Fenoxycarb exposure disrupted the reproductive success of the amphipod Gammarus fossarum with limited effects on the lipid profile

Abstract

Insect growth regulator insecticides mimic the action of hormones on the growth and development of insect pests. However, they can affect the development of non-target arthropods. In the present study, we tested the effects of the growth regulator insecticide fenoxycarb on several endpoints in the freshwater crustacean Gammarus fossarum (Amphipoda). Females carrying embryos in their open brood pouch were exposed to 50 μg L-1 fenoxycarb throughout the entire oogenesis (i.e. 21 days). After exposure, newborn individuals from exposed embryos were removed from the maternal open brood pouch for lipidomic analysis, while males were added to assess the reproductive success. After fertilization, the lipid profile, energy reserve content (lipids, proteins and glycogen), and activity of phenoloxidase - an enzyme involved in the immune response - were measured in females. No significant effect of fenoxycarb exposure was observed on the lipid profile of both newborn individuals and females, while reproductive success was severely impaired in exposed females. Particularly, precopulatory behavior was significantly reduced and fertilized eggs were unviable. This study highlighted the deleterious effects of the insect growth regulator fenoxycarb on gammarid reproduction, which could have severe repercussions on population dynamics.

Fig 1. Experimental design and measured endpoints in G. fossarum exposed to 50 μg L^-1 fenoxycarb.

Fig 2. Reproductive parameters in the control group and in the 50 μg L^-1 fenoxycarb-exposed group.

Pairing success in percent (A), success of fertilization in paired gammarid in percent (B), number of fertilized eggs per female (mean±standard deviation; numbers above the bars indicate the number of females that were observed) (C) and embryo viability in percent (50 embryos/condition) (D). Asterisks indicate significant differences compared to the control group.

Fig 3. Biochemical markers in control group and in the 50 μg L^-1 fenoxycarb-exposed group.

Phenoloxidase activity (A), lipid content (B), protein content (C) and glycogen content (D). Ten females and 15 females were analyzed in the control and fenoxycarb-exposed groups, respectively.

Fig 4. PCA scores of the lipid profiles plotted on the two first components of the PCA.

Females in the control (green) and fenoxycarb-exposed group (pink) and newborns in the control (blue) and fenoxycarb-exposed group (orange).

Fig 5. Observation of lipid droplets in newborns.

Newborn individual observed under a stereomicroscope (A), newborn individual observed with a fluorescence microscope after Nile red staining (lipid droplets are concentrated into the hepatopancreas) (B) and fluorescent area in the two study conditions (20 individuals/condition) (C).