Multidimensionality and intra-individual variation in host manipulation by an acanthocephalan

Trophically-transmitted parasites frequently alter multiple aspects of their host's phenotype. Correlations between modified characteristics may suggest how different traits are mechanistically related, but these potential relationships remain unexplored. We recorded 5 traits from individual isopods infected with an acanthocephalan (Acanthocephalus lucii): hiding, activity, substrate colour preference, body (pereon) coloration, and abdominal (pleon) coloration. Infected isopods hid less and had darker abdominal coloration than uninfected isopods. However, in 3 different experiments measuring hiding behaviour (time-scales of observation: 1 h, 8 h, 8 weeks), these two modified traits were not correlated, suggesting they may arise via independent mechanisms. For the shorter experiments (1 h and 8 h), confidence in this null correlation was undermined by low experimental repeatability, i.e. individuals did not behave similarly in repeated trials of the experiment. However, in the 8-week experiment, hiding behaviour was relatively consistent within individuals, so the null correlation at this scale indicates, less equivocally, that hiding and coloration are unrelated. Furthermore, the difference between the hiding behaviour of infected and uninfected isopods varied over 8 weeks, suggesting that the effect of A. lucii infection on host behaviour changes over time. We emphasize the importance of carefully designed protocols for investigating multidimensionality in host manipulation.