Northwestern Australia Research Articles

Bodies in space: XR documentary in Australia

ABSTRACT This article discusses a selection of interactive and immersive works from the past twenty years in Australia and argues that these have emerged from a specific cultural and geographical perspective in relation to space and place. In the context of settler colonial or migrant Australians, who have fraught and unresolved relationships to place, technologies that intervene with and implicate the audience can further expand documentary's capacity to frame, interpret and challenge these relationships. In this article, we discuss five specific interactive and immersive Australian documentary works. Each of these projects re-frames an encounter with space and place through the methods by which the participant-as-audience is situated in relation to the subject matter and virtual environment. The article explores the controversial asylum-seeker documentary game, Escape From Woomera ([2003]. Australia: EFW Collective); Lynette Wallworth's Collisions which recounts the atomic bomb testing in the desert (2012); Oscar Raby's examination of history, identity and witnessing, Assent (2013); Joan Ross's examination of the colonial relationship to the environment in Did you ask the river? (2019) and Tyson Mowarin's VR of the Ngarluma people of North Western Australia and the threats to their culture and land in the VR work Thalu: Dreamtime is Now (2018).

The nuanced nature of mesic refugia in arid landscapes: a tale of two peas.

Understanding how genetic diversity is distributed and maintained within species is a central tenet of evolutionary and conservation biology, yet is understudied in arid regions of the globe. In temperate, glaciated environments, high genetic diversity in plant species is frequently found in refugial areas, which are often associated with southern non-glaciated landscapes. In arid, unglaciated environments, landscape features providing mesic conditions are likely to be refugia, although our understanding needs more refinement in these biomes. We test whether refugia and nuclear diversity hotspots occur in high-elevation, topographically complex areas for co-distributed shrubs (Petalostylis labicheoides and Indigofera monophylla; Fabaceae) in the ancient, arid Pilbara bioregion of north-western Australia. We conducted extensive sampling of the Pilbara (>1400 individuals from 62 widespread populations) to detect patterns in nuclear diversity and structure based on 13-16 microsatellite loci. Evidence of historical refugia was investigated based on patterns of diversity in three non-coding chloroplast (cp) sequence regions for approx. 240 individuals per species. Haplotype relationships were defined with median-joining networks and maximum likelihood phylogenetic trees. We found cpDNA evidence for a high-elevation refugium in P. labicheoides but not for I. monophylla that instead exhibited extraordinary haplotype diversity and evidence for persistence across a widespread area. Nuclear diversity hotspots occurred in, but were not exclusive to, high-elevation locations and extended to adjacent, low-elevation riparian areas in both species. Phylogeographic refugia in arid environments may occur in high-elevation areas for some species but not all, and may be influenced by species-specific traits: a mesic montane refugium in P. labicheoides could be related to its preference for growth in water-gaining areas, while a lack of such evidence in I. monophylla could be related to maintenance of cpDNA diversity in a large soil seed bank and dynamic evolutionary history. Mesic environments created by the intersection of topographically complex landscapes with riparian zones can be contemporary reservoirs of genetic diversity in arid landscapes.

Evolutionary responses of a reef-building coral to climate change at the end of the last glacial maximum.

Climate change threatens the survival of coral reefs on a global scale, primarily through mass bleaching and mortality as a result of marine heatwaves. While these short-term effects are clear, predicting the fate of coral reefs over the coming century is a major challenge. One way to understand the longer-term effect of rapid climate change is to examine the response of coral populations to past climate shifts. Coastal and shallow-water marine ecosystems such as coral reefs have been reshaped many times by sea-level changes during the Pleistocene, yet few studies have directly linked this with its consequences on population demographics, dispersal, and adaptation. Here we use powerful analytical techniques, afforded by haplotype-phased whole-genomes, to establish such links for the reef-building coral, Acropora digitifera. We show that three genetically distinct populations are present in northwestern Australia, and that their rapid divergence since the last glacial maximum (LGM) can be explained by a combination of founder-effects and restricted gene flow. Signatures of selective sweeps, too strong to be explained by demographic history, are present in all three populations and overlap with genes that show different patterns of functional enrichment between inshore and offshore habitats. In contrast to rapid divergence in the host, we find that photosymbiont communities are largely undifferentiated between corals from all three locations, spanning almost 1000 km, indicating that selection on host genes, and not acquisition of novel symbionts, has been the primary driver of adaptation for this species in northwestern Australia.

