Effects of waterborne antidepressants on colour change and camouflage in two juvenile marine invertebrates, Sepia officinalis and Carcinus maenas
Abstract
Camouflage is a widespread anti-predator defence. It enables animals to hide from their predator by blending into the environment. The expression of highly cryptic patterns is ubiquitous among all unshelled cephalopods, like the European cuttlefish, Sepia officinalis, but can also be observed in juvenile crabs, such as Carcinus maenas, which are particularly vulnerable to predators. The dynamic change of patterns and the intensity of colouration can be achieved very rapidly as in S. officinalis, or more slowly as in C. maenas, either being controlled nervously, or by neuropeptide hormones, respectively. Neuronal and neurohormonal control, in turn, is influenced by neurotransmitters, such as serotonin. Constant release of psychoactive drugs that act on the serotonergic system, such as fluoxetine (Prozac®) or venlafaxine (Effexor®) can potentially modify colour change and may impair background matching. Furthermore, behavioural mechanisms that allow choosing optimal backgrounds in heterogeneous habitats to which the animals are best adapted could be affected. We, therefore, compare neuronal and hormonal mechanisms of colour change and camouflage in two different marine invertebrates and investigate whether environmental pollution can modify effective cryptic colouration and/or behavioural traits. Cuttlefish exposed to low concentrations (2.5 to 5 ng.L-1) of fluoxetine and venlafaxine (fluoxetine alone or in mixture with venlafaxine) showed a decrease in predation motivation and success, and altered camouflage in certain conditions. First results on juvenile crabs confirm reversible colour change by darkening or brightening when placed on dark or white backgrounds. It is now examined whether psychoactive drugs at environmental concentrations disturb colour change and behaviour within juvenile crabs.