Longispina Populations Research Articles

Ecology of predator-induced morphological defense traits in Daphnia longispina (Cladocera, Arthropoda)

Inducible defenses against predators are widespread among plants and animals. For example, some Daphnia species form neckteeth against predatory larvae of the dipteran genus Chaoborus. Though thoroughly studied in D. pulex, knowledge about neckteeth in other Daphnia species is limited. The occurrence of this trait in the D. longispina species complex is only sporadically reported and the specific shape of neckteeth or the occurrence of other morphological defense traits is scarcely known in this widespread group. Here, we explored neckteeth occurrence in a large number of D. longispina populations across Scandinavia and studied neckteeth formation and other morphological defense traits on three D. longispina clones in the laboratory. In the study region, neckteeth on juvenile D. longispina s. str. were observed frequently in permanent ponds, but only when Chaoborus spp. larvae were present. In the laboratory experiments, all three D. longispina clones developed neckteeth (very similar to D. pulex) in response to Chaoborus kairomone exposure. The D. longispina clones also developed a longer tail spine, wider body, and larger neckteeth pedestal in response to predation threat—likely as a defense against the gape-limited predator. The intensity of neckteeth expression also depended on the clone studied and the concentration of Chaoborus kairomone. Our results demonstrate that neckteeth on D. longispina can be common in nature and that D. longispina can also induce other morphological defenses against predators. The similarity of neckteeth in D. longispina and D. pulex imposes yet unresolved questions on the evolutionary origin in these distantly related Daphnia groups.

Combined effects of interspecies interaction, temperature, and zinc on Daphnia longispina population dynamics.

Under natural conditions, organisms can experience a variety of abiotic (e.g., temperature, pH) and biotic (e.g., species interactions) factors, which can interact with toxicant effects. By ignoring species interactions conventional ecotoxicological studies (i.e., single-species tests) oversimplify the actual field situation. We investigated whether temperature and interspecific competition affected the effects of zinc (Zn) on a Daphnia longispina population. The D. longispina populations were exposed in a full factorial design to 3 different Zn treatments (background, 29, and 110 μg Zn/L), 2 different temperature regimes (cold, 17-18 °C; warm, 21-22 °C), and 2 interspecific competition levels (no interspecific Brachionus competition = no Brachionus calyciflorus added; interspecific Brachionus competition = B. calyciflorus added). Interspecific Brachionus competition and temperature by itself had a limited effect on the Daphnia abundance but significantly interacted with the highest Zn concentration. Without Brachionus competition the D. longispina juvenile and adult abundances under warm conditions were up to 5.5 and 21 times lower, respectively, in the high Zn treatment in comparison with the Zn control, whereas under cold conditions no significant Zn effect was observed. However, with Brachionus competition the highest Zn treatment was on average 2.2 times less toxic to the D. longispina juvenile abundance at higher temperatures. Under cold conditions the highest Zn treatment affected the juvenile abundance sooner and up to 9 times more negatively when simultaneously faced with Brachionus competition. It is possible that the competition for food reduced the amount of energy that could be used by D. longispina for reproduction, and the metabolic costs increased as a result of Zn stress. The present study clearly illustrated the influence of temperature and competition on the effects of a chemical stressor. Thus, not considering such factors in ecological risk assessment may underestimate or overestimate risks in aquatic ecosystems when extrapolating data from standard single-species tests to the field. Environ Toxicol Chem 2018;37:1668-1678. © 2018 SETAC.

Biochemical and populational responses of an aquatic bioindicator species, Daphnia longispina, to a commercial formulation of a herbicide (Primextra® Gold TZ) and its active ingredient (S-metolachlor)