Pilbarana, a new subterranean amphipod genus (Hadzioidea: Eriopisidae) of environmental assessment importance from the Pilbara, Western Australia

The Pilbara and nearby regions in north-western Western Australia have an exceptionally high diversity of short-range endemic invertebrates inhabiting threatened groundwater-dependent habitats. Amphipod crustaceans, in particular, are dominant in these communities, but are poorly understood taxonomically, with many undescribed species. Recent molecular phylogenetic analyses of Pilbara eriopisid amphipods have, nonetheless, uncovered a previously unknown biodiversity. In this study, we formally establish a new genus, Pilbarana Stringer & King gen. nov., and describe two new species, P. grandis Stringer & King sp. nov. from Cane River Conservation Park and P. lowryi Stringer & King sp. nov. from the Fortescue River Basin near the Hamersley Range, using a combination of molecular and morphological data. The new genus is similar morphologically to the two additional Western Australian eriopisid genera, Nedsia Barnard & Williams, 1995 and Norcapensis Bradbury & Williams, 1997, but represents a genetically divergent, reciprocally monophyletic lineage, which can be differentiated by its vermiform body shape, the presence of an antennal sinus, and by the length and form of the antennae and uropods. This research signifies an important contribution to knowledge of Pilbara subterranean communities and has critical implications for future environmental impact assessments and conservation management.

Comment on “Kawahara, H., Yoshida, H., Yamamoto, K., Katsuta, N., Nishimoto, S., Umemura, A., Kuma, R., 2022. Hydrothermal formation of Fe-oxide bands in zebra rocks from northern Western Australia. Chemical Geology 590 (2022), 120699”

This comment questions an hypothesis for formation of the ornamental stone “zebra rock” from Ediacaran red shales of northwestern Australia as hydrothermal alteration zones. The hypothesis is falsified by absence of Eu anomalies in REE arrays, lack of associated carbonate, low degree of chemical weathering, associated soluble gypsum, strata concordance in narrow bands, low thermal stability of magnetization, modest diagenetic alteration, and patterns unlike liesegang banding. Rather than Cambrian hydrothermal veins, zebra rocks were gleyed paleosols with redox banding, from acid sulfate weathering at low temperature during the Ediacaran.

Hydrodynamic drivers of fine‐scale connectivity within a coral reef atoll

AbstractAn accurate representation of physical and biological processes is crucial to resolve larval dispersal pathways and characterize connectivity of coral reef ecosystems. We investigate how hydrodynamic forcings drive larval retention rates during the bi‐annual mass coral spawning of the coral genus Acropora within a coral reef atoll (Mermaid Reef), located off northwestern Australia. By analyzing hydrodynamic conditions during 41 yr of historical spring and autumn coral spawning events, we identify typical and extreme hydrodynamic forcing conditions. Particle tracking using the output from a fine‐scale coupled wave‐flow hydrodynamic model forced with typical hydrodynamic conditions during coral spawning, revealed a mean transport of larvae eastward across the atoll. Transport was mainly driven by a combination of wave and tidal currents, where the residual tidal flow and unidirectional wave flow increased the net export of particles, and the oscillatory tidal (non‐residual) flow reduced the net export of particles from the reef. Importantly, however, numerical simulations forced with extreme hydrodynamic conditions generated by episodic tropical cyclones (11 out of 41 yr) showed large deviations from the typical eastward flow during autumn spawning, generating different connectivity pathways within the reef. Considering the substantial time larvae can be retained within reef systems, overlooking fine‐scale hydrodynamic processes may greatly overestimate larval transport distances between adjacent coral reef atolls. As a result, we emphasize the need to consider fine‐scale hydrodynamic processes within regional connectivity predictions, which is generally not considered yet critical to understand the capacity of reefs to recover following disturbances.

