Subtle population genetic structure in the Hawaiian grouper, Epinephelus quernus (Serranidae) as revealed by mitochondrial DNA analyses

The endemic Hawaiian grouper, Epinephelus quernus , is a commercially important species experiencing intense fishing pressure in part of its distributional range. We examined population genetic structure with 398 base pairs of the mitochondrial control region across a large portion of the range of E. quernus , spanning approximately 2000 km of the Hawaiian archipelago. Examination of genetic diversity shows that Gardner Island, situated midway along the island chain, harbours the most diverse haplotypes. F -statistics and Bayesian estimates of migration also reveal the mid-archipelago as genetically differentiated, where the first significant break among adjacent pairs of populations lies between the islands of Nihoa and Necker. Most island comparisons beyond Necker and Gardner to the north-west and among the lower five islands to the south-east show little to no genetic differences. Evidence of historical population expansion across the islands was also found by Maximum Likelihood analyses. The results suggest that management should be structured to reflect the genetic differentiation and diversity in the mid-archipelago, the patterns of which may be associated with oceanic current patterns.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81 , 449–468.     

Molecular phylogeny and biogeography of the endemic Hawaiian Succineidae (Gastropoda: Pulmonata)

The endemic Hawaiian Succineidae represent an important component of the exceptionally diverse land snail fauna of the Hawaiian Islands, yet they remain largely unstudied. We employed 663-bp fragments of the cytochrome oxidase I (COI) mitochondrial gene to investigate the evolution and biogeography of 13 Hawaiian succineid land snail species, six succineid species from other Pacific islands and Japan, and various outgroup taxa. Results suggest that: (1) species from the island of Hawaii are paraphyletic with species from Tahiti, and this clade may have had a Japanese (or eastern Asian) origin; (2) species from five of the remaining main Hawaiian islands form a monophyletic group, and the progression rule, which states that species from older islands are basal to those from younger islands, is partially supported; no geographic origin could be inferred for this clade; (3) succineids from Samoa are basal to all other succineids sampled (maximum likelihood) or unresolved with respect to the other succineid clades (maximum parsimony); (4) the genera Succinea and Catinella are polyphyletic. These results, while preliminary, represent the first attempt to reconstruct the phylogenetic pattern for this important component of the endemic Hawaiian fauna.     

Life history,larval dispersal,and connectivity in coral reef fish among the Scattered Islands of the Mozambique Channel

The Western Indian Ocean harbors one of the world’s most diverse marine biota yet is threatened by exploitation with few conservation measures in place. Primary candidates for conservation in the region are the Scattered Islands (Îles Éparses), a group of relatively pristine and uninhabited islands in the Mozambique Channel. However, while optimal conservation strategies depend on the degree of population connectivity among spatially isolated habitats, very few studies have been conducted in the area. Here, we use highly variable microsatellite markers from two damselfishes (Amphiprion akallopisos and Dascyllus trimaculatus) with differing life history traits [pelagic larval duration (PLD), adult habitat] to compare genetic structure and connectivity among these islands using classic population structure indices as well as Bayesian clustering methods. All classical fixation indexes F _ST, R _ST, G′_ST, and Jost’s D show stronger genetic differentiation among islands for A. akallopisos compared to D. trimaculatus, consistent with the former species’ shorter PLD and stronger adult site attachment, which may restrict larval dispersal potential. In agreement with these results, the Bayesian analysis revealed clear genetic differentiation among the islands in A. akallopisos, separating the southern group (Bassas da India and Europa) from the center (Juan de Nova) and northern (Îles Glorieuses) islands, but not for D. trimaculatus. Local oceanographic patterns such as eddies that occur along the Mozambique Channel appear to parallel the results reported for A. akallopisos, but such features seem to have little effect on the genetic differentiation of D. trimaculatus. The contrasting patterns of genetic differentiation between species within the same family highlight the importance of accounting for diverse life history traits when assessing community-wide connectivity, an increasingly common consideration in conservation planning.