The growing demand of human populations for food supplies has led to an increase in the use of synthetic products, mainly pesticides, which induce adverse effects not only to target organisms, but also to non-target biota of agroecosystems. Aquatic ecosystems in the proximity of agricultural areas are particularly vulnerable to pesticides, which cause underperformance or extinction of non-target sensitive species. Once in the aquatic system, these chemicals can affect biological processes at multiple levels (molecular, individual, populational), causing ecosystem imbalance across multiple scales. In this study, the effect of a commercial formulation of a herbicide (Primextra® Gold TZ) and its main active ingredient (a.i., S-metolachlor) was studied on a freshwater cladoceran species (Daphnia longispina), at different levels of biological organization and temporal scales. S-metolachlor is used in many herbicide formulations applied in corn/maize cultures, which is a relevant culture worldwide. As a first step, the acute and chronic effects of both commercial formulation and a.i. were quantified, and both formulations negatively affected the cladoceran's survival and reproductive parameters (age at first reproduction, number of offspring and number of broods), as well as the population's rate of increase. Whilst acute effects were comparable, the commercial formulation was slightly more toxic (EC50 was two-times lower) than the a.i. in chronic exposures, being prejudicial to D. longispina populations above 4.0mg/L of S-metolachlor. In a second experimental step, we focused on the potential multi-generational impacts of the exposure to the a.i. alone on biochemical (lipid biomarkers, namely fatty acids) and populational responses, because of the relevance of S-metolachlor as a biosynthesis inhibitor in many herbicidal formulations. The herbicide caused a significant decrease in Daphnia fecundity (in the size of the 1st clutch), but no concomitant alterations were found in fatty acid profiles of mothers or offspring. More important, this experiment showed that S-metolachlor did not cause effects in the subsequent generation, thus suggesting that biotic communities may recover after exposure to the xenobiotic.

Strong differences in the clonal variation of two Daphnia species from mountain lakes affected by overwintering strategy

BackgroundThe population structure of cyclical parthenogens such as water fleas is strongly influenced by the frequency of alternations between sexual and asexual (parthenogenetic) reproduction, which may differ among populations and species. We studied genetic variation within six populations of two closely related species of water fleas of the genus Daphnia (Crustacea, Cladocera). D. galeata and D. longispina both occur in lakes in the Tatra Mountains (Central Europe), but their populations show distinct life history strategies in that region. In three studied lakes inhabited by D. galeata, daphnids overwinter under the ice as adult females. In contrast, in lakes inhabited by D. longispina, populations apparently disappear from the water column and overwinter as dormant eggs in lake sediments. We investigated to what extent these different strategies lead to differences in the clonal composition of late summer populations.ResultsAnalysis of genetic variation at nine microsatellite loci revealed that clonal richness (expressed as the proportion of different multilocus genotypes, MLGs, in the whole analysed sample) consistently differed between the two studied species. In the three D. longispina populations, very high clonal richness was found (MLG/N ranging from 0.97 to 1.00), whereas in D. galeata it was much lower (0.05 to 0.50). The dominant MLGs in all D. galeata populations were heterozygous at five or more loci, suggesting that such individuals all represented the same clonal lineages rather than insufficiently resolved groups of different clones.ConclusionsThe low clonal diversities and significant deviations from Hardy-Weinberg equilibrium in D. galeata populations were likely a consequence of strong clonal erosion over extended periods of time (several years or even decades) and the limited influence of sexual reproduction. Our data reveal that populations of closely related Daphnia species living in relatively similar habitats (permanent, oligotrophic mountain lakes) within the same region may show strikingly different genetic structures, which most likely depend on their reproductive strategy during unfavourable periods. We assume that similar impacts of life history on population structures are also relevant for other cyclical parthenogen groups. In extreme cases, prolonged clonal erosion may result in the dominance of a single clone within a population, which might limit its microevolutionary potential if selection pressures suddenly change.

Population dynamics of Daphnia longispina (O.F. Müller, 1785) and Diaphanosoma brachyurum (Lievin, 1848) (Crustacea, Cladocera) under stable and graded temperature regimes

Laboratory experiments have been performed to study the effects of different temperature regimes-constant (16.3 +/- 0.8, 20.3 +/- 0.8, and 24.6 +/- 0.7 degrees C) and graded, with temperatures changing at intervals of 4.4 or 8.8 degrees C within the range of 15.1-25.4 degrees C--on the population dynamics of two dominant species of littoral zooplankton, Daphnia longispina and Diaphanosoma brachyurum. The results show that aperiodic stepwise changes in temperature within the ranges of 16.3-20.4, 20.4-25.1, and 16.3-25.1 degrees C, which may take place in water bodies of the temperate zone in the summer period, can exert either stimulating (direct or delayed) or inhibitory effect on the natural development of D. longispina populations. The development of D. brachyurum, a more stenothermic thermophile, is stimulated only by a stable elevated temperature (24.5 +/- 0.9 degrees C). All temperature changes within the above range, except for rapid heating from 16.3 to 25.1 degrees C, either inhibit the development of D. brachyurum populations or have no significant effect on them.

