Toxoplasma gondii and mouse behaviour: The importance of individual differences

Toxoplasma gondii is often cited as a classic example of a parasite that can manipulate the behaviour of its intermediate hosts, but inconsistencies in the literature mean this phenomenon is not well understood. A longitudinal study was undertaken to explore the effect of T. gondii infection on mouse behaviour in a comprehensive manner. Multiple behavioural measures were taken from three behavioural tests; the open field (OF), elevated plus maze (EPM), and a custom designed predator odour avoidance arena. Exploratory factor analysis was employed to define a subset of behavioural measures that reflected activity, boldness, spatial preference and response to predator odour. Behaviour of experimental groups was characterised prior to infection, to properly assess change in behaviour post infection. Repeated measures from the same individuals allowed subtle effects on behaviour to be examined, including effects on repeatability and associations between behaviours. These aspects of behaviour have not previously been explored in the rodent/T. gondii system. Prior to infection, mice showed slight avoidance of cat urine on average (0.46 vs. 0.50 expected by chance, p=0.040), but there was considerable variation between individuals. Many behaviours measured were repeatable over time, and taking into account mouse ID during analysis was therefore valuable and informative. Activity level was consistent across tests, but measures of boldness were not, indicating that different tests measured different aspects of boldness. T. gondii had a limited effect on behaviour based on comparison of group means, inducing a transient increase in OF activity at 17 weeks post infection (wpi), but no effect on other behaviours. However, T. gondii exposure led to decreased repeatability of some behaviours and disrupted an association between OF activity and EPM boldness. Furthermore, T. gondii exposure appeared to affect behaviour in a baseline-dependent manner; parasite exposure increased EPM activity in individuals with low baseline activity and decreased EPM activity in individuals with high baseline activity. These results emphasise the importance of taking into account individual differences in behaviour and the value of a longitudinal, pre- and post-infection, repeated measures approach in the study of parasite-induced behavioural changes

Additional file 1: Table S1. of A comparative molecular and 3-dimensional structural investigation into cross-continental and novel avian Trypanosoma spp. in Australia

Tissue samples collected from 93 birds. Bird identification number (ID), bird species, and tissues extracted from each individual are included. Tissues extracted include heart (H), liver (L), spleen (S), kidney (K), lung (Ln), striated or skeletal muscle (Sm), brain (B), and thoracic muscle (T). (DOCX 31 kb