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.     

Invasive aphids attack native Hawaiian plants

Invasive species have had devastating impacts on the fauna and flora of the Hawaiian Islands. While the negative effects of some invasive species are obvious, other species are less visible, though no less important. Aphids (Homoptera: Aphididae) are not native to Hawai’i but have thoroughly invaded the Island chain, largely as a result of anthropogenic influences. As aphids cause both direct plant feeding damage and transmit numerous pathogenic viruses, it is important to document aphid distributions and ranges throughout the archipelago. On the basis of an extensive survey of aphid diversity on the five largest Hawaiian Islands (Hawai’i, Kaua’i, O’ahu, Maui, and Moloka’i), we provide the first evidence that invasive aphids feed not just on agricultural crops, but also on native Hawaiian plants. To date, aphids have been observed feeding and reproducing on 64 native Hawaiian plants (16 indigenous species and 48 endemic species) in 32 families. As the majority of these plants are endangered, invasive aphids may have profound impacts on the island flora. To help protect unique island ecosystems, we propose that border vigilance be enhanced to prevent the incursion of new aphids, and that biological control efforts be renewed to mitigate the impact of existing species.     

Hawai‘i’s Mountain-to-Sea Ecosystems: Social–Ecological Microcosms for Sustainability Science and Practice

There is an urgent need to develop the underlying theory and principles of “sustainability science,” based on an understanding of the fundamental interactions between nature and humans. This requires a new research and education paradigm that embraces biocomplexity, integrates the physical, biological, and social sciences, and uses a coupled, human–natural systems approach. An initiative aligned with this paradigm and approach, and centered on the Hawaiian Island’s unique mountain-to-sea ecosystems, is developing at the University of Hawai‘i. These ecosystems, extending from upland tropical forests to the fringing coral reefs, correspond to the roughly wedge-shaped catchments, traditionally called ahupua‘a in the Hawaiian language. Despite the collapse of the ahupua‘a system and, tragically, the Native Hawaiian population, its legacy of ecological and cultural stewardship remains. This legacy, and the potential of these ecosystems as microcosms for addressing the core questions of sustainability science, has provided the impetus for a growing number of projects employing a social–ecological systems perspective. An overview of three projects that employ a “learning community” approach and cultural stewardship perspective inspired by the ahupua‘a system is provided. These include the Ecosystems Thrust Area of Hawai‘i EPSCoR, a U.S. National Science Foundation research infrastructure program, focused on ecosystem research and monitoring activities; a sustainability curriculum program, Mālama I Ka ‘Āina, of the College of Education; and a project that builds on programs of the Division of Ecology and Health and its affiliated Asia-Pacific Center for Infectious Disease Ecology, linking ecosystem resilience and infectious diseases.     

Mesophotic coral ecosystems in the Hawaiian Archipelago

Efforts to map coral reef ecosystems in the Hawaiian Archipelago using optical imagery have revealed the presence of numerous scleractinian, zoothanthellate coral reefs at depths of 30–130+ m, most of which were previously undiscovered. Such coral reefs and their associated communities have been recently defined as mesophotic coral ecosystems (MCEs). Several types of MCEs are found in Hawai‘i, each of which dominates a different depth range and is characterized by a unique pattern of coral community structure and colony morphology. Although MCEs are documented near both ends of the archipelago and on many of the islands in between, the maximum depth and prevalence of MCEs in Hawai‘i were found to decline with increasing latitude. The Main Hawaiian Islands (MHI) had significantly deeper and greater percentages of scleractinian coral, and peaks in cover of both scleractinian corals and macroalgae occurred within depth bins 20 m deeper than in the Northwestern Hawaiian Islands (NWHI). Across the archipelago, as depth increased the combined percentage of living cover of mega benthic taxa declined sharply with increasing depth below 70 m, despite the widespread availability of hard substrate.     

