Ovarian cycle and embryonic development in Gammarus fossarum: Application for reproductive toxicity assessment

Abstract

Among freshwater invertebrates, Gammarus fossarum is an important test organism and is currently used in ecotoxicology for acute and chronic assays; nevertheless, reproductive toxicity test methods are not yet available for these species. In the present study, the reproductive cycle in Gammarus fossarum was characterized in order to propose a reproductive toxicity test encompassing molting, follicle growth, and embryonic development that will provide a better understanding of the mode of action of chemicals disrupting these hormone-regulated processes. A detailed description of the reproductive cycle in Gammarus fossarum was obtained. As in some amphipods, molt and reproductive cycles of G. fossarum females occur concurrently, lasting 30 d at 12°C. Each molt stage is characterized by a specific marsupial embryonic development stage and the size of developing follicles visible on the ovarian membrane. Based on these results, a 21-d reproductive toxicity test is proposed for this species. This new bioassay was applied to identify the specific impact of different stressors: cadmium, methomyl, nonylphenol, and a starvation diet. Good reproducibility was obtained for different endpoints under control conditions and throughout the experiments. Preliminary robust reference values or benchmarks were proposed for these endpoints. Cadmium was found to specially inhibit secondary vitellogenesis. Nonylphenol had a specific concentration-dependent effect on embryonic development, with an increase in the percent abnormality from a concentration of 0.05 µg/L. A restricted food diet led to a significant delay in the molt cycle, which in turn induced inhibition of secondary vitellogenesis.

Review of the reproductive biology of amphipods and their endocrine regulation: Identification of mechanistic pathways for reproductive toxicants

“…During development and until ovulation, the number of oocytes in the ovary decreased by cytolysis and resorption [46]. In contrast, Geffard et al [38] noted that the number of oocytes visualized externally undergoing secondary vitellogenesis in G. fossarum for the next reproductive cycle was similar to the number of embryos observed in the marsupium of the gravid females. In the continuous-breeding amphipod Melita plumulosa, oocytes also develop over two molt cycles, with oocytes in primary vitellogenesis measuring up to 50 mm in length and a final size of about 330 mm at ecdysis (Fig.…”

“…1). In some amphipods, such as Hyalella azteca and Gammarus fossarum, ovarian maturation can be observed through their translucent body when pigment is deposited in the oocytes [37,38]. The various stages of oogenesis in amphipods have been studied in O. gammarella [39].…”

“…However, the cause of the pathologies in G. pulex is uncertain because, in the laboratory, crustaceans (crabs and shrimps) did not produce vitellin in response to estrogens [117]. Gefford et al [38] recently developed a reproductive toxicity test using the amphipod G. fossarum, encompassing molting, follicle growth, and embryonic development, to provide a better understanding of the effects of substances disrupting these processes. Cadmium was found to inhibit secondary vitellogenesis, and nonylphenol had a specific concentration-dependent effect on embryonic development; however, the mechanistic pathway by which these toxicants caused the toxicity was not determined.…”

Proteogenomics of Gammarus fossarum to Document the Reproductive System of Amphipods

“…They also constitute a food reserve for macroinvertebrates and fish. Finally, gammarids can be easily maintained in the laboratory or used for in situ bioassays (2), in which one can assess the impact of pollutants by measuring molecular markers related to diverse modes of action, such as neurotoxicity (4), as well as by using life-history-trait reproductive features (5). Alterations of sexual phenotype (intersexuality) have been reported in situ (6), as well as alterations by xenobiotics of various physiological parameters related to reproductive success (i.e.…”

“…Alterations of sexual phenotype (intersexuality) have been reported in situ (6), as well as alterations by xenobiotics of various physiological parameters related to reproductive success (i.e. gametogenesis, embryogenesis, fecundity, or molt) (5). However, the molecular mechanisms involved in these reproductive impairments are unknown.…”