![]() Species boundaries appear to be maintained due to assortative mating based on learned song cues (Ratcliffe and Grant 1983, 1985 Grant and Grant 1996, 1997a, b Grant 1999), despite well-documented hybridization among several species on multiple islands (Grant and Grant 1994, 1997a Grant et al. The recognized species possess a variety of distinct ecological niches associated with morphological traits (Lack 1947 Grant 1999), though phylogenetic studies of these species have been limited in scope and somewhat contradictory (Freeland and Boag 1999 Petren et al. 1976, 2001 Boag 1983 Grant and Grant 2002a, b, 2006) on highly heritable traits such as beak shape (Boag and Grant 1978 Boag 1983). The radiation of finches is typically accredited to strong natural selection (Grant et al. The mechanism of species accumulation within the Galápagos finches is still largely unknown due to unresolved phylogenetic relationships (Petren et al. The Galápagos archipelago is an ideal system in which to study the dynamics of endemic radiations because of its oceanic isolation, variety of island sizes and proximities, discrete geographical nature, and known geological age of islands (Geist et al. Additionally, meta-population dynamics and interspecies introgression must be addressed specifically in these systems as increasing evidence supports models of speciation and morphological differentiation in the presence of gene flow between populations or species (Shaw 2002 Grant et al. Reconstructing the dynamics of these adaptive radiations through time and space is difficult, as typical phylogenetic, phylogeographic, and island biogeographic methods are limited in their ability to reconstruct history for recently divergent lineages (Maddison 1997). In many of these cases, the question remains as to how these fragmented populations are able to diversify so rapidly into distinct evolutionary entities. 2013), the Hawaiian honeycreepers (Tarr and Fleischer 1995), the African cichlids (Day et al. Several model systems have demonstrated the power of fragmented landscapes in facilitating the adaptive radiation of phenotypes including the Caribbean Anolis lizards (Knox et al. This landscape perspective highlights a likely role for isolation of peripheral populations in initial divergence, and demonstrates that peripheral populations may maintain genetic diversity through outbreeding during the initial stages of speciation. Second, peripheral islands have more admixed populations while central islands maintain more distinct species boundaries. First, several species exhibit concordant patterns of population divergence across the channel separating the Galápagos platform islands from the separate volcanic province of northern islands. Interisland gene flow and interspecies introgression vary geographically in predictable ways. The ground and tree finch clades lack species-level phylogenetic structure. difficilis) basal to all ground and tree finches. Phylogenetic species-trees recovered seven major finch clades: ground, tree, vegetarian, Cocos Island, grey and green warbler finches, and a distinct clade of sharp-beaked ground finches ( Geospiza cf. We combined sequence data from 14 nuclear introns, mitochondrial markers, and microsatellite variation from 51 populations of all 15 recognized species. Here we combine phylogenetic and landscape genetic approaches to understand diversification in Darwin's finches, a model adaptive radiation. Many classic examples of adaptive radiations take place within fragmented systems such as islands or mountains, but the roles of mosaic landscapes and variable gene flow in facilitating species diversification is poorly understood.
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