Effect of alternative natural diet on microplastic ingestion, functional responses and trophic transfer in a tri-trophic coastal pelagic food web.

The patchy distribution of microplastics (MP) and their size range similar to planktonic organisms, are likely to have major ecological consequences, through MP ingestion, food dilution, and transfer across trophic levels. Our study applied a community module using tritrophic food chain with zooplankton as prey, and a planktivorous seabass fry as predator. We conducted a series of feeding experiments and recorded the direct uptake of MP under six different concentrations ranging from 25 to 800 particles L-1. We also estimated the indirect transfer of MP via trophic link. The ingestion rates for Brachionus plicatilis, Mesocyclops isabellae, and Lates calcarifer, were 3.7 ± 0.3 MP ind-1 min-1, 1.69 ± 0.1 MP ind-1 min-1, and 3.51 ± 0.52 MP ind-1 h-1, respectively. In the presence of a natural diet, rotifers and copepods ingested significantly lower number, whereas, fish fry ingested a higher number of MP, suggesting further vulnerability to the consumers of MP-contaminated fish and potential biomagnification at higher trophic levels. Overall, the MP uptake rate increased with increasing concentration, and finally leveled off, indicating a type II functional response to MP concentration. The presence of natural diet led to a lower Km value. In the indirect transfer experiment, 74 % of B. plicatilis and 78 % of M. isabellae individuals were contaminated with MP, when offered as prey. Brachionid mastax and MP particles were observed in the gut of copepods. The fish fry gut content also recorded brachionid mastax, MP-contaminated copepods, and MP particles, showing direct evidence of trophic transfer pointing to a cascading effect on higher trophic levels including humans via piscivory.

Multigenerational resilience of the marine rotifer Brachionus plicatilis to high temperature after additive exposure to high salinity and nanoplastics.

To study multigenerational resilience to high temperature (HT) conditions, we exposed Brachionus plicatilis marine rotifers to HT, high salinity (HS), and nanoplastics (NPs), and measured reproductive and life-cycle endpoints. After exposure to HT, rotifer lifespans were reduced, but daily production of offspring increased. However, both combined HT/HS and HT/HS/NP exposure led to additional decreases in longevity and reproductive ability; the antioxidant defense mechanisms of the rotifers were also notably upregulated as measured by reactive oxygen species levels. Fatty-acid profiles were reduced in all conditions. In multigenerational experiments, the negative effects of HT dissipated rapidly; however, the effects of HT/HS and HT/HS/NPs required four generations to disappear completely. The findings indicated that B. plicatilis were able to recover from these environmental stressors. This study demonstrated the resilience of aquatic organisms in response to changing environmental conditions and provides insights into the complex interactions of different abiotic stressors.

Ultrastructure and function of the mastax in Dicranophorus forcipatus (Rotifera: Monogononta).

Rotifers are characterized by a complex set of cuticularized jaw elements in the pharynx. The fine structure of the jaw elements has been the subject of SEM studies for some time, but only very limited information exists on the ultrastructure of the jaw elements and their function beyond taxonomic considerations. Drawing on SEM and TEM techniques, the present study presents a detailed analysis of the mastax in Dicranophorus forcipatus, a carnivorous monogonont rotifer species from freshwater habitats characterized by an extrusible, grasping jaw apparatus. Based on ultrathin serial sections, the jaw elements are reconstructed and, in total, nine paired and two unpaired muscles identified. Possibly homologous muscles in other rotifer species are discussed and functional considerations of the forcipate mastax are suggested.

Performance of Debaryomyces hansenii as a Diet for Rotifers for Feeding Zebrafish Larvae.