     

Microevolutionary patterns and processes of the Native Hawaiian colonizing fern Odontosoria chinensis (Lindsaeaceae)

Abstract.— The vascular‐plant flora of the Hawaiian Islands is characterized by one of the highest rates of species endemism in the world. Among flowering plants, approximately 89% of species are endemic, and among pteridophytes, about 76% are endemic. At the single‐island level, however, rates of species endemism vary dramatically between these two groups with 80% of angiosperms and only 6% of pteridophytes being single‐island endemics. Thus, in many groups of Hawaiian angiosperms, it is possible to link studies of phylogeny, evolution, and biogeographic history at the interspecific and interisland levels. In contrast, the low level of single‐island species endemism among Hawaiian pteridophytes makes similar interspecific and interisland studies nearly impossible. Higher levels of interisland gene flow may account for the different levels of single‐island endemism in Hawaiian pteridophytes relative to angiosperms. The primary question we addressed in the present study was: Can we infer microevolutionary patterns and processes among populations within widespread species of Hawaiian pteridophytes wherein gene flow is probably common? To address this broad question, we conducted a population genetic study of the native Hawaiian colonizing species Odontosoria chinensis. Data from allozyme analyses allowed us to infer: (1) significant genetic differentiation among populations from different islands; (2) historical patterns of dispersal between particular pairs of islands; (3) archipelago‐level patterns of dispersal and colonization; (4) founder effects among populations on the youngest island of Hawaii; and, (5) that this species primarily reproduces via outcrossing, but may possess a mixed‐mating system.     

Adaptive radiation of island plants: evidence from Aeonium (Crassulaceae) of the Canary Islands

The presence of diverse and species-rich plant lineages on oceanic islands is most often associated with adaptive radiation. Here we discuss the possible adaptive significance of some of the most prominent traits in island plants, including woodiness, monocarpy and sexual dimorphisms. Indirect evidence that such traits have been acquired through convergent evolution on islands comes from molecular phylogenies; however, direct evidence of their selective value rarely is obtained. The importance of hybridization in the evolution of island plants is also considered as part of a more general discussion of the mechanisms governing radiations on islands. Most examples are from the Hawaiian and Canarian floras, and in particular from studies on the morphological, ecological and molecular diversification of the genus Aeonium, the largest plant radiation of the Canarian Islands.     

Colonization history and population genetics of the color-polymorphic hawaiian happy-face spider theridion grallator (araneae, theridiidae)

Past geological and climatological processes shape extant biodiversity. In the Hawaiian Islands, these processes have provided the physical environment for a number of extensive adaptive radiations. Yet, single species that occur throughout the islands provide some of the best cases for understanding how species respond to the shifting dynamics of the islands in the context of colonization history and associated demographic and adaptive shifts. Here, we focus on the Hawaiian happy-face spider, a single color-polymorphic species, and use mitochondrial and nuclear allozyme markers to examine (1) how the mosaic formation of the landscape has dictated population structure, and (2) how cycles of expansion and contraction of the habitat matrix have been associated with demographic shifts, including a "quantum shift" in the genetic basis of the color polymorphism. The results show a marked structure among populations consistent with the age progression of the islands. The finding of low genetic diversity at the youngest site coupled with the very high diversity of haplotypes on the slightly older substrates that are highly dissected by recent volcanism suggests that the mosaic structure of the landscape may play an important role in allowing differentiation of the adaptive color polymorphism.     

SEQUENTIAL RADIATIONS AND PATTERNS OF SPECIATION IN THE HAWAIIAN CRICKET GENUS LAUPALA INFERRED FROM DNA SEQUENCES

The tremendous diversity of endemic Hawaiian crickets is thought to have originated primarily through intraisland radiations, in contrast to an interisland mode of diversification in the native Hawaiian Drosophila. The Hawaiian cricket genus Laupala (family Gryllidae) is one of several native genera of flightless crickets found in rain-forest habitat across the Hawaiian archipelago. I examined the phylogenetic relationships among mitochondrial DNA (mtDNA) sequences sampled from 17 species of Laupala, including the 12S ribosomal RNA (rRNA), transfer RNA (RNA)^val and 16S rRNA regions. The distribution of mtDNA variants suggests that species within Laupala are endemic to single islands. The phylogenetic estimate produced from both maximum likelihood and maximum parsimony supports the hypothesis that speciation in Laupala occurred mainly within islands. The inferred biogeographical history suggests that diversification in Laupala began on Kauai, the oldest rain-forested Hawaiian island. Subsequently, colonization to younger islands in the archipelago resulted in a radiation of considerable phylogenetic diversity. Phylogenetic patterns in mtDNA are not congruent with prior systematic or taxonomic hypotheses. Hypotheses that may explain the conflict between the phylogenetic patterns of mtDNA variation and the species taxonomy are discussed.     

