Parasitic infection reduces dispersal of ciliate host

Abstract

Parasitic infection can modify host mobility and consequently their dispersal capacity. We experimentally investigated this idea using the ciliate Paramecium caudatum and its bacterial parasite Holospora undulata. We compared the short-distance dispersal of infected and uninfected populations in interconnected microcosms. Infection reduced the proportion of hosts dispersing, with levels differing among host clones. Host populations with higher densities showed lower dispersal, possibly owing to social aggregation behaviour. Parasite isolates that depleted host populations most had the lowest impact on host dispersal. Parasite-induced modification of dispersal may have consequences for the spatial distribution of disease, host and parasite genetic population structure, and coevolution.

Figure 1.

Effect of infection and population density on the proportion of dispersing hosts. Regression lines illustrate density–dispersal relationship for infected and uninfected populations. Open circles, uninfected and crosses, infected.

Figure 2.

Relationship between parasite effect on host density and dispersal. Mean (±s.e.) residual density or dispersal calculated per parasite isolate, after statistically controlling for host clone effects.