1,307 research outputs found
Molecular footprints of the Holocene retreat of dwarf birch in Britain
© 2014 The Authors. Molecular Ecology Published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited
Sharks of the order Carcharhiniformes from the British Coniacian, Santonian and Campanian (Upper Cretaceous).
Bulk sampling of phosphate-rich horizons within the British Coniacian to Campanian (Upper Cretaceous) yielded very large samples of shark and ray teeth. All of these samples yielded teeth of diverse members of the Carcharhiniformes, which commonly dominate the fauna. The following species are recorded and described: Pseudoscyliorhinus reussi (Herman, 1977) comb. nov., Crassescyliorhinus germanicus (Herman, 1982) gen. nov., Scyliorhinus elongatus (Davis, 1887), Scyliorhinus brumarivulensis sp. nov., ? Palaeoscyllium sp., Prohaploblepharus riegrafi (Müller, 1989) gen. nov., ? Cretascyliorhinus sp., Scyliorhinidae inc. sedis 1, Scyliorhinidae inc. sedis 2, Pteroscyllium hermani sp. nov., Protoscyliorhinus sp., Leptocharias cretaceus sp. nov., Palaeogaleus havreensis Herman, 1977, Paratriakis subserratus sp. nov., Paratriakis tenuis sp. nov., Paratriakis sp. indet. and ? Loxodon sp. Taxa belonging to the families ?Proscylliidae, Leptochariidae, and Carcharhinidae are described from the Cretaceous for the first time. The evolutionary and palaeoecological implications of these newly recognised faunas are discussed
The Spin of Holographic Electrons at Nonzero Density and Temperature
We study the Green's function of a gauge invariant fermionic operator in a
strongly coupled field theory at nonzero temperature and density using a dual
gravity description. The gravity model contains a charged black hole in four
dimensional anti-de Sitter space and probe charged fermions. In particular, we
consider the effects of the spin of these probe fermions on the properties of
the Green's function. There exists a spin-orbit coupling between the spin of an
electron and the electric field of a Reissner-Nordstrom black hole. On the
field theory side, this coupling leads to a Rashba like dispersion relation. We
also study the effects of spin on the damping term in the dispersion relation
by considering how the spin affects the placement of the fermionic quasinormal
modes in the complex frequency plane in a WKB limit. An appendix contains some
exact solutions of the Dirac equation in terms of Heun polynomials.Comment: 27 pages, 11 figures; v2: minor changes, published versio
Where are you from, stranger? The enigmatic biogeography of North African pond turtles (Emys orbicularis) .
Abstract The European pond turtle (Emys orbicularis) is a
Nearctic element in the African fauna and thought to have
invaded North Africa from the Iberian Peninsula. All North
African populations are currently identified with the subspecies
E. o. occidentalis. However, a nearly range-wide sampling in
North Africa used for analyses of mitochondrial and microsatellite
DNA provides evidence that only Moroccan populations
belong to this taxon, while eastern Algerian and Tunisian pond
turtles represent an undescribed distinct subspecies. These two
taxa are most closely related to E. o. galloitalica with a native
distribution along the Mediterranean coast of northern Spain
through southern France to western and southern Italy. This
group is sister to a clade comprising several mitochondrial lineages
and subspecies of E. orbicularis from Central and Eastern
Europe plus Asia, and the successive sisters are E. o. hellenica
and E. trinacris. Our results suggest that E. orbicularis has been
present in North Africa longer than on the Iberian Peninsula and
that after an initial invasion of North Africa by pond turtles from
an unknown European source region, there was a phase of
diversification in North Africa, followed by a later re-invasion
of Europe by one of the African lineages. The differentiation of
pond turtles in North Africa parallels a general phylogeographic
paradigm in amphibians and reptiles, with deeply divergent
lineages in the western and eastern Maghreb. Acknowledging
their genetic similarity, we propose to synonymize the previously
recognized Iberian subspecies E. o. fritzjuergenobsti with E. o.
occidentalis sensu stricto. The seriously imperiled Moroccan
populations of E. o. occidentalis represent two Management
Units different in mitochondrial haplotypes and microsatellite
markers. The conservation status of eastern Algerian pond turtles
is unclear, while Tunisian populations are endangered.