Extreme erosion by submarine slides

Abstract Submarine slides (including slides, slumps, and debris flows) pose major geohazards by triggering tsunami and damaging essential submarine infrastructure. Slide volume, a key parameter in hazard assessments, can increase markedly through substrate and/or water entrainment. However, the erosive potential of slides is uncertain. We quantified slide erosivity by determining the ratio of deposited (Vd) to initially evacuated (Ve) sediment volumes; i.e., slides that gain volume through erosion have a Vd/Ve ratio >1. We applied this method to the Gorgon slide, a large (500 km3), seismically imaged slide offshore northwestern Australia, and reviewed Vd/Ve ratios for 11 other large slides worldwide. Nine of the 11 slides have Vd/Ve > 1 (median value = 2), showing emplaced volumes increased after initial failure. The Gorgon slide is the most erosive slide currently documented (Vd/Ve = 13), possibly reflecting its passage across a highly erodible carbonate ooze substrate. Our new approach to quantifying erosion is important for hazard assessments given substrate-flow interactions control slide speed and runout distance. The variations in slide volume also have important implications for submarine infrastructure impact assessments, including more robust tsunami modeling.

Modelling climate suitability for Striga asiatica, a potential invasive weed of cereal crops

Striga asiatica (L.) Kuntze (Lamiales: Orobanchaceae), a hemi-parasitic plant native to sub-Saharan Africa and tropical Asia, is particularly problematic to rice, corn, and sorghum cultivation in Africa. Striga asiatica produces a large number of small sized (<0.5 mm) seeds, thereby facilitating easy dispersion by commercial exchange of contaminated grains. The distribution of this species in Africa is regulated by climate, which is the main factor determining local suitability. Modelling is a useful tool to analyse climate suitability for species. This study aimed to determine the areas more vulnerable to S. asiatica invasion both in the present and under the projected climate change model using two methods: MaxEnt (as a correlative approach) and CLIMEX (as a semi-mechanistic approach). The MIROC-H Global Climate Model and the A2 and RCP 8.5 scenarios (the most pessimistic one) were used. Our projections indicated areas suitable for S. asiatica invasion in all continents under both present and projected climate change, with high suitability areas in South America, Africa, and Europe. We found agreement and disagreement between CLIMEX and MaxEnt outputs and the extent of disagreement on the increases in climate suitability by 2050 and 2100 in North America, Europe, and eastern, southern, and western Australia. This study provides a useful tool to design strategies aimed at preventing the introduction and establishment of S. asiatica in South America, with considerable agreement between CLIMEX and MaxEnt outputs.

Unravelling Stratified Microbial Assemblages in Australia’s Only Deep Anchialine System, The Bundera Sinkhole

Bundera sinkhole, located in north-western Australia, is the only known continental anchialine system in the Southern Hemisphere. Anchialine environments are characterised by stratified water columns with complex physicochemical profiles spanning hypoxic and anoxic regions, often displaying high levels of endemism. Research on these systems has focused on eukaryotic fauna, however interest in the microbial diversity of these environments is growing, enabled by next-generation DNA sequencing. Here we report detailed analyses of the microbial communities across a depth profile within Bundera sinkhole (from 2 to 28 m), involving parallel physicochemical measurements, cell population counts and 16S rRNA amplicon analyses. We observed clear shifts in microbial cell counts, community diversity, structure and membership across the depth profile, reflecting changing levels of light, organic and inorganic energy sources as well as shifts in pH and salinity. While Proteobacteria were the most abundant phylum found, there was a high degree of taxonomic novelty within these microbial communities, with 13,028 unique amplicon sequence variants (ASVs) identified, belonging to 67 identifiable bacterial and archaeal phyla. Of these ~4,600, more than one third of the total, were unclassified below family level. A small number of ASVs were highly abundant at select depths, all of which were part of the set not classified below family level. The 2 m and 6 m samples had in common two highly abundant ASVs, belonging to the Ectothiorhodospiraceae and Thiotrichaceae families, while the 8 m community contained a single predominant ASV belonging to family Thioglobaceae. At lower depths a different Ectothiorhodospiraceae ASV comprised up to 68% relative abundance, peaking at 26 and 28 m. Canonical correspondence analyses indicated that community structure was strongly influenced by differences in key physicochemical parameters, particularly salinity, dissolved organic and inorganic carbon, phosphate and sulphate concentrations. This work highlights the potential for anchialine systems to house considerable microbial novelty, potentially driven by adaptations to the specific physicochemical makeup of their local environment. As only a small number of anchialine systems have been examined via microbial community studies to date, this work is particularly valuable, contributing new insight regarding the microbial residents of these important and sensitive environments.

