A planet within the debris disk around the pre-main-sequence star AU Microscopii.

AU Microscopii (AU Mic) is the second closest pre-main-sequence star, at a distance of 9.79 parsecs and with an age of 22 million years1. AU Mic possesses a relatively rare2 and spatially resolved3 edge-on debris disk extending from about 35 to 210 astronomical units from the star4, and with clumps exhibiting non-Keplerian motion5-7. Detection of newly formed planets around such a star is challenged by the presence of spots, plage, flares and other manifestations of magnetic 'activity' on the star8,9. Here we report observations of a planet transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of 8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4 Jupiter radii, and a mass of less than 0.18 Jupiter masses at 3σ confidence. Our observations of a planet co-existing with a debris disk offer the opportunity to test the predictions of current models of planet formation and evolution.

Publisher Correction: A planet within the debris disk around the pre-main-sequence star AU Microscopii.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Pulsed accretion in a variable protostar.

Periodic increases in luminosity arising from variable accretion rates have been predicted for some pre-main-sequence close binary stars as they grow from circumbinary disks. The phenomenon is known as pulsed accretion and can affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formation. Accretion variability is a common feature of young stars, with a large range of amplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodic variations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers, albeit intermittently with accretion luminosity variations ranging from zero to 50 per cent from orbit to orbit. Here we report that the infrared luminosity of a young protostar (of age about 10(5) years) increases by a factor of ten in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseen binary companion. The strength and regularity of this accretion signal is surprising; it may be related to the very young age of the system, which is a factor of ten younger than the other pulsed accretors previously studied.

Does Size Matter? An Experimental Evaluation of the Relative Abundance and Decay Rates of Aquatic Environmental DNA.

Environmental DNA (eDNA) is increasingly used to monitor aquatic macrofauna. Typically, short mitochondrial DNA fragments are targeted because these should be relatively more abundant in the environment as longer fragments will break into smaller fragments over time. However, longer fragments may permit more flexible primer design and increase taxonomic resolution for eDNA metabarcoding analyses, and recent studies have shown that long mitochondrial eDNA fragments can be extracted from environmental water samples. Nuclear eDNA fragments have also been proposed as targets, but little is known about their persistence in the aquatic environment. Here we measure the abundance of mitochondrial eDNA fragments of different lengths and of short nuclear eDNA fragments, originating from captive fish in experimental tanks, and we test whether longer mitochondrial and short nuclear fragments decay faster than short mitochondrial fragments following fish removal. We show that when fish are present, shorter mitochondrial fragments are more abundant in water samples than both longer mitochondrial fragments and short nuclear eDNA fragments. However, the rate of decay following fish removal was similar for all fragment types, suggesting that the differences in abundance resulted from differences in the rates at which different fragment types were produced rather than differences in their decay rates.

Swinging back from the brink? Polygamous mating strategies revealed for an iconic threatened freshwater fish.

Catastrophic fish death events are increasing in frequency and severity globally. A series of major recent fish deaths in the semi-arid lower Darling-Baaka river system (LDBR) of Australia are emblematic of these issues with tens of millions of native fish perishing. In 2018-2019 there was a major death event for Australia's largest freshwater fish, Murray cod (Maccullochella peelii). To aid the recovery and guide restoration activities of local Murray cod populations, it is essential to gather information on the mating strategies and effective population size following the fish death event. After the fish deaths, we collected larvae during the 2020 and 2021 breeding seasons and used single nucleotide polymorphisms (SNPs) to provide insight mating strategies and to estimate effective population size. Larvae were detected in both years along the entire length of the LDBR. Sixteen percent of the inferred breeding individuals were found to contribute to multiple pairings, confirming a complex and polygamous mating system. A high frequency of polygamy was evident both within and between years with 100 % polygamy identified among parents that produced offspring in both 2020 and 2021 and 95 % polygamy identified among parents involved in multiple spawning events within years. Post-larval Murray cod samples collected between 2016 and 2021 were co-analysed to further inform kinship patterns. Again, monogamy was rare with no confirmed cases of the same male-female pair contributing to multiple breeding events within or between seasons. Effective population size based on Murray cod collected after the fish death event was estimated at 721.6 (CI 471-1486), though this has likely declined following a subsequent catastrophic fish death event in the LDBR in March 2023. Our data provide insight into the variability of Murray cod mating strategies, and we anticipate that this knowledge will assist in planning conservation actions to ultimately help recover a species in crisis.

Identifying error and accurately interpreting environmental DNA metabarcoding results: A case study to detect vertebrates at arid zone waterholes.

Environmental DNA (eDNA) metabarcoding surveys enable rapid, noninvasive identification of taxa from trace samples with wide-ranging applications from characterizing local biodiversity to identifying food-web interactions. However, the technique is prone to error from two major sources: (a) contamination through foreign DNA entering the workflow, and (b) misidentification of DNA within the workflow. Both types of error have the potential to obscure true taxon presence or to increase taxonomic richness by incorrectly identifying taxa as present at sample sites, but multiple error sources can remain unaccounted for in metabarcoding studies. Here, we use data from an eDNA metabarcoding study designed to detect vertebrate species at waterholes in Australia's arid zone to illustrate where and how in the workflow errors can arise, and how to mitigate those errors. We detected the DNA of 36 taxa spanning 34 families, 19 orders and five vertebrate classes in water samples from waterholes, demonstrating the potential for eDNA metabarcoding surveys to provide rapid, noninvasive detection in remote locations, and to widely sample taxonomic diversity from aquatic through to terrestrial taxa. However, we initially identified 152 taxa in the samples, meaning there were many false positive detections. We identified the sources of these errors, allowing us to design a stepwise process to detect and remove error, and provide a template to minimize similar errors that are likely to arise in other metabarcoding studies. Our findings suggest eDNA metabarcoding surveys need to be carefully conducted and screened for errors to ensure their accuracy.

