787 research outputs found
Toward a DNA Taxonomy of Alpine Rhithrogena (Ephemeroptera: Heptageniidae) Using a Mixed Yule-Coalescent Analysis of Mitochondrial and Nuclear DNA
Aquatic larvae of many Rhithrogena mayflies (Ephemeroptera)
inhabit sensitive Alpine environments. A number of species are on the IUCN Red
List and many recognized species have restricted distributions and are of
conservation interest. Despite their ecological and conservation importance,
ambiguous morphological differences among closely related species suggest that
the current taxonomy may not accurately reflect the evolutionary diversity of
the group. Here we examined the species status of nearly 50% of European
Rhithrogena diversity using a widespread sampling scheme of
Alpine species that included 22 type localities, general mixed Yule-coalescent
(GMYC) model analysis of one standard mtDNA marker and one newly developed nDNA
marker, and morphological identification where possible. Using sequences from
533 individuals from 144 sampling localities, we observed significant clustering
of the mitochondrial (cox1) marker into 31 GMYC species.
Twenty-one of these could be identified based on the presence of topotypes
(expertly identified specimens from the species' type locality) or
unambiguous morphology. These results strongly suggest the presence of both
cryptic diversity and taxonomic oversplitting in Rhithrogena.
Significant clustering was not detected with protein-coding nuclear PEPCK,
although nine GMYC species were congruent with well supported terminal clusters
of nDNA. Lack of greater congruence in the two data sets may be the result of
incomplete sorting of ancestral polymorphism. Bayesian phylogenetic analyses of
both gene regions recovered four of the six recognized
Rhithrogena species groups in our samples as monophyletic.
Future development of more nuclear markers would facilitate multi-locus analysis
of unresolved, closely related species pairs. The DNA taxonomy developed here
lays the groundwork for a future revision of the important but cryptic
Rhithrogena genus in Europe
Extended X-ray emission in the IC 2497 - Hanny's Voorwerp system: energy injection in the gas around a fading AGN
We present deep Chandra X-ray observations of the core of IC 2497, the galaxy
associated with Hanny's Voorwerp and hosting a fading AGN. We find extended
soft X-ray emission from hot gas around the low intrinsic luminosity
(unobscured) AGN ( erg s). The
temperature structure in the hot gas suggests the presence of a bubble or
cavity around the fading AGN (\mbox{E_{\rm bub}} \sim 10^{54} - 10^{55}
erg). A possible scenario is that this bubble is inflated by the fading AGN,
which after changing accretion state is now in a kinetic mode. Other
possibilities are that the bubble has been inflated by the past luminous quasar
( erg s), or that the temperature gradient is
an indication of a shock front from a superwind driven by the AGN. We discuss
the possible scenarios and the implications for the AGN-host galaxy
interaction, as well as an analogy between AGN and X-ray binaries lifecycles.
We conclude that the AGN could inject mechanical energy into the host galaxy at
the end of its lifecycle, and thus provide a source for mechanical feedback, in
a similar way as observed for X-ray binaries.Comment: 9 pages, 5 figures, accepted for publication in MNRA
Global diversity of mayflies (Ephemeroptera, Insecta) in freshwater
The extant global Ephemeroptera fauna is represented by over 3,000 described species in 42 families and more than 400 genera. The highest generic diversity occurs in the Neotropics, with a correspondingly high species diversity, while the Palaearctic has the lowest generic diversity, but a high species diversity. Such distribution patterns may relate to how long evolutionary processes have been carrying on in isolation in a bioregion. Over an extended period, there may be extinction of species, but evolution of more genera. Dramatic extinction events such as the K-T mass extinction have affected current mayfly diversity and distribution. Climatic history plays an important role in the rate of speciation in an area, with regions which have been climatically stable over long periods having fewer species per genus, when compared to regions subjected to climatic stresses, such as glaciation. A total of 13 families are endemic to specific bioregions, with eight among them being monospecific. Most of these have restricted distributions which may be the result of them being the relict of a previously more diverse, but presently almost completely extinct family, or may be the consequence of vicariance events, resulting from evolution due to long-term isolation
Global diversity of mayflies (Ephemeroptera, Insecta) in freshwater
The extant global Ephemeroptera fauna is represented by over 3,000 described species in 42 families and more than 400 genera. The highest generic diversity occurs in the Neotropics, with a correspondingly high species diversity, while the Palaearctic has the lowest generic diversity, but a high species diversity. Such distribution patterns may relate to how long evolutionary processes have been carrying on in isolation in a bioregion. Over an extended period, there may be extinction of species, but evolution of more genera. Dramatic extinction events such as the K-T mass extinction have affected current mayfly diversity and distribution. Climatic history plays an important role in the rate of speciation in an area, with regions which have been climatically stable over long periods having fewer species per genus, when compared to regions subjected to climatic stresses, such as glaciation. A total of 13 families are endemic to specific bioregions, with eight among them being monospecific. Most of these have restricted distributions which may be the result of them being the relict of a previously more diverse, but presently almost completely extinct family, or may be the consequence of vicariance events, resulting from evolution due to long-term isolation
DISCOVERY OF A NEW MAYFLY SPECIES (EPHEMEROPTERA, BAETIDAE)NEAR CENDERAWASIH UNIVERSITY CAMPUS IN PAPUA, INDONESIA
Material collected just behind the Cenderawasih University campus in Jayapura, Papua Province, Indonesia, revealed a new species of the Labiobaetis claudiae group, which is here described and illustrated based on larvae, subimago, male and female imagos. The total number of Labiobaetis species on the island New Guinea increased to 33, the total number for Indonesia increased to 26, and the total number of Labiobaetis species worldwide is augmented to 147. A key to the larvae of the L. claudiae group is provided. The interspecific K2P distances between species of the L. claudiae group are between 20% and 23%.