A new AVO fluid indicator using the fluid line: Theory and application

A number of seismic fluid indicators are derived from seismic amplitude variations with offset. The fluid indictors typically measure the anomalous behavior of the seismic response related to hydrocarbon's saturation. This anomalous behavior can be observed in different domains such as P-wave velocity vs. S-wave velocity, P-wave reflectivity vs. S-wave reflectivity, and intercept vs. gradient, among others. In this paper, we introduce a new AVO attribute for fluid detection. The attribute is expressed as a linear combination of AVO's intercept and gradient and measures the deviation caused by pore fluid from the background fluid line defined in the Intercept-Gradient domain. The attribute can be calibrated to local geology for better performance. We test the attribute on data collected from different basins. We compare the fluid detection ability of the attribute against existing fluid indicators commonly used in AVO analysis and interpretation. The new fluid indicator shows promising performance and success in fluid detection. Next, we apply the attribute on synthetic data calculated from well data, and seismic field data from North Western Australia. The target formation is Mid-Jurassic fluvial-deltaic sandstone and is comprised of three reservoir units interbedded in shale. The attribute could help detect the gas-saturated reservoirs and distinguish them from the overall background reflectivity.

A new lizard species (Scincidae: Ctenotus) highlights persistent knowledge gaps on the biodiversity of Australia’s central deserts

Australia harbors the most diverse lizard assemblages on Earth, yet the biodiversity of its vast arid zone remains incompletely characterized. Recent sampling of remote regions has revealed new species with unique phenotypes and unclear evolutionary affinities. Here, we describe a new species of scincid lizard that appears to be widely distributed across the Great Victoria Desert and adjacent regions. The new species was previously overlooked among specimens of the wide-ranging desert taxon Ctenotus schomburgkii but is distinguished from it by coloration and scalation characters. Phylogenetic analyses based on mitochondrial and genome-wide nuclear loci confirmed that the new species is highly divergent from C. schomburgkii, with which it appears to be sympatric across much of its range. In addition to the new species, our survey of genetic variation within C. schomburgkii as currently recognized revealed three additional lineages that approach one another in southern and northwestern Australia, and which may also represent distinct species. These results suggest that our knowledge of the extraordinary biodiversity of arid Australia remains incomplete, with implications for the conservation and management of this unique fauna. The targeted collection of voucher specimens in undersampled regions, coupled with population genetic screening of lineage diversity, will be crucial for characterizing species boundaries and understanding the composition of Australia’s vertebrate communities.

Art centres supporting our Elders - 'old people, that's where our strength comes from' - results from a national survey of Australian Aboriginal and Torres Strait Islander community controlled art centres.