Identification of roots in lava tube caves using molecular techniques: implications for conservation of cave arthropod faunas

Lava tube cave ecosystems on the volcanic islands of Hawai‘i support communities of rare and highly specialized cave arthropods. In these cave ecosystems, plant roots, both living and dead, provide the main energy source for cave animals. Loss of deep-rooted plants over caves will affect populations of cave-adapted animals living below. Furthermore, the loss of native plant species will likely eliminate host specific cave animals. Thus, identification of plant roots currently found in caves is necessary for the development of effective management actions that encourage the growth of appropriate deep-rooted plant species, thereby protecting the underlying cave ecosystem. We used molecular techniques to identify plant roots found within cave ecosystems on the islands of Maui and Hawai‘i. Sequences of the internal transcribed spacer (ITS) regions and the 5.8S gene of nuclear ribosomal DNA from cave roots were compared to sequences of known plant species either collected on the surface over the footprint of each cave or to sequences accessioned in GenBank. Roots in the cave ecosystem studied on Maui belonged to two alien tree species: Eucalyptus tereticornis and Grevillea robusta. Within the Hawai‘i cave ecosystem, roots of two plant species were identified: the alien tree G. robusta and the native vine Cocculus orbiculatus. The Maui cave ecosystem supports populations of at least 28 species of arthropods, including eight that are blind obligate cave inhabitants. The Hawai‘i cave ecosystem supports 18 arthropod species, of which three are cave-adapted. Creating protected reserves around biologically significant caves, controlling, and preventing the introduction of harmful invasive plant species within the cave footprint, and encouraging the establishment of deep-rooted native plant species is essential for the continued survival of the unique ecosystems found within Hawaiian lava tube cave systems.     

The association of tree species,landform, soils and erosion on Narrabeen sandstone west of Putty,New South Wales

An exploratory study was made of the tree species, landform, soils and erosional sequence along altitudinal transects from interfluve to stream channel in a valley incised into Narrabeen Group sandstones and shales to the west of Putty, NSW. Four groups of soils with similar edaphic features were identified. These ranged from duplex soils on the apparently old and stable valley rim, through eroded earths on zones of depletion and sandy regoliths with thick surface horizons on zones of accumulation, to mature duplex soils with thick surface horizons on the colluvial toeslopes. Four communities of tree species were found associated with the four groups of soils. A Eucalyptus punctata –E. piperita open-forest was found on the stable valley rim and a related Eucalyptus punctata –E. piperita – E. oblonga open-forest to low woodland was found on zones of depletion. An Angophora costata open-forest was found associated with the sandy regoliths on zones of accumulation and a Eucalyptus viminalis – E. tereticornis open-forest to tall open-forest occurred on thick soils of the colluvial waning slopes. It was found that the landform fitted a hypothetical nine unit land surface model. The soil types and plant communities were found to reflect the dominant contemporary pedogenetic and geomorphic processes which are also used to define the units of this model. Erosion was evident in the catchment, and the sequence of alluvial soils on the valley floor was found to be consistent with previous suggestions of widespread slope instability during the Quaternary period. Speculation is offered about the effects of management of the valley, especially in terms of land surface instability.     

Mating asymmetry and the direction of evolution in the Hawaiian cricket genus Laupala

Based on studies from native Hawaiian Drosophila, a model was proposed to explain sexual isolation and mating asymmetry, from which one could potentially infer the 'direction of evolution'. We examined sexual isolation between allopatric cricket species of the genus Laupala, another endemic Hawaiian insect with an elaborate mating system, to begin to explore the nature of sexual isolation and mating asymmetry in closely related Hawaiian organisms. We studied sexual isolation and mating asymmetry in two contrasts. First, an inter-island comparison, including L. makaio from the older island of Maui and L. paranigra from the younger island of Hawaii, and second, an intra-island (Hawaii) comparison, including L. nigra from the older volcano of Mauna Kea and L. paranigra with a primary distribution on the younger volcanoes of Mauna Loa and Kilauea. We used a 'no-choice' experimental design, pairing individual males and females in homospecific or heterospecific combinations. Several behavioural aspects of courtship (proportion of male singing, latency to male singing, production of spermatophores and courtship initiation speed) were quantified as well as the success or failure of matings. We demonstrate asymmetry in sexual isolation between reciprocal combinations of L. makaio and L. paranigra. This result is examined in light of the differences in courtship behaviour manifest in the experiments with these two species. We did not find evidence of asymmetry in sexual isolation between L. nigra and L. paranigra, although differences in courtship initiation speed were evident between reciprocal combinations of these two species. In addition to the geological argument that species on older islands and older volcanoes give rise to species on younger islands and younger volcanoes, we discuss phylogenetic evidence consistent with these biogeographic hypotheses of relationships among the focal taxa. The patterns of asymmetrical sexual isolation and mating asymmetry are consistent with those found in the native Hawaiian Drosophila.     

