Influence of Ga/N ratio on morphology, vacancies, and electrical transport in GaN grown by molecular beam epitaxy at high temperature

The effect of Ga/N flux ratio on surface morphology, incorporation of point defects and electrical transport properties of GaN films grown by plasma-assisted molecular beam epitaxy in a recently developed high-temperature growth regime was investigated. The homoepitaxial (0001) GaN films grown at ∼780–790 °C showed smoothest morphologies near the cross-over between N-rich and Ga-rich growth(0.75<Ga/N<1.1) contrasting previous observations for low-temperature growth. The higher-quality growth near Ga/N∼1 resulted from lower thermal decomposition rates and was corroborated by slightly lower Ga vacancy concentrations [VGa], lower unintentional oxygen incorporation, and improved electron mobilities. The consistently low [VGa], i.e., ∼10exp16 cm−3 for all films attribute further to the significant benefits of the high-temperature growth regime.Peer reviewe

Disentangling canid howls across multiple species and subspecies: Structure in a complex communication channel.

Wolves, coyotes, and other canids are members of a diverse genus of top predators of considerable conservation and management interest. Canid howls are long-range communication signals, used both for territorial defence and group cohesion. Previous studies have shown that howls can encode individual and group identity. However, no comprehensive study has investigated the nature of variation in canid howls across the wide range of species. We analysed a database of over 2000 howls recorded from 13 different canid species and subspecies. We applied a quantitative similarity measure to compare the modulation pattern in howls from different populations, and then applied an unsupervised clustering algorithm to group the howls into natural units of distinct howl types. We found that different species and subspecies showed markedly different use of howl types, indicating that howl modulation is not arbitrary, but can be used to distinguish one population from another. We give an example of the conservation importance of these findings by comparing the howls of the critically endangered red wolves to those of sympatric coyotes Canis latrans, with whom red wolves may hybridise, potentially compromising reintroduced red wolf populations. We believe that quantitative cross-species comparisons such as these can provide important understanding of the nature and use of communication in socially cooperative species, as well as support conservation and management of wolf populations.Recording work was approved by the Institutional Animal Care and Use Committee of the University of Tennessee. AK is supported by a Herchel Smith postdoctoral fellowship at the University of Cambridge. Part of this work was carried out while AK was a Postdoctoral Fellow at the National Institute for Mathematical and Biological Synthesis, an Institute sponsored by the National Science Foundation through NSF Award #DBI-1300426, with additional support from The University of Tennessee, Knoxville. BH is thankful to the State Forest Departments of Himachal Pradesh, J&K, and Maharashtra, and to various zoos in India for permitting us to record howls. HRG is grateful to all who helped with the project: the staff at Colchester Zoo; the Wildwood Trust, the Borror Laboratory of Bioacoustics; the British Library; Lupus Laetus; Polish Mammal Research Institute; Tigress Productions; the BBC Natural History Unit; Longleat Safari Park; Tierstimmen Archiv; Wild Sweden; Wolf Park; the Macaulay Sound Library and the UK Wolf Conservation Trust; and Mike Collins, Teresa Palmer, Monty Sloan, Karl-Heinz Frommolt, Yorgos Iliopoulos, Christine Anhalt, Louise Gentle, Richard Yarnell, Victoria Allison Hughes and Susan Parks. BRM thanks the USDA/APHIS/WS/National Wildlife Research Center for supporting his doctoral research and providing access to captive coyotes; recording work was approved by the NWRC IACUC. SW thanks Mariana Olsen for assistance with data collection, and Yellowstone National Park for permission to record.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.beproc.2016.01.00

Marine Incursion: The Freshwater Herring of Lake Tanganyika Are the Product of a Marine Invasion into West Africa

The spectacular marine-like diversity of the endemic fauna of Lake Tanganyika, the oldest of the African Great Lakes, led early researchers to suggest that the lake must have once been connected to the ocean. Recent geophysical reconstructions clearly indicate that Lake Tanganyika formed by rifting in the African subcontinent and was never directly linked to the sea. Although the Lake has a high proportion of specialized endemics, the absence of close relatives outside Tanganyika has complicated phylogeographic reconstructions of the timing of lake colonization and intralacustrine diversification. The freshwater herring of Lake Tanganyika are members of a large group of pellonuline herring found in western and southern Africa, offering one of the best opportunities to trace the evolutionary history of members of Tanganyika's biota. Molecular phylogenetic reconstructions indicate that herring colonized West Africa 25–50MYA, at the end of a major marine incursion in the region. Pellonuline herring subsequently experienced an evolutionary radiation in West Africa, spreading across the continent and reaching East Africa's Lake Tanganyika during its early formation. While Lake Tanganyika has never been directly connected with the sea, the endemic freshwater herring of the lake are the descendents of an ancient marine incursion, a scenario which may also explain the origin of other Tanganyikan endemics

Self-induced growth of vertical free-standing InAs nanowires on Si(111) by molecular beam epitaxy

&nbsp;We report self-induced growth of vertically aligned (i.e. along the [ 111] direction), free-standing InAs nanowires on Si(111) substrates by solid-source molecular beam epitaxy. Implementation of an ultrathin amorphous SiO(x) mask on Si(111) facilitated epitaxial InAs nanowire growth, as confirmed by high-resolution x-ray diffraction 2 theta-omega scans and transmission electron microscopy. Depending on growth temperature (in the range of 400-520 degrees C) substantial size variation of both nanowire length and diameter was found under preservation of uniform, non-tapered hexagon-shaped geometries. The majority of InAs nanowires exhibited phase-pure zinc blende crystal structure with few defective regions consisting of stacking faults. Photoluminescence spectroscopy at 20 K revealed peak emission of the InAs nanowires at 0.445 eV, which is similar to 30 meV blueshifted with respect to the emission of the bulk InAs reference due to radial quantum confinement effects. These results show a promising route towards integration of well-aligned, high structural quality InAs-based nanowires with the desired aspect ratio and tailored emission wavelengths on an Si platform