Daphnia fitness over a food gradient : is body size the single trait predicting exploitative ability?

Phytoplankton dynamics in freshwater ecosystems can be faced as a meaningful natural stressor for its main grazers, and hence constrain bottom-up interactions within the trophic structure of the food-web. Filter-feeding zooplankters, such as Daphnia, cope with resources fluctuations by adjusting their life-history as a function of balances in the energy allocation rules. Additionally, Daphnia populations often withstand interspecific competition within coexisting related species, and it is generally assumed that body size is a strategic trait conditioning exploitative ability and the related competitive advantage of species. The lifehistory responses of one Daphnia magna population and three populations of Daphnia cf longispina to a discrete gradient of algae concentration were assessed. This experiment was focused on (i) how these distinct populations regulate life-history when feeding over low, intermediate and high food-levels; and on (ii) whether the large-bodied D. magna can be better in exploiting resources over the gradient than can the smaller D. cf longispina populations. We found evidences that body size might not be the single trait influencing the exploitative ability of related species. The D. cf longispina populations were often better than D. magna in exploiting different levels of resources, and remarkable differences in fitness were found between these similar-sized individuals within food-level; indeed, these differences were frequently of higher scale than those found between the larger D. magna and any of the D. cf longispina populations.

Effects of food availability on the acute and chronic toxicity of the insecticide methomyl to Daphnia spp.

The widespread increase of pesticides application in crops threats vicinal freshwater lentic ecosystems, frequently leading to their contamination. Due to their position in the aquatic food web, the responses to these pesticide inputs of freshwater filter-feeding zooplankters, as daphnids, provide relevant information the general risk to the ecosystem of xenobiotics. Moreover, cladoceran grazers often face fluctuations in food availability due to the phytoplankton dynamics in lentic water bodies, and food acquisition naturally conditions their fitness. In this study, the responses of Daphnia magna, and of three genotypes within the Daphnia longispina complex, to acute and chronic exposures of methomyl, were assessed. In addition, we focused on whether the food level can model the Daphnia life-history responses to the insecticide. Results showed that methomyl was acutely and chronically toxic to both D. magna and the D. cf longispina populations at very low concentrations, and remarkable differences in sensitivity were noticed when comparing the responses to the toxic among taxa/genotypes. Furthermore, food availability conditioned the overall fitness of the species although not interacting specifically on the response to the toxicant stress.

Baltic Eubosmina morphological radiation: Sensitivity to invertebrate predators (induction) and observations on genetic differences

Cladocerans in the genus Eubosmina exhibit spectacular and confusing morphological diversification in the Baltic region. The paleolimnological record suggests that lineages in regional lakes diverged recently from morphologically conservative E. longispina/coregoni-like ancestors and developed strong seasonal elongation of antennules, mucrones, or dorsal humps (cyclomorphosis). Allozyme studies on Schleswig-Holstein populations by DE MELO agree with this interpretation by demonstrating: 1) genetic difference between geographically distant E. longispina populations, 2) clustering of E. coregoni forms with local E. longispina lineages, and 3) great genetic similarity among regional E. coregoni forms, despite major morphological differences. Retention of distinguishing traits (shape of dorsal humps, antennule length) in common-garden experiments emphasizes that micro-evolutionary (genetic) differences underlie form phenotypes. However, regression of extreme summer forms towards a more conservative morphology in laboratory culture indicates that part of the seasonal variability is attributable to developmental plasticity. Split-clone laboratory experiments demonstrate that longer antennule lengths of an exuberant form, E. coregoni kessleri from the Grosser Ploner See, are increased (induced) in the presence of predatory cyclopoids. Induction responses strengthen the notion that long-term transformations involve evolutionary responses to invertebrate predators (cyclopoid copepods, Leptodora) which colonized large lakes during post-glacial periods, with the particulars of responses showing lineage and lake specificity.