The zebrafish larval stage is a critical moment due to high mortality rates associated with inadequate supplies of nutritional requirements. Larval feeding has important challenges associated with such factors as small mouth gape (≈100 µm), the low activity of digestive enzymes, and the intake of live food. A common zebrafish live food at the onset of exogenous feeding is rotifers, mainly Brachionus plicatilis. These rotifers should be fed with other microorganisms such as microalgae or yeast, mostly from the Saccharomyces genus. In the laboratory, the culture of microalgae is more expensive than the culture of yeast. The aim of this study was to evaluate the performance of Debaryomyces hansenii as a diet for rotifers in comparison to a microalgae-based diet (Rotigrow®). To achieve this aim, we assessed the rotifer total protein content, the rotifers fatty acid profile, zebrafish larval growth performance, the expression of key growth, and endocrine appetite regulation genes. The total protein and fatty acids content were similar in both rotifer cultures, averaging 35% of dry matter (DM) and 18% of DM, respectively. Interestingly, the fatty acids profile showed differences between the two rotifer cultures: omega-3 fatty acids were only observed in the Microalgae/rotifer, whereas, omega-6 fatty acids presented similar levels in both rotifer cultures. No differences were observed in the larval body length distribution or mortalities between the rotifer cultures. However, gh, igf-1, and cck gene expression showed significantly higher upregulation in zebrafish fed the Microalgae/rotifer diet compared with those fed the Debaryomyces/rotifer diet. In conclusion, D. hansenii could be an alternative diet for rotifer used as a live food in zebrafish larvae at the onset of exogenous feeding. The gene responses observed in this work open up the opportunity to study the effect of omega-3 supply on growth regulation in zebrafish.

Do Species Exist in Asexuals? Theory and Evidence from Bdelloid Rotifers.

The possibility for independently evolving entities to form and persist in the absence of sexual recombination in eukaryotes has been questioned; nevertheless, there are organisms that are known to be asexual and that have apparently diversified into multiple species as recognized by taxonomists. These organisms have therefore been identified as an evolutionary paradox. We explore three alternative hypotheses attempting to solve the apparent paradox, focusing on bdelloid rotifers, the most studied group of organisms in which all species are considered asexual: (1) they may have some hidden form of sex; (2) species do not represent biological entities but simply convenient names; and (3) sex may not be a necessary requirement for speciation. We provide ample evidence against the first two hypotheses, reporting several studies supporting (1) bdelloids asexuality from different approaches, and (2) the existence of species from genetics, jaw morphology, ecology, and physiology. Thus, we (3) explore the role of sex in speciation comparing bdelloid and monogonont rotifers, and conclude with some caveats that could still change our understanding of bdelloid species.

Soft Bodies, Hard Jaws: An Introduction to the Symposium, with Rotifers as Models of Jaw Diversity.

Jaws have evolved numerous times in the animal kingdom and they display a wide variety of structural, compositional, and functional characteristics that reflect their polyphyletic origins. Among soft-bodied invertebrates, jaws are known from annelids, chaetognaths, flatworms, gnathostomulids, micrognathozoans, mollusks, rotifers, and several ecdysozoans. Depending on the taxon, jaws may function in the capture of prey (e.g., chaetognaths and flatworms), processing of prey (e.g., gnathostomulids and onychophorans), or both (e.g., rotifers). Although structural diversity among invertebrates' jaws is becoming better characterized with the use of electron microscopy, many details remain poorly described, including neuromuscular control, elemental composition, and physical characteristics, such as hardness and resistance to wear. Unfortunately, absence of relevant data has impeded understanding of their functional diversity and evolutionary origins. With this symposium, we bring together researchers of disparately jawed taxa to draw structural and mechanistic comparisons among species to determine their commonalities. Additionally, we show that rotifers' jaws, which are perhaps the best-characterized jaws among invertebrates, are still enigmatic with regard to their origins and mechanics. Nevertheless, technologies such as energy dispersive X-ray spectroscopy (EDX) and 3D modeling are being used to characterize their chemical composition and to develop physical models that allow exploration of their mechanical properties, respectively. We predict that these methods can also be used to develop biomimetic and bioinspired constructs based on the full range of the complexity of jaws, and that such constructs also can be developed from other invertebrate taxa. These approaches may also shed light on common developmental and physiological processes that facilitate the evolution of invertebrates' jaws.

