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Predator–prey cycles rank among the most fundamental concepts in ecology, are predicted by the simplest ecological models and enable, theoretically, the indefinite persistence of predator and prey 1 – 4 . However, it remains an open question for how long cyclic dynamics can be self-sustained in real communities. Field observations have been restricted to a few cycle periods 5 – 8 and experimental studies indicate that oscillations may be short-lived without external stabilizing factors 9 – 19 . Here we performed microcosm experiments with a planktonic predator–prey system and repeatedly observed oscillatory time series of unprecedented length that persisted for up to around 50 cycles or approximately 300 predator generations. The dominant type of dynamics was characterized by regular, coherent oscillations with a nearly constant predator–prey phase difference. Despite constant experimental conditions, we also observed shorter episodes of irregular, non-coherent oscillations without any significant phase relationship. However, the predator–prey system showed a strong tendency to return to the dominant dynamical regime with a defined phase relationship. A mathematical model suggests that stochasticity is probably responsible for the reversible shift from coherent to non-coherent oscillations, a notion that was supported by experiments with external forcing by pulsed nutrient supply. Our findings empirically demonstrate the potential for infinite persistence of predator and prey populations in a cyclic dynamic regime that shows resilience in the presence of stochastic events. The potential for infinite persistence of planktonic predator and prey cycles is experimentally demonstrated and these cycles show resilience in the presence of stochastic events.

Maternal effect senescence—a decline in offspring survival or fertility with maternal age—has been demonstrated in many taxa, including humans. Despite decades of phenotypic studies, questions remain about how maternal effect senescence impacts evolutionary fitness. To understand the influence of maternal effect senescence on population dynamics, fitness, and selection, we developed matrix population models in which individuals are jointly classified by age and maternal age. We fit these models to data from individual-based culture experiments on the aquatic invertebrate, Brachionus manjavacas (Rotifera). By comparing models with and without maternal effects, we found that maternal effect senescence significantly reduces fitness for B. manjavacas and that this decrease arises primarily through reduced fertility, particularly at maternal ages corresponding to peak reproductive output. We also used the models to estimate selection gradients, which measure the strength of selection, in both high growth rate (laboratory) and two simulated low growth rate environments. In all environments, selection gradients on survival and fertility decrease with increasing age. They also decrease with increasing maternal age for late maternal ages, implying that maternal effect senescence can evolve through the same process as in Hamilton’s theory of the evolution of age-related senescence. The models we developed are widely applicable to evaluate the fitness consequences of maternal effect senescence across species with diverse aging and fertility schedule phenotypes.

The ecotoxicological effects of Ciprofloxacin hydrochloride (CIP) were tested on population densities of plankton assemblages consisting of two algae ( Isochrysis galbana and Platymonas subcordiformis ) and a rotifer ( Brachionus plicatilis ). The I. galbana showed a significant decrease in densities when concentrations of CIP were above 2.0 mg L −1 in single-species tests, while P. subcordiformis and B. plicatilis were stable in densities when CIP were less than10.0 mg L −1 . The equilibrium densities of I. galbana in community test increased with CIP concentrations after falling to a trough at 5.0 mg L −1 , showed a completely different pattern of P. subcordiformis which decreased with CIP concentrations after reaching a peak at 30.0 mg L −1 . The observed beneficial effect was a result of interspecies interactions of trophic cascade that buffered for more severe direct effects of toxicants. The community test-based NOEC of CIP (2.0 mg L −1 ), embodying the indirect effects, was different from the extrapolated one derived by single-species tests (0.5 mg L −1 ), but all lacked confidence interval. A CIP threshold concentration of obvious relevance to ecological interaction was calculated with a simplified plankton ecological model, achieving a value of 1.26 mg L −1 with a 95% bootstrapping confidence interval from 1.18 to 1.31 mg L −1 .

