Effects of natal experience on habitat selection when individuals make choices in groups: a multilevel analysis

We studied the effects of natal experience on preference for a postdispersal habitat (natal habitat preference induction, NHPI) in groups of newly eclosed female Drosophila melanogaster, using multilevel statistical models to take into account dependencies of responses from individuals making choices within the same hour. Groups consisting of flies with one of five genotypes (crosses of highly inbred female isolines) were allowed free access to a high-quality natal habitat after emergence from their pupae. The flies were then allowed to select one of two new habitats in a large ‘seminatural’ environment over the next 3 days. The flies showed strong positive effects of training habitat on their choice of a new habitat, after controlling for potential dependence in choices within hours and trials. The genotypes also varied with respect to the effects of conspecifics and humidity on individual choice. A second analysis using data aggregated at the trial level and a traditional statistical approach (a generalized linear model, GLM) also detected effects of training on habitat choice. However, the GLM produced other results that may have been artefacts resulting from the omission of within-trial factors with important effects on choice in this trial-level analysis. This study shows the advantages of using multilevel models rather than aggregating data to control for interactions among subjects when animals select items in groups.