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The island syndrome is a widespread biological phenomenon that describes a suite of morphological, behavioural, demographic and life‐history changes associated with island dwelling. These similar evolutionary responses among disparate groups of animals and plants represent a remarkable case of convergent evolution. Among animals, birds are a highly suitable group to study the island syndrome; they are a comparatively data‐rich taxon, are frequent island colonisers, and sometimes display extreme adaptations such as the loss of flight. However, the avian island syndrome literature is fragmented, and multiple components are rarely considered together even though many are inextricably linked. We reviewed multi‐species comparative studies, single‐species or population‐level studies and anecdotal accounts, to summarise and assess the support for individual components of the island syndrome for birds, and to identify suites of traits that should be considered together. The weight of evidence for island syndrome patterns in morphology is substantial, but is more partial or even anecdotal for various aspects of behaviour, life history and physiology. Full validation of the island syndrome in birds will require the less‐studied components to be treated in a comparative framework, and for covarying components to be examined in an integrated way. An improved description of the scope of the syndrome will pave the way to understanding its drivers. [ABSTRACT FROM AUTHOR]

Body size variation is an enigma. We do not understand why species achieve the sizes they do, and this means we also do not understand the circumstances under which gigantism or dwarfism is selected. We develop size-structured integral projection models to explore evolution of body size and life history speed. We make few assumptions and keep models simple: all functions remain constant across models except for the one that describes development of body size with age. We set sexual maturity to occur when size attains 80% of the asymptotic size, which is typical of a large mammal, and allow negative density dependence to only affect either reproduction or juvenile survival. Fitness -- the quantity that is maximized by adaptive evolution -- is carrying capacity in our models, and we are consequently interested in how it changes with size at sexual maturity, and how this association varies with development rate. The simple models generate complex dynamics while providing insight into the circumstances when extremes of body size evolve. The direction of selection leading to either gigantism or dwarfism crucially depends on the proportion of the population that is sexually mature, which in turn depends on how the development function determines the survivorship schedule. The developmental trajectories consequently interact with size-specific survival or reproductive rates to determine the best life history and the optimal body size emerges from that interaction. These dynamics result in trade-offs between different components of the life history, with the form of the trade-off that emerges depending upon where in the life history density dependence operates most strongly. Empirical application of the approach we develop has potential to help explain the enigma of body size variation across the tree of life.

Colonization, speciation and extinction are dynamic processes that influence global patterns of species richness.sup.1-6. Island biogeography theory predicts that the contribution of these processes to the accumulation of species diversity depends on the area and isolation of the island.sup.7,8. Notably, there has been no robust global test of this prediction for islands where speciation cannot be ignored.sup.9, because neither the appropriate data nor the analytical tools have been available. Here we address both deficiencies to reveal, for island birds, the empirical shape of the general relationships that determine how colonization, extinction and speciation rates co-vary with the area and isolation of islands. We compiled a global molecular phylogenetic dataset of birds on islands, based on the terrestrial avifaunas of 41 oceanic archipelagos worldwide (including 596 avian taxa), and applied a new analysis method to estimate the sensitivity of island-specific rates of colonization, speciation and extinction to island features (area and isolation). Our model predicts--with high explanatory power--several global relationships. We found a decline in colonization with isolation, a decline in extinction with area and an increase in speciation with area and isolation. Combining the theoretical foundations of island biogeography.sup.7,8 with the temporal information contained in molecular phylogenies.sup.10 proves a powerful approach to reveal the fundamental relationships that govern variation in biodiversity across the planet. Using a global molecular phylogenetic dataset of birds on islands, the sensitivity of island-specific rates of colonization, speciation and extinction to island features (area and isolation) is estimated., Author(s): Luis Valente [sup.1] [sup.2] [sup.3] [sup.4] , Albert B. Phillimore [sup.5] , Martim Melo [sup.6] [sup.7] [sup.8] , Ben H. Warren [sup.9] , Sonya M. Clegg [sup.10] [sup.11] , [...]

While the role of selection in divergence along the speciation continuum is theoretically well understood, defining specific signatures of selection in the genomic landscape of divergence is empirically challenging. Modelling approaches can provide insight into the potential role of selection on the emergence of a heterogenous genomic landscape of divergence. Here, we extend and apply an individual‐based approach that simulates the phenotypic and genotypic distributions of two populations under a variety of selection regimes, genotype–phenotype maps, modes of migration, and genotype‐environment interactions. We show that genomic islands of high differentiation and genomic valleys of similarity may respectively form under divergent and parallel selection between populations. For both types of between‐population selection, negative and positive frequency‐dependent selection within populations generated genomic islands of higher magnitude and genomic valleys of similarity, respectively. Divergence rates decreased under strong dominance with divergent selection, as well as in models including genotype‐environment interactions under parallel selection. For both divergent and parallel selection models, divergence rate was higher under an intermittent migration regime between populations, in contrast to a constant level of migration across generations, despite an equal number of total migrants. We highlight that interpreting a particular evolutionary history from an observed genomic pattern must be done cautiously, as similar patterns may be obtained from different combinations of evolutionary processes. Modelling approaches such as ours provide an opportunity to narrow the potential routes that generate the genomic patterns of specific evolutionary histories. [ABSTRACT FROM AUTHOR]

The way that organisms diverge into reproductively isolated species is a major question in biology. The recent accumulation of genomic data provides promising opportunities to understand the genomic landscape of divergence, which describes the distribution of differences across genomes. Genomic areas of unusually high differentiation have been called genomic islands of divergence. Their formation has been attributed to a variety of mechanisms, but a prominent hypothesis is that they result from divergent selection over a small portion of the genome, with surrounding areas homogenized by gene flow. Such islands have often been interpreted as being associated with divergence with gene flow. However, other mechanisms related to genomic structure and population history can also contribute to the formation of genomic islands of divergence.We currently lack a quantitative framework to examine the dynamics of genomic landscapes under the complex and nuanced conditions that are found in natural systems. Here, we develop an individual‐based simulation to explore the dynamics of diverging genomes under various scenarios of gene flow, selection and genotype–phenotype maps.Our modelling results are consistent with empirical observations demonstrating the formation of genomic islands under genetic isolation. Importantly, we have quantified the range of conditions that produce genomic islands. We demonstrate that the initial level of genetic diversity, drift, time since divergence, linkage disequilibrium, strength of selection and gene flow are all important factors that can influence the formation of genomic islands. Because the accumulation of genomic differentiation over time tends to erode the signal of genomic islands, genomic islands are more likely to be observed in recently divergent taxa, although not all recently diverged taxa will necessarily exhibit islands of genomic divergence. Gene flow primarily slows the swamping of islands of divergence with time.By using this framework, further studies may explore the relative influence of particular suites of events that contribute to the emergence of genomic islands under sympatric, parapatric and allopatric conditions. This approach represents a novel tool to explore quantitative expectations of the speciation process, and should prove useful in elucidating past and projecting future genomic evolution of any taxa. [ABSTRACT FROM AUTHOR]

The multiple sources of information on the pattern of morphological adaptation and selection on the Capricorn silvereye, Zosterops lateralis chlorocephalus, on Heron Island, Australia, are used to study the evolutionary divergence in a population of island land bird. The estimates from the contemporary selection gradients revealed generally weak directional selection and provide a rare description of heterogeneity in long-term natural regimes.

The phenomenons like generalist foraging and niche expansion are not the full explanation for morphological shifts in island dwelling white eyes. Hence, the article reviews briefly five alternative explanations for morphological divergence in insular populations.