Evolution Of Islands Research Articles

A pilot study into the geochronological and geomorphic context for the archaeology of Barrow Island, Western Australia

The island sanctuary of Barrow Island on the edge of the inner North-West continental shelf of Australia holds significant environmental as well as Indigenous and colonial cultural value. Insights on past occupation dynamics, particularly in response to Post-Glacial sea-level rise, continue to emerge from analysis of archaeological assemblages. However, there is limited temporal and landscape information from the wider island with which to better contextualise the physical site formation history of these cultural records. We present a new, modelled Post-Glacial sea-level curve for the region and new geochronological and sedimentological data (including rare earth element and quartz microtextural data) from non-archaeological site contexts to help infer changes in the coastal environment. This new data provides new insights on the island's paleogeography and evolution since approximately 80 ka BP in the context of inherited Last Interglacial features and highly dynamic oceanographic processes. Ongoing physical weathering processes have influenced dune building and reworking, such that neither colour nor numeric age are reliable indicators of sediment compositional and textural maturity. The results continue to emphasise how the continued integration of the island's geological, sedimentological and archaeological records help to understand aspects of cultural site formation, as well as expose some of the limiting factors in our understanding of past and present island physical dynamics.

The effects of epistasis and linkage on the invasion of locally beneficial mutations and the evolution of genomic islands

We study local adaptation of a peripheral population by investigating the fate of new mutations using a haploid two-locus two-allele continent-island migration model. We explore how linkage, epistasis, and maladaptive gene flow affect the invasion probability of weakly beneficial de-novo mutations that arise on the island at an arbitrary physical distance to a locus that already maintains a stable migration-selection polymorphism. By assuming a slightly supercritical branching process, we deduce explicit conditions on the parameters that permit a positive invasion probability and we derive approximations for it. They show how the invasion probability depends on the additive and epistatic effects of the mutant, on its linkage to the polymorphism, and on the migration rate. We use these approximations together with empirically motivated distributions of epistatic effects to analyze the influence of epistasis on the expected invasion probability if mutants are drawn randomly from such a distribution and occur at a random physical distance to the existing polymorphism. We find that the invasion probability generally increases as the epistasis parameter increases or the migration rate decreases, but not necessarily as the recombination rate decreases. Finally, we shed light on the size of emerging genomic islands of divergence by exploring the size of the chromosomal neighborhood of the already established polymorphism in which 50% or 90% of the successfully invading mutations become established. These ‘window sizes’ always decrease in a reverse sigmoidal way with stronger migration and typically increase with increasing epistatic effect.

The paradox of island evolution

AbstractAimAfter colonising isolated islands, many types of plants and animals undergo extreme morphological diversification. In stark contrast, other island taxa change more subtly and converge evolutionarily on intermediate body size (the island rule). This paradox of island evolution has gone undetected for decades, perhaps because each pattern has been investigated separately using different analytical tools. Here, I investigate the paradox of island evolution in the endemic floras of four oceanic archipelagos in the Southwest Pacific.LocationChatham, Kermadec, Lord Howe & Norfolk Islands.TaxonWoody plants.MethodsI test whether the sizes of ‘solitary endemics’ (species that evolved anagenetically in the absence of co‐occurring endemic congeners) are correlated with their closest mainland ancestors. I also test whether island–mainland size relationships in 'solitary endemics' differ from isometry, as predicted by the island rule. Next, I test whether the stature of ‘co‐occurring endemics’ (closely related, often cladogenetic species) exhibits exaggerated differentiation.ResultsThe stature of 'solitary endemics' was correlated with their mainland relatives, and two out of the four archipelagos showed evidence of the island rule. On the other hand, the stature of 'co‐occurring endemics' was unrelated to their closest mainland relatives and often highly differentiated.Main conclusionsOverall results suggest that the island paradox arises from two distinct evolutionary pathways. Solitary endemics evolve more slowly and often converge on intermediate morphology, while co‐occurring endemics evolve more rapidly and often exhibit highly differentiated morphology. Future work aimed at a better understanding of the mechanisms underpinning the island paradox could help to further unite phylogenetic work on adaptive radiations and macroecological tests of the island rule under a single conceptual umbrella.

