5‐m2 field enclosures, we examined the effects of Elodea canadensis on zooplankton communities and on the trophic cascade caused by 4–5 year old (approximately 16 cm) roach. We also tested the hypothesis that roach in Elodea beds use variable food resources as their diet, mainly benthic and epiphytic macroinvertebrates, and feed less efficiently on zooplankton. Switching of the prey preference stabilises the zooplankton community and, in turn, also the fluctuation of algal biomass. The factorial design of the experiment included three levels of Elodea (no‐, sparse‐ and dense‐Elodea) and two levels of fish (present and absent).2. During the 4‐week experiment, the total biomass of euplanktonic zooplankton, especially that of the dominant cladoceran Daphnia longispina, decreased with increase in Elodea density. The Daphnia biomass was also reduced by roach in all the Elodea treatments. Thus, Elodea provided neither a favourable habitat nor a good refuge for Daphnia against predation by roach.3. The electivity of roach for cladocerans was high in all the Elodea treatments. Roach were able to prey on cladocerans in Elodea beds, even when the abundance and size of these prey animals were low. In addition to cladocerans, the diet of roach consisted of macroinvertebrates and detrital/plant material. Although the biomass of macroinvertebrates increased during the experiment in all Elodea treatments, they were relatively unimportant in roach diets regardless of the density of Elodea beds.4. Euplanktonic zooplankton species other than Daphnia were not affected by Elodea or fish and the treatments had no effects on the total clearance rate of euplanktonic zooplankton. However, the chlorophyll a concentration increased with fish in all the Elodea treatments, suggesting that fish enhanced algal growth through regeneration of nutrients. Thus, our results did not unequivocally show that Elodea hampered the trophic cascade of fish via lowered predation on grazing zooplankton.5. In treatments with dense Elodea beds (750 g FW m−2), chlorophyll a concentration was always low suggesting that phytoplankton production was controlled by Elodea. Apparently, the top‐down control of phytoplankton biomass by zooplankton was facilitated by the macrophytes and operated simultaneously with control of phytoplankton production by Elodea.

Genetic Determination of Tolerance to Lethal and Sublethal Copper Concentrations in Field Populations of Daphnia longispina

In order to study the effects of environmental pollution on the genetic diversity of natural populations, two field populations of the cladoceran Daphnia longispina were sampled: one in a reference site (uncontaminated) and the other in a site historically stressed with acid mine drainage (AMD). Five hypotheses were formulated: (1) the stressed population presents a higher tolerance to lethal levels of copper than the reference population, (2) differences in tolerance to lethal levels, observed between the two populations, are due to the loss of sensitive lineages, (3) differences in tolerance to lethal levels of copper between the two populations are due to the appearance of new genotypes, (4) the acquisition of tolerance to lethal levels of copper involved changes in life-history patterns and fitness costs under optimal conditions, and (5) historical contamination by AMD resulted in tolerance differences to sublethal levels between populations, within categories similarly tolerant to lethality, specifically, lineages with similar tolerance to lethal levels from both populations show differences in tolerance to sublethal levels, the stressed population being more tolerant to sublethal levels of contamination than the reference population. Over 125 acclimated cloned lineages, from each population, were exposed to different copper concentrations for 24 hours. At the end of each assay, mortality and feeding inhibition were monitored. Life-cycle traits under optimal conditions were also monitored (time to first brood, number of neonates per brood, inter-brood time, body length, and ingested algae). At lethal levels of copper, significant differences were found in the frequency of sensitive lineages between the two populations. The stressed population did not include the most sensitive lineages, though the most tolerant ones were also present in the reference population. Thus, the hypothesis of presence of new genotypes in the stressed population resulting in an overall increase tolerance of the population at lethal levels was rejected. Changes in life-history patterns were detected, though they were not fully consistent with predictions of life-history theory. Furthermore, these changes in life-history patterns did not involve fitness costs. The fifth hypothesis was rejected since, at sublethal levels of copper, no significant differences were found between the feeding inhibitions of similarly lethal tolerant lineages of the two populations, with only one exception. Therefore, the present study further confirmed the genetic erosion hypothesis and gave further support to the incorporation of genetic diversity measurements into risk assessments.