An insight into the prey spectra and livestock predation by cheetahs in Kenya using faecal DNA metabarcoding.

Dietary composition is a fundamental part of animal ecology and an important component of population dynamics. Therefore, obtaining accurate information on what an animal consumes is important for conservation planning, especially for wild large carnivores that exist in human-dominated landscapes where they are prone to direct conflicts with local people. We used faecal DNA metabarcoding to identify the vertebrate taxa commonly predated on by cheetahs (Acinonyx jubatus) with an emphasis on domestic taxa and determine the drivers of livestock predation by cheetahs residing in the Maasai Mara and Amboseli ecosystems which are important population strongholds in southern Kenya. From 84 cheetah faeces that we analysed, a total of 14 prey taxa were identified, including birds, wild and domestic mammals. The livestock taxa identified in cheetah faeces occurred at moderate frequency (12.8%) and the results showed that livestock predation was influenced neither by the sex of the cheetah nor by season. In general, our study shows that cheetahs prey on a diverse range of prey taxa including birds, wild ungulates of various sizes and occasionally on domestic animals, and that the faecal DNA metabarcoding approach represents a valuable complement to traditional dietary analysis methods.

Food from faeces: Evaluating the efficacy of scat DNA metabarcoding in dietary analyses.

Scat DNA metabarcoding is increasingly being used to track the feeding ecology of elusive wildlife species. This approach has greatly increased the resolution and detection success of prey items contained in scats when compared with other classical methods. However, there have been few studies that have systematically tested the applicability and reliability of this approach to study the diet of large felids species in the wild. Here we assessed the effectiveness of this approach in the cheetah Acinonyx jubatus. We tested how scat degradation, meal size, prey species consumed and feeding day (the day a particular prey was consumed) influenced prey DNA detection success in captive cheetahs. We demonstrated that it is possible to obtain diet information from 60-day old scats using genetic approaches, but the efficiency decreased over time. Probability of species-identification was highest for food items consumed one day prior to scat collection and the probability of being able to identify the species consumed increased with the proportion of the prey consumed. Detection success varied among prey species but not by individual cheetah. Identification of prey species using DNA detection methods from a single consumption event worked for samples collected between 8 and 72 hours post-feeding. Our approach confirms the utility of genetic approaches to identify prey species in scats and highlight the need to account for the systematic bias in results to control for possible scat degradation, feeding day, meal size and prey species consumed especially in the wild-collected scats.

Toward an ecoregion scale evaluation of eDNA metabarcoding primers: A case study for the freshwater fish biodiversity of the Murray-Darling Basin (Australia).

High-throughput sequencing of environmental DNA (i.e., eDNA metabarcoding) has become an increasingly popular method for monitoring aquatic biodiversity. At present, such analyses require target-specific primers to amplify DNA barcodes from co-occurring species, and this initial amplification can introduce biases. Understanding the performance of different primers is thus recommended prior to undertaking any metabarcoding initiative. While multiple software programs are available to evaluate metabarcoding primers, all programs have their own strengths and weaknesses. Therefore, a robust in silico workflow for the evaluation of metabarcoding primers will benefit from the use of multiple programs. Furthermore, geographic differences in species biodiversity are likely to influence the performance of metabarcoding primers and further complicate the evaluation process. Here, an in silico workflow is presented that can be used to evaluate the performance of metabarcoding primers on an ecoregion scale. This workflow was used to evaluate the performance of published and newly developed eDNA metabarcoding primers for the freshwater fish biodiversity of the Murray-Darling Basin (Australia). To validate the in silico workflow, a subset of the primers, including one newly designed primer pair, were used in metabarcoding analyses of an artificial DNA community and eDNA samples. The results show that the in silico workflow allows for a robust evaluation of metabarcoding primers and can reveal important trade-offs that need to be considered when selecting the most suitable primer. Additionally, a new primer pair was described and validated that allows for more robust taxonomic assignments and is less influenced by primer biases compared to commonly used fish metabarcoding primers.

Methods to maximise recovery of environmental DNA from water samples.

The environmental DNA (eDNA) method is a detection technique that is rapidly gaining credibility as a sensitive tool useful in the surveillance and monitoring of invasive and threatened species. Because eDNA analysis often deals with small quantities of short and degraded DNA fragments, methods that maximize eDNA recovery are required to increase detectability. In this study, we performed experiments at different stages of the eDNA analysis to show which combinations of methods give the best recovery rate for eDNA. Using Oriental weatherloach (Misgurnus anguillicaudatus) as a study species, we show that various combinations of DNA capture, preservation and extraction methods can significantly affect DNA yield. Filtration using cellulose nitrate filter paper preserved in ethanol or stored in a -20°C freezer and extracted with the Qiagen DNeasy kit outperformed other combinations in terms of cost and efficiency of DNA recovery. Our results support the recommendation to filter water samples within 24hours but if this is not possible, our results suggest that refrigeration may be a better option than freezing for short-term storage (i.e., 3-5 days). This information is useful in designing eDNA detection of low-density invasive or threatened species, where small variations in DNA recovery can signify the difference between detection success or failure.