You wouldn’t think that biologists could learn much about evolution by studying the flies that live on the hills and mountainsides of the Hawaiian islands. But these are not ordinary flies.
Approximately 800 species of flies belonging to the genera Drosophila and Scaptomyza live in the forests of Hawaii. Collectively known as drosophilids, these flies differ significantly from the houseflies that buzz around kitchens and garbage piles. Houseflies belong to a different biological family and were brought to Hawaii by human colonizers over the last few hundred years. The drosophilids have lived in Hawaii for millions of years and are the products of a spectacular evolutionary history.
The different drosophilid species in Hawaii vary greatly. Some species are large and others are small. They have differently shaped bodies and contrasting behaviors. Different species lay their eggs in leaves, bark, fungi, fruit, or even spider eggs. One particularly well-studied group of about a hundred species has bold black markings on their wings. These species are known as picture-winged drosophilids.
Many drosophilid species have elaborate sex lives. First the males establish a mating territory called a lek. Then they defend this area from other males of the same species. Males of one species, called Drosophila heteroneura, use their hammer-shaped head as a battering ram to drive other males away (see Figure 1). The males of other species lock legs and wings and wrestle each other into submission until one flees. In another species, males make a buzzing roar with special muscles in their abdomen.
When a female fly visits the lek, the male gets to work. In many species, the males have an elaborate but specific dance that they use to attract females. Others buzz their wings in a special way or place their heads under the female’s wings. One species releases attractant chemicals known as pheromones in the female’s direction.
Even if the male does everything perfectly, his efforts may not pay off. If the female chooses not to mate with that male, she will fly away.