Fire salamander larvae are top predators in limnic habitats and feed on a wide spectrum of prey. For our study, we hypothesized that the larvae have a top-down effect on meiofauna, but that this effect varies depending on the habitat the larvae originate from. Therefore, we collected larvae from ponds and streams and placed them individually into microcosms with sediment and benthos. After either one week or two weeks, we removed the larvae and counted the number of nematodes, oligochaetes, and rotifers. Already after week one, the abundance of meiofauna was significantly reduced, as was their biomass. Nematodes were more strongly reduced by pond larvae during this week, while oligochaetes were primarily affected by stream larvae but not by pond larvae, regardless of the sampling time. The rotifers were reduced by larvae from both habitats, but only during the first week and not during the second week. Our findings suggest that fire salamander larvae not only have a top-down effect on pelagic or macrobenthic organisms, as often described in other studies, but can also shape the community of small endobenthic organisms. Depending on habitat-specific adaptations in feeding behavior, morphology, or physiology, these effects can vary.

Epigenetic modifications, including histone post-translational modifications, are central drivers of age-associated structural and functional changes in the genome, influencing gene expression and leading to changes in cellular resilience. Epigenetic modifications are thus a target for therapies to prevent or treat age-related decline in health and lifespan. In this study, we measured the effects of inhibiting histone deacetylases (HDACs) and the histone methyltransferase, SETDB1, on lifespan, reproduction, and stress response in the rotifer Brachionus manjavacas , a model organism for aging studies. Rotifers were exposed to three pharmaceutical compounds, the HDAC inhibitors β-hydroxybutyrate and sodium butyrate and the SETDB1 inhibitor mithramycin A. Changes in global histone modification levels, lifespan, reproduction, and heat stress resistance were quantified. Global histone acetylation levels increased with β-hydroxybutyrate and sodium butyrate treatments. Histone 3 lysine 9 trimethylation (H3K9me3) levels were reduced by treatment with mithramycin A. β-hydroxybutyrate significantly extended lifespan without modifying heat stress resistance. In contrast, mithramycin A increased both lifespan and heat stress tolerance. Sodium butyrate specifically improved heat stress resistance without affecting lifespan. Importantly, none of the three treatments had a significant impact on lifetime reproduction. These findings provide insights into the role of histone modifications in aging and suggest potential interventions targeting epigenetic marks to promote longevity and resilience.

Bdelloid rotifers are microinvertebrates with unique characteristics: they have survived tens of millions of years without sexual reproduction; they withstand extreme desiccation by undergoing anhydrobiosis; and they tolerate very high levels of ionizing radiation. Recent evidence suggests that subtelomeric regions of the bdelloid genome contain sequences originating from other organisms by horizontal gene transfer (HGT), of which some are known to be transcribed. However, the extent to which foreign gene expression plays a role in bdelloid physiology is unknown. We address this in the first large scale analysis of the transcriptome of the bdelloid Adineta ricciae: cDNA libraries from hydrated and desiccated bdelloids were subjected to massively parallel sequencing and assembled transcripts compared against the UniProtKB database by blastx to identify their putative products. Of ~29,000 matched transcripts, ~10% were inferred from blastx matches to be horizontally acquired, mainly from eubacteria but also from fungi, protists, and algae. After allowing for possible sources of error, the rate of HGT is at least 8%-9%, a level significantly higher than other invertebrates. We verified their foreign nature by phylogenetic analysis and by demonstrating linkage of foreign genes with metazoan genes in the bdelloid genome. Approximately 80% of horizontally acquired genes expressed in bdelloids code for enzymes, and these represent 39% of enzymes in identified pathways. Many enzymes encoded by foreign genes enhance biochemistry in bdelloids compared to other metazoans, for example, by potentiating toxin degradation or generation of antioxidants and key metabolites. They also supplement, and occasionally potentially replace, existing metazoan functions. Bdelloid rotifers therefore express horizontally acquired genes on a scale unprecedented in animals, and foreign genes make a profound contribution to their metabolism. This represents a potential mechanism for ancient asexuals to adapt rapidly to changing environments and thereby persist over long evolutionary time periods in the absence of sex.

