scholarly journals Opsin-based photopigments expressed in the retina of a South American pit viper, Bothrops atrox (Viperidae)

2018 ◽  
Vol 35 ◽  
Author(s):  
Christiana Katti ◽  
Micaela Stacey-Solis ◽  
Nicole A. Coronel-Rojas ◽  
Wayne I.L. Davies
Keyword(s):  
Opsin Gene ◽  
South American ◽  
Long Wavelength ◽  
Rods And Cones ◽  
The Past ◽  
Different Types ◽  
The Common ◽  
Cone Opsins ◽  
General Studies ◽  
Bothrops Atrox

AbstractAlthough much is known about the visual system of vertebrates in general, studies regarding vision in reptiles, and snakes in particular, are scarce. Reptiles display diverse ocular structures, including different types of retinae such as pure cone, mostly rod, or duplex retinas (containing both rods and cones); however, the same five opsin-based photopigments are found in many of these animals. It is thought that ancestral snakes were nocturnal and/or fossorial, and, as such, they have lost two pigments, but retained three visual opsin classes. These are the RH1 gene (rod opsin or rhodopsin-like-1) expressed in rods and two cone opsins, namely LWS (long-wavelength-sensitive) and SWS1 (short-wavelength-sensitive-1) genes. Until recently, the study of snake photopigments has been largely ignored. However, its importance has become clear within the past few years as studies reconsider Walls’ transmutation theory, which was first proposed in the 1930s. In this study, the visual pigments of Bothrops atrox (the common lancehead), a South American pit viper, were examined. Specifically, full-length RH1 and LWS opsin gene sequences were cloned, as well as most of the SWS1 opsin gene. These sequences were subsequently used for phylogenetic analysis and to predict the wavelength of maximum absorbance (λmax) for each photopigment. This is the first report to support the potential for rudimentary color vision in a South American viper, specifically a species that is regarded as being nocturnal.

Positive selection of the long-wavelength opsin gene in South American cichlid fishes

Hydrobiologia ◽  
2021 ◽  
Author(s):  
Thomaz Mansini Carrenho Fabrin ◽  
Luciano Seraphim Gasques ◽  
Rodrigo Junio da Graça ◽  
Sônia Maria Alves Pinto Prioli ◽  
Weferson Júnio da Graça ◽  
...  
Keyword(s):  
Positive Selection ◽  
Opsin Gene ◽  
South American ◽  
Long Wavelength ◽  
Cichlid Fishes ◽  
Selection Of

Sociolinguistic typology and the uniformitarian hypothesis

2020 ◽  
pp. 44-57
Author(s):  
Peter Trudgill
Keyword(s):  
Social Factors ◽  
Historical Linguistics ◽  
Human Mind ◽  
Methodological Principle ◽  
Human Language ◽  
Language Faculty ◽  
The Past ◽  
Different Types ◽  
The Common ◽  
Linguistic Structures

One of the bases of historical linguistics is the uniformitarian principle: knowledge of processes that operated in the past can be inferred by observing ongoing processes in the present. This leads us to the methodological principle of using the present to explain the past. This chapter presents a sociolinguistic-typological perspective which investigates the extent to which it is possible to produce sociolinguistic explanations for linguistic structures. Insofar as the characteristics of individual languages are due to the nature of the human language faculty, there cannot be any questioning of the uniformitarian principle. But what if some of the characteristics of individual languages are due to social factors? Then the common faculty of the human mind will produce different types of structure in different societies at different moments in history. So the linguistic present might not altogether be like the linguistic past; and the methodology of using-the-present-to-explain-the-past could be less useful the further back in time we go.

scholarly journals Types of E-Procurement Systems and Technologies Used in the Nigerian Construction Environment

2020 ◽  
Vol 9 (4) ◽  
pp. 1444-1452
Keyword(s):  
Construction Project ◽  
Project Delivery ◽  
Limited Capacity ◽  
Web Portals ◽  
Construction Sites ◽  
The Past ◽  
Different Types ◽  
The Common ◽  
E Mail ◽  
Construction Works

