Fine-scale temporal and spatial variation of taxon and clonal structure in the Daphnia longispina hybrid complex in heterogeneous environments

Background: Cyclical parthenogenetic water fleas of the genus Daphnia have become a prominent model organism in ecology and evolution. In the past, analyses of their population structure have been limited by the prevailing use of allozyme markers, which in general do not allow for the distinction of individual clones. In this study, we used 10 microsatellite markers to track changes in the taxonomic and clonal composition of Daphnia populations, and traced the abundance of the most common clones in two European reservoirs. One of the localities was inhabited by a single species of the Daphnia longispina complex (D. galeata), the other by two parental species (D. galeata and D. longispina) and their interspecific hybrids. The study took place during the transition from summer stratification to autumn mixing, representing a period of major environmental change within lake habitats. Results: In both reservoirs, we observed temporal (generation-to-generation) and spatial (along the heterogeneous reservoir environment) changes in Daphnia community structure. In the single-species reservoir, the clonal diversity of D. galeata increased with time, as a few dominant clones were replaced by a higher number of less common clones. A loss in selective advantage for the dominant clones may have been due to gradual changes in the environment, or due to selection acting in a negative frequency-dependent manner. In the multispecies reservoir, there were no apparent temporal trends in clonal diversity but we observed significantly lower clonal diversity in the interspecific hybrids than in the coexisting parental species, supporting the existence of reproductive barriers between the parental genomes. Conclusions: Our study, tracing clonal lineages of Daphnia in time and space by the fine-resolution markers, contributes to the understanding of how clonal reproduction impacts community structure in cyclically parthenogenetic organisms

Population structure of a microparasite infecting Daphnia: spatio-temporal dynamics

Background: Detailed knowledge of spatial and temporal variation in the genetic population structure of hosts and parasites is required for understanding of host - parasite coevolution. As hot-spots of contemporary coevolution in natural systems are difficult to detect and long-term studies are restricted to few systems, additional population genetic data from various host - parasite systems may provide important insights into the topic. This is particularly true for parasites, as these players have been under-investigated so far due to the lower availability of suitable molecular markers. Here, we traced genetic variation (based on sequence variants in the internal transcribed spacer region, ITS) among seven geographically isolated populations of the ichthyosporean Caullerya mesnili, a common microparasite of the cladoceran Daphnia (here, the D. longispina hybrid complex). At three sites, we also studied parasite genetic variation over time (three to four sampling points) and tested for associations between parasite genotypes and host species. Results: Parasite (and host) populations were significantly structured across space, indicating limited dispersal. Moreover, the frequency of parasite genotypes varied significantly over time, suggesting rapid evolutionary change in Caullerya. However, the distribution of parasite genotypes was similar across different host species, which might in turn have important consequences for parasite epidemiology. Conclusions: The approach proposed here can be applied to track spatial and temporal changes in the population structure of other microparasite species for which sequence variation in the ITS or other highly variable genome regions has been documented but other types of polymorphic markers are lacking. Screening of parasite sequence variants allows for reliable detection of cross-species infections and, using advanced sequencing techniques in the near future, for detailed studies of parasite evolution in natural host - parasite systems

Daphnia as a model organism in limnology and aquatic biology: some aspects of its reproduction and development

