Living with the enemy in a warmer, polluted and changeable world: how do multiple stressors interact to influence host-parasite interactions in fish?

Background:
In degraded habitats, fish experience multiple anthropogenic stressors in concert, with additive, synergistic or antagonistic interactions potentially generating severe effects on populations [1]. In addition, fish face a range of natural enemies, including parasites and diseases, whose effects can be exacerbated by environmental change [2]. Yet although an understanding of how factors such as global warming and pollution can alter infection prevalence and disease phenotypes [3,4] their effects are typically studied in isolation. Little is known about how stressors combine to affect host-parasite interactions under realistic degraded conditions.

Aim:
The proposed project will provide the first experimental test of the hypothesis that environmental stressors interact to affect (a) the susceptibility of fish to parasite infections, and (b) the infection phenotypes that emerge. The latter is important because it will determine how the ecological impact of parasitism is affected under changing environmental conditions

Approach:
Two experimentally-amenable fish models (3-spined sticklebacks [5] and zebrafish [1]) will be used. Lab-bred fish will be held under controlled (normal/elevated) temperature, and with/without exposure to environmentally-relevant concentrations of various pollutants (incl. heavy metals, endocrine disrupting chemicals, or treated sewage effluent). In one type of experiment, the effects of single stressors (e.g. warming OR pollutant) or paired stressors (e.g. warming AND pollutant) on infection susceptibility will be tested against suitable controls. This will be quantified using immunegene expression profiling [6] and by controlled exposure to infective stages of experimentally amenable parasites (Schistocephalus - sticklebacks [7]; Diplostomum - both species [8]). In the second type of experiment, the effects of single and multiple stressors on infection phenotypes among experimentally-parasitised fish will be quantified, by determining ecologically-relevant fitness correlates including fish growth, energetics, sexual development (11-ketotestosterone & spiggin expression in males; gonadogenesis & vitellogenin titres in females) and behavioural profiles (incl. reproductive, foraging, social, aggressive and antipredator behaviours).

Novelty: Our results will represent the first rigorous experimental test of the hypothesis that multiple anthropogenic stressors can interact to significantly influence host-parasite interactions in fish

CASE partnership:
The student will spend 3 extended periods at Cefas Weymouth, under the supervision of the CASE supervisor, Dr Ioanna Katsiadaki (IK). In Winter 2017/18 the student will be trained in key analytical techniques (incl. ELISA, radioimmune assay, qPCR) for quantifying the molecular signatures and physiological endpoints of fish sexual development, as well as learning more broadly about the work undertaken at Cefas. The second and third visits (Summer 2018 & 19) will allow the student to learn key techniques and SOPs for performing and analysing chemical dosing experiments. The student will benefit by being embedded in two closely-associated yet differently focused research teams at UoL (sticklebacks/parasites/behaviour [IB], zebrafish/behaviour/neuro-endocrinology [WN]), and IK’s Cefas team (chemical exposures/environmental effects on development & physiology). Each supervisor will provide hands-on training for the student, who will also benefit from their extended academic networks.