Sludge reduction potential of metazoa in membrane bioreactors.

In order to check the sludge reduction capacity of metazoa in a membrane bioreactor (MBR), pilot-scale studies were conducted. Three MBRs had been set in a wastewater treatment plant at Tokyo, Japan and they were receiving real wastewater. Initially pH inside the three MBRs was controlled as pH 7, 6 and 5 respectively. Then metazoa population was monitored along with MLSS change. It was found that the presence or absence of the metazoa population did not have any significant effect on the increasing pattern of MLSS. In the MBR with pH 6 highest accumulation of sludge was observed though a high and steady level of metazoa (1,000-2,000 per ml) was present there. But in this MBR a lot of metazoa attached in the membrane was also observed and here the increase in transmembrane pressure was less than in the other two. So, metazoa population especially the attached one in the membrane plays an effective role in fouling control of the membrane. Presence of attached media may provide a suitable niche for metazoa in the process. So, attached media known as DB lace was also inserted in MBRs for testing its capacity along with inoculum of oligochaete worms. Accumulation of sludge was not satisfactory in the attached string and it seems that inoculated worm could not adjust to the environment as they were not sludge originated. So, in the next experimental stage, attached media was inserted in the form of a bundle and this time no inoculation of worm was used. A steady metazoa population was observed in the system but the accumulation of sludge in the attached media was the same as before.

Carnivorous planktonic Difflugia (Protista, Amoebina Testacea) and their predators.

Four planktonic species of Difflugia co-occurring in a south Chinese reservoir were found to be carnivorous, but the diet was widest in the largest species (D. tuberspinifera) and narrowest in the smallest (D. hydrostatica). It included rotifers, ciliates, dinoflagellates, floating eggs, and small particles associated with organic debris. Scavenging and cannibalism were also observed. Species with a collared test (D. biwae, D. mulanensis) showed a form of suction-feeding, while species with teeth on the pseudostome used these, together with their pseudopods, as "inverted crown corks", providing leverage for opening the lorica of their (rotifer) prey. Predators of Difflugia included cyclopoid copepods. In addition, the rotifers Asplanchna priodonta, Ploesoma hudsoni and, occasionally, big ciliates (Stentor sp.) all ingested their prey as a whole.

Microgravity and hypergravity effect on survival and reproduction of microinvertebrates.

Preliminary to carry out long-term experiments on the International Space Station (ISS) using living orgainisms, the capacity of the experimental organisms to cope with perturbations of gravity should be tested. Actually, animals have evolved under gravity, because on earth gravity force cannot be eluded, and several features that influence life-history traits may be affected by the presence of gravity. Among the other features, feeding efficiency may be affected by gravity if the animals feed by filtering suspended particles, creating currents that carry the particulate food to their mouth opening. In presence of gravity the food particles tend to sink to the bottom and filter-feeders must be able to suspend and collect the particles with some apparatus such as ciliary wreaths. It can be predicted that hypergravity, increasing the particle sedimentation rate, will reduce the animal filtering efficiency, while microgravity will increase filtering rate. Differently, some bacteriophagous animals do not possess structures to collect their food, but commonly live and move into sediment and feed on the bacteria upon encounter. Hypergravity will apply higher pressure on their bodies, and could force them to adhere to some surface and to reduce their displacement, and microgravity could impede adhesion to the surface and make food item encounters improbable. Thus, gravity perturbations may affect animal life-history traits, such as survival or fecundity, by influencing their feeding efficiency. In this study we exposed a filter-feeding organism (Macrotrachela quadricornifera, Rotifera Bdelloidea) and a bacteriophagous one (Panagrolaimus rigidus, Nematoda) to both microgravity and hypergravity to test their reproduction capacity under such stressful conditions, and their suitability as models for experiments on the ISS.