Invertebrates comprise the overwhelming majority of all animal species - around 95% of described species, not including substantial cryptic variation. As it is an extremely diverse and heterogeneous group, research on various invertebrate taxa often follows parallel trajectories, with little interaction among experts on different groups. To promote sharing of knowledge within as well as across taxa, the International Society of Invertebrate Reproduction and Development (ISIRD) was established in 1975 in Calicut, India. Since that time, the ISIRD has organised international conferences at three-year intervals where various aspects of invertebrate biology are presented and discussed, naturally with the focus on reproduction and development. Traditionally, marine invertebrate groups have been well represented at all ISIRD congresses, but freshwater invertebrates have often been relatively overlooked at these meetings. The 12th ISIRD congress took place between August 16 and 20, 2010 in Prague, the Czech Republic. Several different Czech institutions collaborated on the organisation of this meeting. As aquatic invertebrate research has a long tradition in the country, we decided to include a section dedicated to popular model organisms in aquatic ecology and evolutionary biology, the "water fleas", cladocerans of the genus Daphnia. The section entitled "Daphnia and other cladocerans as model organisms" was open to any aspects of cladoceran biology directly or indirectly related to their reproduction or development. Unfortunately, the timing of the Prague congress completely overlapped the triennial congress of the International Society of Theoretical and Applied Limnology (SIL) in Cape Town, South Africa. This large meeting in a very attractive setting attracted many cladocerologists from all over the world, including Europe. Therefore, the Daphnia section of the Prague ISIRD meeting remained moderate in size, attracting 13 contributions (eight talks and five poster presentations). The presenting authors mostly originated from Central European countries (the Czech Republic, Poland, Germany, and Austria) but the conference also attracted a visitor from overseas (Mexico). Although the section was small, some of the presentations evoked considerable interest among conference participants working on marine crustaceans. Information exchange between marine and freshwater biologists was promoted, and will hopefully persist at future ISIRD meetings. The contributions presented in the session covered a very wide range of topics, such as the interplay of sexual and asexual reproduction and its impact on seasonal population development and its clonal structure, the impact of major environmental disturbances (floods) on the status of Daphnia diapausing egg banks, factors promoting male production, the importance of Daphnia ageing, the effect of cyanobacteria on Daphnia growth, and the formation of antipredator morphological structures under different conditions. In this special insert, we present five papers from authors that attended the ISIRD meeting, from one German, two Czech, and two Polish teams

On the presence of Daphnia galeata in Lake Orta (N. Italy)

Lake Orta is a very interesting environment because of its history of heavy chronic pollution and biota re-colonization. It was the first deep lake in Italy in which allozyme techniques were used to investigate clonal diversity. In 1986, a newly established Daphnia obtusa population, able to colonize stressed environments, resulted composed by just one multilocus genotype, detected through an analysis of 27 different allozymes, fifteen of which active and stable for up to 12 generations. This result was interpreted as indicative of a colonization by a single clone, able to establish after a strong selection. This species was allochthonous for the lake, and in 1996 was replaced by a Daphnia longispina of the same morphotype as that originally described from its pelagic environment, the latter apparently remaining the only Daphnia species also in the lake’s littoral until 2001, i.e. until a regular sampling to monitor the lake was accomplished. During an accidental sampling in 2004, for detecting the occurrence and prevalence of parasites in Daphnia parental species and hybrids in several lakes located North and South of the Alps, Daphnia galeata was first found in Lake Orta’s pelagic environment, as revealed by morphological and allozyme analyses. Lake Orta zooplankton was then resampled in June 2006, to detect species as well as clonal composition of the Daphnia population, using the same techniques of morphotype and allozyme analyses. We expected to find low clone diversity and the occurrence of hybrids, whose success is enhanced in disturbed environments. Although preliminary, our results confirm that clone diversity Lake Orta’s Daphnia population is low, thus suggesting a recent colonization by D. galeata and providing evidence for a founder effect. In addition, the detection of the M variant at the AO locus, we interpret as a rare allele of D. galeata/D. longispina hybrids, perfectly fits the hypothesis of an enhancement of hybrid success in disturbed environments such as the once heavy polluted Lake Orta

Repeated flood disturbance enhances rotifer dominance and diversity in a zooplankton community of a small dammed mountain pond

