A Study of early and delayed effects of permethrin, a neurotoxic pesticide, on phenotypic traits of the mangrove killifish Kryptolebias marmoratus

Details

Supervisors

Silvestre, Frédéric

Faculty

Faculté des sciences

Degree label

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

Abstract

The constant interactions with the environment can have major effects on the phenotype of animals and thus their fitness. The early developmental stages are most vulnerable to disturbances of any kind. However, in fish, little research has been done to study the impact of environmental stresses experienced during development on the phenotype of individuals. Here, we studied how early exposure to permethrin, a pyrethroid neurotoxic compound found in numerous insecticides, influences developmental phenotypic plasticity of juvenile mangrove rivulus Kryptolebias marmoratus and the delayed effects on them in adulthood. This species is unique among vertebrates due to its ability to self-fertilize, thus producing natural homozygous individuals within isogenic lineages while maintaining a high degree of phenotypic plasticity. By working with minimal genetic variation, this species can provide valuable insights into how the environment including chemical pollutants can impact both morphological and behavioural phenotypes without a change in the genotype. We exposed K. marmoratus larvae to different concentrations of permethrin (PM) (0, 5 and 200 µg/L) to study the effects on life-history traits, behaviour, and hormones levels in 7-day-old subjects. In addition, we studied the possible effects on growth, aggressive behaviour, and hormone levels in 148-day-old K. marmoratus adults. Size measurements from four timepoints (Day 1, 7, 70, 149 post-hatch) showed that growth was impacted. In fact, from day 1 to 70 post hatch (dph), individuals exposed to 200µg/L of PM grew significantly less than those of the two other groups (5µg/L and control), however from day 70 to 149, individuals exposed to 200µg/L grew significantly more than those of the control group providing evidence of compensatory growth. PM exposure during development significantly affected the behaviour of juveniles, hypoactivity and a reduced anxiety-like behaviour for PM exposed individuals compared to control fish was observed. The resulting smaller, slower, and less mobile fish also proved to have less predation success. However, no effect on pre-fight cortisol, pre-fight testosterone, aggressive behaviour or fight outcome was found in adults during “combats” between two adult hermaphrodites. We therefore provided evidence that PM has adverse immediate effects on phenotype and behaviour in Kryptolebias marmoratus larvae that seem to recover over time before reaching adulthood. We have also investigated DNA methylation levels and differential expression of certain target genes which will be discussed in a subsequent study.