Effect of cypermethrin exposure on behavior and gene expression of the mangrove rivulus, Kryptolebias marmoratus

Details

Supervisors

Silvestre, Frédéric

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie, à finalité approfondie

Abstract

Most living organisms are in contact with pesticides, and the mangrove rivulus, Kryptolebias marmoratus, is no exception. Cypermethrin, a widely used insecticide belonging to the pyrethroid family, can be found in mangroves and may impact resident organisms. This insecticide is highly toxic to fish, blocking sodium channels in nerve membranes and thereby preventing the transmission of nerve impulses. K. marmoratus is unique among vertebrates for its mixed mating strategy, called androdioecy, in which populations consist of hermaphroditic individuals forming isogenic lines, alongside males that can cross-fertilize, promoting genetic diversity. The aim of this study is to investigate the effects of cypermethrin on behaviour and changes in brain gene expression of adult mangrove rivulus. The fish used are from the most isogenic population of this species, with a selfing rate of 97% in the wild. Fish were exposed to cypermethrin (0.5, 5, 10, 25 and 50 µg/L) for four days, starting at 90 days post-hatching (dph), as they reach sexual maturity. Behavioral assessments were conducted using a shelter test after 24 and 96 hours of exposure, measuring both concentration- and time-dependent effects. The total distance moved, the cumulative duration time spent in the shelter and the proportion of time spent at the center and edge of the arena were measured. At the end of exposure, the expression levels of targeted genes related to detoxification process and the regulation of neurobehavioral functions (Mecp2, NIPBL, GSS, MAOA, DNMT3a and TOLLIP) were quantified. The level of acetylcholinesterase activity, an enzyme critical for neuronal function, was also assessed. Significant mortality was observed at the two highest concentrations (25 and 50 µg/L), with a survival probability reaching zero before the end of the test at the highest concentration. Despite the lethal effect of cypermethrin on the mangrove rivulus, its neurotoxic effect was not highlighted by this research, as the behavioural, genetic and enzymatic assessment showed no significative changes. Exploring additional toxicity could provide deeper insights into the modes of action of cypermethrin in Kryptolebias marmoratus.