Long-term population trends of endangered Hawaiian waterbirds

We analyzed long-term winter survey data (1956–2007) for three endangered waterbirds endemic to the Hawaiian Islands, the Hawaiian moorhen (Gallinula chloropus sandvicensis), Hawaiian coot (Fulica alai), and Hawaiian stilt (Himantopus mexicanus knudseni). Time series were analyzed by species–island combinations using generalized additive models, with alternative models compared using Akaike information criterion (AIC). The best model included three smoothers, one for each species. Our analyses show that all three of the endangered Hawaiian waterbirds have increased in population size over the past three decades. The Hawaiian moorhen increase has been slower in more recent years than earlier in the survey period, but Hawaiian coot and stilt numbers still exhibit steep increases. The patterns of population size increase also varied by island, although this effect was less influential than that between species. In contrast to earlier studies, we found no evidence that rainfall affects counts of the target species. Significant population increases were found on islands where most wetland protection has occurred (Oahu, Kauai), while weak or no increases were found on islands with few wetlands or less protection (Hawaii, Maui). Increased protection and management, especially on Maui where potential is greatest, would likely result in continued population gains, increasing the potential for meeting population recovery goals.     

Repeated range expansion and niche shift in a volcanic hotspot archipelago: Radiation of C4 Hawaiian Euphorbia subgenus Chamaesyce (Euphorbiaceae)

Woody perennial plants on islands have repeatedly evolved from herbaceous mainland ancestors. Although the majority of species in Euphorbia subgenus Chamaesyce section Anisophyllum (Euphorbiaceae) are small and herbaceous, a clade of 16 woody species diversified on the Hawaiian Islands. They are found in a broad range of habitats, including the only known C₄ plants adapted to wet forest understories. We investigate the history of island colonization and habitat shift in this group. We sampled 153 individuals in 15 of the 16 native species of Hawaiian Euphorbia on six major Hawaiian Islands, plus 11 New World close relatives, to elucidate the biogeographic movement of this lineage within the Hawaiian island chain. We used a concatenated chloroplast DNA data set of more than eight kilobases in aligned length and applied maximum likelihood and Bayesian inference for phylogenetic reconstruction. Age and phylogeographic patterns were co‐estimated using BEAST. In addition, we used nuclear ribosomal ITS and the low‐copy genes LEAFY and G3pdhC to investigate the reticulate relationships within this radiation. Hawaiian Euphorbia first arrived on Kaua`i or Ni`ihau ca. 5 million years ago and subsequently diverged into 16 named species with extensive reticulation. During this process Hawaiian Euphorbia dispersed from older to younger islands through open vegetation that is disturbance‐prone. Species that occur under closed vegetation evolved in situ from open vegetation of the same island and are only found on the two oldest islands of Kaua`i and O`ahu. The biogeographic history of Hawaiian Euphorbia supports a progression rule with within‐island shifts from open to closed vegetation.     

Hydra of Hawaii: phylogenetic relationships with continental species

The presence of freshwater hydra in the Hawaiian Islands, over 3,700 km from the nearest continental margin, provokes the question of how these animals could reach the islands. We examined three islands for hydra and found two species (the brown hydra, Hydra vulgaris Pallas 1766, and green hydra, H. viridissima Pallas 1766) present at multiple locations on Oahu and Kauai, and at a single site on Hawaii. Phylogenetic analysis based on the internal transcribed spacer (ITS1 and ITS2) regions of ribosomal DNA indicates that all collected strains of brown hydra were closely related to each other—consistent with a single introduced origin. The analysis also shows that all sampled Hawaiian brown hydra fall within a specific clade of H. vulgaris. This clade is sister to a North American clade and nested within a deeper North/Central America clade. The clade with all the Hawaiian brown hydra includes also individuals from Southern California, suggesting a Californian origin for the brown Hawaiian hydra. Hawaiian hydra were probably transported to the islands by man.     

