Mating behavior of Daphnia: impacts of predation risk, food quantity, and reproductive phase of females

Persistent and sex-independent effects of decreased calcium concentration inhibiting morphological defense of Daphnia: Evidences from morphological traits and expression of the associated genes

The continuous decline in calcium concentration in freshwater as a widespread environmental stress can have complex effects on the interspecific relationships of organisms, such as interference with the anti-predation defenses of Daphnia with high calcium demand. The natural population of Daphnia includes individuals with different developmental stages and sexes. Here, we measured the effects of decreased calcium concentration on morphological defense of Daphnia after different numbers of molts or under various sexes and the expression of genes related to signal recognition, carapace formation, reproductive allocation, and stress defense. Results showed that decreased Ca concentration resulted in the altered effects of fish kairomone on the change rates of body size, change rates of spine length, and change rates of relative spine length disappear. Furthermore, male Daphnia also developed morphological defense under fish predation risk, which was also inhibited by decreased Ca concentration, but no significant difference was observed in the intensity of induced defense between male and female Daphnia at low Ca concentrations. Importantly, decreased Ca concentrations did not alter the increase in expressions of genes related to neural signaling by fish kairomone. Fish kairomone promoted the expression of reproduction-related genes, whereas decreased Ca concentration inhibited their expression. Fish kairomone altered the expression of carapace-related genes, but most were disturbed by decreased Ca concentration. Decreased Ca concentration inhibited the increased expression of stress defense-related genes by fish kairomone. This study contributes to a more comprehensive understanding of the effects of environmental changes on interspecific relationships among aquatic organisms of different developmental stages and different sexes.

Novel peptide identified from viable-cell based phage display technique regulates growth cycle of Daphnia magna

Phage display is a widely used technique for selecting specific binding peptides, but presenting antigens in their natural form can be challenging, as protein coating may induce structural changes. In this study, we employed a whole cell-based phage display technique without a coating step to select peptides that bind specifically to Daphnia magna eggs. Boiled eggs were used as a control to ensure that antigens were presented in their natural forms. We identified a peptide, DEP1 (LYALPLSHLKSHGGG), with the highest binding affinity to D. magna eggs. DEP1 did not affect zebrafish eggs, but it inhibited normal hatching and reproductive ability in D. magna eggs, and hindered growth in neonates before their first ecdysis. Morphological analysis revealed that DEP1 caused intestinal damage and tissue abnormalities. Our findings demonstrate that the whole cell-based phage display technique is successful in presenting antigens in their natural form, and that the DEP1 peptide can be applied to regulate the growth cycle of D. magna. These results have implications for the use of phage display in environmental research and the potential use of DEP1 for hazardous organisms in aquatic systems.

Acute toxicity, oxidative stress, and apoptosis due to short-term triclosan exposure and multi- and transgenerational effects on in vivo endpoints, antioxidant defense, and DNA damage response in the freshwater water flea Daphnia magna

In this study, we measured the acute toxicity of triclosan (TCS) in neonate and adult Daphnia magna water fleas. The median lethal concentrations were 184.689 and 349.511 μg/L, respectively. Oxidative stress induced by TCS was analyzed based on changes in reactive oxygen species (ROS) content and antioxidant enzymatic activities in D. magna. Based on these endpoints, TCS concentrations of 50 and 100 μg/L induced oxidative stress. However, several apoptosis-mediated proteins showed TCS-induced oxidative-stress damage in response to 25 μg/L, indicating that apoptotic proteins were the most sensitive mediators. We also evaluated the multi- and transgenerational effects of TCS on D. magna over three generations in terms of various in vivo endpoints, DNA damage responses, and biochemical reactions. The transgenerational group exposed to TCS exhibited greater negative impacts on antioxidant responses, DNA fragmentation status, and biological endpoints compared with the multigenerational exposure group, leading to decreased reproductive rates and higher ROS content. The transcriptional expression levels of glutathione S-transferase genes in the transgenerational exposure group were upregulated compared to those in the multigenerational group but were fully recovered in F2 offspring. Our findings provide an in-depth understanding of the adaptive effects of multigenerational exposure to TCS.

