CONCORDANT EVOLUTIONARY PATTERNS AMONG INDO-WEST PACIFIC BUTTERFLYFISHES

Genetic differences within a 495 base pair section of the mitochondria l cytochrome b gene reveal a striking concordance among species in two monophyletic groups of Indo-west Pacific butterflyfishes. In both spe cies groups, an approximately 2.0% genetic break clearly partitions in dividuals between the Indian Ocean and Pacific Ocean. However, levels of intra-Pacific mtDNA variation are low, on average less than 1.0%, a nd fail to cluster by species boundaries defined by colour pattern. In dividuals from different species, separated by thousands of kilometers , often possess identical cytochrome b sequences, whereas conspecifics from the same reefs can show up to 1.5% difference. The discrepancy b etween the mtDNA gene tree and species boundaries may reflect retained ancestral variation or may be the result of hybridization. The strong temporal and phylogenetic concordance between these two independent s pecies groups suggests that genetic differentiation was influenced by common environmental factors. Low levels of within- and between-specie s genetic differences imply a recent divergence time and suggest a lin k between speciation within each group and Pleistocene climatic fluctu ations. These results paint a turbulent picture of the recent evolutio nary history of the Indo-West Pacific.