The influence of gene flow and drift on genetic and phenotypic divergence in two species ofZosteropsin Vanuatu

Abstract

Colonization of an archipelago sets the stage for adaptive radiation. However, some archipelagos are home to spectacular radiations, while others have much lower levels of diversification. The amount of gene flow among allopatric populations is one factor proposed to contribute to this variation. In island colonizing birds, selection for reduced dispersal ability is predicted to produce changing patterns of regional population genetic structure as gene flow-dominated systems give way to driftmediated divergence. If this transition is important in facilitating phenotypic divergence, levels of genetic and phenotypic divergence should be associated. We consider population genetic structure and phenotypic divergence among two co-distributed, congeneric (Genus: Zosterops) bird species inhabiting the Vanuatu archipelago. The more recent colonist, Z. lateralis, exhibits genetic patterns consistent with a strong influence of distance-mediated gene flow. However, complex patterns of asymmetrical gene flow indicate variation in dispersal ability or inclination among populations. The endemic species, Z. flavifrons, shows only a partial transition towards a drift-mediated system, despite a long evolutionary history on the archipelago. We find no strong evidence that gene flow constrains phenotypic divergence in either species, suggesting that levels of inter-island gene flow do not explain the absence of a radiation across this archipelago.

Comparative phylogeography of the centipedes Cryptops pictus and C. niuensis (Chilopoda) in New Caledonia, Fiji and Vanuatu

“…To date, very few studies at the population level have been performed in the South Pacific (Clegg and Phillimore 2010;Kirchman and Franklin 2007;Kurata et al 2008), and few have been evaluated in a comparative framework among island archipelagos (Garb and Gillespie 2006). Considering that New Caledonia and Fiji are roughly of the same size, the difference in the amount of genetic variation observed could be linked (in addition to difference in isolation) to the evolutionary timescale (Hamilton et al 2009;Keppel et al 2009).…”

Vicariance and marine migration in continental island populations of a frog endemic to the Atlantic Coastal forest

“…Migration between continental islands and the mainland may be more common, while species on oceanic islands that exist along an archipelago can exhibit gene flow among adjacent islands (Illera et al, 2007;Clegg and Phillimore, 2010;Illera et al, 2014;Bell et al, 2015a, b). This distinction is a generalization; the migration levels in both oceanic and continental islands will depend on the dispersal ability of particular colonizing organisms and the degree to which marine environments act as barriers to dispersal.…”

Darwin's Galápagos finches in modern biology

“…Ground finches explore the soil and large rocks for seeds, cactus finches penetrate cactus flowers and fruits with their pointed beaks, Warbler finches probe leaves of trees and bushes for small arthropods and sharp-beaked finches peck on feather buds to drink blood from boobies or crack their eggs by pushing them over rocks. In one of the most extraordinary examples in all birds, woodpecker finches will make a tool from a twig or branch to remove an insect larva from a crevice in the tree trunk when they are unable to reach it with their beak (Lack 1947;Bowman 1961). Such diverse and neophilic behaviours probably have a profound genetic component, but how and when such behaviours evolved in Darwin's finches remained a matter of speculation.…”

“…He later described them and asked John Gould of the Museum of the Zoological Society in London to study and catalogue them. It was Gould who realized that all of these species, though extremely diverse in terms of their shapes and sizes, which presumably reflected differences in diets, were otherwise closely related to each other and, more distantly, to species on the South American mainland (Bowman 1961). Such key 'case studies' combined with the crucial insights gleaned from other evidence, such as the fossil record, artificial selection and world biogeography, eventually led Charles Darwin to conclude that biological species are subject to change and such change is not random, but is driven by continuous adaptation to the environment (Lack 1947;Bowman 1961).…”

“…It was Gould who realized that all of these species, though extremely diverse in terms of their shapes and sizes, which presumably reflected differences in diets, were otherwise closely related to each other and, more distantly, to species on the South American mainland (Bowman 1961). Such key 'case studies' combined with the crucial insights gleaned from other evidence, such as the fossil record, artificial selection and world biogeography, eventually led Charles Darwin to conclude that biological species are subject to change and such change is not random, but is driven by continuous adaptation to the environment (Lack 1947;Bowman 1961). Many species of living organisms are being studied to understand a multitude of important aspects of evolutionary biology but few other species have as much historical, symbolic and scientific importance to the evolutionary theory as Darwin's finches (Darwin 1859;Lack 1947;Grant 1986Grant , 1999Grant & Grant 2008 and population diversity to conservation status of the mangrove finch, the most rare species of the group, to evolution of cognitive behaviours, to the role for hybridization and gene flow in finch speciation and to the development and biomechanical significance of beak shapes.…”