Erosion and the Rejuvenation of Weathering-derived Nutrient Supply in an Old Tropical Landscape

Studies of long-term soil and ecosystem development on static geomorphic surfaces show that old soils become depleted in most rock-derived nutrients. As they are depleted, however, static surfaces also are dissected by fluvial erosion. This fluvial erosion leads to colluvial soil transport on the resulting slopes, which in turn can rejuvenate the supply of weathering-derived nutrients to plants. We evaluated the influence of erosion and consequent landscape evolution on nutrient availability along a slope on the Island of Kauai, near the oldest, most nutrient-depleted site on a substrate age gradient across the Hawaiian Islands. Noncrystalline minerals characteristic of younger Hawaiian soils increased from 3% of the soil on the static constructional surface at the top of the slope to 13% on the lower slope, and the fraction of soil phosphorus (P) that was occluded (and hence unavailable) decreased from 80% to 56% at midslope. Foliar nitrogen and P concentrations in Metrosideros polymorpha increased from 0.82% and 0.062% to 1.13% and 0.083% on the constructional surface and lower slope, respectively. The increase in foliar P over a horizontal difference of less than 250 m represents nearly half of the total variation in foliar P observed over 4.1 million years of soil and ecosystem development in Hawaii. The fraction of foliar strontium (Sr) derived from weathering of Hawaiian basalt was determined using ⁸⁷Sr:⁸⁶Sr; it increased from less than 6% on the constructional surface to 13% and 31% on lower slope and alluvial positions. Erosional processes increase both nutrient supply on this slope and the fine-scale biogeochemical diversity of this old tropical landscape; it could contribute to the relatively high level of species diversity observed on Kauai.     

Diversity despite dispersal: colonization history and phylogeography of Hawaiian crab spiders inferred from multilocus genetic data

The Hawaiian archipelago is often cited as the premier setting to study biological diversification, yet the evolution and phylogeography of much of its biota remain poorly understood. We investigated crab spiders (Thomisidae, Mecaphesa ) that demonstrate contradictory tendencies: (i) dramatic ecological diversity within the Hawaiian Islands, and (ii) accompanying widespread distribution of many species across the archipelago. We used mitochondrial and nuclear genetic data sampled across six islands to generate phylogenetic hypotheses for Mecaphesa species and populations, and included penalized likelihood molecular clock analyses to estimate arrival times on the different islands. We found that 17 of 18 Hawaiian Mecaphesa species were monophyletic and most closely related to thomisids from the Marquesas and Society Islands. Our results indicate that the Hawaiian species evolved from either one or two colonization events to the archipelago. Estimated divergence dates suggested that thomisids may have colonized the Hawaiian Islands as early as ~10 million years ago, but biogeographic analyses implied that the initial diversification of this group was restricted to the younger island of Oahu, followed by back-colonizations to older islands. Within the Hawaiian radiation, our data revealed several well-supported genetically distinct terminal clades corresponding to species previously delimited by morphological taxonomy. Many of these species are codistributed across multiple Hawaiian Islands and some exhibit genetic structure consistent with stepwise colonization of islands following their formation. These results indicate that dispersal has been sufficiently limited to allow extensive ecological diversification, yet frequent enough that interisland migration is more common than speciation.     

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.     

