Aims and objectives

This exercise is designed to:

1. Investigate the life history of the cestode, Schistocephalus solidus, and its effect on its stickleback host.

2. Collect and analyse quantitative data on parasite loads, stomach contents and body condition in fish.

3. Conduct behavioural experiments, and interpret the data that such experiments generate.

4. Practice summarising and synthesising conclusions from experimental studies into a report.

Introduction

Schistocephalus solidus is a cestode that matures in the intestine of piscivorous (fish-eating) birds, with the three-spined stickleback serving as an intermediate host (see Fig. 7.5.1 for details of the parasite's life cycle). While in the stickleback, the worm is in the form of a plerocercoid metacestode or juvenile stage. Plerocercoids can grow to an enormous size, regularly reaching 40% of the host's mass, and in extreme cases weighing as much as the host itself. S. solidus infection is known to alter the behaviour of both the copepod and the fish hosts (for example by suppressing the escape response) in ways that make both intermediate hosts more vulnerable to predation by the next host in the life cycle.

The aim of this exercise is to familiarise you with this common host-parasite system, and to enable you to carry out an investigation into some of the important effects infection can have on the foraging behaviour and nutrient status of hosts. In addition, you will use data from a number of recent studies examining how the parasite influences foraging and body condition in fishes.