The zooplankton community in a relatively small and mountain pond was studied during the spring growing season. To investigate which factors operate in the community structure, we explored several physical conditions, such as high inflows, and the biotic dynamics of the main zooplankton groups (i.e., rotifers, cladocerans and copepods).  Two extreme flood events occurred during the investigated period and caused dramatic changes in physical conditions and reduction of the planktonic community abundances. The short period between both high-flow events was enough for the recovery of microplankton, but not for the metazoan zooplankton. Our results are in agreement with the common situation in which high flood events commonly favour rotifers over crustaceans, likely due to rotifer species have great colonization ability and grow faster. However, we found that the dominance of rotifers over crustaceans in our system is evidenced by an extremely, unusual high ratio between their abundances.  We observed that, at the time of the great floods, crustacean abundances as well as rotifer populations notably decreased until near zero values. Although rotifer abundance began declining before high floods, the decrease was particularly notable when the great flood happened.  Our results evidenced that i) dilution rate and temperature were the main drivers which are operating in the structure of the zooplankton community; and ii) no negative biotic interactions were detected between large and small cladocerans and rotifers. Additionally, we found surprisingly that a repeated disturbance caused by high flood events does increase the species diversity of rotifers. Finally, our study also detected some cues which may indicate that diapausing egg bank is also playing an important role in the zooplankton community, favouring the dominance of rotifers; however, this phenomenon deserves further studies. </p

Daphnia microsatellites

Daphnia microsatellite

Data from: Population structure of a microparasite infecting Daphnia: spatio-temporal dynamics

Background: Detailed knowledge of spatial and temporal variation in the genetic population structure of hosts and parasites is required for understanding of hostparasite coevolution. As hot-spots of contemporary coevolution in natural systems are difficult to detect and long-term studies are restricted to few systems additional population genetic data from various hostparasite systems may provide important insights into the topic. This is particularly true for parasites as these players have been under-investigated so far due to the lower availability of suitable molecular markers. Here we traced genetic variation (based on sequence variants in the internal transcribed spacer region ITS) among seven geographically isolated populations of the ichthyosporean Caullerya mesnili a common microparasite of the cladoceran Daphnia (here the D. longispina hybrid complex). At some sites we also studied parasite genetic variation over time. Then we tested for associations between parasite genotypes and host species. Results: Parasite (and host) populations were significantly structured across space indicating limited dispersal. Moreover the frequency of parasite genotypes varied significantly over time suggesting rapid evolutionary change in Caullerya. Finally the distribution of parasite genotypes was similar across different host species which might in turn have important consequences for parasite epidemiology. Conclusions: The approach proposed here can be applied to track spatial and temporal changes in the population structure of other microparasite species for which sequence variation in the ITS or other highly variable genome regions has been documented but other types of polymorphic markers are lacking. Screening of parasite sequence variants allows for reliable detection of cross-species infections and using advanced sequencing techniques in the near future for detailed studies of parasite evolution in natural hostparasite systems

Recovery of dialysis patients with COVID-19: health outcomes 3 months after diagnosis in ERACODA

© The Author(s) 2022.Background. Coronavirus disease 2019 (COVID-19)-related short-term mortality is high in dialysis patients, but longer-term outcomes are largely unknown. We therefore assessed patient recovery in a large cohort of dialysis patients 3 months after their COVID-19 diagnosis. Methods. We analyzed data on dialysis patients diagnosed with COVID-19 from 1 February 2020 to 31 March 2021 from the European Renal Association COVID-19 Database (ERACODA). The outcomes studied were patient survival, residence and functional and mental health status (estimated by their treating physician) 3 months after COVID-19 diagnosis. Complete follow-up data were available for 854 surviving patients. Patient characteristics associated with recovery were analyzed using logistic regression. Results. In 2449 hemodialysis patients (mean ± SD age 67.5 ± 14.4 years, 62% male), survival probabilities at 3 months after COVID-19 diagnosis were 90% for nonhospitalized patients (n = 1087), 73% for patients admitted to the hospital but not to an intensive care unit (ICU) (n = 1165) and 40% for those admitted to an ICU (n = 197). Patient survival hardly decreased between 28 days and 3 months after COVID-19 diagnosis. At 3 months, 87% functioned at their pre-existent functional and 94% at their pre-existent mental level. Only few of the surviving patients were still admitted to the hospital (0.8–6.3%) or a nursing home (∼5%). A higher age and frailty score at presentation and ICU admission were associated with worse functional outcome. Conclusions. Mortality between 28 days and 3 months after COVID-19 diagnosis was low and the majority of patients who survived COVID-19 recovered to their pre-existent functional and mental health level at 3 months after diagnosis