Floristic biogeography of the Hawaiian Islands: influences of area, environment and paleogeography

Aim A detailed database of distributions and phylogenetic relationships of native Hawaiian flowering plant species is used to weigh the relative influences of environmental and historical factors on species numbers and endemism. Location The Hawaiian Islands are isolated in the North Pacific Ocean nearly 4000 km from the nearest continent and nearly as distant from the closest high islands, the Marquesas. The range of island sizes, environments, and geological histories within an extremely isolated archipelago make the Hawaiian Islands an ideal system in which to study spatial variation in species distributions and diversity. Because the biota is derived from colonization followed by extensive speciation, the role of evolution in shaping the regional species assemblage can be readily examined. Methods For whole islands and regions of each major habitat, species–area relationships were assessed. Residuals of species–area relationships were subjected to correlation analysis with measures of endemism, isolation, elevation and island age. Putative groups of descendents of each colonist from outside the Hawaiian Islands were considered phylogenetic lineages whose distributions were included in analyses. Results The species–area relationship is a prominent pattern among islands and among regions of each given habitat. Species number in each case correlates positively with number of endemics, number of lineages and number of species per lineage. For mesic and wet habitat regions, island age is more influential than area on species numbers, with older islands having more species, more single‐island endemics, and higher species : lineage ratios than their areas alone would predict. Main conclusions Because species numbers and endemism are closely tied to speciation in the Hawaiian flora, particularly in the most species‐rich phylogenetic lineages, individual islands’ histories are central in shaping their biota. The Maui Nui complex of islands (Maui, Moloka‘i, Lāna‘i and Kaho‘olawe), which formed a single large landmass during most of its history, is best viewed in terms of either the age or area of the complex as a whole, rather than the individual islands existing today.     

A Millennium of Human Activity at Makauwahi Cave, Māhāūulepū, Kauaūi

A cave system in the eolianite deposits of the Māhā′ulepū/Pā′ā area of Kaua′i, Hawai′i, contains a rich fossil record of prehuman Holocene conditions and also preserves a thousand-year record of human activity. Details concerning pre-Contact Polynesian life have been extracted from subaqueous middens and artifacts, including perishable materials such as wood, gourd, and cordage. Oral traditions concerning the cave and vicinity generally show good agreement with the archaeological and paleoecological record and provide rich stories said to derive from as early as the fourteenth century A.D. Fossil evidence highlights biotic and landscape changes before, during, and after initial Polynesian and subsequent European settlement. The approximate temporal coincidence of evidence for human arrival and last occurrence of some now-extinct species is too great to ignore the possibility that humans played a role in some extinctions of native taxa before European colonization. Old maps, an 1824 sketch, records of the Land Court Awards, and old photographs confirm stratigraphic inferences and oral accounts concerning demographic and ecological conditions of the early historical period. Feral livestock proliferated in the nineteenth and early twentieth centuries, with loss of vegetative cover to overgrazing, decline of most of the native flora, and subsequent dune reactivation. Sedimentation rates reach their peak later in the twentieth century after the establishment of agricultural and mining operations nearby.     

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.     

Phylogenetic position and biogeography of Hillebrandia sandwicensis (Begoniaceae): a rare Hawaiian relict

The Begoniaceae consist of two genera, Begonia, with approximately 1400 species that are widely distributed in the tropics, and Hillebrandia, with one species that is endemic to the Hawaiian Islands and the only member of the family native to those islands. To help explain the history of Hillebrandia on the Hawaiian Archipelago, phylogenetic relationships of the Begoniaceae and the Cucurbitales were inferred using sequence data from 18S, rbcL, and ITS, and the minimal age of both Begonia and the Begoniaceae were indirectly estimated. The analyses strongly support the placement of Hillebrandia as the sister group to the rest of the Begoniaceae and indicate that the Hillebrandia lineage is at least 51-65 million years old, an age that predates the current Hawaiian Islands by about 20 million years. Evidence that Hillebrandia sandwicensis has survived on the Hawaiian Archipelago by island hopping from older, now denuded islands to younger, more mountainous islands is presented. Various scenarios for the origin of ancestor to Hillebrandia are considered. The geographic origin of source populations unfortunately remains obscure; however, we suggest a boreotropic or a Malesian-Pacific origin is most likely. Hillebrandia represents the first example in the well-studied Hawaiian flora of a relict genus.     

