Abstract
Studies of divergence and speciation patterns in island systems have played an important role in the development and establishment of the allopatric speciation model. However, recent empirical support for divergence and speciation with gene flow means the importance of isolation for divergence in island systems needs to be re-examined. Here I explore the roles of geographic isolation and gene flow in the early stages of divergence of evolutionarily independent replicate populations of the Rufous Fantail Rhipidura rufifrons on satellite islands in southeastern Solomon Islands. These populations differ in the extent of morphological divergence from the main island, providing a unique opportunity to test between modes of divergence in an island system. Patterns of population structure, gene flow, and the evolutionary history of the system were determined from one mtDNA and five nuclear genetic markers. Two demographic factors, gene flow and divergence time, are closely associated with neutral genetic divergence and may explain the pattern of morphological divergence across the system. Additionally, extensive morphological divergence in this system is only occurring between islands experiencing little gene flow, providing support for the prevalence of allopatric divergence in island systems.