Population changes of Daphnia caused by declined calcium concentration: Evidences from population dynamics and sexual reproduction

The decline in freshwater calcium has become a new environmental stressor to Daphnia with high calcium demand, however, the population dynamics and sexual reproduction of Daphnia under low calcium stress are still lack of deep understanding. To evaluate the impact of declined calcium on Daphnia from population level, we respectively exposed two clones of Daphnia pulex (CH and SH) to different calcium concentrations (0.5, 1.0, 1.5, 5.0, 10.0, 25.0 mg L^-1) for 30 days and recorded the population indicators. Results showed that total biomass, average dry weight per individual, total number of ephippia, total number of resting eggs of Daphnia pulex CH clone at 1.0 mg L^-1 calcium decreased by 75.5%, 34.0%, 83.6%, and 77.6% compared with those at 25 mg L^-1 calcium, while SH clone at 1.0 mg L^-1 calcium decreased by 64.6%, 26.1%, 94.5%, and 82.2%, respectively. Importantly, Ca content in dry Daphnia pulex population of CH clone at 1.0 and 1.5 mg L^-1 calcium decreased by 32.7% and 6.7% compared to those at 25 mg L^-1 calcium, and SH clone at 1.0 mg L^-1 and 1.5 mg L^-1 calcium also decreased by 30.9% and 10.5%, respectively. Furthermore, low calcium significantly decreased the perimeter and surface area of ephippia. Interestingly, observation by scanning electron microscope found that low calcium changed the surface of ephippia. The negative impact of calcium decline on Daphnia population and sexual reproduction will inevitably endanger the persistence of species and genes at meta population level.

Sex ratio effects on reproductive success of male and female Daphnia

The intensity of mating competition and the opportunity for sexual selection are thought to depend on the operational sex ratio, the ratio of sexually active males to fertilizable females. Cyclic parthenogens, organisms that alternate between sexual reproduction and female-only parthenogenesis, show particularly high variation in sex ratios in natural populations but the effects of this variation on mating competition and reproductive success of each sex are poorly understood. In a series of experiments with Daphnia magna, we experimentally imposed five sex ratio categories, varying from one male per 81 females to an even sex ratio. We found that, in males, reproductive success strongly and monotonically decreased with decreasing number of females per male. In females, in contrast, mating success and reproductive success were reduced only at the most female-biased sex ratio (1:81), when many females remained unmated and unfertilized, and then again at equal sex ratios, probably due to negative effects of high density or stress induced by numerous males. Our results suggest that females experienced male limitation at heavily female-biased sex ratios below one male to about 50 females. As this is well within the sex ratio variation observed in natural Daphnia populations, we conclude that mating competition and the opportunity for sexual selection may exist not only in males but, at least periodically, also in females.

Fear of sex: sexual conflict exposed as avoidance in a parthenogenetic invertebrate

Abstract

Males and females often have divergent evolutionary interests, generating sexual conflicts. This is particularly true in organisms that exhibit facultative sexuality, whereby females are capable of reproducing without fitness costs of mating. Here, we provide the first documented evidence with quantitative tracking showing that sex interacts with social context to determine space-use of females, in a pattern resembling predator avoidance. To achieve this, we labelled Daphnia magna with fluorescent nanoparticles and utilized a 3-D tracking platform to record pairs of individuals swimming. The recordings comprised either same-sex or opposite-sex pairings. We found that females swam faster, deeper, more horizontally, and more linearly when exposed to males than when exposed to females. Simultaneously, we found that male behavior did not differ depending on swimming partner and, importantly, we observed no sexual dimorphism in swimming behaviors when swimming with the same sex. Our results suggest that the presence of males in a population has the potential to influence the distribution of individuals, similarly to known threats, such as predation. This highlights that sexual conflict has clear spatial consequences and should be considered in such ecological frameworks, like the Landscape of Fear (LOF) concept. In a broader context, the connection of the evolutionary and social concept of sexual conflict and the ecological concept of LOF may improve our understanding of population dynamics and the spatial and temporal distribution of individuals in natural ecosystems.

Significance statement

Despite the wealth of studies that detail how predators affect their prey’s spatial behaviors, studies on the role of sex and social context on spatial behavior are rare. Addressing this dearth of information, we studied the swimming behaviors of an organism that can reproduce with or without sex, when exposed to an individual of either the same or opposite sex. We found no difference between the sexes in swimming behaviors; however, we revealed that females avoided males by swimming deeper in the water column, reminiscent of the response to predation. Our results highlight that social conflict between the sexes strongly affects the demographics of a population and may therefore have a substantial role in the spatial ecology of organisms in the wild.

