Changes in key life-history traits and transcriptome regulations of marine rotifer Brachionus plicatilis in eliminating harmful algae Phaeocystis

Warming masks the inhibitory effect of low concentration of cadmium on rotifer eliminating Phaeocystis population

The impact of heavy metal pollution on plankton in the context of climate warming may become more complex, especially on the population dynamics of zooplankton and algae. To address this important scientific issue, we studied the effect of heavy metal cadmium pollution (6 μM: environmentally relevant concentration; 12 μM: non-lethal concentration but causing negative effect on reproductive performance of rotifer Brachionus plicatilis) on the removal of harmful alga Phaeocystis globosa population by rotifer B. plicatilis under warming condition. Results showed that there was an interaction between temperature and cadmium on rotifers eliminating P. globosa population. Warming accelerated the removal of P. globosa population by rotifers under cadmium free and low cadmium conditions. Although the concentration of cadmium used was not lethal but reduced reproductive performance, it prevented rotifers from completely eliminating P. globosa population, indicating that cadmium had a significantly greater negative impact on rotifer population than on life history traits. The environmentally relevant concentration of cadmium delayed the removal of P. globosa population by rotifers at normal temperature, but this delay effect did not occur under high temperature conditions, indicating that warming completely masked the negative effects of environmentally relevant concentration of cadmium on rotifers eliminating P. globosa. The findings suggested that dual stress of warming and heavy metal pollution comprehensively impacted the top-down effect of zooplankton on algae, which may result in a substantial consequence on the population dynamics and energy flow between primary producers and primary consumers.

Response of life-history traits, population dynamics, offspring size of Brachionus plicatilis exposure to BTBPE

The novel brominated flame retardant 1, 2-bis (2,4,6 tribromophenoxy) ethane (BTBPE) has been widely used since the mid-1970s and detected in the aquatic environment and organisms; however, little information is available regarding its biotoxicity. In this study, the life-history parameters, transcriptomic regulation, multi-generational offspring size, and population dynamics of rotifers were determined in response to BTBPE (0, 0.01, 1, and 100 μg/L). The results showed that BTBPE (>1 μg/L) significantly increased the pre-reproductive time, shortened both reproduction periods and the lifespan, and decreased the total number of rotifer offspring. Transcriptomic analysis revealed that the expression of key genes involved in the pathways of citrate cycle, 2-oxocarboxylic acid metabolism, carbon metabolism, and propanoate metabolism was affected. Moreover, BTBPE has transgenerational effects on rotifers, the size of the F1 to F5 generations decreased significantly in response to BTBPE. Finally, the population density in the 100 μg/L BTBPE treatment group was significantly reduced by 30 % compared to the control group, suggesting that the population growth of rotifers was inhibited by BTBPE exposure. The findings of this study indicate that BTBPE has effects on the individual reproduction, population growth, offspring quality, and energy metabolism of rotifers. These findings highlighted the potential impacts of BTBPE on dominant zooplankton species, providing useful baseline information for evaluating the potential ecological risk of novel brominated flame retardant.

The comprehensive effects of varied photoperiods and algal abundance fluctuations on the key life history parameters of herbivorous rotifer Brachionus plicatilis

The variation of photoperiod affects the photosynthesis of primary producer algae in the ocean, leading to fluctuations in algal abundance. The changes in photoperiod and algal abundance may have complex integrated effects on primary consumer herbivorous zooplankton. Therefore, in this study, we exposed two clones of rotifer Brachionus plicatilis to the combinations of five photoperiods (0 L: 24 D, 6 L: 18 D, 14 L: 10 D, 18 L: 6 D, and 24 L: 0 D) and three algal abundances (3 × 104, 10 × 104, and 100 × 104 cells mL-1) and recorded the key life history traits. Results showed that the two clones of rotifer B. plicatilis had similar responses to the combinations of photoperiod and algal abundance. Reduced algal abundance delayed development and impaired fecundity, but prolonged survival time. Algal abundance fluctuations affected the resource allocation patterns of rotifers. Short photoperiods had a tendency to reduce the life span of rotifers. There was a significant interaction between photoperiod and algal abundance on the key life history parameters of rotifers. As algal abundance decreased, extreme photoperiods delayed the sexual maturity time of rotifers. Low algal abundance exacerbated the negative effects of light deficiency on rotifers, while high algal abundance alleviated the effects of the extreme photoperiod. Such findings are of great significance for understanding the effects of food fluctuations on the structural stability of the bottom food chain in aquatic ecosystems under the variation of photoperiod with different latitudes and seasons.

