Sympatric speciation, the origin of species without geographic isolation, is an outstanding and controversial issue for evolutionary biology. Theoretical work has shown it is plausible but difficult, mainly because it requires strong divergent selection and tight linkage among loci coding for different traits. Clear cases from nature were scarce until recently when sympatric speciation became the most likely explanation for the origins of sister species of cichlid fish, fruit flies and island palms. Although these examples are well supported, the processes underlying sympatric speciation remain unresolved. The aim of the proposed research is to develop and test two competing models for the sympatric speciation of sister palm tree species endemic to Lord Howe Island. In the allochronic speciation model, we expect speciation to be initiated by reduced gene flow caused by environmental effects on flowering time and temporal (neutral) assortative mating. This model is supported by a six weeks difference in the flowering peaks between the two species that is influenced by the soil type on which they grow. The allochronic model will be based on previous work by the applicant (Devaux & Lande 2008). The competing scenario will be a classical ecological speciation model in which divergent selection to contrasted ecological niches drives speciation. In this case study, divergent selection is supported by specialization of each species to different soil types. The island palm system has been intensively studied by the host group (Savolainen et al. 2006), therefore the proposed modeling work would feed on empirical data and, as outlined in the proposal, it would illuminate back empirical research towards measuring key parameters predicted by the comparison of the two models. We expect this research to provide testable predictions for the processes leading to sympatric speciation in flowering plants in general.
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