| While the effects of endocrine-disrupting compounds (EDCs) on growth, development, and reproduction have been extensively studied in vertebrate species, much less is known regarding the effects of EDCs in invertebrates (e.g., crustaceans). In crustaceans, molting, development, and aspects of reproduction are mediated by ecdysteroids, with 20-hydroxyecdysone (20HE) identified as the predominant biologically active metabolite. The current research evaluated the ability of the meiobenthic copepod Amphiascus tenuiremis to mature and reproduce while exposed to the pesticides tebufenozide, a 20HE agonist, and fenarimol, a 20HE inhibitor. Tebufenozide has been shown to induce lethal precious molting in some invertebrate species. However, the present study demonstrated that survival of copepods reared and mated in tebufenozide was not adversely affected throughout two generations (F0 and F1) of exposure. Despite the absence of mortality, a significant increase in the abundance of male copepods, relative to females, in both generations, and a significant acceleration of the juvenile development rate for the F0 offspring was observed. No meaningful changes in ecdysteroid levels were observed in F0 or F1 adult male and female copepods. In a similar experiment, a single generation of A. tenuiremis was exposed to the anti-ecdysteroid fenarimol. As with tebufenozide, a significant increase in the rate of juvenile development compared to untreated copepods was observed. The abundance of male copepods, relative to females, or reproductive output was not adversely affected. However, significant ecdysteroid suppressions in both male and female copepods were observed following exposure to fenarimol, possibly indicating an alternative control on molting in this species. Follow-up experiments using the estuarine amphipod Leptocheirus plumulosus resulted in the induction of P-glycoprotein (P-gp), a multi-xenobiotic transporter, by tebufenozide and the inhibition of P-gp transporter activity by fenarimol. Amphipods exposed to binary mixtures of tebufenozide and fenarimol also demonstrated a marked reduction in ecdysteroid levels. This response is consistent with the increased metabolic degradation of 20HE observed in invertebrates sensitive to tebufenozide. Subsequently, the absence of adverse effects in crustaceans resistant to tebufenozide may be due, in part, to a tebufenozide-induced upregulation of P-gp that, in turn, may be mitigated following exposure to P-gp inhibiting compounds. |