Diurnal patterns of antioxidant activity in alpine and arctic Daphnia under in situ UV-radiation

Diurnal variation in the activity of the antioxidant enzymes catalase (CAT), glutathione transferase (GST) and superoxide dismutase (SOD) were studied in one arctic Daphnia tenebrosa and two alpine D. longispina populations. Both the alpine ponds were shallow and transparent, yet they were inhabited by different colour morphs due to carapace melanization (hyaline or melanic). Hyaline animals showed significantly higher activity of GST and SOD, but lower activity of CAT compared to the melanic morph. In the melanic morph significant diurnal variation was found only in GST activity with a minimum around noon. In the hyaline morph diurnal variation was observed in both CAT and SOD activity with a maximum at mid-day. Hyaline Daphnia may experience higher stress from UV-induced reactive oxygen species than animals with carapace melanization since the latter are well protected from harmful radiation due to their pigmentation. Compared to the alpine populations the arctic population displayed similar SOD activity, higher CAT and far lower GST activity, but the diurnal fluctuations were all small and insignificant.

Chaoborus and fish-mediated influences on Daphnia longispina population structure, dynamics and life history strategies.

This study examined the long term effects of predation by larvae of the midge Chaoborus and simulated fish predation on experimental Daphnia longispina populations. Chaoborus predation, relative to fish predation, led to populations composed of larger individuals as a whole, larger egg-bearing individuals, and a larger primiparous instar. Daphnia retained helmets beyond the first instar in response to the presence of Chaoborus. Both types of predation, relative to predator-free controls, reduced prey population size and rates of increase, but increased population death rates. The reduction in population size due to predation led to increased resource availability for individuals remaining in the populations and increased individual fecundity in the predation treatments. The differences noted between the Chaoborus, fish, and control treatments increased with predation intensity.

The spatial distribution of zooplankton populations in the presence and absence of fish

The spatial distribution patterns of the main zooplankton groups in two small experimental ponds, one which contained fish and one which did not, were measured over a twelve month period from March 1983. Populations of all zooplankton groups were generally distributed non-randomly and with varying degrees of aggregation. The aggregation ofDaphnia longispina populations was inversely related to ambient wind speed, indicating a breakdown of behavioural clumping by wind-induced water currents. Evidence that populations ofDaphnia aggregate in response to fish predation was inconclusive. In contrast cyclopoid nauplii showed no evidence of behavioural clumping and the degree of aggregation was not related to wind speed. Nauplii aggregations were however greater in the absence than in the presence of fish.

Fate and effects of 3,4‐dichloroaniline in the laboratory and in outdoor ponds: II. chronic toxicity to Daphnia SPP. and other invertebrates

AbstractThe effects of 3,4,‐dichloroaniline (DCA) on survival, growth and reproduction of the planktonic crustacean Daphnia magna were evaluated in the laboratory using a procedure based on Organization for Economic Cooperation and Development guidelines. Effects on reproduction, the most sensitive of the measured biological responses, occurred at a concentration of 20 μg/L but not at 10 μg/L or at lower concentrations. These, and similar results reported elsewhere, were used to calculate the maximum acceptable toxicant concentration (MATC) for D. magna.In acute toxicity tests with D. magna and D. longispina the 48‐h EC50 values were 290 and 440 μg/L, respectively. An estimate of the MATC for D. longispina was then obtained by multiplication of the MATC for D. magna by the ratio of the 48‐h EC50 values for the two species.A field experiment was carried out to compare the chronic toxicity of DCA in the laboratory with effects on populations of zooplankton and communities of macroinvertebrates in outdoor ponds. Three ponds were treated with DCA at a nominal concentration of 45 μg/L and three at 450 μg/L. These concentrations were maintained in the water for 28 d. Three untreated ponds were used as controls. Population densities of the dominant species of zooplankton were monitored before, during and after treatment with DCA. Samples of the macroinvertebrate communities were taken immediately after the end of treatment. Birth, death and growth rates of D. longispina populations were monitored using Perspex cylinders to confine samples of adults in situ for periods of 24 h.Population densities of D. longispina were significantly affected (p ≤ 0.05) by both treatment levels. There were no adverse effects on the population densities of two species of copepods and no changes were observed in the structure of macroinvertebrate communities. It was concluded that the Cladocera were much more susceptible to DCA than were other groups of invertebrates in the outdoor ponds.Birth and growth rates of D. longispina populations were highly sensitive to the effects of DCA. They were depressed when concentrations of DCA were maintained at a level greater than the MATC and increased rapidly when concentrations decreased below this level. Thus, the MATC, derived from the results of toxicity tests, provided an accurate estimate of threshold concentrations affecting field populations of D. longispina.