In this new Excellence-project funded by the Spanish Ministry for Science, we aim to evaluate the varied impacts that Matching Habitat Choice may have on individuals, populations and even species. For this we use different lines of genetically modified Fruit flies. When these special flies are exposed to a pulse of light of a specific colour, a subset of their neurons become activated, and the fly perceives something about the environment (e.g. the presence of CO2 gas) – even when that isn’t actually true! This cool new technique is called optogenetics. It has been developed in Neurobiology in order to figure out what each neuron does, but we use it to manipulate the perception of flies about different habitats, after which they are allowed to choose the one they like most. This spatial movement based on the perception of local performance allows us to test how this behaviour affects reproductive output, capacity to invade novel habitats, interactions with other species, and even the potential for speciation. UPDATE: the technique is now up and running, and we are doing the first experiments.