ICESat-2 Applications for Investigating Emerging Volcanoes

Submarine volcanism in shallow waters (<100 m), particularly in remote settings, is difficult to monitor quantitatively and, in the rare formation of islands, it is challenging to understand the rapid-paced erosion. However, these newly erupted volcanic islands become observable to airborne and/or satellite remote sensing instruments. NASA’s ICESat-2 satellite laser altimeter, combined with visible imagery (optical and microwave), provide a novel method of evaluating the elevation characteristics of newly emerged volcanoes and their subaerial eruption products. Niijima Fukutoku-Okanoba (NFO) is a submarine volcano 1300 km south of Tokyo (Ogasawara Archipelago of Japan) that periodically breaches the ocean surface to create new islands that are subsequently eroded. The recent eruption in August 2021 is a rare opportunity to investigate this island evolution using high-resolution satellite datasets with geodetic-quality ICESat-2 altimetry. Lansdat-8 and Planet imagery provide a qualitative analysis of the exposed volcanic deposits, while ICESat-2 products provide elevation profiles necessary to quantify the physical surface structures. This investigation determines an innovative application for ICESat-2 data in evaluating newly emerged islands and how the combination of satellite remote sensing (visible and lidar) to investigate these short-lived volcanic features can improve our understanding of the volcanic island system in ways not previously possible.

Morpho-stratigraphic characterization of the southern shelf of Porto Santo Island (Madeira Archipelago): Insights for small-scale instability processes and post-LGM sedimentary architecture

Shelves surrounding volcanic islands represent only a small portion of the entire submarine edifice that can extend to a few thousand meters below sea level. Despite their small areas, shelves show a significant morphologic imprint made by the erosional, depositional, tectonic and volcanic processes when compared to those left on slopes or the submarine bases of islands. Therefore, shelf morphology can be used to improve our knowledge about the island evolution, especially the more recent events. In this study, we use multibeam bathymetry, side scan sonar and seismic reflection profiles of the southern shelf of Porto Santo Island in Madeira Archipelago to map its seabed morphology and seismic stratigraphy from the nearshore to the shelf edge. Based on morphological and seismo-stratigraphic differences, the study area has been divided in three sectors (Western, Central and Eastern). In general, the shelf consists of an erosive rocky surface mostly covered by sediments, and locally outcropping on the seafloor, especially on the Western and Eastern sectors. On these sectors two sets of submerged erosional terraces have been mapped at different depths (35–45 m, 50–75 m). The depth range of the terraces and their absence in the Central sector suggests that these were formed/modified at least by the Marine Isotope Stages (MIS) 5a-5d stillstands or even by older relative sea-level stillstands. Dykes, which are more resistant to erosion than the surrounding outcrops, have orientations that are similar to the volcanic and structural features present on the island (NNE-SSW and NW-SE). The sedimentary cover on the shelf is highly varied both in thickness and internal architecture, mainly due to different onshore sediment supply and available accommodation space. Two main seismic units have been recognized: the lower one (U1) is interpreted as a transgressive deposit, formed during the sea level rise after the Last Glacial Maximum (LGM); the upper one (U2) is interpreted as a modern highstand deposit. The Western sector is practically sediment-starved, except for a local thin sedimentary cover of U2 on the inner and outer shelf. The Central sector shows U2 as a sigmoidal-oblique progradational clinoform characterized by inner prograding geometry on top of U1. The Eastern sector shows U2 as sigmoidal clinoform extending over a large area and having a more aggradational component. The shelf edge shows an overall arcuate shape that strongly matches the coastline configuration, suggesting the occurrence of an old large-scale landslide event (LS1) prior to the shelf formation. Further incisions in the shelf edge of the Central sector are interpreted as resulting from mass-movements, classified as LS2 and LS3. LS2 is at least older than seismic unit U1 and LS3 formed during the late Holocene. The volume of the LS2 event (0.6 km3) suggests that it might have caused a hazardous tsunami if it failed as a single event. The recent LS3 events, due to their small magnitude were probably not hazardous. These observations provided a more comprehensive understanding of the recent evolution of Porto Santo insular shelf in terms of mass-movement processes and post-LGM sedimentary architecture.