Dehydrogenase and urease activities of maize (Zea mays L.) field soils

Summary Dehydrogenase and urease activities, bacterial and fungal populations and physicochemical characteristics of maize (Zea mays L.) field soils have been studied for one crop cycle. A comparison has been made among soils of three different agricultural systemsviz permanent agriculture on plain lands in valleys, recently introduced terrace land agriculture and age old ‘slash and burn’ type of shifting agriculture on slopes. Results demonstrate that the enzyme activities, microbial population as well as most of the physico-chemical characteristics of soils followed the trend permanent agriculture on plain lands>terrace land agriculture>‘slash and burn’ type of shifting agriculture. Moisture and nutrient levels and topography of the lands were found to be major factors responsible for the trend.     

Two deep-sea spiny eels, <Emphasis Type="Italic">Notacanthus abbotti</Emphasis> and <Emphasis Type="Italic">Lipogenys gillii</Emphasis> (Albuliformes: Notacanthidae), from the Hawaiian Archipelago and Emperor Seamounts with notes on their identification and biogeography

Deep-sea spiny eels (Notacanthidae) were previously reported from the Hawaiian Archipelago; however, these reports lacked detailed information to confirm the identity of the species. We provide collection and taxonomic data for the earlier records. The first central Pacific specimen of Lipogenys gillii is reported from Hawai’i Island. A record of Notacanthus abbotti from the Hancock Seamounts, at the northern end of the Archipelago, is confirmed. Specimens from Maui, main Hawaiian Islands, previously reported as N. chemnitzii, are reidentified as N. abbotti. The Hawaiian records of notacanthids are the only reports of the family from the Pacific tectonic plate.     

A Complex Evolutionary History in a Remote Archipelago: Phylogeography and Morphometrics of the Hawaiian Endemic Ligia Isopods

Compared to the striking diversification and levels of endemism observed in many terrestrial groups within the Hawaiian Archipelago, marine invertebrates exhibit remarkably lower rates of endemism and diversification. Supralittoral invertebrates restricted to specific coastal patchy habitats, however, have the potential for high levels of allopatric diversification. This is the case of Ligia isopods endemic to the Hawaiian Archipelago, which most likely arose from a rocky supralittoral ancestor that colonized the archipelago via rafting, and diversified into rocky supralittoral and inland lineages. A previous study on populations of this isopod from Oʻahu and Kauaʻi revealed high levels of allopatric differentiation, and suggested inter-island historical dispersal events have been rare. To gain a better understanding on the diversity and evolution of this group, we expanded prior phylogeographic work by incorporating populations from unsampled main Hawaiian Islands (Maui, Molokaʻi, Lanaʻi, and Hawaiʻi), increasing the number of gene markers (four mitochondrial and two nuclear genes), and conducting Maximum likelihood and Bayesian phylogenetic analyses. Our study revealed new lineages and expanded the distribution range of several lineages. The phylogeographic patterns of Ligia in the study area are complex, with Hawaiʻi, Oʻahu, and the Maui-Nui islands sharing major lineages, implying multiple inter-island historical dispersal events. In contrast, the oldest and most geographically distant of the major islands (Kauaʻi) shares no lineages with the other islands. Our results did not support the monophyly of all the supralittoral lineages (currently grouped into L. hawaiensis), or the monophyly of the terrestrial lineages (currently grouped into L. perkinsi), implying more than one evolutionary transition between coastal and inland forms. Geometric-morphometric analyses of three supralittoral clades revealed significant body shape differences among them. A taxonomic revision of Hawaiian Ligia is warranted. Our results are relevant for the protection of biodiversity found in an environment subject to high pressure from disturbances.     

