The Evolution of Conditional Dispersal and Reproductive Isolation Along Environmental Gradients

Dispersal modulates gene flow throughout a population's spatial range. Gene flow affects adaptation at local spatial scales, and consequently impacts the evolution of reproductive isolation. A recent theoretical investigation has demonstrated that local adaptation along an environmental gradient, facilitated by the evolution of limited dispersal, can lead to parapatric speciation even in the absence of assortative mating. This and other studies assumed unconditional dispersal, so individuals start dispersing without regard to local environmental conditions. However, many species disperse conditionally their propensity to disperse is contingent upon environmental cues, such as the degree of local crowding or the availability of suitable mates. Here, we use an individual-based model in continuous space to investigate by numerical simulation the relationship between the evolution of threshold-based conditional dispersal and parapatric speciation driven by frequency-dependent competition along environmental gradients. We find that, as with unconditional dispersal, parapatric speciation occurs under a broad range of conditions when reproduction is asexual, and under a more restricted range of conditions when reproduction is sexual. In both the asexual and sexual cases, the evolution of conditional dispersal is strongly influenced by the slope of the environmental gradient: shallow environmental gradients result in low dispersal thresholds and high dispersal distances, while steep environmental gradients result in high dispersal thresholds and low dispersal distances. The later, however, remain higher than under unconditional dispersal, thus undermining isolation by distance, and hindering speciation in sexual populations. Consequently, the speciation of sexual population under conditional dispersal is triggered by a steeper gradient than under unconditional dispersal. Enhancing the disruptiveness of frequency-dependent selection, more box-shaped competition kernels dramatically lower the speciation-enabling slope of the environmental gradient

1.5µm Er³⁺:Yb³⁺ doped fibre DBF laser

We report the first DFB fiber laser. When pumped with a 980nm diode laser, the 2cm-long laser has an output power of 2mW at 1.534µm and a RIN of < -156dB/Hz

Genonets server-a web server for the construction, analysis and visualization of genotype networks.

A genotype network is a graph in which vertices represent genotypes that have the same phenotype. Edges connect vertices if their corresponding genotypes differ in a single small mutation. Genotype networks are used to study the organization of genotype spaces. They have shed light on the relationship between robustness and evolvability in biological systems as different as RNA macromolecules and transcriptional regulatory circuits. Despite the importance of genotype networks, no tool exists for their automatic construction, analysis and visualization. Here we fill this gap by presenting the Genonets Server, a tool that provides the following features: (i) the construction of genotype networks for categorical and univariate phenotypes from DNA, RNA, amino acid or binary sequences; (ii) analyses of genotype network topology and how it relates to robustness and evolvability, as well as analyses of genotype network topography and how it relates to the navigability of a genotype network via mutation and natural selection; (iii) multiple interactive visualizations that facilitate exploratory research and education. The Genonets Server is freely available at http://ieu-genonets.uzh.ch

Enhanced photosensitivity in tin-codoped germanosilicate optical fibres

Enhanced photosensitivity is found in Tin-codoped germanosilicate optical fibers. A photo-induced refractive index change (~1.4 x 10-3 times larger than that observed in pure germanosilicate fibers has been demonstrated. Unlike the technique of using Boron-codoping to enhance the photosensitivity of germanosilicate fibers, Tin-doping does not have a significant effect on fiber loss at the important telecommunication window of 1.55µm. High temperature stability of the gratings in Tin-codoped germanosilicate fibers is also much over Boron-codoped fibers

Grating formulation in a phosphorus-doped germanosilicate fibre

Refractive index changes as high as ~5 x 10-4 in a phosphorus-doped germanosilicate fibre were observed for the first time without hydrogen loading during grating formation with a 193 nm laser. Dynamics was studied and it was found that Type IIa gratings was easily formed in this fibre

Optical Spectra of SNR Candidates in NGC 300

We present moderate-resolution (<5A) long-slit optical spectra of 51 nebular objects in the nearby Sculptor Group galaxy NGC 300 obtained with the 2.3 meter Advanced Technology Telescope at Siding Spring Observatory, Australia. Adopting the criterion of [SII]/Ha>=0.4 to confirm supernova remnants (SNRs) from optical spectra, we find that of 28 objects previously proposed as SNRs from optical observations, 22 meet this criterion with six showing [SII]/Ha of less than 0.4. Of 27 objects suggested as SNRs from radio data, four are associated with the 28 previously proposed SNRs. Of these four, three (included in the 22 above) meet the criterion. In all, 22 of the 51 nebular objects meet the [SII]/Ha criterion as SNRs while the nature of the remaining 29 objects remains undetermined by these observations.Comment: Accepted for publication in Astrophysics & Space Scienc

Photosensitivity in germanosilicate fibres: electronic change or physical change?

Presentation slides<br/

Simulation of powder metal fabrication with high pressure gas atomization

A computational/analytical technique has been developed which models the physics of high pressure gas atomization. The technique uses an uncoupled approach, such that the gas flowfield is initially calculated with a commercially-available Navier-Stokes code. The liquid metal droplet breakup, dynamics, and thermodynamics, are then calculated using the pre-computed flowfield by a separate computer program written by the authors. The atomization code models the primary breakup of the liquid metal stream, tracks the droplets resulting from primary breakup through the flowfield until they undergo secondary breakup, and then tracks the subdroplets until they breakup, solidify, or leave the flowfield region of interest. The statistical properties of the metal powder produced are then computed from the characteristics of these droplets. Comparisons between experimental measurements and computations indicate that the Navier-Stokes code is predicting the gas flowfield well, and that the atomization code is properly modeling the physics of the droplet dynamics and breakup

RNA-mediated gene regulation is less evolvable than transcriptional regulation.

Much of gene regulation is carried out by proteins that bind DNA or RNA molecules at specific sequences. One class of such proteins is transcription factors, which bind short DNA sequences to regulate transcription. Another class is RNA binding proteins, which bind short RNA sequences to regulate RNA maturation, transport, and stability. Here, we study the robustness and evolvability of these regulatory mechanisms. To this end, we use experimental binding data from 172 human and fruit fly transcription factors and RNA binding proteins as well as human polymorphism data to study the evolution of binding sites in vivo. We find little difference between the robustness of regulatory protein-RNA interactions and transcription factor-DNA interactions to DNA mutations. In contrast, we find that RNA-mediated regulation is less evolvable than transcriptional regulation, because mutations are less likely to create interactions of an RNA molecule with a new RNA binding protein than they are to create interactions of a gene regulatory region with a new transcription factor. Our observations are consistent with the high level of conservation observed for interactions between RNA binding proteins and their target molecules as well as the evolutionary plasticity of regulatory regions bound by transcription factors. They may help explain why transcriptional regulation is implicated in many more evolutionary adaptations and innovations than RNA-mediated gene regulation