Resurvey of historical collection sites for Balston’s Pygmy Perch in the South West Linkages Target Area

Balston’s Pygmy Perch (Nannatherina balstoni) is one of the rarest native freshwater fishes endemic to south-western Australia (Morgan et al. 2011, 2014). The species inhabits near-coastal lakes, wetlands and flowing streams, and was historically distributed between the Moore River (north of Perth) and the Angove River (east of Albany) (Morgan et al. 2011, 2014). Numerous anthropogenic stressors including habitat destruction, pollution, river regulation, and water abstraction have resulted in an approximate 31% decline in the distribution, with the species apparently having been extirpated from the Swan Coastal Plain and a number of other systems across its range (Morgan et al. 2014). The contemporary distribution extends from the upper reaches of the Margaret River to the Angove River near Two Peoples Bay (Morgan & Beatty 2003; FFGFHU unpubl. data) (see Figure 1). Remnant populations are highly fragmented within this range (Morgan et al. 2014). In light of its typically low abundance and restricted distribution, N. balstoni has been formally recognised as Vulnerable to extinction under the Commonwealth Government’s Environment Protection and Biodiversity Conservation (EPBC) Act 1999 and is listed under Schedule 1 (“fauna that is rare or is likely to become extinct”) of the Western Australian Government’s Wildlife Conservation Act 1950. Accordingly, this fish is the flagship species of the current project entitled “Protecting threatened fishes in the South West Linkages Target Area”. A thorough review of the historical distribution of N. balstoni was conducted at the outset of this project and has now been published in the scientific literature (see Morgan et al. 2014). To complement this review, one of the project’s primary aims was to resurvey a number of historical collection sites in order to ground-truth the current status of resident N. balstoni populations. The results of this survey should provide valuable data for authorities in developing management and recovery strategies for the conservation of this threatened south-western Australian endemic

Isotropic-nematic transition in liquid crystals confined between rough walls

The effect of rough walls on the phase behaviour of a confined liquid crystal (LC) fluid is studied using constant pressure Monte Carlo simulations. The LC is modelled as a fluid of soft ellipsoidal molecules and the rough walls are represented as a hard wall with a number of molecules randomly embedded in them. It is found that the isotropic-nematic (IN) transition is shifted to higher pressures for rougher walls.Comment: 4 pages, 4 figures Accepted in Chemical Physics Letter

Sustained MAPK/ERK activation in adult Schwann cells impairs nerve repair

The MAPK/ERK pathway has a critical role in PNS development. It is required for Schwann cell (SC) differentiation and myelination; sustained embryonic MAPK/ERK activation in SCs enhances myelin growth overcoming signals that normally end myelination. Excess activation of this pathway can be maladaptive as in adulthood acute strong activation of MAPK/ERK has been shown to cause SC dedifferentiation and demyelination. We used a mouse model (including male and female animals) in which gain of function Mek1DD allele produces sustained MAPK/ERK activation in adult SCs and we determined the impact of such activation on nerve repair. In the uninjured nerve, MAPK/ERK activation neither impaired myelin nor did it re-activate myelination. However, in the injured nerve it was detrimental and resulted in delayed repair and functional recovery. In the early phase of injury the rate of myelin clearance was faster. Four weeks following injury, when nerve repair is normally advanced, myelinated axons of Mek1DD mutants demonstrated higher rates of myelin decompaction, a reduced number of Cajal bands and decreased internodal length. We noted the presence of abnormal Remak bundles with long SCs processes and reduced numbers of C-fibres/Remak bundle. Both the total number of regenerating axons and the intra-epidermal nerve fibres density in the skin were reduced. Sustained activation of MAPK/ERK in adult SCs is therefore deleterious to successful nerve repair, emphasising the differences in the signalling processes coordinating nerve development and repair. Our results also underline the key role of SCs in axon regeneration and successful target einnervation.SIGNIFICANCE STATEMENTThe MAPK/ERK pathway promotes developmental myelination and its sustained activation in SCs induced continuous myelin growth, compensating for the absence of essential myelination signals. However, the strength of activation is fundamental because acute strong induction of MAPK/ERK in adulthood induces demyelination. What has been unknown is the effect of a mild but sustained MAPK/ERK activation in SCs on nerve repair in adulthood. This promoted myelin clearance but led to abnormalities in non-myelinating and myelinating SCs in the later phases of nerve repair, resulting in slowed axon regeneration, cutaneous reinnervation and functional recovery. Our results emphasise the distinct role of the MAPK/ERK pathway in developmental myelination versus remyelination and the importance of signalling between SCs and axons for successful axon regeneration

Dynamics of an Unbounded Interface Between Ordered Phases

We investigate the evolution of a single unbounded interface between ordered phases in two-dimensional Ising ferromagnets that are endowed with single-spin-flip zero-temperature Glauber dynamics. We examine specifically the cases where the interface initially has either one or two corners. In both examples, the interface evolves to a limiting self-similar form. We apply the continuum time-dependent Ginzburg-Landau equation and a microscopic approach to calculate the interface shape. For the single corner system, we also discuss a correspondence between the interface and the Young tableau that represents the partition of the integers.Comment: 9 pages, 11 figures, 2-column revtex4 format. V2: references added and discussion section expanded slightly. Final version for PRE. V3: A few small additional editorial change

Surface tension of the isotropic-nematic interface

We present the first calculations of the pressure tensor profile in the vicinity of the planar interface between isotropic liquid and nematic liquid crystal, using Onsager's density functional theory and computer simulation. When the liquid crystal director is aligned parallel to the interface, the situation of lowest free energy, there is a large tension on the nematic side of the interface and a small compressive region on the isotropic side. By contrast, for perpendicular alignment, the tension is on the isotropic side. There is excellent agreement between theory and simulation both in the forms of the pressure tensor profiles, and the values of the surface tension.Comment: Minor changes; to appear in Phys. Rev.

