Hawaiian Islands--some of the most isolated islands in the world

2. Hawaiian Islands--some of the most isolated islands in the world • 90% of Hawaiian flora consists of endemic species • About 800 species of Drosophila on the islands--about 1300 species are described worldwide • Numerous endemic species in other taxonomic groups

3. How were/are the Hawaiian islands being formed? • The Hawaiian islands and islands near them are not associated with a particular midoceanic ridge.

4. Wilson suggested hot spot model • Hot spot: a weak point in the earth's mantle that doesn't move and through which magma is released. When oceanic plates move over this hotspot, volcanoes are produced. Hence, islands end up being produced in a linear arrray as the plate moves over the hotspot.

6. Islands started forming about 75 mya • Kure island is approximately 30 my old, the oldest of the emergent islands today. • Kauai is the oldest of the five major islands at 5.1 my • Oahu, Molokai, Maui, and Hawaii are successively younger. • The island of Hawaii is located directly above the hot spot and is the youngest of the Hawaiian islands, about 700,000 years old. • A new island, Loihi, is forming to the east of Hawaii and should be above sea level in 15-20,000 years.

8. Some of the islands have tremendously varying environments—Hawaii rises from sea level to above 3000 m and has both rainforest and arid habitats on different sides of the island.

9. Affinities of most of the flora and fauna of Hawaii are with the Oriental biogeographic region • There are more stepping stones between this region and Hawaii than between the Americas and Hawaii. • Organisms from the Oriental region are coming from environments more similar to those found on Hawaii than on much of the North American mainland.

11. 168 spp of ferns in Hawaii--almost 50% related to species in the Oriental region, 12% to species in the Americas.

12. Some predictions (based on ideas of dispersal and vicariance events) • 1. The oldest members of taxonomic groups should occur on the oldest islands while the youngest members should occur on the youngest islands--this is called the progression rule.

13. Predicted area cladogram based on simple progression

14. Some predictions • 2. Different taxa should show congruent patterns if the geological history of the islands has influenced the distribution of the different taxa similarly.

15. Some predictions • 3. The most closely related taxa within a taxonomic group should inhabit islands that are close to each other

16. Outgroup--group used for comparative purposes in a phylogenetic analysis. Outgroups cannot contain any members of the group being studied.

17. Prediction one (the progression rule) is supported from data on Drosophila spp. as well as data from Hibiscadelphus, and some data from subclades of Schiedea and Alsinidendron.

18. Tetramolopium do not support the progression rule

19. Prediction 2 is supported to some degree because some groups show similar patterns. However, there are numerous instances where patterns for different groups vary, suggesting that different levels of dispersal for different groups may overlay patterns based only on vicariance

20. Prediciton 3. The most closely related taxa within a taxonomic group should inhabit islands that are close to each other • Limited support for prediction 3 (see Drosophila, Tetramolopium)

21. We are not sure whether and when species arrived on some islands and dispersed to other islands. • If one island has better conditions for the preservation of fossils or pollen than another, we can be more confident about whether and when particular species were on that island

22. Drepanidinae • Ancestor of drepanids probably from Asia and ate nectar and insects. Today 11 endemic genera and endemic family Drepanididae. • The data from the honeycreepers show that speciation in isolation and then colonization of other islands occurred, because many closely related species are found on different islands.

23. Adaptive radiation of drepanids occurred with adaptive radiation of lobeliads, a plant family • Leaves of Cyanea genus are extremely variable. Many have tubular, brightly colored flowers, that often attract birds.

24. For many insects and plant species, it appears that much speciation occurred within islands • Prognathogryllus crickets, for example, did not disperse from one island to another frequently but there has been much within-island speciation.

25. Were these organisms particularly susceptible to isolation within an island because of limited mobility, or does sympatric speciation occur more frequently than we expect?

26. Hawaiian Drosophila • First drosophilid ancestor arrived from Asia to Kure and then diverged into a new species

27. Some patterns • 1. ancestral species tend to be found on the old islands while the younger islands don't tend to have ancestral species

28. Some patterns • 2. numerous colonizations from one island to another, with more colonizations taking place between close islands than distant islands

29. Numbers on lines represent the number of hypothesized dispersal events

30. Some patterns • 3. adaptive radiations within islands--species on southern part of island Hawaii (200,000 years old) evolved from those on northern part (400,000-600,000 years old).

31. Many of the islands have a variety of climate and habitat types, having led to isolation and then specialization in many Drosophila species. • Patches of vegetation are sometimes isolated by lava, creating conditions for allopatric speciation. • The Drosophila have specialized on using decaying plant material as sites for raising young, a niche with few competitors.