Effect of diflubenzuron on the maturation and reproductive success of the copepod Eurytemora affinis

Susceptibility of the Non-Targeted Crustacean Eurytemora affinis to the Endocrine Disruptor Tebufenozide: A Transcriptomic Approach

Copepods are zooplanktonic crustaceans ubiquitously widespread in aquatic systems. Although they are not the target, copepods are exposed to a wide variety of pollutants such as insect growth regulators (IGRs). The aim of this study was to investigate the molecular response of a non-targeted organism, the copepod Eurytemora affinis, to an IGR. Adult males and females were exposed to two sub-lethal concentrations of tebufenozide (TEB). Our results indicate a sex-specific response with a higher sensitivity in males, potentially due to a differential activation of stress response pathways. In both sexes, exposure to TEB triggered similar pathways to those found in targeted species by modulating the transcription of early and late ecdysone responsive genes. Among them were genes involved in cuticle metabolism, muscle contraction, neurotransmission, and gametogenesis, whose mis-regulation could lead to moult, locomotor, and reproductive impairments. Furthermore, genes involved in epigenetic processes were found in both sexes, which highlights the potential impact of exposure to TEB on future generations. This work allows identification of (i) potential biomarkers of ecdysone agonists and (ii) further assessment of putative physiological responses to characterize the effects of TEB at higher biological levels. The present study reinforces the suitability of using E. affinis as an ecotoxicological model.

RNA-Seq-based transcriptome profiling and expression of 16 cytochrome P450 genes in the benzo[α]pyrene-exposed estuarine copepod Eurytemora affinis

The calanoid copepod Eurytemora affinis is one of the most abundant estuarine species and is considered to be an ideal candidate species for ecotoxicological research. An RNA-Seq-based transcriptome was developed from whole bodies of this species. Among 142,442 contigs of the de novo assembly by Trinity, 48,480 open reading frame (ORF) contigs were found using TransDecoder. A total of 17,762 genes were identified by BLAST analysis, which covers about 75% of the annotated genes in the E. affinis genome. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that most annotated sequences were related to metabolism pathways, including xenobiotic biodegradation. Using transcriptome data, we identified putative transcripts related to xenobiotic processing genes including phase I enzymes, phase II enzymes, transporters, and transcription factors. To understand the CYP-mediated detoxification metabolism of xenobiotics, we measured the transcriptional levels of 16 CYPs (within full sequences) of E. affinis in response to benzo[α]pyrene (B[α]P). Most Ea-CYP genes were significantly down- and/or up-regulated (P < 0.05) in response to B[α]P, suggesting that Ea-CYP genes are likely involved in detoxification (mainly in biotransformation of xenobiotics) with particular genes, demonstrating significant upregulation or downregulation compared to others, as shown in other copepod model species (e.g. Tigriopus japonicus and Paracyclopina nana). This study will provide insight into the potential role of E. affinis in response to various toxic or xenobiotic chemicals in the marine environment.

Heavy metal exposure reduces hatching success of Acartia pacifica resting eggs in the sediment

The potential effects of three heavy metals (Cu, Pb, and Cd) on hatching success of Acartia pacifica resting eggs in the sediment of Xiamen Bay were experimentally investigated. The number ofA. pacifica nauplii hatched from the sediment sharply decreased with the increase of metal concentration and exposure time from 3 to 30 d. An increase of the Cu concentration from 34.8 to 348 mg/kg, reduced the number of hatched nauplii by 46.6%-100%. An increase of the Pb concentration from 75.2 to 752 mg/kg, reduced the number of hatched nauplii by 21.4%-78.9%. An increase of the Cd concentration from 0.68 to 6.8 mg/kg, reduced the number of hatched nauplii by 31.6%-94.7%. The number of nauplii also significantly decreased with the increase of mixed-metal concentration and exposure time in the mixed-metal test. Trimmed Spearman-Karber analysis gave sediment metal 72-h LC50 values of 1.25 mmol Cu/kg, 1.73 mmol Pb/kg, and 0.054 mmol Cd/kg, which suggested that Cd was the most toxic to A. pacifica resting eggs in the three tested metals. The results indicate that heavy metals with higher concentrations can reduce recruitment of A. pacifica nauplii from benthic resting eggs to planktonic population.