Molecular phylogeny and speciation patterns in host-specific monogeneans (Cichlidogyrus, Dactylogyridae) parasitizing cichlid fishes (Cichliformes, Cichlidae) in Lake Tanganyika

Cichlidogyrus (including Scutogyrus) is the most speciose dactylogyridean monogenean genus known from African and Levantine cichlid fishes (Cichlidae). While its taxonomy is well established, little is known about the phylogenetic relationships and evolutionary history of this ectoparasite, especially from hosts belonging to one of the most impressive vertebrate radiations, the cichlid fishes from the East African Great Lakes and surrounding hydrological systems. Phylogenetic inference based on DNA sequences of the nuclear 18S, internal transcribed spacer 1 and 28S rDNA genes revealed that Cichlidogyrus parasitizing mainly West African cichlid tribes is paraphyletic with respect to species parasitizing hosts belonging to the East African cichlid radiation, which constitute a well-supported monophylum. Members of Cichlidogyrus from tylochromine and oreochromine hosts that colonised Lake Tanganyika only recently, cluster with their non-Lake Tanganyika relatives, indicating that they colonised Lake Tanganyika with their current host species, and did not jump over from any of the many cichlid species already present in the lake. The diversification of Cichlidogyrus in Lake Tanganyika seems to be driven by failure to diverge in old lineages of cichlids, cospeciation in more recently evolved ones, and host switching followed by parasite duplication at the level of the various host tribes. Evaluation of host specificity and structural evolution of haptoral and reproductive organs in Lake Tanganyika Cichlidogyrus revealed that strict specialist species together with larval hook size represent the ancestral state of haptor configuration, suggesting that members of Cichlidogyrus in this system evolved from a very simple form to a more complex one similarly to their West African congeners. Generalist species among Cichlidogyrus with a sclerotized vagina parasitizing ancient Lake Tanganyika lineages seem to have developed a different hook configuration, most probably to ensure successful colonisation of new, phylogenetically unrelated hosts.(c) 2022 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.The authors are grateful to C. Sturmbauer (University of Graz, Austria), W. Salzburger (University of Basel, Switzerland), D. Muzumani Risasi (CRH-Uvira, DR Congo) for their precious help with cichlid collection and identification; M. Reichard and R. Blazˇek (Czech Academy of Sciences, Czech Republic) for their help with fish collection, dissection and providing us with the photographs of cichlid species during the field trip; A. Meyer (University of Konstanz, Germany), G. Banyankimbona (University of Burundi), the Schreyen-Brichard family (Fishes of Burundi) and T. Veall and O. R. Mangwangwa (Rift Valley Tropicals, Zambia) for sample collection and fish identification; P. Masilya Mulungula, T. Mulimbwa N’sibula , V. Lumami Kapepula, E. Bahane Byaragi, S. Kambale Mukeranya and F. Muterezi Bukinga (CRH-Uvira, DR Congo) for coorganising the field work and their scientific contribution on LT cichlids; Š. Mašová, V. Michálková, E. Rˇehulková, I. Prˇikrylová, L. Raisingerová, N. Kmentová, K. Civánˇová, E. Jirounková, K. Koukalová, and M. Seifertová (Masaryk University, Brno, Czech Republic) for their help with fish dissection, parasite isolation and fixation and molecular laboratory analyses; and B. Egger, J. Rajkov and A. Anh-Thu Weber (University of Basel) for providing samples of Astatotilapia burtoni from Zambian systems. The first author thanks D. Ortiz Martínez (Masaryk University, Brno, Czech Republic) for stimulating discussions and constructive suggestions and criticisms related to phylogenetics. Finally, the authors would like to thank M. Gelnar for the continuous help he provided during this research. This research was funded by the Czech Science Foundation project no. P505/12/G112 - European Centre of Ichtyoparasitology (ECIP) and the Special Research Fund of Hasselt University (BOF20TT06, to M.P.M.V.). Fieldwork was partly supported by the Research Foundation—Flanders (FWO-Vlaanderen) (travel grants V.4.096.10.N.01 and K.2.032.08.N.01 to M.P.M.V., Research Programme G.0553.10) and a travel grant from the King Leopold III Fund for Nature Conservation and Exploration (to M.P. M.V.). Sampling was performed in accordance with mission statements no. 013/MNRST/CRHU/2010, 022/MINEURS/CRH-U/2013 and 031/MINRST/CRH-U/2016 from the Ministère de la Recherche Scientifique et Technologique–CRH-Uvira. The funders had no role in study design, data collection and analyses, decision to publish, or preparation of the manuscript

Origin and status of the Great Lakes wolf

An extensive debate concerning the origin and taxonomic status of wolf-like canids in the North American Great Lakes region and the consequences for conservation politics regarding these enigmatic predators is ongoing. Using maternally, paternally and biparentally inherited molecular markers, we demonstrate that the Great Lakes wolves are a unique population or ecotype of gray wolves. Furthermore, we show that the Great Lakes wolves experienced high degrees of ancient and recent introgression of coyote and western gray wolf mtDNA and Y-chromosome haplotypes, and that the recent demographic bottleneck caused by persecution and habitat depletion in the early 1900s is not reflected in the genetic data.</p