Multiple stressor effects of methoprene, permethrin, and salinity on limb regeneration and molting in the mud fiddler crab (UCA pugnax)

Abstract

Exposure to multiple stressors from natural and anthropogenic sources poses risk to sensitive crustacean growth and developmental processes. Applications of synthetic pyrethroids and insect growth regulators near shallow coastal waters may result in harmful mixture effects depending on the salinity regime. The potential for nonadditive effects of a permethrin (0.01 2 gg/L), methoprene (0.03-10 tg/L ), and salinity (10-40 ppt) exposure on male and female Uca pugnax limb regeneration and molting processes was evaluated by employing a central composite rotatable design with multifactorial regression. Crabs underwent single-limb autotomy followed by a molting challenge under I of 16 different mixture treatments. During the exposure (21-66 d), individual limb growth, major molt stage duration, abnormal limb regeneration, and respiration were monitored. At 6 d postmolt, changes in body mass, carapace width, and body condition factor were evaluated. Dorsal carapace tissue was collected, and protein and chitin were extracted to determine the composition of newly synthesized exoskeleton. The present results suggest chronic, low-dose exposures to multiple pesticide stressors cause less-than-additive effects on U. pugnax growth processes. Under increasing concentrations of methoprene and permethrin, males had more protein in their exoskeletons and less gain in body mass, carapace width, and body condition compared to females. Females exhibited less gain in carapace width than controls in response to methoprene and permethrin. Females also displayed elevated respiration rates at all stages of molt, suggesting a high metabolic rate. Divergent growth and fitness between the sexes over the long term could influence crustacean population resilience.

A microcosm experiment on the effects of permethrin on a free-living nematode assemblage

“…Research with the freshwater amphipod, Hyalella azteca, indicated similar results with growth inhibition at levels as low as 44-73 ng g −1 (Amweg et al, 2005;Holmes et al, 2008). Results from Stueckle et al (2009) suggested that permethrin disturbed limb regeneration and moulting in the mud fiddler crab, Uca pugnax. Singh and Srivastava (1999) found a significant reduction in the activity of lactate dehydrogenase and cytochrome oxidase and an enhancement in succinate dehydrogenase activity in the tissues of the freshwater fish, Channa striatus, exposed to permethrin.…”

Pyrethroid Insecticides: Use, Environmental Fate, and Ecotoxicology

“…Similarly, those invertebrates that undergo specialized growth and re-generation may also be especially susceptible to the effects of sublethal pyrethroid exposure. For instance, chronic exposures to permethrin (<2 µg/L) disrupted male fiddler crab (Uca pugnax) limb re-generation, although female limb development was unaffected (Stueckle et al, 2009). …”

More ecological ERA: Incorporating natural environmental factors and animal behavior

“…For example, Van der Geest et al () showed strong interaction between hypoxia and Cu toxicity in the mayfly Ephoron virgo : whereas 50% reduction in O 2 content and Cu concentration of 50 μg/L separately had no effect on the survival of the mayflies, the 2 factors combined resulted in 50% mortality. In marine ecosystems, the synergetic effect of increased salinity on the toxicity of chemicals has been demonstrated (Stueckle et al ; Lavado et al ). In terrestrial ecosystems, exposure to toxicants has been shown to significantly decrease drought tolerance.…”