Study on the Spatial-Temporal Pattern and Evolution of Surface Urban Heat Island in 180 Shrinking Cities in China

Study on the Spatial-Temporal Pattern and Evolution of Surface Urban Heat Island in 180 Shrinking Cities in China

Understanding Urban Growth through Heat Islands Using Remotely Sensed Data: Yaounde Case Study, Cameroon

Studies in urban dynamics have focused on population growth, urban sprawl and activities expansion to determine, understand and study the phenomenon of urbanization in the world. The methods used in these studies have explore remotely sense data from Global Positioning Systems (GPS), satellite imagery, aerial and ground photography for interpretation, analysis and explanation of urban land use and land cover evolution. This data is often combined with ground observations and other methods in social sciences to understand urban growth. In this article, data is tapped from temperature differences analysis in multi-date satellite images and combined with population statistics, human activities and infrastructure build up to explain the phenomenon of urbanization. The results of the findings will enrich our knowledge in Urban Geography on approaches and methods used in understanding urbanization and its problems. Drawing on case study material from Yaounde in Cameroon, this article examines how remote sensing techniques can help in understanding urban heat island in Yaounde and its negative outcomes on urban population, activity and the environment. As the study shows, urban growth has a direct relation with temperature increase and an inverse relation with vegetation change. Also, Increase in bare surfaces due to deforestation for development and settlement increases surface temperature and vice versa. Vegetation regulates surface temperature by absorbing energy from solar radiation and remission in the form of latent heat through the process of photosynthesis. Analysis of surface temperature increase through remote sensing techniques, urban land use evolution, determinants and implications of Yaounde heat islands constitute the focus of this paper. The implications of rise in surface temperature and relations with urban growth are important for decision making. This knowledge is essential for urban geography research, new methodological approaches to urbanization and policy.

How hazardous are tsunamis triggered by small-scale mass-wasting events on volcanic islands? New insights from Madeira – NE Atlantic

Mass-wasting events are a key process in the evolution of volcanic ocean islands. They occur at various dimensional scales and present a major source of hazard. When the collapsed material plunges into the sea, destructive tsunamis can be generated. Yet, the hazard potential of collapse-induced tsunamis is still poorly understood with different opinions on what consequences to expect from this type of events, particularly those related to massive volcanic island flank collapses. In this paper, however, we explore the hazard extent of tsunamis triggered by the smaller – but more frequent – coastal cliff-failures, in order to isolate critical factors in the generation, propagation and impact of these tsunamis. To achieve this, we use the prime example of Madeira, a volcanic island in the Atlantic Ocean highly vulnerable to cliff-failure. Particularly, we explore the March 4th, 1930 Cabo Girão event that triggered a deadly tsunami. The coastal impact of the 1930 “Deadly Wave”, as the island's inhabitants referred to the generated tsunami, resulted in 19 fatalities. We use historical description, morphological analysis, and numerical modelling to better understand the tsunamigenesis of tall island cliffs failing into the sea. Interestingly, we find that a relatively small-scale mass-wasting event (∼0.003 km3 volume) was the cause of the reported tsunami that inundated the nearest coasts. Our numerical results, fairly agreeing with the available collapse and subsequent tsunami descriptions, suggest that the tsunami impact was mainly localized on the southern coast of Madeira Island. Furthermore, our study allows proposing a novel morphology-based conceptional model for the tsunamigenesis and hazard extent induced by mass-wasting events on oceanic volcanic islands.