The use of e-Procurement in the acquisition of construction works and services has witnessed a tremendous growth in the past three decades across the world. However, in a developing country like Nigeria, there is the lack of understanding of the different types of e-Procurement systems and specific technologies used to support the execution of construction procurement tasks. This study, therefore, relied on a questionnaire survey of 759 users of e-Procurement to systematically identify the different types of e-Procurement systems and technologies used in the Nigerian construction environment. The results of data analysis revealed that whereas the common e-Procurement systems used in the study area are those that help in disseminating/receiving information on tender opportunities, exchanging construction project information/data, submitting tenders, awarding contracts, placing orders and making/receiving payment for materials/equipment and services, the use of systems that help in tracking the movement of materials/equipment and monitoring the progress of work on construction sites was not very common. In addition, it was also found that the main e-Procurement technologies used to support the execution of construction procurement activities in the study area were e-Mails, websites and web portals. The study concludes that the over reliance on simple e-Procurement technologies such as e-Mail and websites/portals with limited capacity to engender collaboration, integration and coordination of tasks is inconsistent with the growing sophistication and advancement in construction procurement activities and processes and that this has a tendency to limit the benefits associated with e-Procurement in construction project delivery in Nigeria.

Identification and distribution of photoreceptor subtypes in the neotenic tiger salamander retina

1998 ◽  
Vol 15 (6) ◽  
pp. 1175-1187 ◽  
Author(s):  
DAVID M. SHERRY ◽  
DAI D. BUI ◽  
WILLEM J. DEGRIP
Keyword(s):  
Morphological Characteristics ◽  
Model System ◽  
Tiger Salamander ◽  
Long Wavelength ◽  
Rods And Cones ◽  
Cone Opsin ◽  
Spectral Class ◽  
Cone Opsins ◽  
Uv Cone ◽  
Photoreceptor Mosaic

The neotenic tiger salamander retina is a major model system for the study of retinal physiology and circuitry, yet there are unresolved issues regarding the organization of the photoreceptors and the photoreceptor mosaic. The rod and cone subtypes in the salamander retina were identified using a combination of morphological and immunocytochemical markers for specific rod and cone opsin epitopes. Because the visual pigment mechanisms present in the tiger salamander retina are well characterized and the antibodies employed in these studies are specific for particular rod and cone opsin epitopes, we also were able to identify the spectral class of the various rod and cone subtypes. Two classes of rods corresponding to the “red” and “green” rods previously reported in amphibian retinas were identified. In serial semithin section analyses, rods and cones comprised 62.4 ± 1.4% and 37.6 ± 1.4% of all photoreceptors, respectively. One rod type comprising 98.0 ± 0.7% of all rods showed the immunological and morphological characteristics of “red” rods, which are maximally sensitive to middle wavelengths. The second rod subtype comprised 2.0 ± 0.7% of all rods and possessed the immunological and morphological characteristics of “green” rods, which are maximally sensitive to short wavelengths. By morphology four cone types were identified, showing three distinct immunological signatures. Most cones (84.8 ± 1.5% of all cones), including most large single cones, the accessory and principal members of the double cone, and some small single cones, showed immunolabeling by antisera that recognize long wavelength-sensitive cone opsins. A subpopulation of small single cones (8.4 ± 1.7% of all cones) showed immunolabeling for short wavelength-sensitive cone opsin. A separate subpopulation of single cones which included both large and small types (6.8 ± 1.4% of all cones) was identified as the UV-Cone population and showed immunolabeling by antibodies that recognize rod opsin epitopes. Analysis of flatmounted retinas yielded similar results. All photoreceptor types appeared to be distributed in all retinal regions. There was no obvious crystalline organization of the various photoreceptor subtypes in the photoreceptor mosaic.