Feral Cat Globetrotters: genetic traces of historical human‐mediated dispersal

Endemic species on islands are highly susceptible to local extinction, in particular if they are exposed to invasive species. Invasive predators, such as feral cats, have been introduced to islands around the world, causing major losses in local biodiversity. In order to control and manage invasive species successfully, information about source populations and level of gene flow is essential. Here, we investigate the origin of feral cats of Hawaiian and Australian islands to verify their European ancestry and a potential pattern of isolation by distance. We analyzed the genetic structure and diversity of feral cats from eleven islands as well as samples from Malaysia and Europe using mitochondrial DNA (ND5 and ND6 regions) and microsatellite DNA data. Our results suggest an overall European origin of Hawaiian cats with no pattern of isolation by distance between Australian, Malaysian, and Hawaiian populations. Instead, we found low levels of genetic differentiation between samples from Tasman Island, Lana'i, Kaho'olawe, Cocos (Keeling) Island, and Asia. As these populations are separated by up to 10,000 kilometers, we assume an extensive passive dispersal event along global maritime trade routes in the beginning of the 19th century, connecting Australian, Asian, and Hawaiian islands. Thus, islands populations, which are characterized by low levels of current gene flow, represent valuable sources of information on historical, human‐mediated global dispersal patterns of feral cats.     

Biogeography and the evolution of flightlessness in a radiation of Hawaiian moths (Xyloryctidae: Thyrocopa)

Aim Although the ability to fly confers benefits to most insects, some taxa have become secondarily flightless. Insect flightlessness may be more likely to evolve in environments such as islands and other windswept and alpine areas, but this prediction has rarely been tested while controlling for phylogenetic effects. Here we present a phylogeny for the endemic Hawaiian Lepidoptera genus Thyrocopa, which has two flightless species that occur in alpine areas on Maui and Hawaii islands, in order to determine whether the flightless species are sister to each other or represent separate losses of flight. We also explore divergence times and biogeographic patterns of inter‐island colonization in Thyrocopa, and present the first Hawaiian study to sample a genus from nine islands. Location The Hawaiian Islands. Methods The phylogeny is composed of 70 individuals (including 23 Thyrocopa species and 7 outgroup species) sequenced for portions of cytochrome c oxidase subunit I, elongation factor 1α and wingless genes, for a total of 1964 base pairs, and was estimated using both parsimony (paup *) and Bayesian inference (Mr Bayes ). Divergence times were estimated using the beast software package. Results Our results indicate that two independent invasions of alpine habitats with concomitant loss of flight have occurred in Thyrocopa. Based on current taxon sampling, Thyrocopa colonized the Hawaiian Islands slightly before the formation of Kauai. In terms of overall patterns of diversification, subclades generally follow a progression from older to younger islands. The genus has the greatest number of species on Kauai, with species numbers generally decreasing with decreasing island age. Main conclusions Loss of flight ability has evolved twice in a short period of geological time in Thyrocopa, perhaps as a result of low temperatures, high winds and/or a lack of predation pressure. However, several other Thyrocopa species that live on small islands with consistently high winds, such as Necker and Nihoa islands, retain the ability to fly.     

Prey‐associated head‐size variation in an invasive lizard in the Hawaiian Islands

Biological invasions are recognized as a primary driver of large‐scale changes in global ecosystems. This study addresses ecomorphological variation in head size within and among populations of an ecologically destructive invasive predator, and evaluates the potential roles of environmental components in phenotypic differentiation. We used four size‐corrected measurements of head morphology in Jackson's chameleons, Trioceros jacksonii xantholophus (N = 319), collected from multiple Hawaiian Islands to assess phenotypic variation among and within islands. Results of analysis of variance (ANOVA) comparing chameleon head size (PC1) among islands revealed significant differences (mean difference > 5%) associated with variation in both rainfall and diet composition using Mann–Whitney U‐tests and chi‐squared analyses. These results suggest that morphological differentiation among populations from different islands has occurred over a relatively short ecological timescale, and is likely the result of ecomorphological adaptation to differences in exploited prey hardness. Intra‐island allopatric population variation, however, was also detected in this study. Although we might expect that genetic change is the more likely explanation for differences between islands than within, and that plasticity may be more likely an explanation for the within‐ than the between‐island differences, it is also possible that both within‐ and between‐island patterns are the results of genetic change, or of plasticity.     

