Figure 2.

Colonization of northern latitudes by Drosophilidae and simplified activity patterns of tropical and subarctic flies. (a) Drosophilids are thought to have their origin in the tropics. Certain species still have a tropical or subtropical habitat (red). Others have colonized temperate regions (green) and still others colonized subarctic regions (blue). (b) The tropics are characterized by photoperiods that remain close to 12 hr throughout the year and hot midday temperatures. Flies living in this region (e.g., Zaprionus indianus) avoid the midday heat by taking a siesta and being active during the morning and evening. The summers in subarctic regions are characterized by very long photoperiods with moderate temperatures that are most pleasant during the afternoon. Flies living in this region (e.g., Drosophila montana) show a broad activity band in the afternoon that extends until dusk