Effects of urbanization on the relationship between greenspace patterns and evolution of regional heat island in cities of Ethiopia

Green space (GS) is a central element of urban ecosystems while, urbanization is substantially changed green land into impervious ecosystems, which has then troubled the equilibrium of the surface thermal energy and the ecosystem services fluxes. This study was intended to explore the response of relative land surface temperature (RLST) intensities to the urban ecosystem- agglomeration dynamics as well as regional thermal environment (RTE) effects on green space in four major cities (i.e., Addis Ababa-Hawassa-Adama-Bahir Dar) of Ethiopia from 1990-2020, using a set of remote sensing images, single-channel algorism, and geospatial analyses. The results showed the trends of GS evolution were: GS loss > GS gain > GS exchange. Besides, the distinct ecosystems as high-temperature zones (RLST more than 2°C) were gradually augmented and significantly intensified between 2010-2020 in all cities, while the proportion of green space was significantly decreased. Due to this, the segregated urban heat islands were gradually inter-weaved and interacted with each other and forming regional heat islands. However, the newly established green space has fewer cooling effects than urban forest and greenery, because RLST of green space loss and gain are substantially disparate. We also confirmed that the regional thermal environment is not only prejudiced by ecosystem patterns and processes besides substantially conquered by the particular GS change processes as well as RHI dynamics and evolution rate.

Spatiotemporal evolution of urban development and surface urban heat island in Guangdong-Hong Kong-Macau greater bay area of China from 2013 to 2019

As one of the major bay areas in the world, the Guangdong-Hong Kong-Macau Greater Bay Area (GBA) has been experiencing a remarkable urbanization process, accompanied by the deterioration of the thermal environment quality. This study tried to explore how urbanization dynamically and regionally affects the thermal environment, by examining the spatiotemporal variation of the local climate zone (LCZ), the centroid movement of the urban form, and surface urban heat island (SUHI) in GBA during 2013 and 2019. The results revealed that the urban areas have expanded from the central GBA to adjacent cities and the gravity center moved from the urban core to the rural periphery, indicating the ongoing urban expansion in GBA. Meanwhile, the SUHI value was calculated and corresponding spatial association analysis was carried out to clarify the pattern and dynamics of the SUHI spatiotemporal change during the study period. The increased proportion of the slightly high SUHI level and expanded high-high aggregation indicated that the thermal environment of GBA has been heated up. Large increments of SUHI occurred mostly in the areas of non-traditional development and areas with high intensity of urban expansion. These increments were attributed to the land occupation of limited or agricultural development zones for urbanization. This study provides insights into the balance between urban thermal environmental and rapid urbanization. Future researches are recommended to address novel and sustainable urban planning strategies that are able to maintain the required urban growth without deteriorating the thermal environment.

The Temperature-Dependent Expression of the High-Pathogenicity Island Encoding Piscibactin in Vibrionaceae Results From the Combined Effect of the AraC-Like Transcriptional Activator PbtA and Regulatory Factors From the Recipient Genome.

The high-pathogenicity island irp-HPI is widespread among Vibrionaceae encoding the piscibactin siderophore system. The expression of piscibactin genes in the fish pathogen Vibrio anguillarum is favored by low temperatures. However, information about the regulatory mechanism behind irp-HPI gene expression is scarce. In this work, in-frame deletion mutants of V. anguillarum defective in the putative regulators AraC1 and AraC2, encoded by irp-HPI, and in the global regulators H-NS and ToxRS, were constructed and their effect on irp-HPI gene expression was analyzed at 15 and 25°C. The results proved that only AraC1 (renamed as PbtA) is required for the expression of piscibactin biosynthesis and transport genes. PbtA inactivation led to an inability to grow under iron restriction, a loss of the outer membrane piscibactin transporter FrpA, and a significant decrease in virulence for fish. Inactivation of the global repressor H-NS, which is involved in silencing of horizontally acquired genes, also resulted in a lower transcriptional activity of the frpA promoter. Deletion of toxR-S, however, did not have a relevant effect on the expression of the irp-HPI genes. Therefore, while irp-HPI would not be part of the ToxR regulon, H-NS must exert an indirect effect on piscibactin gene expression. Thus, the temperature-dependent expression of the piscibactin-encoding pathogenicity island described in V. anguillarum is the result of the combined effect of the AraC-like transcriptional activator PbtA, harbored in the island, and other not yet defined regulator(s) encoded by the genome. Furthermore, different expression patterns were detected within different irp-HPI evolutionary lineages, which supports a long-term evolution of the irp-HPI genomic island within Vibrionaceae. The mechanism that modulates piscibactin gene expression could also be involved in global regulation of virulence factors in response to temperature changes.

