Passive, broadband suppression of radiation of low-frequency sound.

Anthropogenic noise pollution of the ocean is an acute and growing problem. This letter explores one possible mechanism of noise abatement. The far-field acoustic pressure due to a compact underwater source can be suppressed by placing a small compliant body in the vicinity of the source. Here, the feasibility and efficiency of the suppression are evaluated by quantifying the reduction in radiated acoustic energy for several simple geometries, which include sound sources in an unbounded fluid, near a reflecting boundary, or in a shallow-water waveguide. The analysis is streamlined using analytic solutions for sound diffraction by simple shapes.

Rayleigh scattering of a cylindrical sound wave by an infinite cylinder.

Rayleigh scattering, in which the wavelength is large compared to the scattering object, is usually studied assuming plane incident waves. However, full Green's functions are required in a number of problems, e.g., when a scatterer is located close to the ocean surface or the seafloor. This paper considers the Green's function of the two-dimensional problem that corresponds to scattering of a cylindrical wave by an infinite cylinder embedded in a homogeneous fluid. Soft, hard, and impedance cylinders are considered. Exact solutions of the problem involve infinite series of products of Bessel functions. Here, simple, closed-form asymptotic solutions are derived, which are valid for arbitrary source and receiver locations outside the cylinder as long as its diameter is small relative to the wavelength. The scattered wave is given by the sum of fields of three linear image sources. The viability of the image source method was anticipated from known solutions of classical electrostatic problems involving a conducting cylinder. The asymptotic acoustic Green's functions are employed to investigate reception of low-frequency sound by sensors mounted on cylindrical bodies.

Human predation contributed to the extinction of the Australian megafaunal bird Genyornis newtoni ∼47 ka.

Although the temporal overlap between human dispersal across Australia and the disappearance of its largest animals is well established, the lack of unambiguous evidence for human-megafauna interactions has led some to question a human role in megafaunal extinction. Here we show that diagnostic burn patterns on eggshell fragments of the megafaunal bird Genyornis newtoni, found at >200 sites across Australia, were created by humans discarding eggshell in and around transient fires, presumably made to cook the eggs. Dating by three methods restricts their occurrence to between 53.9 and 43.4 ka, and likely before 47 ka. Dromaius (emu) eggshell occur frequently in deposits from >100 ka to present; burnt Dromaius eggshell first appear in deposits the same age as those with burnt Genyornis eggshell, and then continually to modern time. Harvesting of their eggs by humans would have decreased Genyornis reproductive success, contributing to the bird's extinction by ∼47 ka.

Genetic diversity loss in a biodiversity hotspot: ancient DNA quantifies genetic decline and former connectivity in a critically endangered marsupial.

The extent of genetic diversity loss and former connectivity between fragmented populations are often unknown factors when studying endangered species. While genetic techniques are commonly applied in extant populations to assess temporal and spatial demographic changes, it is no substitute for directly measuring past diversity using ancient DNA (aDNA). We analysed both mitochondrial DNA (mtDNA) and nuclear microsatellite loci from 64 historical fossil and skin samples of the critically endangered Western Australian woylie (Bettongia penicillata ogilbyi), and compared them with 231 (n = 152 for mtDNA) modern samples. In modern woylie populations 15 mitochondrial control region (CR) haplotypes were identified. Interestingly, mtDNA CR data from only 29 historical samples demonstrated 15 previously unknown haplotypes and detected an extinct divergent clade. Through modelling, we estimated the loss of CR mtDNA diversity to be between 46% and 91% and estimated this to have occurred in the past 2000-4000 years in association with a dramatic population decline. In addition, we obtained near-complete 11-loci microsatellite profiles from 21 historical samples. In agreement with the mtDNA data, a number of 'new' microsatellite alleles was only detected in the historical populations despite extensive modern sampling, indicating a nuclear genetic diversity loss >20%. Calculations of genetic diversity (heterozygosity and allelic rarefaction) showed that these were significantly higher in the past and that there was a high degree of gene flow across the woylie's historical range. These findings have an immediate impact on how the extant populations are managed and we recommend the implementation of an assisted migration programme to prevent further loss of genetic diversity. Our study demonstrates the value of integrating aDNA data into current-day conservation strategies.

Fossil avian eggshell preserves ancient DNA.

Owing to exceptional biomolecule preservation, fossil avian eggshell has been used extensively in geochronology and palaeodietary studies. Here, we show, to our knowledge, for the first time that fossil eggshell is a previously unrecognized source of ancient DNA (aDNA). We describe the successful isolation and amplification of DNA from fossil eggshell up to 19 ka old. aDNA was successfully characterized from eggshell obtained from New Zealand (extinct moa and ducks), Madagascar (extinct elephant birds) and Australia (emu and owl). Our data demonstrate excellent preservation of the nucleic acids, evidenced by retrieval of both mitochondrial and nuclear DNA from many of the samples. Using confocal microscopy and quantitative PCR, this study critically evaluates approaches to maximize DNA recovery from powdered eggshell. Our quantitative PCR experiments also demonstrate that moa eggshell has approximately 125 times lower bacterial load than bone, making it a highly suitable substrate for high-throughput sequencing approaches. Importantly, the preservation of DNA in Pleistocene eggshell from Australia and Holocene deposits from Madagascar indicates that eggshell is an excellent substrate for the long-term preservation of DNA in warmer climates. The successful recovery of DNA from this substrate has implications in a number of scientific disciplines; most notably archaeology and palaeontology, where genotypes and/or DNA-based species identifications can add significantly to our understanding of diets, environments, past biodiversity and evolutionary processes.