BAT AGN Spectroscopic Survey I: Spectral Measurements, Derived Quantities, and AGN Demographics
We present the first catalog and data release of the Swift-BAT AGN
Spectroscopic Survey (BASS). We analyze optical spectra of the majority of AGN
(77%, 641/836) detected based on their 14-195 keV emission in the 70-month
Swift BAT all-sky catalog. This includes redshift determination, absorption and
emission line measurements, and black hole mass and accretion rate estimates
for the majority of obscured and un-obscured AGN (74%, 473/641) with 340
measured for the first time. With ~90% of sources at z<0.2, the survey
represents a significant census of hard-X-ray selected AGN in the local
universe. In this first catalog paper, we describe the spectroscopic
observations and datasets, and our initial spectral analysis. The FWHM of the
emission lines show broad agreement with the X-ray obscuration (~94%), such
that Sy 1-1.8 have NH10^21.9 cm^-2.
Seyfert 1.9 show a range of column densities. Compared to narrow line AGN in
the SDSS, the X-ray selected AGN have a larger fraction of dusty host galaxies
suggesting these types of AGN are missed in optical surveys. Using the most
sensitive [OIII]/Hbeta and [NII]/Halpha emission line diagnostic, about half of
the sources are classified as Seyferts, ~15% reside in dusty galaxies that lack
an Hbeta detection, but for which the line upper limits imply either a Seyfert
or LINER, ~15% are in galaxies with weak or no emission lines despite high
quality spectra, and a few percent each are LINERS, composite galaxies, HII
regions, or in known beamed AGN.Comment: Accepted ApJ, see www.bass-survey.com for dat
Biogeography and ecological diversification of a mayfly clade in New Guinea
Understanding processes that have driven the extraordinary high level of biodiversity in the tropics is a long-standing question in biology. Here we try to assess whether the large lineage richness found in a New Guinean clade of mayflies (Ephemeroptera), namely the Thraulus group (Leptophlebiidae) could be associated with the recent orogenic processes, by applying a combination of phylogenetic, biogeographic and ecological shift analyses. New Guinean representatives of the Thraulus group appear monophyletic, with the possible exception of a weakly-supported early-diverging clade from the Sunda Islands. Dating analyses suggest an Eocene origin of the Thraulus group, predating by several million years current knowledge on the origin of other New Guinean aquatic organisms. Biogeographic inferences indicate that 27 of the 28 inferred dispersals (96.4%) occurred during the Eocene, Oligocene and Miocene, while only one dispersal (3.6%) took place during the Pliocene-Pleistocene. This result contrasts with the higher number of altitudinal shifts (15 of 22; 68.2%) inferred during the Pliocene-Pleistocene time slice. Our study illustrates the role played by – potentially ecological - diversification along the elevation gradient in a time period concomitant with the establishment of high-altitude ecological niches, i.e., during orogenesis of the central New Guinean mountain range. This process might have taken over the previous main mode of diversification at work, characterized by dispersal and vicariance, by driving lineage divergence of New Guinean Leptophlebiidae across a wide array of habitats along the elevation gradient. Additional studies on organisms spanning the same elevation range as Thraulus mayflies in the tropics are needed to evaluate the potential role of the ecological opportunity or taxon cycles hypotheses in partly explaining the latitudinal diversity gradient
A model for AGN variability on multiple timescales
We present a framework to link and describe AGN variability on a wide range
of timescales, from days to billions of years. In particular, we concentrate on
the AGN variability features related to changes in black hole fuelling and
accretion rate. In our framework, the variability features observed in
different AGN at different timescales may be explained as realisations of the
same underlying statistical properties. In this context, we propose a model to
simulate the evolution of AGN light curves with time based on the probability
density function (PDF) and power spectral density (PSD) of the Eddington ratio
() distribution. Motivated by general galaxy population
properties, we propose that the PDF may be inspired by the
distribution function (ERDF), and that a single (or limited number of) ERDF+PSD
set may explain all observed variability features. After outlining the
framework and the model, we compile a set of variability measurements in terms
of structure function (SF) and magnitude difference. We then combine the
variability measurements on a SF plot ranging from days to Gyr. The proposed
framework enables constraints on the underlying PSD and the ability to link AGN
variability on different timescales, therefore providing new insights into AGN
variability and black hole growth phenomena.Comment: 5 pages, 2 figures, letter accepted for publication in MNRA
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