In the 19^th century, the Drosophila on Hawaii were classified as 400 species in 9 genera, now it is known that there are 800 species, of which 500 have been classified. These are put into two genera, Drosophila and scraptomisa.

The internal morphology and the chromosomes are much the same. There are five pairs of chromosomes, and they can be differentiated by the pattern of bands, the protein products and at the DNA base level. There are few differences between the species.

As an example of some differences:

All the species are obviously closely related, they probably all came from a single founder event, presumably a single gravid female 6 million years ago. This can be calculated by looking for ancestral and derived features.

Here is a pictorial representation of when some species were formed. Each branching point is a new founding event:

It is possible to calculate how many founder events there have been over the whole set of islands. If we concentrate just on the Picture Wing Drosophila, of which there are 103 species on the Hawaiian islands, there have been 43 founder events. Which means there has been an average of 2.5 species formed per Founder event. Some of them, necessarily going back onto a previously conquered island.

Here are the number of species on each island, as well as the ages that the islands were forming:

Picture taken from: A brief overview of Hawaii

We can examine the way in which each species has arisen by examining the chromosomes. For example, Hexachatae, which is found on Oaku, has a particular characteristic inversion on chromosome 5. This is known as 5d. It shares this with the following species:

It is possible to tell that Virgulate is ancestral by looking at the other characteristic chromosome patterns., Hexachatae has another inversion pattern on chromosome 3 called 3q which is not shared by Virgulate. The following picture also shows the relationship between two particular species investigated by the University of Hawaii:

These have been studied to examine the role of sexual selection in the females. Speciation seems to occur because of the elaborate courtship rituals. It would seem that planitibia is much more selective in its choice of mates than silvestris. This would be logical, due to the fact that silvestris females would have less choice over male partners. There would be a strong selective pressure to being less specific in looking for a mate. This can be shown because Silvestris females will mate with males of either species, but it does not happen the other way round.

As the species develops, the frequency of non-discriminatory genes will increase, and morphological change follows due to a pleiotropic effect. This leads to an increase in variation.

In Hawaii, geographic seperation occurs due to other reasons as well as the seperation from island to island. Areas of the islands get stranded by volcanic ash or lava into 'Kipukas', which are islands of vegetation. Drosophila are poor fliers, and so this does mean a true seperation. If the Kipuka is formed by lava trapping an area of forest, it will take thousands of years for the area to be recolonised, which leads to species formation. If the Kipuka is formed by ash, it will be reclaimed in hundreds of years, meaning there will not be enough time for species formation, but genetic variation will arise, and will lead to a more varied gene pool when the drosophila are recombined later.

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