Pi-Wen Tsai R. Terry Chesser Rong-Chien Lin Cheng-Te Yao Xiu-Hua Tian Shou-Hsien Li Carol K.L. Yeung 2011 Although founder effect speciation has been a popular theoretical model for the speciation of geographically isolated taxa, its empirical importance has remained difficult to evaluate due to the intractability of past demography, which in a founder effect speciation scenario would involve a speciational bottleneck in the emergent species and the complete cessation of gene flow following divergence. Using regression-weighted approximate Bayesian computation, we tested the validity of these two fundamental conditions of founder effect speciation in a pair of sister species with disjunct distributions: the royal spoonbill <i>Platalea regia</i> in Australasia and the black-faced spoonbill <i>Pl. minor</i> in eastern Asia. When compared with genetic polymorphism observed at 20 nuclear loci in the two species, simulations showed that the founder effect speciation model had an extremely low posterior probability (1.55 &times; 10^-8) of producing the extant genetic pattern. In contrast, speciation models that allowed for postdivergence gene flow were much more probable (posterior probabilities were 0.37 and 0.50 for the bottleneck with gene flow and the gene flow models, respectively) and postdivergence gene flow persisted for a considerable period of time (more than 80% of the divergence history in both models) following initial divergence (median = 197,000 generations, 95% credible interval [CI]: 50,000-478,000, for the bottleneck with gene flow model; and 186,000 generations, 95% CI: 45,000-477,000, for the gene flow model). Furthermore, the estimated population size reduction in <i>Pl. regia</i> to 7,000 individuals (median, 95% CI: 487-12,000, according to the bottleneck with gene flow model) was unlikely to have been severe enough to be considered a bottleneck. Therefore, these results do not support founder effect speciation in <i>Pl. regia</i> but indicate instead that the divergence between <i>Pl. regia</i> and <i>Pl. minor</i> was probably driven by selection despite continuous gene flow. In this light, we discuss the potential importance of evolutionarily labile traits with significant fitness consequences, such as migratory behavior and habitat preference, in facilitating divergence of the spoonbills. application/pdf 10.1093/molbev/msq210 en Oxford Journals Testing founder effect speciation: Divergence population genetics of the Spoonbills <i>Platalea regia</i> and <i>Pl. minor</i> (Threskiornithidae, Aves) article