Rocks and clocks: linking geologic history and rates of genetic differentiation in anchialine organisms

The geologic history of a region can significantly impact the development of its flora and fauna, with past events shaping community patterns and evolutionary trajectories of species. In this context, islands are excellent “natural laboratories” for studying the fundamental processes of evolution due to their discrete geographical nature and dynamic geologic histories. An island system meeting these criteria is the Hawaiian Archipelago, which is ideal for testing how island geologic history influences the processes leading to population genetic variation and differentiation. One Hawaiian endemic whose evolutionary history is closely tied to the geology of the islands is the anchialine atyid shrimp Halocaridina, whose mitochondrial cytochrome oxidase I (COI) gene is hypothesized to be evolving at the rate of 20% per million years. To validate this rapid evolutionary rate, time since divergence estimates between geographically close, yet genetically distinct, populations were calculated for Halocaridina from anchialine habitats on the islands of Hawai’i, Maui, and O’ahu. On the younger (i.e., <1.5 million years) islands of Hawai’i and Maui, where all anchialine habitats occur in basalt, application of the Halocaridina molecular clock identified a strong correlation between levels of genetic divergence and the geologic age of the region inhabited by those populations. In contrast, this relationship weakened when similar analyses were conducted for Halocaridina from limestone anchialine habitats on the older (i.e., >2.75 million years) island of O’ahu. These results suggest geologic age, basin origin and/or composition are important factors that should be taken into consideration when conducting molecular clock analyses on anchialine flora and fauna as well as island populations in general.     

Phylogeographic patterns of Hawaiian Megalagrion damselflies (Odonata: Coenagrionidae) correlate with Pleistocene island boundaries

The Pleistocene geological history of the Hawaiian Islands is becoming well understood. Numerous predictions about the influence of this history on the genetic diversity of Hawaiian organisms have been made, including the idea that changing sea levels would lead to the genetic differentiation of populations isolated on individual volcanoes during high sea stands. Here, we analyse DNA sequence data from two closely related, endemic Hawaiian damselfly species in order to test these predictions, and generate novel insights into the effects of Pleistocene glaciation and climate change on island organisms. Megalagrion xanthomelas and Megalagrion pacificum are currently restricted to five islands, including three islands of the Maui Nui super-island complex (Molokai, Lanai, and Maui) that were connected during periods of Pleistocene glaciation, and Hawaii island, which has never been subdivided. Maui Nui and Hawaii are effectively a controlled, natural experiment on the genetic effects of Pleistocene sea level change. We confirm well-defined morphological species boundaries using data from the nuclear EF-1alpha gene and show that the species are reciprocally monophyletic. We perform phylogeographic analyses of 663 base pairs (bp) of cytochrome oxidase subunit II (COII) gene sequence data from 157 individuals representing 25 populations. Our results point to the importance of Pleistocene land bridges and historical island habitat availability in maintaining inter-island gene flow. We also propose that repeated bottlenecks on Maui Nui caused by sea level change and restricted habitat availability are likely responsible for low genetic diversity there. An island analogue to northern genetic purity and southern diversity is proposed, whereby islands with little suitable habitat exhibit genetic purity while islands with more exhibit genetic diversity.     

