Using Proales similis (Rotifera) for toxicity assessment in marine waters

Abstract

There is a need to develop more animal species for assessing toxicity in marine environments. Cyst‐based toxicity tests using invertebrates are especially fast, technically simple, cost‐effective, and sensitive to a variety of toxicants. Over the past 30 years, a variety of toxicity endpoints have been measured using the marine rotifer Brachionus plicatilis hatched from cysts, including mortality, reproduction, ingestion, swimming, enzyme activity, and gene expression. A consensus has developed that the most ecologically relevant toxicity measurements should be made using more than one species. Furthermore, it has been noted that the rotifer species toxicant sensitivity distribution is much broader than which endpoint is measured. This implies that toxicity should be measured with the simplest, fastest, least expensive test available on as many species as feasible. If a battery of test species is to be used to estimate toxicity, diapause egg‐based toxicity tests that do not require culturing of test animals will be key. In this paper, we describe how diapause eggs of a new marine rotifer, Proales similis, can be produced, stored and hatched under controlled conditions to produce animals for toxicity tests. Methods are described for quantifying the toxicity of copper, mercury and cadmium based on mortality, ingestion, reproduction, and diapause egg hatching endpoints. We found that reproduction and ingestion endpoints were generally more sensitive to the metals than mortality or diapause egg hatching. When the copper sensitivity of P. similis was compared to Brachionus manjavacas and B. plicatilis using an ingestion test, similar EC50s were observed. In contrast, the B. rotundiformis ingestion EC50 for copper was about 4× more sensitive. Although diapause egg hatching was not the most sensitive endpoint, it is the most ecologically relevant for assessing sediment toxicity. Our discovery of diapausing eggs in the P. similis life cycle has created a conundrum. We have not observed males or sex in P. similis populations, which is a direct contradiction to the orthodox view of the monogonont rotifer life cycle. Work is needed to clarify how diapause egg production is accomplished by P. similis and whether sexual reproduction is involved.

Complete mitochondrial genome of the marine monogonont rotifer Proales similis (Rotifera, Proalidae)

“…salinity, microalgal density) (Rebolledo et al 2018) and larviculure (Hagiwara and Marcial 2019). Among many rotifers, P. similis establishes yet another potential model for toxicity assessment of marine waters (Snell et al 2019), implying that this species is useful for aquaculture and ecotoxicology. The sequence analysis of P. similis mitochondrial genome is also important to identify field-sampled and laboratory stocks.…”

Trait-Based Research on Rotifera: The Holy Grail or Just Messy?

“…Trait-based ecology advances our understanding of ecological dynamics in a rapidly changing, human-influenced world [85] and is mentioned among the five future challenges for plankton diversity [86]. Several topics may be studied by trait-based analysis such as (1) trophic mismatch [87], (2) natural [88] and artificial [89] stresses from acids, (3) changes in salinity [90,91], (4) experimental studies of effects of heavy metals [92] and organics [93,94], (5) effects of ingesting nanoparticle microplastic pollutants [95,96], (6) combinatorial effects [97][98][99], and (7) functional homogenization [95]. We hope that our assembled trait matrix paves the way for more research on rotifer functional diversity, diminishes the misclassification of rotifer genera into trait categories, and enables studies across trophic levels.…”

Key to sessile gnesiotrochan rotifers: Families, monospecific species in Flosculariidae, species of Atrochidae, Conochilidae, and Limnias

“…They are used in aquaculture as food for commercially important target species, including crabs, shrimps, and fishes (Lubzens et al 1989;Turgay et al 2020). Certain rotifers are employed as models in aging studies (Gribble & Mark Welch 2017;Gribble & Snell 2018) and toxicology assessments of various chemicals (Park et al 2022;Shin et al 2022;Snell et al 2019). Regardless of the type of research, it is critical that workers correctly identify the species that they are studying.…”