There are approximately 90 Aboriginal and Torres Strait Islander community controlled art centres across Australia, the majority in geographically remote locations. This survey explored how these centres are supporting older people, including people living with dementia, if and how they are collaborating with aged care services and what challenges and opportunities they identify in these arrangements. An online survey was developed by a team of Aboriginal and non-Aboriginal researchers, art centre staff and art centre consultants. The survey was distributed in 2018 to art centres across Australia via their four art centre peak bodies: Desart; the Association of Northern, Kimberley and Arnhem Aboriginal Artists; the Indigenous Art Centre Alliance - Far North Queensland and Torres Strait Islands; and the Aboriginal Art Centre Hub - Western Australia. The survey was also conducted face-to-face with participants at art centre annual events; and on field trips to North Western and Central Australia, conducted as part of an overarching study. There were 53 completed surveys, with the highest proportion of responses (43%) from art centre managers. The survey generated 330 qualitative responses to the 13 questions that provided this option. The results showed that art centres play a wide ranging and vital role in supporting the health and wellbeing of older artists, many of whom are considered Elders within their communities, and that this reaches far beyond the production of art. The results showed that art centres are a safe place providing older people with the purpose and means to generate income, to enact governance, and to share cultural knowledge through intergenerational connection. Additionally, the results indicate that art centres provide a significant amount of direct care for older people, and that relationships are fundamental to delivering this social, emotional, spiritual and physical care. Furthermore, they showed a great deal of collaboration between art centres and aged care services, although little of this is formally documented or resourced. The survey results demonstrate that art centres play a significant and previously unexplored role in supporting the wellbeing of older people and people living with dementia in remote Aboriginal and Torres Strait Islander communities across Australia. Respondents shared diverse examples of providing physical, social, emotional, spiritual and cultural care, assistance with navigating health and aged care systems, as well as examples of collaborations with aged care and health providers. The results demonstrate opportunities to recognise and resource this vital work. These findings are particularly important in the context of Australia's recent Royal Commission into Aged Care Quality and Safety, which found that systemic change is urgently required. Additionally, Indigenous scholars have called for a swell of system reform to address inequities in health and aged care systems. They advocate for a fundamental shift from biomedical and siloed models of care to integrated models that centralise culture, intergenerational connection and the cultural determinants of health. The results show that art centres could bring their expertise to this conversation.

Detection of hydrocarbon- saturated reservoirs in a challenging geological setting using AVO attributes: A case study from Poseidon field, Offshore Northwest region of Australia

Amplitude Versus Offset (AVO) methods relate seismic amplitude variations to subsurface pore fluid and lithology changes. Over the past decades, numerous AVO attributes have been extracted from seismic data and combined to detect seismic expressions associated with hydrocarbon-charged sediments. In this paper, we use an AVO attribute combination composed of gradient and scaled-Poisson reflectivity (SPR) to detect hydrocarbon expressions. Irrespective of sand-shale impedance contrast, the SPR and the gradient G produce negative anomalies for shale over gas saturated reservoir. We demonstrate that SPR-G product is a good alternative to the Intercept-Gradient product which works only for unconsolidated sands. The dataset used in this study is from Poseidon field, North Western Australia. The gas reservoirs belong to the Middle Jurassic-aged Plover Formation. The Plover Formation comprises sandstone, mudstone, and coal that deposited in a fluvial-deltaic environment. AVO analysis at a well location indicates the reservoirs belong to AVO Class II, which is characterized by small zero offset reflectivity and an anomalously large G. Due to the low impedance contrast between the reservoirs and the shale intervals, the I × G product failed to detect the fluid expressions of the reservoirs. The SPR × G product and SPR-G crossplot showed better fluid detection and lithology discrimination. Furthermore, the computation of the product SPR × G volume helped highlight the fluid response and spatial distribution of the reservoir units. New prospective undrilled areas could be identified using the SPR-G product.

Are charter and private-boat recreational fishers learning to live with shark depredation?

The loss of hooked fish from shark depredation has become an increasing problem in marine recreational fisheries worldwide, particularly among charter and private-boat recreational fishers. There is growing need to understand the prevalence of shark encounters, where depredation occurs and how recreational fishers respond to and mitigate depredation. This study of 1340 charter and private-boat recreational fishers in north-western Australia, included both probability-based (telephone and online) and opt-in (online) survey methods and is the first to document mitigation methods used by recreational fishers. More than half of the respondents (728) who completed the survey indicated that they had attempted to mitigate depredation. In the probability-based survey, the main mitigation methods reported by charter and private-boat fishers were to move spots, use wire trace or stop fishing. Depredation evokes strong opinions from some sections of the fishing population. Although more avid fishers self-selected for the opt-in surveys, the inclusion of information from these respondents, particularly from open-ended questions, provided detailed information on attitudes among fishers where this issue is of concern. This study highlights the wide range of views and concerns regarding depredation, all of which need to be considered when developing policies and guidelines around this issue. As with other contentious issues where changes in fishing behaviour are required, decision-makers will need to devise strategies to inform and educate the fishing public in how to mitigate against depredation.

