Complex interactions between an individual's genotype and its environment determine characteristics such as body size. However, gene-environment interactions should not be seen as being restricted to individual ontogeny: the diversity of the local gene pool can be greatly influenced by habitat variables and population history (e.g., landscape connectivity and propagule size). In this paper I use a model species, the bushcricket Metrioptera roeseli, and data from long-term experimental population introductions to examine individual body size as an indicator of the constraints placed on the gene pool by ecological variables following colonization of new environments. These broad-scale population-environment interactions are useful in understanding species ecology, species invasions and in managing successful reintroductions in conservation biology.