Reproductive Isolation in a Threespine Stickleback Hybrid Zone

In many estuarine sites, morphological and genetic differences between anadromous and freshwater threespine sticklebacks are maintained despite breeding in sympatry. Here, we investigate the maintenance of this morphological divergence in a natural hybrid zone in the River Tyne, Scotland. We provide a morphological description of the hybrid zone, and using a Bayesian MCMC approach, identified distinct anadromous and freshwater genetic clusters. Anadromous and freshwater sticklebacks breed in spatial and temporal sympatry in the lower reaches of the River Tyne. The frequency of hybrids within these sites (33%) indicates prezygotic isolation is not complete, and suggests that assortative mating is not strong. However, significant heterozygote deficit and cytonuclear disequilibrium in juveniles collected from sympatric sites confirms that barriers to gene flow exist between the morphs in the wild. In addition, we found no evidence of a directional bias in hybridisation, although hybrids with anadromous mothers were more common because anadromous females outnumbered freshwater females within the hybrid zone. We discuss the potential contribution of temporal, spatial, and sexual prezygotic barriers to the observed reproductive isolation as well as postzygotic selection against hybrid zygotes or fry

Comparative studies using EXAFS and PAC of lattice damage in semiconductors

We have used the perturbed angular correlation (PAC) method and extended X-ray absorption fine structure spectroscopy (EXAFS), along with microscopic methods to investigate the implantation induced disorder and characterize the ion-induced amorphisation of elemental and compound semiconductors

Structure and low-temperature thermal relaxation of ion-implanted germanium

The structure of implantation-induced damage in Ge has been investigated using high resolution extended X-ray absorption fine structure spectroscopy(EXAFS). EXAFS data analysis was performed with the Cumulant Method. For the crystalline-to-amorphous transformation, a progressive increase in bond-length was observed without the presence of an asymmetry in interatomic distance distribution (RDF). Beyond the amorphization threshold the RDF was dose dependent and asymmetric, where the bond-length and asymmetry increased as functions of ion dose. Such an effect was attributed to the formation of three- and five-fold coordinated atoms within the a morphous phase. Low-temperature thermal annealing resulted in structural relaxation of the amorphous phase as evidenced by a reduction in the centroid ,asymmetry and width of the RDF, as consistent with a reduction in the fraction of non four-fold coordinated atoms.The results have been compared to other EXAFS studies of amorphous Ge, and it issuggested thatthe range of bond-lengths reported therein is related to the sample preparation method and state of relaxation.</jats:p

Micro- and macro-structure of implantation-induced disorder in Ge

The structure of ion implantation-induced damage in Ge substrates has been investigated with a combination of ion- and photon-based techniques including Rutherford backscattering spectrometry (RBS), perturbed angular correlation (PAC) and extended X-ray absorption fine structure (EXAFS) spectroscopy. For MeV Ge ion implantation at -196°C, the dose dependence of the decrease in local atomic order, determined from EXAFS and PAC, was compared to the number of displaced atoms determined from RBS measurements. An EXAFS determined damage fraction was shown to be a better estimate of amorphous fraction than the number of displaced atoms. PAC was used to elucidate the evolution of defective configurations, and was compared to the RBS and EXAFS results. A fit to the Overlap model with the overlap of two ion cascades for complete amorphization best described the experimental results