Phylogeography, population structure and evolution of coral-eating butterflyfishes (Family Chaetodontidae, genus Chaetodon, subgenus Corallochaetodon)

Aim: This study compares the phylogeography, population structure and evolution of four butterflyfish species in the Chaetodon subgenus Corallochaetodon, with two widespread species (Indian Ocean – C. trifasciatus and Pacific Ocean – C. lunulatus), and two species that are largely restricted to the Red Sea (C. austriacus) and north-western (NW) Indian Ocean (C. melapterus). Through extensive geographical coverage of these taxa, we seek to resolve patterns of genetic diversity within and between closely related butterflyfish species in order to illuminate biogeographical and evolutionary processes. Location: Red Sea, Indian Ocean and Pacific Ocean. Methods: A total of 632 individuals from 24 locations throughout the geographical ranges of all four members of the subgenus Corallochaetodon were sequenced using a 605 bp fragment (cytochrome b) of mtDNA. In addition, 10 microsatellite loci were used to assess population structure in the two widespread species. Results: Phylogenetic reconstruction indicates that the Pacific Ocean C. lunulatus diverged from the Indian Ocean C. trifasciatus approximately 3 Ma, while C. melapterus and C. austriacus comprise a cluster of shared haplotypes derived from C. trifasciatus within the last 0.75 Myr. The Pacific C. lunulatus had significant population structure at peripheral locations on the eastern edge of its range (French Polynesia, Johnston Atoll, Hawai'i), and a strong break between two ecoregions of the Hawaiian Archipelago. The Indian Ocean C. trifasciatus showed significant structure only at the Chagos Archipelago in the central Indian Ocean, and the two range-restricted species showed no population structure but evidence of recent population expansion. Main conclusions: Patterns of endemism and genetic diversity in Corallochaetodon butterflyfishes have been shaped by (1) Plio-Pleistocene sea level changes that facilitated evolutionary divergences at biogeographical barriers between Indian and Pacific Oceans, and the Indian Ocean and Red Sea, and (2) semi-permeable oceanographic and ecological barriers working on a shorter time-scale. The evolution of range-restricted species (Red Sea and NW Indian Ocean) and isolated populations (Hawai'i) at peripheral biogeographical provinces indicates that these areas are evolutionary incubators for reef fishes

Coupled virus - bacteria interactions and ecosystem function in an engineered microbial system

Viruses are thought to control bacterial abundance, affect community composition and influence ecosystem function in natural environments. Yet their dynamics have seldom been studied in engineered systems, or indeed in any system, for long periods of time. We measured virus abundance in a full-scale activated sludge plant every week for two years. Total bacteria and ammonia oxidising bacteria (AOB) abundances, bacterial community profiles, and a suite of environmental and operational parameters were also monitored. Mixed liquor virus abundance fluctuated over an order of magnitude (3.18 × 108 – 3.41 × 109 virus’s mL-1) and that variation was statistically significantly associated with total bacterial and AOB abundance, community composition, and effluent concentrations of COD and NH4+- N and thus system function. This suggests viruses play a far more important role in the dynamics of activated sludge systems than previously realised and could be one of the key factors controlling bacterial abundance, community structure and functional stability and may cause reactors to fail. These finding are based on statistical associations, not mechanistic models. Nevertheless, viral associations with abiotic factors, such as pH, make physical sense giving credence to these findings and highlighting the role that physical factors play in virus ecology. Further work is needed to identify and quantify specific bacteriophage and their hosts to enable us to develop mechanistic models of the ecology of viruses in wastewater treatment systems. However, since we have shown that viruses can be related to effluent quality and virus quantification is simple and cheap, practitioners would probably benefit from quantifying viruses now

Molecular chirality and the orbital angular momentum of light

Optical beams with a new and distinctive type of helicity have become the subject of much recent interest. While circularly polarised light comprises photons with spin angular momentum, these optically engineered 'twisted beams' (optical vortices) are endowed with orbital angular momentum. Here, the wave- front surface of the electromagnetic fields assumes helical form. To date, optical vortices have generally been studied only in their interactions with achiral matter. This study assesses what new features, if any, can be expected when such beams are used to interrogate a chiral system.Comment: 16 pages including 1 tabl

Proximity effect in ultrathin Pb/Ag multilayers within the Cooper limit

We report on transport and tunneling measurements performed on ultra-thin Pb/Ag (strong coupled superconductor/normal metal) multilayers evaporated by quench condensation. The critical temperature and energy gap of the heterostructures oscillate with addition of each layer, demonstrating the validity of the Cooper limit model in the case of multilayers. We observe excellent agreement with a simple theory for samples with layer thickness larger than 30\AA . Samples with single layers thinner than 30\AA deviate from the Cooper limit theory. We suggest that this is due to the "inverse proximity effect" where the normal metal electrons improve screening in the superconducting ultrathin layer and thus enhance the critical temperature.Comment: 4 pages, 4 figure