Bidimensional microcosms reveal dispersal syndromes and decisions in the ciliate Tetrahymena thermophila

Details

Supervisors

Schtickzelle, Nicolas ; Manzi, Florent

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie, à finalité approfondie

Abstract

enDispersal is a fundamental process for a species ecology and evolution, especially in the face of threats to biodiversity, such as habitat destruction and fragmentation. Many studies used the ciliate Tetrahymena thermophila as a model species to study dispersal in microcosms, experimentally testing various aspects of dispersal: variation between and within genotypes, responses to environmental changes such as congener density, temperature or resource abundance, as well as the link with cooperation and informed dispersers. Although these studies provided many insights on dispersal, they were all limited by the experimental systems, restricting the measures collection after dispersal. The role of dispersal syndromes and decisions at each of the three dispersal phases (emigration, transience and immigration) therefore remains unknown. In this study, innovative 2D microcosms recreating landscapes affected by fragmentation per se (two habitat patches linked by a corridor of variable length) were used to test dispersal in T. thermophila. Automated data acquisition in the form of pictures recreating short videos, and image analysis were used to identify individual cells and to reconstruct their trajectories, from which morphological and behavioural data were extracted. On the technical point of view, our results show that 2D microcosms are an appropriate tool for studying dispersal during its three phases, because of their high level of control and their representativeness of dispersal conditions, as the observed movements can be attributed to real dispersal. On a biological point of view, for the first time shifts in behavioural and morphology averages at emigration and immigration were demonstrated. By adjusting their movements during the transience phase, individuals show contrasted reactions in terms of swimming speed and movement linearity. We also confirmed the strong intraspecific variation observed in previous studies, adding that this variation also extends to dispersal syndromes and decisions during transience. Finally, we showed that fragmentation, by increasing the distance to be covered during dispersal, impacts on the population by reducing the propensity to disperse and slowing down the process, as well as at the individual level by favouring bigger cells.