Considering that Algerian and Tunisian pond turtles represent
an endemic taxon, their situation throughout the historical range
should be surveyed to establish a basis for conservation
measures
Biology and conservation of freshwater bivalves : past, present and future perspectives
Freshwater bivalves have been highly
threatened by human activities, and recently their
global decline has been causing conservational and
social concern. In this paper, we review the most
important research events in freshwater bivalve biology
calling attention to the main scientific achievements.
A great bias exists in the research effort, with
much more information available for bivalve species
belonging to the Unionida in comparison to other
groups. The same is true for the origin of these studies,
since the publishing pattern does not always correspond
to the hotspots of biodiversity but is concentrated in the northern hemisphere mainly in
North America, Europe and Russia, with regions such
as Africa and Southeast Asia being quite understudied.
We also summarize information about past, present
and future perspectives concerning the most important
research topics that include taxonomy, systematics,
anatomy, physiology, ecology and conservation of
freshwater bivalves. Finally, we introduce the articles
published in this Hydrobiologia special issue related
with the International Meeting on Biology and Conservation
of Freshwater Bivalves held in 2012 in
Braganc¸a, Portugal.We would like to express our gratitude to our sponsors and institutions, especially to the Polytechnic Institute of Braganca for all the logistic support. We acknowledge all keynote speakers, authors, session chairpersons and especially to all attendees whose contributions were fundamental for the success of this meeting. We would also like to thank all referees of this special issue and to Koen Martens, Editor-in-Chief of Hydrobiologia, for all the valuable comments and suggestions. The chronogram was built with the help of the expert opinion of fellow colleagues Rafael Araujo, Arthur Bogan, Kevin Cummings, Dan Graf, Wendell Haag, Karl-Otto Nagel and David Strayer to whom we are very grateful. The authors acknowledge the support provided by Portuguese Foundation for Science and Technology (FCT) and COMPETE funds-projects CONBI (Contract: PTDC/AAC-AMB/117688/2010) and ECO-IAS (Contract: PTDC/AAC-AMB/116685/2010), and by the European Regional Development Fund (ERDF) through the COMPETE, under the project "PEst-C/MAR/LA0015/2011"
First description of a fossil chamaeleonid from Greece and its relevance for the European biogeographic history of the group
The fossil record of Chamaeleonidae is very scarce and any new specimen is therefore considered important for our understanding of the evolutionary and biogeographic history of the group. New specimens from the early Miocene of Aliveri (Evia Island), Greece constitute the only fossils of these lizards from southeastern Europe. Skull roofing material is tentatively attributed to the Czech species Chamaeleo cf. andrusovi, revealing a range extension for this taxon, whereas tooth-bearing elements are described as indeterminate chamaeleonids. The Aliveri fossils rank well among the oldest known reptiles from Greece, provide evidence for the dispersal routes of chameleons out of Africa towards the European continent and, additionally, imply strong affinities with coeval chamaeleonids from Central Europe
Imagining Sisyphus happy: DNA barcoding and the unnamed majority
The vast majority of life on the Earth is physically small, and is classifiable as micro- or meiobiota. These organisms are numerically dominant and it is likely that they are also abundantly speciose. By contrast, the vast majority of taxonomic effort has been expended on ‘charismatic megabionts’: larger organisms where a wealth of morphology has facilitated Linnaean species definition. The hugely successful Linnaean project is unlikely to be extensible to the totality of approximately 10 million species in a reasonable time frame and thus alternative toolkits and methodologies need to be developed. One such toolkit is DNA barcoding, particularly in its metabarcoding or metagenetics mode, where organisms are identified purely by the presence of a diagnostic DNA sequence in samples that are not processed for morphological identification. Building on secure Linnaean foundations, classification of unknown (and unseen) organisms to molecular operational taxonomic units (MOTUs) and deployment of these MOTUs in biodiversity science promises a rewarding resolution to the Sisyphean task of naming all the world's species. This article is part of the themed issue ‘From DNA barcodes to biomes’
Stigmaphyllon bannisterioides, the correct name for a well‐known neotropical species of Stigmaphyllon (Malpighiaceae)
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149719/1/tax01262.pd
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