Population variation and hybridization: Comparison of finches from two archipelagos

Summary Some populations of Darwin's Finches (Emberizinae) are exceptionally variable in body size and beak traits as a result of introgressive hybridization. A study of museum specimens of honeycreeper-finches (Carduelinae) from the Hawaiian islands was undertaken to see if the same phenomenon was manifested by a different phyletic group of finches in a different archipelago. Five hundred and twenty-four specimens of the seven species with finch-like bills were measured and their coefficients of variation were compared with those of the ground finch group (six species) of Darwin's Finches. Coefficients were smaller in the Hawaiian finches. Sympatric and, hence, potentially hybridizing species on the island of Hawaii were not consistently more variable than the allopatric species on other islands in the archipelago. The one species with both sympatric and allopatric populations did not show greater variation in the sympatric population. There is little evidence from these comparisons of hybridization occurring in the last 100 years. The difference between the two finch faunas can be explained in terms of two factors. Finches have been present for a longer time in the Hawaiian archipelago than in the Galápagos archipelago and have had more time to not only diversify but to evolve pre- and post-zygotic isolating mechanisms. In the generally less seasonal and floristically richer Hawaiian islands they have evolved greater dietary specializations. Beak traits adapted to specialist feeding may have been under stronger stabilizing selection and hybrids (if formed) may have been at a strong disadvantage in the absence of an ecological niche intermediate between the niches of the two parental species. Results of published electrophoretic studies of genetic variation suggest that the early phase of differentiation, involving occasional introgressive hybridization, may last for up to 5 million years.     

Seed plants of Fiji: an ecological analysis

An annotated list of indigenous Fijian seed plant genera is presented and comprises 484 genera and 1315 species in 137 families. The relative diversity of the largest families and genera in Fiji is indicated and compared with floras in New Caledonia and the Upper Watut Valley, Papua New Guinea. Differences and similarities appear to be due to biogeographical/phylogenetic factors rather than ecological differences or means of dispersal. Generic diversity for the seed plants as a whole is greatest between 0–100 m and decreases monotonically with altitude. However, in the largest family, Orchidaceae, maximum diversity occurs between 200–400 m. Fifty percent of the families are recorded from shore habitat. Twenty‐seven percent of the families and 80 species occur in or around mangrove, where the most diverse families are Orchidaceae, Rubiaceae, and the legumes. Some of the mangrove‐associate species are pantropical or Indo‐Pacific but most are locally or regionally endemic. Fifty‐six percent of the Fijian families are recorded on limestone. Twenty‐nine species are restricted to limestone and 12 species usually occur on limestone. The importance of calcium in reducing the effects of salinity is emphasized and 39 species are recorded from both mangrove and limestone. A plagiotropic habit occurs in 38 species which occur on limestone or around beaches, and 20 of these are Pacific endemics. Genera restricted to higher altitudes include many present elsewhere in Melanesia but absent from Australia despite suitable habitat there, again indicating the importance of biogeographical and historical factors. Altitudinal anomalies in Fiji taxa are cited and include 7 anomalously high records from northern Viti Levu, a site of major uplift, and 22 anomalously low altitudinal records in the Lau Group, a site of subsidence. It is suggested that the Fijian flora has not been derived from immigrants from Asia, but has evolved more or less in situ. Taxa would have survived as metapopulations on the individually ephemeral volcanic islands always found at oceanic subduction zones and hot spots, and the atolls which characterize areas of subsidence. The complex geology of Fiji is determined by its position between two subduction zones of opposite polarity, the Vanuatu and Tonga Trenches, in what is currently a region of transform faulting. The large islands comprise fragments of island arcs that have amalgamated and welded together. There has been considerable uplift as well as subsidence in the islands and it is suggested that both these processes have had drastic effects on the altitudinal range of the taxa. Limestone and mangrove floras could have provided a widespread, diverse ancestral species pool from which freshwater swamp forest, lowland rainforest, dry forest, secondary forest, thickets, and montane forest have been derived during phases of uplift. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89 , 407–431.     