Speciation in Daphnia

The microcrustacean Daphnia is arguably one of the most studied zooplankton species, having a well understood ecology, life history, and a relatively well studied evolutionary history. Despite this wealth of knowledge, species boundaries within closely related species in this genus often remain elusive and the major evolutionary forces driving the diversity of daphniids remain controversial. This genus contains more than 80 species with multiple cryptic species complexes, with many closely related species able to hybridize. Here, we review speciation research in Daphnia within the framework of current speciation theory. We evaluate the role of geography, ecology, and biology in restricting gene flow and promoting diversification. Of the 253 speciation studies on Daphnia, the majority of studies examine geographic barriers (55%). While evidence shows that geographic barriers play a role in species divergence, ecological barriers are also probably prominent in Daphnia speciation. We assess the contribution of ecological and nonecological reproductive isolating barriers between closely related species of Daphnia and found that none of the reproductive isolating barriers are restricting gene flow completely. Research on reproductive isolating barriers has disproportionally focused on two species complexes, the Daphnia pulex and Daphnia longispina species complexes. Finally, we identify areas of research that remain relatively unexplored and discuss future research directions that build our understanding of speciation in daphniids.

Knowing the Enemy: Inducible Defences in Freshwater Zooplankton

Phenotypic plasticity in defensive traits is an appropriate mechanism to cope with the variable hazard of a frequently changing predator spectrum. In the animal kingdom these so-called inducible defences cover the entire taxonomic range from protozoans to vertebrates. The inducible defensive traits range from behaviour, morphology, and life-history adaptations to the activation of specific immune systems in vertebrates. Inducible defences in prey species play important roles in the dynamics and functioning of food webs. Freshwater zooplankton show the most prominent examples of inducible defences triggered by chemical cues, so-called kairomones, released by predatory invertebrates and fish. The objective of this review is to highlight recent progress in research on inducible defences in freshwater zooplankton concerning behaviour, morphology, and life-history, as well as difficulties of studies conducted in a multipredator set up. Furthermore, we outline costs associated with the defences and discuss difficulties as well as the progress made in characterizing defence-inducing cues. Finally, we aim to indicate further possible routes in this field of research and provide a comprehensive table of inducible defences with respect to both prey and predator species.

Primary care provider perceptions of enablers and barriers to following guideline-recommended laboratory tests to confirm chronic kidney disease: a qualitative descriptive study

Background

Patients should receive follow-up serum creatinine tests after an initial abnormal result to diagnose chronic kidney disease. However, half of the time this fails to occur in primary care. We interviewed primary care providers to better understand their perceptions of enablers and barriers to following this guideline-recommended care.

Methods

We performed a qualitative descriptive study guided by the Theoretical Domains Framework (TDF), a framework for behavioural change. We used purposeful sampling to recruit primary care providers (physicians and nurse practitioners) based on provider and practice characteristics (rural, solo versus team practice, etc.) from Ontario, Canada. We completed one-on-one interviews with providers using a semi-structured and open-ended interview guide based on the 14 TDF domains. We alternated between data collection and analysis, where we used directed content analysis to identify frequent, important, and conflicting enablers and barriers.

Results

We completed 13 interviews with nine primary care physicians and four nurse practitioners. Nine themes related to the TDF emerged from the data: 1) environmental context and resources, 2) knowledge, 3) memory, attention, and decision processes, 4) beliefs about consequences, 5) goals, 6) social or professional role, 7) behavioural regulation, 8) skills, and 9) optimism. Within these themes, we identified 16 enablers and five barriers. Some enablers included, providers’ knowledge on appropriate testing, their motivation to order these tests, and their use of tools and resources to help order follow-up serum creatinine tests. However, providers perceived some barriers including that ordering confirmatory laboratory tests for chronic kidney disease was not always a priority in regards to other care they wish to provide. Providers also noted that a perceived barrier is patients not going to the laboratory to complete the test.

Conclusions

We identified novel enablers and barriers to primary care providers completing guideline recommended repeat testing for the diagnosis of chronic kidney disease. Similar research is needed to understand the views of patients. These research findings can be used to inform strategies to improve the quality of care.

Electronic supplementary material

The online version of this article (10.1186/s12875-018-0879-2) contains supplementary material, which is available to authorized users.