U-Pb dating reveals multiple Paleoproterozoic orogenic events (Hamersley orogenic cycle) along the southern Pilbara margin (Australia) spanning the onset of atmospheric oxygenation

Abstract The early Paleoproterozoic was a time of unprecedented change in Earth's climate and surface environment. The key to resolving some of the controversies surrounding the timing and causes of these changes lies with supracrustal sequences, such as the 2.45–2.22 Ga Turee Creek Group in the southern Pilbara craton, northwestern Australia. The group preserves a predominantly siliciclastic sequence; however, its precise age, tectonic setting, and postdepositional history are disputed. Although it is interpreted to have been deposited in a foreland basin setting shortly after 2.45 Ga, the oldest well-recognized deformational event, marked by northward folding and thrusting, is the 2.20–2.15 Ga Ophthalmia orogeny. Evidence for a pre-Ophthalmia fabric-forming tectonic event north of the Archean Sylvania Inlier, southeast Pilbara craton, which is marked by tight to isoclinal folding, has been largely overlooked. In this area, we report in situ U-Pb geochronology of authigenic monazite and xenotime in shale with a well-developed tectonic cleavage from the ca. 2.63 Ga Jeerinah Formation. Monazite porphyroblasts, which are locally wrapped by strain fringes aligned in a tectonic cleavage, yielded weighted mean 207Pb/206Pb ages at 2370 ± 11 Ma and 2312 ± 8 Ma, whereas xenotime, which overprints a crenulation cleavage, gave a weighted mean 207Pb/206Pb age of 2291 ± 11 Ma, constraining fabric development to between 2.31 Ga and 2.29 Ga. Our results confirm the existence of a pre-Ophthalmia deformational event in the southeastern Pilbara craton, herein referred to as the Sylvania orogeny, which is part of an ~300 m.y. interval (2.45–2.15 Ga) of northward-directed compression (“Hamersley orogenic cycle”). This orogenic cycle is marked by east-west and northwest-southeast folding, cleavage development, veining, hydrothermal gold mineralization, and isotopic resetting across the southern Pilbara craton. Our results indicate that the syn–Great Oxidation Event Turee Creek Group was deposited in one or more foreland basins after 2.45 Ga. Our results provide a new tectonostratigraphic and geodynamic framework for understanding the timing and origin of geochemical records in a key succession deposited during an interval of global environmental change.

First record of blacknape large-eye bream Gymnocranius satoi (Perciformes: Lethrinidae) in the Philippines

The Philippines has been regarded as the center of the center of marine shorefish biodiversity, having the highest number of fish species per square area in the world. The blacknape large-eye bream, Gymnocranius satoi, has been reported to occur from Southern Japan, Taiwan to Northwestern Australia and to the Coral Sea, but has not previously been recorded from the Philippines. From 2011 – 2019, the National Fisheries Research and Development Institute (NFRDI) collaborated with the National Museum of Natural History of the Smithsonian Institution (NMNH/SI), USA, and the Old Dominion University (ODU), Virgina, USA, to inventory all commercial fish species sold in fish markets around the Philippines. During three (3) fish market surveys (Dumaguete City Market, Negros Oriental; Claveria Public Market, Cagayan, Northern Luzon; and Tabaco City Market, Albay, Southeastern Luzon in 2013, 2016 and 2017, respectively), we collected and eventually identified using morphological and DNA barcoding (COI) analysis, seven (7) specimens of G. satoi, representing the first records of this species from the country. Since the potential to discover new species and first records of fish species in the Philippines is high, further taxonomic study of the genus Gymnocranius is needed.