PACT in practice: comparative historical biogeographic patterns and species–area relationships of the Greater Antillean and Hawaiian Island terrestrial biotas

Aim To compare the evolutionary and ecological patterns of two extensively studied island biotas with differing geological histories (the Hawaiian Islands and the Greater Antilles). We evaluated the results from PACT (phylogenetic analysis for comparing trees), an innovative approach that has been proposed to reveal general patterns of biotic expansion (between regions) and in situ (within a region) diversification, as well as species–area relationships (SAR) and the taxon pulse dynamic. Location The Hawaiian Islands and Greater Antilles. Methods We used the PACT algorithm to construct general area cladograms and identified biotic expansion and in situ nodes. We analysed the power‐law SAR and relative contribution of biotic expansion and in situ diversification events using power‐law and linear regression analyses. Results Both biotic expansion and in situ nodes were prevalent throughout the PACT general area cladograms (Greater Antilles, 55.9% biotic expansion, 44.1% in situ; Hawaiian Islands, 40.6% biotic expansion, 59.4% in situ). Of the biotic expansion events, both forward and backward events occurred in both regions (Greater Antilles, 85.1% forward, 14.9% backward; Hawaiian Islands, 65% forward, 35% backward). Additionally, there is a power‐law SAR for the Greater Antilles but not for the Hawaiian Islands. However, exclusion of Hawai'i (the youngest, largest Hawaiian Island) produced a power‐law SAR for the Hawaiian Islands. Main conclusions The prevalence of in situ events as well as forward and backward biotic expansion events reveals that both Hawaiian and Greater Antillean biotas have evolved through alternating episodes of biotic expansion and in situ diversification. These patterns are characteristic of the taxon pulse dynamic, for which few data have previously been recorded on islands. Additionally, our analysis revealed that historical influences on the power‐law SARs are pronounced in both assemblages: old, small islands are relatively species rich and young, large islands are relatively species poor. Thus, our PACT results are consistent with hypotheses of geological influence on the evolution of island biotas and also provide greater insight into the role of the taxon pulse dynamic in the formation of island equilibria.     

Distributional shifts – not geographic isolation – as a probable driver of montane species divergence

As biodiversity hotspots, montane regions have been a focus of research to understand the divergence process. Like their oceanic counterparts, the diversity of the ‘sky islands’ might be ascribed to geographic isolation of mountaintops. However, because the sky islands, and especially those in northern latitudes, are subject to extreme climatic events such as the glacial cycles that drove both altitudinal and geographical shifts in species’ distributions, the dynamic colonization process is also a possible factor driving divergence. Here we test these two hypotheses (i.e. isolation versus colonization) in a flightless montane grasshopper, Melanoplus oregonensis, which is a member of a diverse group that radiated across the Rocky Mountains of North America. Using approximate Bayesian computation (ABC) and spatially explicit simulations that account for spatial heterogeneity and temporal shifts in species distributions, we show that a colonization model of the sky islands from refugial populations provides a significantly better fit to the empirical genetic data than a model of the geographic isolation among sky islands. Moreover, support for the colonization model holds irrespective of whether the movement of individuals was modeled as a diffusion process or was informed by differences in habitat suitabilities across the landscape. With validation analyses to confirm the models provide a good fit to the data, as well as general power and quality analyses, the research not only adds to a growing body of work on the complex dynamics underlying montane biodiversity, but it also provides much needed evaluation of competing hypotheses based on explicit models of the divergence process, as opposed to inferences about diversification drivers from species diversity patterns.     

ARTIFICIAL HYBRIDIZATION IN HAWAIIAN WIKSTROEMIA (THYMELAEACEAE)

Crosses were performed within and between 19 Hawaiian populations of the mostly dioecious woody shrub Wikstroemia. These populations are from a variety of habitats on the six major islands and are morphologically diverse. The populations are referrable to eight of the 12 species recognized by Peterson. Almost all hybrid combinations produced seeds, and seed-set was not significantly different among three categories of hybrids (within population, between populations on the same island, and between populations on different islands). F₁s from many of the crosses were vigorous and fertile, leading to the conclusion that these populations are not reproductively isolated from each other and the assumption that they are genetically very similar. Natural hybridization was difficult to detect because the species described by Peterson intergrade morphologically and ecologically. The crossability and interfertility of populations of Wikstroemia may be explained by one or more of the following hypotheses: 1) recency of colonization, 2) the founder effect, 3) lack of selection for barriers to interbreeding, and 4) gross morphological changes without associated large genetic changes.