Biological disjunction along the West Caledonian fault, New Caledonia: a synthesis of molecular phylogenetics and panbiogeography

This paper documents a newly discovered pattern of biological disjunction between NW and SE New Caledonia. The disjunction occurs in 87 (mapped) taxa, including plants, moths and lizards, and correlates spatially with the West Caledonian fault. This fault is controversial; some geologists interpret it as a major structure, others deny that it exists. It may have undergone 150-200 km of lateral movement and it is suggested that this has caused the biological disjunction by pulling populations apart. The disjunction matches similar dextral disjunctions of taxa along transform faults in New Zealand, New Guinea, California and Indonesia. Major biogeographic patterns - whether centres of diversity, boundaries of allopatric taxa or disjunctions - all include taxa with many different degrees of differentiation. Studies using a clock model of evolution will therefore interpret a biogeographic pattern as the result of many disparate events. However, this line of reasoning reaches the untenable conclusion that biogeographic patterns, including normal allopatry, are always caused by chance dispersal, never by vicariance. A more productive approach, avoiding the pitfalls of a fossil-based molecular clock, involves a close examination of molecular clades, comparative biogeography and tectonics. The New Caledonia example documented here shows that this can lead to novel, testable predictions. (C) 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158, 470-488.