Transcriptome analysis reveals the different toxic mechanism of three HBCD diastereoisomers to Brachionus plicatilis based on chemical defensome

The emerging contaminants hexabromocyclododecanes (HBCDs) are proved to exhibit highly reproductive toxicity to marine rotifer Brachionus plicatilis, but how about the toxic differentiation among three diastereoisomers of HBCD, and what's the possible hidden mechanism? B. plicatilis was exposed to different concentrations of HBCD diastereoisomers, and the results showed that α-, β- and γ-HBCD exhibited various toxicity on it, the adverse effects on individual life history traits included shortened lifespan, shortened body length and reduced offspring number. Population dynamics analysis showed that the maximum population density and time to reach it were also significantly influenced. The integrated biomarker responses (IBR) were constructed based on key life history traits and population dynamics indicators, and the comprehensive toxicity ranking of HBCD diastereoisomers was β-HBCD> α-HBCD> γ-HBCD, which was consistent with acute experimental results. Results of transcriptome with emphasis on chemical defensome was conducted. Genes including cytochrome P450 enzymes (CYP450s), aldehyde dehydrogenases (ALDHs), glutathione S-transferases (GSTs) and SOD were upregulated under γ-HBCD compared to those under α- and β-HBCD. Results of molecular docking suggested γ-HBCD had stronger affinity with aryl hydrocarbon receptor (AhR) that made it more easily activate the subsequent components of the defending pathway. Moreover, transcriptome result showed the level of autophagy, the newly found protective pathway in B. plicatilis was higher under α- and β-HBCD than that under γ-HBCD and the TEM observation result provided the consist directly proof. The chemical defensome and the subsequently autophagy seemed to be the hidden mechanism for the toxicity differentiation of the HBCD diastereoisomers.

Toxicity and intergenerational accumulation effect of tire wear particles and their leachate on Brachionus plicatilis

Tire wear particles (TWP) are one of the main sources of microplastic (MP) pollution in the marine environment, causing adverse effects on marine life and attracting increasing attention. This study aimed to investigate the chemical composition of TWP (particles and leachate) and their toxic effects on Brachionus plicatilis. The results showed that Zn and acenaphthene were the most frequently detected compounds in the three TWP treatments. In the single-generation exposure experiment, TWP leachate showed the highest toxicity potential, followed by nano-TWP (<1 μm) and micro-TWP (1-20 μm). Both nano-TWP and leachate had negative effects on the lifespan and population of rotifers. High-concentration TWP leachate significantly shortened the reproductive period of rotifers, slowed down their swimming speed, and reduced the number of offspring. These negative effects were mainly attributed to the toxic mixture of nano-TWP with additives in the leachate. Furthermore, in multi-generation exposure experiments, the toxicity pattern showed a new trend: the toxicity of nano-TWP exceeded that of the leachate, while micro-TWP continued to maintain the lowest toxicity level. Continuous exposure to TWP exerted a significant negative impact on rotifer lifespan, and this effect increases cumulatively between generations. Notably, TWP was trans-generationally toxic to the lifespan of rotifers, and repeated exposure was more toxic than maternal exposure and continuous exposure. In addition, rotifers can ingest and accumulate TWP, and maternal transfer was another uptake pathway of TWP in rotifer offspring. This finding provided a new perspective for understanding the transmission mechanism of TWP in the marine food chain.

Combined toxic effects of yessotoxin and polystyrene on the survival, reproduction, and population growth of rotifer Brachionus plicatilis at different temperatures

Yessotoxin (YTX) is a disulfated toxin produced by harmful dinoflagellates and causes risks to aquatic animals. Polystyrene (PS) microplastics could absorb toxins in seawaters but pose threats to organism growth. In this study, the combined toxic effects of YTX (0, 20, 50, and 100 µg L-1) and PS (0, 5, and 10 µg mL-1) on the survival, reproduction, and population growth of marine rotifer Brachionus plicatilis at 20 °C, 25 °C, and 30 °C were evaluated. Results indicated that the survival time (S), time to first batch of eggs (Ft), total offspring per rotifer (Ot), generational time (T0), net reproduction rate (R0), intrinsic growth rate (rm), and population growth rate (r) of rotifers were inhibited by YTX and PS at 25 °C and 30 °C. Low temperature (20 °C) improved the life-table parameters T0, R0, and rm at YTX concentrations less than 100 µg L-1. Temperature, YTX, and PS had interactive effects on rotifers' S, Ft, Ot, T0, R0, rm, and r. The combined negative effects of YTX and PS on rotifers' survival, reproduction, and population growth were significantly enhanced at 30 °C. These findings emphasized the importance of environmental temperature in studying the interactive effects of microplastics and toxins on the population growth of zooplankton in eutrophic seawaters.

