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1. Phylogeography of the highly dispersible landscape‐dominant woody species complex, Metrosideros , in Hawaii

   https://doi.org/10.1111/jbi.13650  

   Stacy, Elizabeth_Ann ; Sakishima, Tomoko ( June 2019 , Journal of Biogeography)

   Little is known about how diversification occurs within long‐lived, highly dispersible and continuously distributed groups. We examined the distribution of genetic variation within the woody genusMetrosiderosacross the Hawaiian Islands for insights into how diversification occurs within this animal‐pollinated, wind‐dispersed group. Among Hawaiian plants,Metrosiderosis unique in its formation of continuous stands within islands that span a remarkable range of environments and comprise numerous predominantly single‐island taxa.

   Hawaiian Islands.

   Metrosideros.

   We performed population genetic analyses of variation at nine nuclear microsatellite loci from 1,486 adults of 23Metrosiderosmorphotypes sampled from five main Hawaiian Islands plus additional Pacific Island populations.

   American Samoa and Tahiti populations clustered most closely with the older islands. Results also revealed isolation by distance across the archipelago, clustering of populations predominantly by island, and evidence of multiple colonizations or back‐colonizations of three islands. The number of genetic clusters peaked on islands of intermediate age, coincident with peak morphotype richness. All islands comprised a broad range of genetic distances among taxa with the greatest overall genetic distance observed on Oahu. The two taxa that are distributed broadly across the archipelago were weakly but significantly differentiated only on volcanically active Hawaii Island, where they partition early‐ and late‐successional environments. One of these taxa was positioned centrally both within individual‐island splitstree networks and across the archipelago‐wide network.

   Distance‐dependent gene flow contributes to isolation ofMetrosiderosacross islands, especially on terminal islands. Morphological diversity likely accumulates rapidly within this group, likely associated with differential adaptation across heterogeneous environments, but isolation of gene pools through speciation within continuousMetrosiderosstands likely requires persistent disruptive selection where environments are stable for long periods. The generalist, wet‐forestM.polymorphavar.glaberrimamay play a central role in the generation of the group's many, largely island‐endemic, taxa.

    

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2. Local endemism and within‐island diversification of shrews illustrate the importance of speciation in building Sundaland mammal diversity

   https://doi.org/10.1111/mec.13820  

   Demos, Terrence_C ; Achmadi, Anang_S ; Giarla, Thomas_C ; Handika, Heru ; Maharadatunkamsi ; Rowe, Kevin_C ; Esselstyn, Jacob_A ( September 2016 , Molecular Ecology)

   Island systems are important models for evolutionary biology because they provide convenient, discrete biogeographic units of study. Continental islands with a history of intermittent dry land connections confound the discrete definitions of islands and have led zoologists to predict (i) little differentiation of terrestrial organisms among continental shelf islands and (ii) extinction, rather than speciation, to be the main cause of differences in community composition among islands. However, few continental island systems have been subjected to well‐sampled phylogeographic studies, leaving these biogeographic assumptions of connectivity largely untested. We analysed nine unlinked loci from shrews of the genusCrocidurafrom seven mountains and two lowland localities on the Sundaic continental shelf islands of Sumatra and Java. Coalescent species delimitation strongly supported all currently recognizedCrociduraspecies from Sumatra (six species) and Java (five species), as well as one undescribed species endemic to each island. We find that nearly all species ofCrocidurain the region are endemic to a single island and several of these have their closest relative(s) on the same island. Intra‐island genetic divergence among allopatric, conspecific populations is often substantial, perhaps indicating species‐level diversity remains underestimated. One recent (Pleistocene) speciation event generated two morphologically distinct, syntopic species on Java, further highlighting the prevalence of within‐island diversification. Our results suggest that both between‐ and within‐island speciation processes generated local endemism in Sundaland, supplementing the traditional view that the region's fauna is relictual and primarily governed by extinction.

