Swimming with ciliates: dispersal and movement ecology of Tetrahymena thermophila, PhD thesis


Dispersal, the movement of individuals among populations, is a life history trait that affects ecological and evolutionary dynamics of species. It has gained much interest in the context of metapopulation dynamics which aim to understand how species cope with habitat loss and fragmentation. In this thesis, I used controlled microcosms of a unicellular organism, the ciliate Tetrahymena thermophila, to experimentally investigate various aspects of dispersal ecology. Firstly, I describe how digital image and video analysis can be used to rapidly and reliably quantify traits and abundances of the model organism. Secondly, I investigated the relative roles of the genotype and the environment on dispersal in a two-patch system by comparing how 44 genetically different lines dispersed in response to conspecific density. We found genetic variation for dispersal plasticity and hence potential for dispersal plasticity to evolve. Thirdly, I report how an individual-based simulation model parameterized with characteristics of video-recorded cell trajectories accounted for 45\% of the variation in dispersal observed among genotypes. Finally, I describe the dispersal syndromes (co-variation of dispersal with other traits) found in this set of genotypes, which bear important information about the costs and evolution of dispersal: (1) negative co-variation of dispersal-related traits with peak cell density and cell survival; (2) the absence of a link between short- and long-distance dispersal. The results in this thesis contribute to our understanding of condition-dependent dispersal, dispersal syndromes, links with the general movement ecology and introduce several methodological advances widely applicable in experimental laboratory systems.

Frank Pennekamp
Postdoctoral researcher in ecology