Multigenerational analysis of reproductive timing and life cycle parameters in the marine rotifer Brachionus plicatilis

Reproductive timing in organisms can influence reproductive success and longevity, yet its long-term effects remain underexplored. This study monitored the first- and last-born offspring of Brachionus plicatilis across five generations to examine the impact of breeding timing on fertility and longevity. The last-born group produced more offspring in the F1 and F2 generations. However, the first-born group produced more offspring from the F3 generation onward, with statistically significant differences observed in the F4 generation. Survival analysis indicated no differences up to the F3 generation. However, the post-reproductive period was significantly shorter in the last group compared to the first group in the F3 and F4 generations. These findings suggest that delayed breeding timing cumulatively reduces reproductive output and lifespan, though recovery may occur in the F5 generation. This study provides valuable insights into the generational effects of breeding timing and may inform reproductive strategies in similar species.

Emerging threat of marine microplastics: Cigarette butt contamination on Yellow Sea beaches and the potential toxicity risks to rotifer growth and reproduction

Cigarette butts have become one of the most common and persistent forms of debris in marine coastal areas, where they pose significant toxicity risks. This study investigated cigarette butt pollution along beaches of the Yellow Sea and used laboratory experiments to assess the toxicity of their leachate and fibers on the euryhaline rotifer Brachionus plicatilis. A pollution index confirmed pollution by this debris across all eight beaches surveyed, where the density of cigarette butts averaged 0.23 butts/m2. In controlled laboratory experiments, both the fibers and leachates from cigarette butts exhibited negative impacts on the development, reproduction, and population growth of rotifers. Unique abnormalities observed under different exposure treatments indicated toxicity specific to certain chemicals and particles. Continuous exposure to cigarette butts initially reduced rotifer fecundity, but this effect diminished over successive generations. However, the exposure induced transgenerational reproductive toxicity in the rotifers. Adaptive responses in rotifers after repeated exposure led to relative reduction in reproductive inhibition in the F3 and F4 generations. Furthermore, rotifers were capable of ingesting and accumulating cigarette butts, and maternal transfer emerged as an alternative pathway for uptake of this material in the offspring. These results increase our understanding of the ecological risks posed by cigarette butts in aquatic environments.

Reproductive toxicity of hexabromocyclododecane in rotifer Brachionus plicatilis: Involvement of reactive oxygen species and calcium signaling pathways

To assess the toxicity of Hexabromocyclododecane (HBCD), the population, individual, and cellular biochemical parameters of the rotifer Brachionus plicatilis exposed to different concentrations of HBCD were investigated. The results showed that the population growth rate, reproductive period, and offspring number in B. plicatilis significantly decreased under 324 μg/L and 648 μg/L HBCD. Antioxidant enzyme activity and mRNA expression of CAT and Mn-SOD were promoted at low concentrations (32 μg/L and 64 μg/L) and inhibited at high concentrations (324 μg/L and 648 μg/L), while MDA content accumulated continuously with increasing HBCD concentrations, indicating that HBCD induced oxidation imbalance in rotifers. Further evidence was provided by the correlation between DNA fragmentation and physiological changes. The increased intercellular concentration of Ca2+ and the expression of CaM mRNA suggested that HBCD activated pathways related to calcium signaling. In summary, the excessive production of ROS induced by HBCD was considered to be the main cause of reproductive toxicity.

Effects of bisphenol A on reproduction, oxidative stress, and lipid regulation in the marine rotifer Brachionus plicatilis

This study reports the effects of bisphenol A (BPA) on the rotifer Brachionus plicatilis, focusing on growth performance, reproductive output, oxidative stress responses, and lipid metabolism genes. High BPA levels disrupted peak daily offspring production and led to oxidative stress and increased superoxide dismutase and catalase activity. The research identified distinctive monoacylglycerol O-acyltransferase (MGAT) and diacylglycerol O-acyltransferase (DGAT) genes in B. plicatilis, B. rotundiformis, and B. koreanus, enhancing understanding of lipid metabolism in these species. BPA exposure significantly altered MGAT and DGAT expression, and feeding status affected these regulatory patterns. When food was unavailable, BPA reduced DGAT2 and MGAT2a expression. However, under feeding conditions, DGAT2 and MGAT1 levels increased, indicating that nutritional status and BPA exposure interact to affect gene expression.