    

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3. Genomic investigation of colour polymorphism and phylogeographic variation among populations of black‐headed bulbul ( Brachypodius atriceps ) in insular southeast Asia

   https://doi.org/10.1111/mec.16089  

   Shakya, Subir B. ; Haryoko, Tri ; Irham, Mohammad ; Suparno ; Prawiradilaga, Dewi M. ; Sheldon, Frederick H. ( August 2021 , Molecular Ecology)

   Intraspecific polymorphism in birds, especially plumage colour polymorphism, and the mechanisms that control it are an area of active research in evolutionary biology. The black‐headed bulbul (Brachypodius atriceps) is a polymorphic species with two distinct morphs, yellow and grey. This species inhabits the mainland and virtually all continental islands of Southeast Asia where yellow morphs predominate, but on two islands in the Sunda region, Bawean and Maratua, grey morphs are common or exclusive. Here, we generated a high‐quality reference genome of a yellow individual and resequenced genomes of multiple individuals of both yellow and grey morphs to study the genetic basis of coloration and population history of the species. Using PCA and STRUCTURE analysis, we found the Maratua Island population (which is exclusively grey) to be distinct from all otherB.atricepspopulations, having been isolated c. 1.9 million years ago (Ma). In contrast, Bawean grey individuals (a subset of yellow and grey individuals on that island) are embedded within an almost panmictic Sundaic clade of yellow birds. UsingF_STandd_xyto compare variable genomic segments between Maratua and yellow individuals, we located peaks of divergence and identified candidate loci involved in the colour polymorphism. Tests of selection among coding‐proteins in highF_STregions, however, did not indicate selection on the candidate genes. Overall, we report on some loci that are potentially responsible for the grey/yellow polymorphism in a species that otherwise shows little genetic diversification across most of its range.

    

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4. When adaptive radiations collide: Different evolutionary trajectories between and within island and mainland lizard clades

   https://doi.org/10.1073/pnas.2024451118  

   Patton, Austin H. ; Harmon, Luke J. ; del Rosario Castañeda, María ; Frank, Hannah K. ; Donihue, Colin M. ; Herrel, Anthony ; Losos, Jonathan B. ( October 2021 , Proceedings of the National Academy of Sciences)

   Oceanic islands are known as test tubes of evolution. Isolated and colonized by relatively few species, islands are home to many of nature’s most renowned radiations from the finches of the Galápagos to the silverswords of the Hawaiian Islands. Despite the evolutionary exuberance of insular life, island occupation has long been thought to be irreversible. In particular, the presumed much tougher competitive and predatory milieu in continental settings prevents colonization, much less evolutionary diversification, from islands back to mainlands. To test these predictions, we examined the ecological and morphological diversity of neotropicalAnolislizards, which originated in South America, colonized and radiated on various islands in the Caribbean, and then returned and diversified on the mainland. We focus in particular on what happens when mainland and island evolutionary radiations collide. We show that extensive continental radiations can result from island ancestors and that the incumbent and invading mainland clades achieve their ecological and morphological disparity in very different ways. Moreover, we show that when a mainland radiation derived from island ancestors comes into contact with an incumbent mainland radiation the ensuing interactions favor the island-derived clade.

    

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5. Insect Radiations on Islands: Biogeographic Pattern and Evolutionary Process in Hawaiian Insects.

   Hembry, DH ; Bennett, GM ; Bess, E ; I, Jordan ; Liebherr, JK ; Magnacca, KN ; Percy, DM ; Polhemus, D ; Rubinoff, D ; Shaw, K ; et al ( January 2021 , The quarterly review of biology)

   The spectacular adaptive radiations on the Hawaiian Islands offer the tantalizing possibility of ascertaining the predictability of evolution, especially with regard to how the archipelago’s dynamic geology suggests a priori hypotheses for evolutionary pattern and process. In the past two decades advances in sequencing and phylogenetics have shed new light on the evolution of this model fauna. Here, we provide an overview of recent research on major endemic Hawaiian insect radiations. We find that, in contrast to earlier views, a substantial fraction of Hawaiian insect clades colonized the archipelago prior to the formation of the current high islands (5.1 Ma) and have persisted through one or more rounds of island formation and subsidence prior to the emergence of the current archipelago. Many Hawaiian insect radiations show elements of the progression rule, a null expectation where biogeographic patterns on the phylogeny mirror the chronological sequence of island formation, but few match its predictions exactly. Diversity in most radiations is shaped by a complicated interplay of among-island dispersal and within-island diversification. Finally, we find a positive relationship between clade age and species richness in Hawaiian insects, but with a great deal of variance that is likely explained by aspects of ecology and clade-specific factors. 

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