Social information from immigrants: multiple immigrant-based sources of information for dispersal decisions in a ciliate

Dispersal is increasingly recognized as being an informed process, based on information organisms obtain about the landscape. While local conditions are often found to drive dispersal decisions, local context is not always a reliable predictor of conditions in neighbouring patches, making the use of local information potentially useless or even maladaptive. In this case, using social information gathered by immigrants might allow adjusting dispersal decisions without paying the costs of prospecting. However, this hypothesis has been largely neglected despite its major importance for ecological and evolutionary processes. We investigated three fundamental questions about immigrant-informed dispersal: Do immigrants convey information that influences dispersal, do organisms use multiple cues from immigrants, and is immigrant-informed dispersal genotype dependent? Using Tetrahymena thermophila ciliates in microcosms, we manipulated the number of immigrants arriving, the density of congeners, the resource quality in neighbouring patches, matrix characteristics and the level of cooperation of individuals in the neighbouring populations. We provide the first experimental evidence that immigrants convey a number of different cues about neighbouring patches and matrix (patch quality, matrix characteristics and cooperation in neighbouring populations) in this relatively simple organism. Furthermore, we demonstrate genotype-dependent immigrant-informed dispersal decisions about patch quality and matrix characteristics. Multiple cues from immigrants and genotype-dependent use of cues have major implications for theoretical metapopulation dynamics and the potential for local adaptation.