A new approach to study the long-term urban heat island evolution using time-dependent spectroscopy

This study presents a new approach to study long-term temperature and urban heat island intensity (UHII) evolution based on the method of time-depended spectroscopy on the example of Moscow megacity. In contrast to standard spectroscopy, this method allows analyzing the changes of the amplitude Fourier spectrum of the time series along the study period. Applying the novel method to the air temperature series for the period of 1977-2020, we demonstrate that ongoing changes of the mean temperature and UHII are accompanied by the changes of their spectra, including the spectral amplitudes corresponding to diurnal, annual and synoptic-scale oscillations. Such changes are complex, often non-linear, and seasonally asymmetric. Steady upward trends are found for summer season, for the spectral amplitudes of diurnal temperature and UHII oscillations, and synoptic-scale UHII oscillations. Spectral amplitudes of annual temperature and UHII oscillations experiences V-shaped dynamics with an increase since 1990th. For UHII such pattern reflects a switch between regimes with wintertime or summertime UHI maximum. Presented results provides an evidence that observed intensification of Moscow's UHI is forced not only by urban growth, but also by changing background meteorological conditions, which are becoming more favorable to UHI appearance in summer and less favorable in winter.

Macaronesia as a Fruitful Arena for Ecology, Evolution, and Conservation Biology

Research in Macaronesia has led to substantial advances in ecology, evolution and conservation biology. We review the scientific developments achieved in this region, and outline promising research avenues enhancing conservation. Some of these discoveries indicate that the Macaronesian flora and fauna are composed of rather young lineages, not Tertiary relicts, predominantly of European origin. Macaronesia also seems to be an important source region for back-colonisation of continental fringe regions on both sides of the Atlantic. This group of archipelagos (Azores, Madeira, Selvagens, Canary Islands, and Cabo Verde) has been crucial to learn about the particularities of macroecological patterns and interaction networks on islands, providing evidence for the development of the General Dynamic Model of oceanic island biogeography and subsequent updates. However, in addition to exceptionally high richness of endemic species, Macaronesia is also home to a growing number of threatened species, along with invasive alien plants and animals. Several innovative conservation and management actions are in place to protect its biodiversity from these and other drivers of global change. The Macaronesian Islands are a well-suited field of study for island ecology and evolution research, mostly due to its special geological layout with 40 islands grouped within five archipelagos differing in geological age, climate and isolation. A large amount of data is now available for several groups of organisms on and around many of these islands. However, continued efforts should be made toward compiling new information on their biodiversity, to pursue various fruitful research avenues and develop appropriate conservation management tools.

Study Of The Current Situation Of The Ubangi Basin In The Face Of Current Geopolitical Challenges

Aim : The objective of this study was to evaluate the flow (monthly and annual), the climate model, the plant biomass, the heat islands, the albedo (hourly and monthly), the evaporation, the precipitation and the evapotranspiration of the Oubangui river basin and to follow the evolution of these parameters with data from 1999 to 2018. Methodology : Thanks to Landsat satellite images and those of the American site Giovanni, we collected data on the flow (monthly and annual), the climate model, plant biomass, heat islands, albedo (hourly and monthly), evaporation, precipitation and evapotranspiration of the Ubangi basin, then analyzed with ArcGis software . Results: The results showed that the monthly flows of the Oubangui River have dropped from 6,000 to 3,000 m3/Sec) from 1940 to the present. The Maximum Plant Biomass Value NDVI from 1999 to 2018 shows that the Biomass has gone from 65% dense vegetation/pixel (dense forest) to 37% dense vegetation/pixel (very degraded dense forest). The analysis on the evolution of Ground Heat Islands per pixel shows that the temperature has evolved from 29.8°C (hot) in 1999 to 42.63°C (hot) in 2018. The ratio of energy released to energy received from the Sun (albedo) in the Ubangi Sangha basin is in the range of 10.68 to 14.29% annual cumulative albedo. The river loses water by free vaporization from 7 to 14 mm/day. Conclusion: This study provides information on recent values of parameters such as: discharge (monthly and annual), climate model, plant biomass, heat islands, albedo (hourly and monthly), evaporation, precipitation and evapotranspiration of the Ubangi River basin for which there is not enough information in the literature