Quantifying Coral Recovery Across A Biophysical Gradient in NorthWestern Australia’s Fringing Coral Reefs

Quantifying Coral Recovery Across A Biophysical Gradient in NorthWestern Australia’s Fringing Coral Reefs

Can deepwater bottom currents generate clinothems? An example of a large, asymmetric mounded drift in Upper Jurassic to Lower Cretaceous sediments from northwestern Australia

Abstract Clinoforms and clinothems are ubiquitous in shallow marine and shelf margin environments, where they show remarkable seaward progradation trends. Consensus holds that these features do not form in deepwater settings. This study describes an example of a large, asymmetric mounded deposit formed in Upper Jurassic to Lower Cretaceous sediments along the Exmouth Plateau (offshore northwestern Australia). Although it formed in deepwater environments, the deposit has previously been interpreted to reflect either a deltaic or shelf margin system based on clinoform and clinothem geometries. We support that this deposit shares similarities with a delta drift that evolved into a large, mounded drift (~180 km in length, ~120 km in width, and up to ~1.7 km in sedimentary thickness) that exhibits two migration trends: one westward and the other northeastward. Three evolutionary phases are proposed: (1) an onset drift stage (ca. 146.5–143.5 Ma); (2) a growth drift stage (ca. 143.5–138.2 Ma); and (3) a burial stage (ca. 138.2 Ma), which marks the completion of the drift and a shift in depositional style. The drift asymmetry and clinoform orientations indicate the influence of a northward-flowing water mass with two main cores. Our analysis thus suggests that bottom currents can create complex deposits with geometries that resemble clinothems in deepwater environments.

Genomic insights into the historical and contemporary demographics of the grey reef shark.

Analyses of genetic diversity can shed light on both the origins of biodiversity hotspots, as well as the conservation status of species that are impacted by human activities. With these objectives, we assembled a genomic dataset of 14,935 single nucleotide polymorphisms from 513 grey reef sharks (Carcharhinus amblyrhynchos) sampled across 17 locations in the tropical Indo-Pacific. We analysed geographic variation in genetic diversity, estimated ancient and contemporary effective population size (Ne) across sampling locations (using coalescent and linkage disequilibrium methods) and modelled the history of gene flow between the Coral Triangle and the Coral Sea. Genetic diversity decreased with distance away from the Coral Triangle and north-western Australia, implying that C. amblyrhynchos may have originated in this region. Increases in Ne were detected across almost all sampling locations 40,000-90,000 generations ago (approximately 0.6-1.5 mya, given an estimated generation time of 16.4 years), suggesting a range expansion around this time. More recent, secondary increases in Ne were inferred for the Misool and North Great Barrier Reef sampling locations, but joint modelling did not clarify whether these were due to population growth, migration, or both. Despite the greater genetic diversity and ancient Ne observed at sites around Australia and the Coral Triangle, remote reefs around north-western New Caledonia had the highest contemporary Ne, demonstrating the importance of using multiple population size assessment methods. This study provides insight into both the past and present demographics of C. amblyrhynchos and contributes to our understanding of evolution in marine biodiversity hotspots.

A Glyptagnostus reticulatus trilobite faunule from the Cambrian of the Northern Qilian Mountains, northwest China, and its paleogeographical implications

AbstractA Glyptagnostus reticulatus (Angelin, 1851)–bearing trilobite assemblage has been found from an unnamed Cambrian formation in the Northern Qilian Mountains area, of which geographical placement in the Cambrian is contested. Glyptagnostus reticulatus is a biostratigraphic indicator of the Furongian Series and Paibian Stage, and three agnostoid and six polymerid taxa from the Changgou section, Daliang area are described herein, along with conspecific forms from the nearby Chuancigou section. This well-preserved assemblage shows strong taxonomic affinity with northwestern Queensland, Australia, and western Hunan–eastern Guizhou, China, and likely comes from deep outer-shelf to slope setting associated with the Northern Qilian arc. It is consistent with other arguments that during the Cambrian, the Northern Qilian arc, along with the Hexi Corridor of the Alxa terrane, were more closely allied to South China than to North China.