The impact of artificial light pollution at night on the life history parameters of rotifer Brachionus plicatilis with different food experiences

Artificial light at night (ALAN) may pose threat to rotifer Brachionus plicatilis. Additionally, the food of rotifer, i.e. algal community composition, often fluctuates. Thus, we selected five wavelengths of ALAN (purple, blue, green, red, white) and a three-colored light flashing mode (3-Flash) to test their impacts on life history traits of B. plicatilis with different food experiences, including those feeding Chlorella vulgaris (RC) or Phaeocystis globosa (RP). Results indicated purple ALAN promoted RC development, white ALAN inhibited RC development, while 3-Flash and white ALAN promoted RP development. Under red and white ALAN, RP increased fecundity but decreased lifespan. High-quality food enhanced rotifer's resistance to the impact of ALAN on lifespan. ALAN and food experience interacted on B. plicatilis. The effect of blue ALAN has less negative effects on B. plicatilis, based on hierarchical cluster analysis. Such findings are helpful to evaluate the potential impact of ALAN on marine zooplankton.

Changes in life history parameters and expression of key genes of Brachionus plicatilis exposed to a combination of organic and inorganic ultraviolet filters

The increasing use of ultraviolet filters has become an emerging contaminant on the coast, posing potential ecological risks. Rotifers are essential components of marine ecosystems, serving as an association between primary producers and higher-level consumers. These organisms frequently encounter ultraviolet filters in coastal waters. This study aimed to assess the comprehensive effects of organic ultraviolet filters, specifically 2-ethylhexyl-4-methoxycinnamate (EHMC), and inorganic ultraviolet filters, namely, titanium dioxide nanoparticles (TiO2 NPs), on the rotifer Brachionus plicatilis. We exposed B. plicatilis to multiple combinations of different concentrations of EHMC and TiO2 NPs to observe changes in life history parameters and the expression of genes related to reproduction and antioxidant responses. Our findings indicated that increased EHMC concentrations significantly delayed the age at first reproduction, reduced the total offspring, and led to considerable alterations in the expression of genes associated with reproduction and stress. Exposure to TiO2 NPs resulted in earlier reproduction and decreased total offspring, although these changes were not synchronised in gene expression. The two ultraviolet filters had a significant interaction on the age at first reproduction and the total offspring of rotifer, with these interactions extending to the first generation. This research offers new insights into the comprehensive effects of different types of ultraviolet filters on rotifers by examining life history parameters and gene expression related to reproduction and stress, highlighting the importance of understanding the impacts of sunscreen products on zooplankton health.

Single and combined effects of increased temperature and methylmercury on different stages of the marine rotifer Brachionus plicatilis

Rapid, anthropogenic activity-induced global warming is a severe problem that not only raises water temperatures but also shifts aquatic environments by increasing the bioavailability of heavy metals (HMs), with potentially complicated effects on aquatic organisms, including small aquatic invertebrates. For this paper, we investigated the combined effects of temperature (23 and 28 °C) and methylmercury (MeHg) by measuring physiological changes, bioaccumulation, oxidative stress, antioxidants, and the mitogen-activated protein kinase signaling pathway in the marine rotifer Brachionus plicatilis. High temperature and MeHg adversely affected the survival rate, lifespan, and population of rotifers, and bioaccumulation, oxidative stress, and biochemical reactions depended on the developmental stage, with neonates showing higher susceptibility than adults. These findings demonstrate that increased temperature enhances potentially toxic effects from MeHg, and susceptibility differs with the developmental stage. This study provides a comprehensive understanding of the combined effects of elevated temperature and MeHg on rotifers. ENVIRONMENTAL IMPLICATION: Methylmercury (MeHg) is a widespread and harmful heavy metal that can induce lethal effects on aquatic organisms in even trace amounts. The toxicity of metals can vary depending on various environmental conditions. In particular, rising temperatures are considered a major factor affecting bioavailability and toxicity by changing the sensitivity of organisms. However, there are few studies on the combinational effects of high temperatures and MeHg on aquatic animals, especially invertebrates. Our research would contribute to understanding the actual responses of aquatic organisms to complex aquatic environments.

