PALEOCEANOGRAPHY AND SPECIATION IN THE SPINY LOBSTER GENUS PANULIRUS IN THE INDO-PACIFIC

The spiny lobster genus Panulirus is a relatively recent one, its some 20 species all having evolved from a common Pacific ancestral type within the past ca. 5 million years. This paper describes the distribution of six Indo-Pacific species of Panulirus in relation to the surface ocean current systems which are responsible for the dispersal and return of their long-lived phyllosoma larvae. Based on previous published works by the same author, a very lengthy larval duration is postulated, which enables phyllosoma larvae to survive during extensive circumoceanic gyral circulation routes. It is hypothesized that larvae of each species will only metamorphose into the settling puerulus stage when they encounter physical and/or chemical cues native to endemic environments. Likely mechanisms inducing speciation are discussed. Speciation appears to have been accelerated during intervals of climatic and oceanographic change such as occurred during the series of interglacial/glacial oscillations characteristic of the Pleistocene epoch. At such times, changes in ocean current systems would have altered the degree of larval interchange between distant populations of the same species, thereby altering rates of gene flow. Lowered sea levels prevailing during glacial periods are postulated to have impeded the exchange of thermocline water, disrupting the transport mechanisms for phyllosoma larvae both within and between the Indian and Pacific Ocean basins.