Evolution on a volcanic conveyor belt: using phylogeographic reconstructions and K–Ar-based ages of the Hawaiian Islands to estimate molecular evolutionary rates

The Hawaiian Islands form as the Pacific Plate moves over a 'hot spot' in the earth's mantle where magma extrudes through the crust to build huge shield volcanos. The islands subside and erode as the plate carries them to the north-west, eventually to become coral atolls and seamounts. Thus islands are ordered linearly by age, with the oldest islands in the north-west (e.g. Kauai at 5.1 Ma) and the youngest in the south-east (e.g. Hawaii at 0.43 Ma). K–Ar estimates of the date of an island's formation provide a maximum age for the taxa inhabiting the island. These ages can be used to calibrate rates of molecular change under the following assumptions: (i) K–Ar dates are accurate; (ii) tree topologies show that derivation of taxa parallels the timing of island formation; (iii) populations do not colonize long after island emergence; (iv) the coalescent point for sister taxa does not greatly predate the formation of the colonized younger island; (v) saturation effects and (vi) among-lineage rate variation are minimal or correctable; and (vii) unbiased standard errors of distances and regressions can be estimated from multiple pairwise comparisons. We use the approach to obtain overall corrected rate calibrations for: (i) part of the mitochondrial cytochrome b gene in Hawaiian drepanidines (0.016 sequence divergence/Myr); (ii) the Yp1 gene in Hawaiian Drosophila (0.019/Myr Kambysellis et al. 1995 ); and (iii) parts of the mitochondrial 12S and 16S rRNA and tRNA^val in Laupala crickets (0.024–0.102/Myr, Shaw 1996 ). We discuss the reliability of the estimates given the assumptions (i–vii) above and contrast the results with previous calibrations of Adh in Hawaiian Drosophila and chloroplast DNA in lobeliods.     

Incorrect handling of calibration information in divergence time inference: an example from volcanic islands

Divergence time studies rely on calibration information from several sources. The age of volcanic islands is one of the standard references to obtain chronological data to estimate the absolute times of lineage diversifications. This strategy assumes that cladogenesis is necessarily associated with island formation, and punctual calibrations are commonly used to date the splits of endemic island species. Here, we re-examined three studies that inferred divergence times for different Hawaiian lineages assuming fixed calibration points. We show that, by permitting probabilistic calibrations, some divergences are estimated to be significantly younger or older than the age of the island formation, thus yielding distinct ecological scenarios for the speciation process. The results highlight the importance of using calibration information correctly, as well as the possibility of incorporating volcanic island studies into a formal, biogeographical hypothesis-testing framework.     

Evolutionary biogeography of the terrestrial biota of the Marquesas Islands,one of the world's remotest archipelagos

Aim

Here I review phylogenetic studies concerning the biogeography of the Marquesas Islands, an oceanic hotspot archipelago in the Pacific Ocean formed <5.5 Ma, and compare patterns (particularly pertaining to colonization and diversification) within the archipelago to those reported from the Hawaiian and Society Islands.

Location

Marquesas Islands, French Polynesia (Pacific Ocean).

Methods

I reviewed 37 phylogenetic studies incorporating Marquesas‐endemic taxa. I asked the following questions: (a) where are the sister‐groups of Marquesas lineages distributed? (b) are Marquesas‐endemic “radiations” monophyletic or polyphyletic? (c) what major between‐island phylogeographic barriers are seen in the Marquesas? (d) what evidence exists for diversification within islands? (e) how old is the Marquesas biota compared to the archipelago's age? Finally, these patterns are compared with those seen in the Society Islands and Hawaii.

Results

Most Marquesan lineages have their closest known relatives on other Pacific plate archipelagos (particularly the Society, Hawaiian, and Austral islands). Most Marquesas‐endemic radiations are found to be monophyletic, and among‐island diversification appears to be common. There is limited evidence for within‐island diversification. Some radiations may be consistent with a weak progression rule in which younger lineages are on younger islands. Crown ages of no Marquesas radiations appear to be older than the age of the archipelago (with one exception).

Main conclusions

Diversification of the Marquesas biota resembles that of the Hawaiian Islands more than that of the Society Islands. Many radiations are monophyletic and some appear to diversify in parallel with the formation of the archipelago.