South American Weakly Electric Fish (Gymnotiformes) Are Long-Wavelength-Sensitive Cone Monochromats

2016 ◽  
Vol 88 (3-4) ◽  
pp. 204-212 ◽  
Author(s):  
Da-Wei Liu ◽  
Ying Lu ◽  
Hong Young Yan ◽  
Harold H. Zakon
Keyword(s):  
Short Wavelength ◽  
Electric Fish ◽  
Sister Group ◽  
Weakly Electric Fish ◽  
Opsin Gene ◽  
South American ◽  
Long Wavelength ◽  
Cone Opsin ◽  
Opsin Genes ◽  
Weakly Electric

Losses of cone opsin genes are noted in animals that are nocturnal or rely on senses other than vision. We investigated the cone opsin repertoire of night-active South American weakly electric fish. We obtained opsin gene sequences from genomic DNA of 3 gymnotiforms (Eigenmannia virescens, Sternopygus macrurus, Apteronotus albifrons) and the assembled genome of the electric eel (Electrophorus electricus). We identified genes for long-wavelength-sensitive (LWS) and medium-wavelength-sensitive cone opsins (RH2) and rod opsins (RH1). Neither of the 2 short-wavelength-sensitive cone opsin genes were found and are presumed lost. The fact that Electrophorus has a complete repertoire of extraretinal opsin genes and conservation of synteny with the zebrafish (Danio rerio) for genes flanking the 2 short-wavelength-sensitive opsin genes supports the supposition of gene loss. With microspectrophotometry and electroretinograms we observed absorption spectra consistent with RH1 and LWS but not RH2 opsins in the retinal photoreceptors of E. virescens. This profile of opsin genes and their retinal expression is identical to the gymnotiform's sister group, the catfish, which are also nocturnally active and bear ampullary electroreceptors, suggesting that this pattern likely occurred in the common ancestor of gymnotiforms and catfish. Finally, we noted an unusual N-terminal motif lacking a conserved glycosylation consensus site in the RH2 opsin of gymnotiforms, a catfish and a characin (Astyanax mexicanus). Mutations at this site influence rhodopsin trafficking in mammalian photoreceptors and cause retinitis pigmentosa. We speculate that this unusual N terminus may be related to the absence of the RH2 opsin in the cones of gymnotiforms and catfish.

scholarly journals Speciation underground in desert aquifers or just another case of hybridisation by blind beetles?

2018 ◽  
Vol 1 ◽  
Author(s):  
Steven Cooper ◽  
Barbara Langille ◽  
Josephine Hyde ◽  
William Humphreys ◽  
Andrew Austin
Keyword(s):  
Nuclear Gene ◽  
Opsin Gene ◽  
Beetle Species ◽  
Long Wavelength ◽  
Introgressive Hybridisation ◽  
Cave Environment ◽  
The Common ◽  
Parapatric Speciation ◽  
Gene Data ◽  
Rule Out

Phylogeographic studies have provided evidence for speciation underground within the confines of a cave environment, questioning the assumption that cave animals evolved from surface ancestors (Juan et al. 2010). However, for many of these studies, it is difficult to rule out the possibility that phylogeographic patterns may have resulted from multiple colonisation events from the same ancestral surface species, introgressive hybridisation among related species, and/or the extinction of surface ancestral lineages. Such is the case for the subterranean diving beetle species (Dytiscidae) of the groundwater calcrete archipelago of central Western Australia, where more than 100 species have been described that appear to have evolved by a combination of ecological/allopatric speciation and in some cases possibly sympatric speciation. We have further explored these speciation theories by phylogeographic analyses of nuclear gene data (WG, TOPO, ARK, Cn) from 86 species in the genera Limbodessus and Paroster, including analyses of genes involved in photoreception for select Paroster taxa. Analyses provide further support for the presence of sympatric sister species, thus, rejecting the hypothesis that previous phylogeographic patterns, based on mitochondrial DNA, resulted from introgressive hybridisation. Our analyses also uncovered deleterious frameshift and stop mutations in a long wavelength opsin gene that mapped to the common ancestor of a sympatric sister triplet of stygobiont species, providing strong evidence that this ancestor was already adapted to living underground and that the species triplet evolved within the confines of a single groundwater calcrete. Our analyses show that while the majority (~75%) of these stygobiont beetle species evolved from surface ancestors, a significant number diversified underground through a process of either sympatric or parapatric speciation.