The effect of food, light intensity and tank volume on resting eggs production in Daphnia carinata

Sexual reproduction is an important stage of cyclical parthenogenesis Daphnia, these cyclic parthenogens need to time their shift from asexual to sexual reproduction correctly, based on environmental cues. We investigated the effect of food quality and quantity, light intensity, and culture tank volume on the resting eggs production of a tropical Daphnia carinata clone of Vietnam. The results showed that sexual ephippia production of the D. carinata was strongly induced when fed with green algae Scenedesmus sp., under moderate light intensity condition. The experiments also showed that food limitation is not an obligate requirement of shifting from parthenogenetic reproduction to sexual ephippia reproduction in D. carinata. Beside of that, culture volume seemed to be an important determinant of successfully forming of embryos inside ephippium. These findings here were from cultures in contaminant free condition, thus they are important basics for further studies of additional effects of environment toxicants on D. carinata species of Vietnam.

Daphnia females adjust sex allocation in response to current sex ratio and density

Cyclical parthenogenesis presents an interesting challenge for the study of sex allocation, as individuals' allocation decisions involve both the choice between sexual and asexual reproduction, and the choice between sons and daughters. Male production is therefore expected to depend on ecological and evolutionary drivers of overall investment in sex, and those influencing male reproductive value during sexual periods. We manipulated experimental populations, and made repeated observations of natural populations over their growing season, to disentangle effects of population density and the timing of sex from effects of adult sex ratio on sex allocation in cyclically parthenogenetic Daphnia magna. Male production increased with population density, the major ecological driver of sexual reproduction; however, this response was dampened when the population sex ratio was more male-biased. Thus, in line with sex ratio theory, we show that D. magna adjust offspring sex allocation in response to the current population sex ratio.

Reproductive switching analysis of Daphnia similoides between sexual female and parthenogenetic female by transcriptome comparison

The water flea Daphnia are planktonic crustaceans commonly found in freshwater environment that can switch their reproduction mode from parthenogenesis to sexual reproduction to adapt to the external environment. As such, Daphnia are great model organisms to study the mechanism of reproductive switching, the underlying mechanism of reproduction and development in cladocerans and other animals. However, little is known about the Daphnia's reproductive behaviour at a molecular level. We constructed a genetic database of the genes expressed in a sexual female (SF) and a parthenogenetic female (PF) of D. similoides using Illumina HiSeq 2500. A total of 1,763 differentially expressed genes (865 up- and 898 down-regulated) were detected in SF. Of the top 30 up-regulated SF unigenes, the top 4 unigenes belonged to the Chitin_bind_4 family. In contrast, of the top down-regulated SF unigenes, the top 3 unigenes belonged to the Vitellogenin_N family. This is the first study to indicate genes that may have a crucial role in reproductive switching of D. similoides, which could be used as candidate genes for further functional studies. Thus, this study provides a rich resource for investigation and elucidation of reproductive switching in D. similoides.

Effects of algal food quality on sexual reproduction of Daphnia magna

The objective of our study was to investigate sexual reproduction of Daphnia magna associated with mating behaviors and hatching rates, according to different algal food sources. Since a diatom is known to contain more abundant long‐chain poly unsaturated fatty acids (PUFAs), we hypothesized that the diatom‐consuming D. magna would exhibit more successful reproduction rates. Upon the hypothesis, we designed three experiments using two algal species, a green alga (Chlorella vulgaris) and a diatom (Stephanodiscus hantzschii). From the results, we found that the mating frequency and copulation duration increased in the treatment with S. hantzschii, resulting in a significant increase of hatching rates of resting eggs. In the other two repetitive mating strategies (e.g., one female vs. multiple males, and one male vs. multiple females), we found that the hatching rates of resting eggs were greater in the S. hantzschii treatment. In addition to the mating strategy, male body size significantly increased in the diatom treatment, hence average diameter of penis was also statistically different among the treatments (greater diameter in the S. hantzschii treatment). To examine the effect of algal food quality, we estimated quantity of fatty acids in the two algal species. Our result showed that S. hantzschii had a higher proportion of long‐chain PUFAs than C. vulgaris. Furthermore, a stable isotope analysis revealed that carbon and nitrogen originated from S. hantzschii were more assimilated to D. magna. In summary, our study manifested that diatom consumption of D. magna leads to more successful sexual reproduction. We then discussed how the diatom consumption of zooplankton influences food web dynamics in a freshwater ecosystem.