Acute exposure to water from the Chicago Area Waterway System induces molecular indices of stress and disturbance in silver carp: implications for deterrence to range expansion

Exposure of an animal to sub-optimal habitat can result in impairment, damage or increased energy expenditure to maintain homeostasis, which can direct resources away from reproduction and reduce fitness. Animals may therefore avoid sub-optimal habitats to minimize physiological costs. Silver carp ( Hypophthalmichthys molitrix ) are a prolific invader in the Mississippi River basin. Despite their propensity for spread, the ‘leading edge’ of silver carp at the northern limit of their distribution in the Illinois River has stalled and not advanced for over a decade. Studies have suggested that contaminants in the Chicago Area Waterway System (CAWS) may be deterring upstream range expansion, but this hypothesis has had limited testing to date. The current study sought to quantify linkages between CAWS water constituents and impaired range expansion of silver carp. For this, CAWS water from beyond the current upstream distribution of silver carp was collected and transported downstream to the core of the population. Silver carp from the population core were collected and exposed to either water from their collection location (control), or to CAWS water from upstream of the current distribution, simulating range expansion. Following exposure, olfactory and liver tissue were collected to quantify genetic expression and histological indices of damage. Results showed that silver carp olfactory tissue experienced increased activity of genes related to xenobiotic defense and oxidative stress following exposure to CAWS water from upstream of the current distribution, highlighting costs associated with inhabiting this environment, providing a role for contaminants in CAWS water at deterring further upstream movement.