The marine East Indies: Diversity and speciation

Aim To discuss the impact of new diversity information and to utilize recent findings on modes of speciation in order to clarify the evolutionary significance of the East Indies Triangle. Location The Indo-Pacific Ocean. Methods Analysis of information on species diversity, distribution patterns and speciation for comparative purposes. Results Information from a broad-scale survey of Indo-Pacific fishes has provided strong support for the theory that the East Indies Triangle has been operating as a centre of origin. It has become apparent that more than two-thirds of the reef fishes inhabiting the Indo-Pacific are represented in the Triangle. An astounding total of 1111 species, more than are known from the entire tropical Atlantic, were reported from one locality on the small Indonesian island of Flores. New information on speciation modes indicates that the several unique characteristics of the East Indian fauna are probably due to the predominance of competitive (sympatric) speciation. Main conclusions It is proposed that, within the East Indies, the high species diversity, the production of dominant species, and the presence of newly formed species, are due to natural selection being involved in reproductive isolation, the first step in the sympatric speciation process. In contrast, speciation in the peripheral areas is predominately allopatric. Species formed by allopatry are the direct result of barriers to gene flow. In this case, reproductive isolation may be seen as a physical process that does not involve natural selection. Allopatric species formation often takes millions of years, while the sympatric process is generally much faster. Following species formation, dispersal from the East Indies appears to take place according to the centrifugal hypothesis.