Investigating Controls on Barrier Island Overwash and Evolution during Extreme Storms

Over short periods of time, extreme storms can significantly alter barrier island morphology, increasing the vulnerability of coastal habitats and communities relative to future storms. These impacts are complex and the result of interactions between oceanographic conditions and the geomorphic, geological, and ecological characteristics of the island. A 2D XBeach model was developed and compared to observations in order to study these interactions along an undeveloped barrier island near the landfall of Hurricane Florence in 2018. Beachface water levels during the storm were obtained from two cross-shore arrays of pressure sensors for comparison to model hydrodynamics. Aerial drone imagery was used to derive pre-storm and post-storm elevation data in order to quantify spatially varying erosion and overwash. Sediment grain size was measured in multiple locations, and we estimated spatially varying friction by using Sentinel-2 satellite imagery. The high spatial and temporal resolution of satellite imagery provided an efficient method for incorporating pre-storm spatially varying land cover. While previous studies have focused on the use of spatially varying friction, we found that the utilization of local median grain sizes and full directional wave spectra was critical to reproducing observed overwash extent.

Density structure of the island of Hawai'i and the implications for gravity-driven motion of the south flank of Kīlauea Volcano

SUMMARYThe discovery that large landslides dissected the Hawaiian Islands, scattering debris over thousands of square kilometres of seafloor, changed our ideas of island growth and evolution. The evidence is consistent with catastrophic flank collapse during volcano growth, and draws our focus to the currently active island of Hawai'i, the volcanoes Mauna Loa and Kīlauea, and particularly to the actively mobile south flank of Kīlauea. Both the weight distribution and pressure within an extensive magmatic system are perceived to affect stability, but the role of gravitational body forces and island density distribution has not been quantitatively assessed. We use seismic velocities derived from tomography to model the density distribution of the island of Hawai'i and find that olivine-rich melts and rocks in Hawaiian volcanoes result in a close association of seismic velocity and density. The resultant density model reproduces more than 95 per cent of the observed gravity disturbance signal wherever tomographic control exists and provides a basis for evaluating the body forces from gravity. We also find that if the decollement is weak, then gravitational body forces can produce slip that explains most seismo-tectonic and volcano-tectonic structural features of Kīlauea. Where the decollement is in a state of incipient slip from this weight distribution, fluctuations in magma pressure can trigger accelerated slip on the decollement. Yet this is only true of the south flank of Kīlauea. Though weight and magma distributions produce significant forces driving the west flank of Mauna Loa seaward, this flank is relatively stable. Stability over most of the last decade indicates a strong foundation beneath the west flank of Mauna Loa, perhaps as a result of past landslides that scraped clay-rich sediments from the decollement.

Time Evolution of the Surface Urban Heat Island

AbstractAtmospheric and surface urban heat islands (UHI) originate from common energetic processes, but the status of scientific knowledge on their time evolution is highly disparate. The diurnal cycles of atmospheric UHI are well known based on years of continuous measurements in cities; the cycles of surface UHI, however, cannot be measured continuously or in situ. In this article, we aim to reconcile these differences. We begin with a synthesis of previous work on the diurnal evolution of surface UHI, which leads to a novel but historically minded approach to the research problem. The approach involves a combination of microscale and mesoscale urban climate models, each of which is forced with universally described urban and rural surface parameters and atmospheric profiles. With these models, we produce theoretical time‐temperature curves for the surface UHI that are comparable to the classic curves of atmospheric UHI. This work prompts a critical look at the use of satellite thermal imagery to assess heat islands and heat risks in cities. To that end, we recommend new and more functional definitions of surface temperature. Conceptually, these represent “incomplete” temperatures defined by specific facets of the urban environment.

