Modes of speciation in Indonesian terrestrial arthropods

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Although it has been well recognized that the biodiversity is richest in tropics, our knowledge on the speciation phenomena in tropical organisms is still poor. In the present study, we tried to elucidate the modes of speciation in several groups of terrestrial arthropods in Indonesia, which stretches from the Oriental region to the Australian region. Particular attention has been paid to the faunal change across the boundary of the two zoogeographic regions known as Wallacea. The following islands have been investigated by us: Sumatra (West Sumatra), Java (all the island) and Bali, belonging to the Malesia land mass; Lombok, Sumbawa and Sulawesi (northeastern part, central part, and southern part) belonging to Wallacea. Unfortunately, the eastern parts of the intended study sites, including Irian Jaya, could not be investigated owing to political reasons. In the last year of the three years survey, we have also examined some groups of insects in the Kura isthmus in the Malay Peninsula, which is known as the boundary of tropic and sub-tropic zones in the Southeast Asia.Patterns of the faunal change across Wallacea seemed different according to the groups of animals. For example, while epilachnine ladybirds showed different faunas in the Oriental and Australia regions, and furthermore, there is a rather characteristic fauna in Sulawesi, no such geographic divergence was suggested for social wasps with high mobility. On the other hand, harvestmen and millipedes decreased in the number of species eastward, possibly affected by increasing aridity. Furthermore, we have discovered several cases of putative host races or host related sibling species (candidates of sympatrically speciated species) in epilachnine ladybird beetles, and were able to perform laboratory experiments to examine performance and preference of some species. These studies will contribute to our better understanding of the mode of speciation in tropical insects and other arthropods.