Both theory and experiments have demonstrated that sex can facilitate adaptation, potentially yielding a group-level advantage to sex. However, it is unclear whether this process can help solve the more difficult problem of the maintenance of sex within populations. Using experimental populations of the facultatively sexual rotifer Brachionus calyciflorus, we show that rates of sex evolve to higher levels during adaptation but then decline as fitness plateaus. To assess the fitness consequences of genetic mixing, we directly compare the fitnesses of sexually and asexually derived genotypes that naturally occur in our experimental populations. Sexually derived genotypes are more fit than asexually derived genotypes when adaptive pressures are strong, but this pattern reverses as the pace of adaptation slows, matching the pattern of evolutionary change in the rate of sex. These fitness assays test the net effect of sex but cannot be used to disentangle whether selection on sex arises because highly sexual lineages become associated with different allele combinations or with different allele frequencies than less sexual lineages (i.e., \"short-\" or \"long-term\" effects, respectively). We infer which of these mechanisms provides an advantage to sex by performing additional manipulations to obtain fitness distributions of sexual and asexual progeny arrays from unbiased parents (rather than from naturally occurring, and thereby evolutionarily biased, parents). We find evidence that sex breaks down adaptive gene combinations, resulting in lower average fitness of sexual progeny (i.e., a short-term disadvantage to sex). As predicted by theory, the advantage to sex arises because sexually derived progeny are more variable in fitness, allowing for faster adaptation. This \"long-term advantage\" builds over multiple generations, eventually resulting in higher fitness of sexual types.

Background The biological effects of spaceflight remain incompletely understood, even in humans ( Homo sapiens ), and are largely unexplored in non-traditional models such as bdelloid rotifers. Results This study analyzes the transcriptomic changes experienced by Adineta vaga , a bdelloid rotifer aboard the International Space Station (ISS), using RNA sequencing. The aim was to investigate the overall effect of spaceflight in Low Earth Orbit (LEO) on these organisms. To this end, new hardware was developed to enable autonomous culturing of rotifers with minimal astronaut intervention. The study revealed significant transcriptomic changes, with 18.61% of genes showing differential expression in response to microgravity and radiation. These changes included upregulation of genes involved in protein synthesis, RNA metabolic processes, and DNA repair. Notably, the study also found a significant enrichment of foreign genes (Horizontal Gene Transfers: HGTs) among the genes that were either over- or under-expressed during spaceflight, suggesting that HGTs play a role in bdelloids’ adaptability to new and potentially atypical environments. Conclusions This research not only enhances our understanding of how organisms respond to microgravity but also proposes A. vaga as a valuable model for future studies in space biology.

A leading hypothesis for the evolutionary maintenance of sexual reproduction proposes that sex is advantageous because it facilitates adaptation. Changes in the environment stimulate adaptation but not all changes are equivalent; a change may occur along one or multiple environmental dimensions. In two evolution experiments with the facultatively sexual rotifer Brachionus calyciflorus, we test how environmental complexity affects the evolution of sex by adapting replicate populations to various environments that differ from the original along one, two, or three environmental dimensions. Three different estimates of fitness (growth, lifetime reproduction, and population density) confirmed that populations adapted to their new environment. Growth measures revealed an intriguing cost of complex adaptations: populations that adapted to more complex environments lost greater amounts of fitness in the original environment. Furthermore, both experiments showed that B. calyciflorus became more sexual when adapting to a greater number of environmental dimensions. Common garden experiments confirmed that observed changes in sex were heritable. As environments in nature are inherently complex these findings help explain why sex is maintained in natural populations.

Micro-nano plastics have emerged as a major ecological concern. The nanoplastics (NPs) pose a huge threat to microscopic animals. Our study aims to decipher the effect of polystyrene nanoplastics (PSNPs) of 50 and 100 nm sizes on a bdelloid rotifer ( Philodina roseola ). Both sizes of PSNPs were analyzed using field emission Scanning electron microscopy, Fourier transform Infrared spectroscopy, and Dynamic light scattering analyses. The LC 50 values for 50 and 100 nm PSNPs at 48 h upon interaction with the rotifers were 16.36 and 22.94 mg/L respectively. The total protein and superoxide dismutase levels decreased with an increase in concentration in both PSNPs upon interaction at various concentrations (4, 8, 12, and 16 mg/L). Whereas the lipid peroxidase and reactive oxygen species levels increased with an increase in concentration for both PSNPs at similar concentrations. Further, both PSNPs were found to cause internal organ damage in rotifers. A delay in the hatching rate was observed when the rotifers interacted with both PSNPs in addition to the decrease in the hatching rate of F 1 generation. Therefore, PSNPs pose a threat to the natural life cycle in the rotifers.