Food of introduced pumpkinseed sunfish: ontogenetic diet shift and seasonal variation

The pumpkinseed sunfish Lepomis gibbosus introduced into Lake Banyoles (Spain) were predominantly littoral but there was a tendency of large fish to use deeper zones. Their diet was dominated by littoral macrobenthos, particularly amphipods (Echinogammarus sp.). There was ontogenetic variation in the diet, with small young‐of‐the‐year (LF&lt;4 cm) feeding on several littoral microcrustaceans, especially the cladoceran Ceriodaphnia reticulata, whereas larger fish shifted to a freshwater shrimp (Atyaephyra desmaresti), snails and damselfly larvae. Seasonal variation in diet was linked to resource availability, with consumption of fish eggs and plant debris in spring and summer. In autumn, pumpkinseeds were partially zooplanktivores, preying on the cladoceran Daphnia longispina. The diet of pumpkinseeds in Lake Banyoles and other Iberian populations shows less molluscivory than North American populations. The potential ecological impact of this successful exotic species involves mainly predation on fish eggs and molluscs.

Oxidative stress and defence mechanisms of the freshwater cladoceran Daphnialongispina exposed to UV radiation

The aim of the present study is to evaluate the occurrence of oxidative stress in the cladoceran Daphnia longispina exposed to UV-A and UV-B radiation. The activity of antioxidant enzymes and lipid peroxidation markers is investigated and the protective action of ascorbic acid determined. Results show differences in the lethality radioinduced by UV-A and UV-B. Both UV-A and UV-B exposure cause an important increase in malonaldehyde (MDA) concentration and catalase activity. Ascorbic acid addition reduces the MDA concentration, indicating that the oxidative stress caused by either UV-A or UV-B radiation can be controlled by antioxidants. The increase of the antioxidant enzymes may be a response mechanism to oxidative stress.

Influence of changing food web structure on nutrient limitation of phytoplankton in a highly humic lake

We determined the potential nutrient limitation of summer phytoplankton production using 2 × 2 × 2 factorial design of enrichment bioassays both before and after the introduction of planktivorous whitefish (Coregonus lavaretus) in a polyhumic lake with an abundant population of the large cladoceran Daphnia longispina. After the fish introduction, Daphnia disappeared and was substituted by the rotifer Keratella cochlearis. During the dominance of Daphnia, additions of nutrients had little or no effect on primary production of phytoplankton in short-term (1-day) incubations. However, 5-day incubations suggested that P most likely was the limiting nutrient. After the fish introduction, both 1- and 5-day enrichment bioassays indicated potential N limitation of phytoplankton production. The strong response of phytoplankton production to combined enrichments with P and N also suggested colimitation by P and N, but this was probably forced by the relatively high additions of nutrients. Consistently low primary production after the combined addition of P and glucose suggests that in the presence of a labile organic C source, epilimnetic bacteria were superior to algae in the uptake of P. Our results suggest that changes in the food web structure may determine the limiting nutrient also in a highly humic lake.

Zooplankton community structure driven by vertebrate and invertebrate predators

A zooplankton community was established in outdoor experimental ponds, into which a vertebrate predator (topmouth gudgeon: Pseudorasbora parva) and/or an invertebrate predator (phantom midge larva: Chaoborus flavicans) were introduced and their predation effects on the zooplankton community structure were evaluated. In the ponds which had Chaoborus but not fish, small- and medium-sized cladocerans and calanoid copepods were eliminated while rotifers became abundant. A large-sized cladoceran Daphnia longispina, whose juveniles had high helmets and long tailspines as anti-predator devices, escaped from Chaoborus predation and increased. In the ponds which had fish but not Chaoborus, the large-sized Daphnia was selectively predated by the fish while small-and medium-sized cladocerans and calanoid copepods predominated. In the ponds containing both Chaoborus and fish, the fish reduced the late instar larvae (III and IV) of Chaoborus but increased the early instar larvae (I and II). Small- and large-sized cladocerans were scarcely found. The former might have been eliminated by predation of the early instar larvae of Chaoborus, while the latter was probably predated by fish. Consequently, the medium-sized cladocerans, which may have succeeded in escaping from both types of predator, appeared abundantly. The results suggest that various combinations of vertebrate and invertebrate predators are able to drive various kinds of zooplankton community structure.

Epizooic ciliates (Vorticella sp.) compete for food with their host Daphnia longispina in a small polyhumic lake.

Clearance rates of epizooic ciliates (Vorticella sp.) were measured together with their host, a planktonic cladoceran Daphnia longispina by using fluorescent latex beads as tracers of food. Vorticellans and their host graze on food of same size range (nanoplanktonic algae and bacteria). Individual clearance rates of Vorticella averaged 6.9 and 7.0 μl ind-1 h-1 and those of Daphnia 463 and 708 μl ind-1 h-1 for beads with diameter 2.00 and 3.92 μm. On the average, epizooic vorticellans together on the carapace of Daphnia cleared particles with rates representing 25-33% of that the host cleared, the maximum rates being 50-80%. In a steeply stratified polyhumic lake vorticellans take advantage of following Daphnia to food patches and they can severely compete for food with their host.