scholarly journals UNASUR and the state-centric perspective of security in South America

2020 ◽  
pp. 7-19
Author(s):  
Sergio Caballero
Keyword(s):  
Security Studies ◽  
South American ◽  
Security Threats ◽  
Critical Security Studies ◽  
Regional Conflicts ◽  
Theoretical Approaches ◽  
Different Types ◽  
Regional Project ◽  
The Common ◽  
The Way

Over the last few decades we have witnessed an emerging interest in security topics and mechanisms to analyse these. In the context of globalization, new threats have appeared (not only interstate, but mainly, intra- and trans-state), as well as theoretical approaches (such as Critical Security Studies, CSS) to deal with them. Regarding the South American region it is useful to consider the constitution of the Unasur as a forum to coordinate policies with a very relevant geostrategic and security influence. In this paper, I deal with the logics that motivated the birth of the UNASUR project, in order to examine the way this regional project acts against different types of security threats and regional crises until 2016-17, when Venezuelan crises escalated. Furthermore, empirical evidences are tested with the common characteristics proposed by Peoples and Vaughan-Williams for the CSS. Some conclusions are drawn as new aspects have been incorporated to the way UNASUR addressed regional conflicts (security as a derivate concept and a broader security agenda), while an important element remained the same: a state-centric perspective.

TEM observation of cylindrite

1989 ◽  
Vol 47 ◽  
pp. 420-421
Author(s):  
Su Wang
Keyword(s):  
Long Range ◽  
Saed Pattern ◽  
The Past ◽  
Main Reflection ◽  
Different Types ◽  
Structural Modulation ◽  
The Common

Cylindrite, approximately FePb3Sn4Sb2S14, contains two different types of layers, pseudo-tetragonal(t-lattice) with PbS structure and pseudo-hexagonal (h-lattice) with SnS2 structure. The two kinds of layers are superimposed in the order of htht.., and the repeat periodicity is a. In the past only the composite SAED pattern corresponding to the b*c* plane of the two lattices was obtained as shown in Fig. 1a. Now we have succeeded, by careful tilting, in taking separate SAED patterns and HREM images of these two lattices(Figs. 2 and 3). The CBED pattern containing two [100] zone axes indicates: , as shown in Fig. lb.In the SAED patterns shown in Figs. 2, 3 and 4, each main reflection is accompanied by a row of satellite spots caused by the common structural modulation of the two lattices shown by the dark bands inthe HREM images. The rows of satellites, defined by q, in general donot parallel to any axes defined by the main reflections. In the q direction, the additional long-range periodicity corresponding to the satellites and the basic periodicity of both lattices are incommensurate.

Study of the Molecular Architecture of Keratin Filaments by Electron Microscopy

1982 ◽  
Vol 40 ◽  
pp. 118-119
Author(s):  
U. Aebi ◽  
P. Rew ◽  
T.-T. Sun
Keyword(s):  
Electron Microscopy ◽  
Structural Organization ◽  
Cell Types ◽  
Structural Features ◽  
Molecular Architecture ◽  
The Past ◽  
Keratin Filaments ◽  
Different Types ◽  
10 Nm Filaments ◽  
Different Cell Types

Various types of intermediate-sized (10-nm) filaments have been found and described in many different cell types during the past few years. Despite the differences in the chemical composition among the different types of filaments, they all yield common structural features: they are usually up to several microns long and have a diameter of 7 to 10 nm; there is evidence that they are made of several 2 to 3.5 nm wide protofilaments which are helically wound around each other; the secondary structure of the polypeptides constituting the filaments is rich in ∞-helix. However a detailed description of their structural organization is lacking to date.

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