Experimental signatures of electron cyclotron wave energy condensation in magnetic islands

Bifurcation of the electron temperature perturbation (ΔT e) in magnetic islands due to electron cyclotron current drive (ECCD) is reported for the first time in toroidal plasmas. In this DIII-D experiment ΔT e spontaneously increases by 50% in a growing 2, 1 island which in turn rapidly shrinks, consistent with improved stabilization by the ECCD due to the temperature bifurcation. This non-linearity of ΔT e maps out a hysteresis in the island evolution cycle, in qualitative agreement with the theoretically predicted radio frequency current condensation effect Reiman and Fisch 2018 (Phys. Rev. Lett. 121 225001). Therefore, this observed bifurcation can be critical for the avoidance of disruptions caused by tearing modes in tokamaks.

Holocene morpho-sedimentary evolution of Marambaia Barrier Island (SE Brazil)

AbstractBarrier islands are sedimentary bodies susceptible to changes in sediment supply, dominant physical processes, and sea level. The aim of this work was to study the sedimentary processes that established Marambaia Barrier Island (SE Brazil) as an elongated sandy body that created Sepetiba Bay. For this purpose, barrier and back-barrier bay environments were analyzed using high-resolution satellite imagery, geophysical and topographic surveys, surface sediment samples and short cores, and radiocarbon and optically stimulated luminescence (OSL) dating techniques. Seven morpho-sedimentary domains were identified: coastal beach ridges, overland flow features, inter-ridge paleo lagoon, bayside beach ridges, marshlands, dune field and tidal wetlands. The results show that Marambaia Barrier Island evolved throughout the Holocene, first under normal regression conditions during sea-level rise, and then by forced regression as sea level lowered to its present position. Concurrent processes related to longshore drift, onshore transport, reworked barrier deposits, eolian transport, bay circulation, and pedogenesis influenced its morpho-sedimentary evolution. Morphological features such as truncated beach ridges, flying spits, and filled channels attest to the occurrence of alternating periods of erosion and accretion, evincing how the morphology of barrier island systems preserves an important archive of environmental changes.

Evolution of rhizobial symbiosis islands through insertion sequence-mediated deletion and duplication

Symbiosis between organisms influences their evolution via adaptive changes in genome architectures. Immunity of soybean carrying the Rj2 allele is triggered by NopP (type III secretion system [T3SS]-dependent effector), encoded by symbiosis island A (SymA) in B. diazoefficiens USDA122. This immunity was overcome by many mutants with large SymA deletions that encompassed T3SS (rhc) and N2 fixation (nif) genes and were bounded by insertion sequence (IS) copies in direct orientation, indicating homologous recombination between ISs. Similar deletion events were observed in B. diazoefficiens USDA110 and B. japonicum J5. When we cultured a USDA122 strain with a marker gene sacB inserted into the rhc gene cluster, most sucrose-resistant mutants had deletions in nif/rhc gene clusters, similar to the mutants above. Some deletion mutants were unique to the sacB system and showed lower competitive nodulation capability, indicating that IS-mediated deletions occurred during free-living growth and the host plants selected the mutants. Among 63 natural bradyrhizobial isolates, 2 possessed long duplications (261–357 kb) harboring nif/rhc gene clusters between IS copies in direct orientation via homologous recombination. Therefore, the structures of symbiosis islands are in a state of flux via IS-mediated duplications and deletions during rhizobial saprophytic growth, and host plants select mutualistic variants from the resultant pools of rhizobial populations. Our results demonstrate that homologous recombination between direct IS copies provides a natural mechanism generating deletions and duplications on symbiosis islands.