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Genomic studies of early-stage speciation show that differentiation accumulates in genomic regions that restrict the homogenizing effects of gene flow between incipient species ( 20). By examining sequences of multiple individuals from their natural environment, it has become possible to “catch in the act” the speciation processes between incipient lineages ( 19). Recent advances in genome sequencing and analyses have greatly improved our ability to examine the genetics of speciation and adaptive radiations. Several classic examples of adaptive radiation occur on oceanic islands, such as Darwin’s finches from the Galapagos islands ( 16), anole lizards from the Caribbean islands ( 9), Hawaiian Drosophilids ( 17), and Hawaiian silverswords ( 18), to name a few. Adaptive radiations in such settings are especially impressive and even paradoxical, given the generation of high species richness from an initially limited gene pool ( 15).
#Radiation island hawaii driver
Adaptive radiations demonstrate the remarkable power of natural selection as a driver of biological diversity, and provide excellent systems for studying evolutionary processes involved in diversification and speciation ( 13).Īdaptive radiations on remote oceanic islands are especially interesting, as colonization of remote islands is expected to involve population bottlenecks that restrict genetic variation ( 14). Differential adaptation results in divergence and, ultimately, reproductive isolation between populations ( 12). Divergent selection, the primary mechanism underlying adaptive radiations, favors extreme phenotypes ( 11) and selects alleles that confer adaptation to unoccupied or under-utilized ecological niches.
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Although definitions of adaptive radiation vary ( 2– 7), all center on ecological opportunity as a driver of adaptation and, ultimately, diversification ( 2, 8– 10). Balancing selection on multiple ancient haplotypes–or time-tested variants–may help to explain how lineages with limited gene pools can rapidly diversify to fill myriad ecological niches on remote islands.Īdaptive radiations exhibit extraordinary levels of morphological and ecological diversity ( 1). These regions experienced recurrent divergent selection as lineages colonized and diversified on new islands, and hybridization likely facilitated the transfer of these ancient variants between taxa. We discovered differentiation outliers have arisen from balancing selection on ancient divergent haplotypes that formed before the initial colonization of the archipelago. We investigated genomic regions with increased differentiation as these regions may harbor variants involved in local adaptation or reproductive isolation, thus forming the genomic basis of adaptive radiation. Gene flow was also detected within and between island taxa, suggesting a complex reticulated evolutionary history. Demographic modeling showed concordance between the divergence times of island-specific lineages and the geological formation of individual islands. We found evidence of population structure that grouped taxa by island. incana and analyzed wholegenome sequences of 131 individuals from 11 taxa sampled across the islands. Using nanopore-sequencing, we created a chromosome-level genome assembly for M. We conducted an evolutionary genomic analysis of genus Metrosideros, a landscape-dominant, incipient adaptive radiation of woody plants that spans a striking range of phenotypes and environments across the Hawaiian Islands. How genetically limited founder populations give rise to the striking phenotypic and ecological diversity characteristic of adaptive radiations is a paradox of evolutionary biology. Some of the most spectacular adaptive radiations begin with founder populations on remote islands.