Hexabromocyclododecane-induced reproductive toxicity in Brachionus plicatilis: Impacts and assessment

Hexabromocyclododecane (HBCD), third-generation brominated flame retardants (BRFs), has aroused worldwide concern because of its wide application and potentially negative impacts on marine ecosystems, but an information gap still exists regarding marine low-trophic organisms. Brachionus plicatilis, the model marine zooplankton, was used in the present study, and its reproductive responses were used as the endpoint to indicate HBCD-induced toxicity. HBCD was suggested to be extremely highly toxic compounds regarding the 96 h-LC50 of 0.58 mg L-1. The sublethal exposure of HBCD injured the reproduction of B. plicatilis: The total number of offspring per female and the key population index calculated from the life table, including the intrinsic rate of population increase (rm) and net reproductive rate (R0), were significantly influenced in a concentration-dependent manner. The reproductive process was also altered, as indicated by the first spawning time, first hatching time and oocyst development time. At the same time, individual survival and growth (body length) were also negatively affected by HBCD. Reactive oxygen species (ROS) were suggested to be responsible for reproductive toxicity mainly because the total ROS contents as well as the main components of •OH and H2O2 greatly increased and resulted in the oxidative imbalance that presented as malondialdehyde (MDA) elevation. Simultaneous activation of the glutathione antioxidant system was accompanied by the apoptosis marker enzymes Caspase-3 and 9, as well as the correlation between ROS content, physiological alteration and cell apoptosis, providing further evidence for this. The integrated biomarker response (IBR) and adverse outcome pathway (AOP) showed that HBCD had a significant toxic effect on B. plicatilis near the concentration range of 96 h-LC50. The establishment of this concentration range will provide a reliable reference for future environmental concentration warning of HBCD in marine.

Changes in transcriptome regulations of a marine rotifer Brachionus plicatilis under methylmercury stress

Mercury (Hg), a heavy metal pollutant worldwide, can be transformed into methylmercury (MeHg) by various aquatic microorganisms in water, thus accumulating along the aquatic food chain and posing a particular challenge to human health. Zooplankton plays a crucial role in aquatic ecosystems and serves as a major component of the food chain. To evaluate the effects of MeHg on the rotifer Brachionus plicatilis and reveal the underlying mechanism of these effects, we exposed B. plicatilis to MeHg by either direct immersion or by feeding with MeHg-poisoned Chlorella pyrenoidesa, respectively, and conducted a transcriptomic analysis. The results showed that B. plicatilis directly exposed to MeHg by immersion showed significant enrichment of the glutathione metabolism pathway for detoxification of MeHg. In addition, the exposure to MeHg by feeding induced a significant enrichment of lysosome and notch signaling pathways of rotifers, supporting the hypothesis that MeHg can induce autophagy dysfunction in cells and disturb the nervous system of rotifers. In two different routes of MeHg exposure, the pathway of cytochrome P450 in rotifers showed significant enrichment for resisting MeHg toxicity. Our results suggest further studies on the potential mechanism and biological responses of MeHg toxicity in other links of the aquatic food chain.

Salinity-dependent top-down effect of rotifer Brachionus plicatilis on removing harmful alga Phaeocystis globosa

Using appropriate zooplankton to transfer the primary productivity of harmful algae to higher trophic levels through food chain is an eco-friendly mode to remove harmful algae. To assess the top-down efficiency of rotifer removing Phaeocystis and the salinity effect, we adopted a series of salinities to carry out Phaeocystis-rotifer population dynamics and rotifer life-history experiments. Results showed that the time for rotifers to remove Phaeocystis population was the shortest when the salinity was ≤20 ‰. With salinity rising to above 25 ‰, although the clearance time of Phaeocystis population by rotifer was significantly prolonged, ultimately the Phaeocystis population were almost completely eliminated at all salinities. Additionally, rotifer matured and reproduced earlier at low salinity, while high salinity significantly delayed first reproductive time and decreased the total offspring. The above findings are helpful to assess the impacts of external environmental factors on the application of zooplankton to control harmful algae.

Variations in life history parameters, population dynamics, and transcriptome regulation of Brachionus plicatilis exposed to triclosan

Triclosan (TCS) poses an ecological health risk due to its lipophilic nature, long half-life, and bioconcentration. To evaluate the toxicity of TCS on aquatic organisms, the life history parameters, population dynamics, and transcriptome regulation of Brachionus plicatilis exposed to TCS were investigated. In this study, the fecundity of rotifers was promoted by 25 μg/L of TCS and inhibited by higher concentrations (100 μg/L, 200 μg/L). The reproductive period of rotifers was shortened by 46.24 % but the post-reproductive period was prolonged by 176.47 % in 200 μg/L TCS. Both population growth and life table parameters indicated that a high concentration of TCS (200 μg/L) had negative impacts on population growth. Transcriptomic analysis showed that the effects of TCS on the life history parameters and population dynamics of rotifers were determined by regulating the expression of functional genes in cilium organization and cilium assembly and involved in pathways of focal adhesion.