Frogs (Anura) are one of the most diverse groups of vertebrates and comprise nearly 90% of living amphibian species. Their worldwide distribution and diverse biology make them well-suited for ...assessing fundamental questions in evolution, ecology, and conservation. However, despite their scientific importance, the evolutionary history and tempo of frog diversification remain poorly understood. By using a molecular dataset of unprecedented size, including 88-kb characters from 95 nuclear genes of 156 frog species, in conjunction with 20 fossil-based calibrations, our analyses result in the most strongly supported phylogeny of all major frog lineages and provide a timescale of frog evolution that suggests much younger divergence times than suggested by earlier studies. Unexpectedly, our divergence-time analyses show that three species-rich clades (Hyloidea, Microhylidae, and Natatanura), which together comprise ∼88% of extant anuran species, simultaneously underwent rapid diversification at the Cretaceous–Paleogene (K–Pg) boundary (KPB). Moreover, anuran families and subfamilies containing arboreal species originated near or after the KPB. These results suggest that the K–Pg mass extinction may have triggered explosive radiations of frogs by creating new ecological opportunities. This phylogeny also reveals relationships such as Microhylidae being sister to all other ranoid frogs and African continental lineages of Natatanura forming a clade that is sister to a clade of Eurasian, Indian, Melanesian, and Malagasy lineages. Biogeographical analyses suggest that the ancestral area of modern frogs was Africa, and their current distribution is largely associated with the breakup of Pangaea and subsequent Gondwanan fragmentation.
Understanding the diversification of phenotypes through time--"descent with modification"--has been the focus of evolutionary biology for 150 years. If, contrary to expectations, similarity evolves ...in unrelated taxa, researchers are guided to uncover the genetic and developmental mechanisms responsible. Similar phenotypes may be retained from common ancestry (homology), but a phylogenetic context may instead reveal that they are independently derived, due to convergence or parallel evolution, or less likely, that they experienced reversal. Such examples of homoplasy present opportunities to discover the foundations of morphological traits. A common underlying mechanism may exist, and components may have been redeployed in a way that produces the "same" phenotype. New, robust phylogenetic hypotheses and molecular, genomic, and developmental techniques enable integrated exploration of the mechanisms by which similarity arises.
Many scientists argue that we are either entering or in the midst of the sixth great mass extinction. Intense human pressure, both direct and indirect, is having profound effects on natural ...environments. The amphibians-frogs, salamanders, and caecilians-may be the only major group currently at risk globally. A detailed worldwide assessment and subsequent updates show that one-third or more of the 6,300 species are threatened with extinction. This trend is likely to accelerate because most amphibians occur in the tropics and have small geographic ranges that make them susceptible to extinction. The increasing pressure from habitat destruction and climate change is likely to have major impacts on narrowly adapted and distributed species. We show that salamanders on tropical mountains are particularly at risk. A new and significant threat to amphibians is a virulent, emerging infectious disease, chytridiomycosis, which appears to be globally distributed, and its effects may be exacerbated by global warming. This disease, which is caused by a fungal pathogen and implicated in serious declines and extinctions of >200 species of amphibians, poses the greatest threat to biodiversity of any known disease. Our data for frogs in the Sierra Nevada of California show that the fungus is having a devastating impact on native species, already weakened by the effects of pollution and introduced predators. A general message from amphibians is that we may have little time to stave off a potential mass extinction.
We describe the sample design for the SDSS-IV MaNGA survey and present the final properties of the main samples along with important considerations for using these samples for science. Our target ...selection criteria were developed while simultaneously optimizing the size distribution of the MaNGA integral field units (IFUs), the IFU allocation strategy, and the target density to produce a survey defined in terms of maximizing signal-to-noise ratio, spatial resolution, and sample size. Our selection strategy makes use of redshift limits that only depend on i-band absolute magnitude (Mi), or, for a small subset of our sample, Mi and color (NUV − i). Such a strategy ensures that all galaxies span the same range in angular size irrespective of luminosity and are therefore covered evenly by the adopted range of IFU sizes. We define three samples: the Primary and Secondary samples are selected to have a flat number density with respect to Mi and are targeted to have spectroscopic coverage to 1.5 and 2.5 effective radii (Re), respectively. The Color-Enhanced supplement increases the number of galaxies in the low-density regions of color-magnitude space by extending the redshift limits of the Primary sample in the appropriate color bins. The samples cover the stellar mass range and are sampled at median physical resolutions of 1.37 and 2.5 kpc for the Primary and Secondary samples, respectively. We provide weights that will statistically correct for our luminosity and color-dependent selection function and IFU allocation strategy, thus correcting the observed sample to a volume-limited sample.
Abstract
We measure $\lambda _{R_{\rm e}}$, a proxy for galaxy specific stellar angular momentum within one effective radius, and the ellipticity, ε, for about 2300 galaxies of all morphological ...types observed with integral field spectroscopy as part of the Mapping Nearby Galaxies at Apache Point Observatory survey, the largest such sample to date. We use the $(\lambda _{R_{\rm e}}, \epsilon )$ diagram to separate early-type galaxies into fast and slow rotators. We also visually classify each galaxy according to its optical morphology and two-dimensional stellar velocity field. Comparing these classifications to quantitative $\lambda _{R_{\rm e}}$ measurements reveals tight relationships between angular momentum and galaxy structure. In order to account for atmospheric seeing, we use realistic models of galaxy kinematics to derive a general approximate analytic correction for $\lambda _{R_{\rm e}}$. Thanks to the size of the sample and the large number of massive galaxies, we unambiguously detect a clear bimodality in the $(\lambda _{R_{\rm e}}, \epsilon )$ diagram which may result from fundamental differences in galaxy assembly history. There is a sharp secondary density peak inside the region of the diagram with low $\lambda _{R_{\rm e}}$ and ε < 0.4, previously suggested as the definition for slow rotators. Most of these galaxies are visually classified as non-regular rotators and have high velocity dispersion. The intrinsic bimodality must be stronger, as it tends to be smoothed by noise and inclination. The large sample of slow rotators allows us for the first time to unveil a secondary peak at ±90° in their distribution of the misalignments between the photometric and kinematic position angles. We confirm that genuine slow rotators start appearing above M ≥ 2 × 1011 M⊙ where a significant number of high-mass fast rotators also exist.
We explore the cosmological implications of the angle-averaged correlation function, ...(s), and the clustering wedges, ...(s) and ...(s), of the LOWZ and CMASS galaxy samples from Data Releases 10 ...and 11 of the Sloan Digital Sky Survey III (SDSS-III) Baryon Oscillation Spectroscopic Survey. Our results show no significant evidence for a deviation from the standard ... cold dark matter model. The combination of the information from our clustering measurements with recent data from the cosmic microwave background is sufficient to constrain the curvature of the Universe to ...k = 0.0010 ± 0.0029, the total neutrino mass to ... < 0.23 eV (95 per cent confidence level), the effective number of relativistic species to Neff = 3.31 ± 0.27 and the dark energy equation of state to wDE = -1.051 ± 0.076. These limits are further improved by adding information from Type Ia supernovae and baryon acoustic oscillations from other samples. In particular, this data set combination is completely consistent with a time-independent dark energy equation of state, in which case we find wDE = -1.024 ± 0.052. We explore the constraints on the growth rate of cosmic structures assuming f(z) = ... and obtain ... = 0.69 ± 0.15, consistent with the predictions of general relativity of ... = 0.55. (ProQuest: ... denotes formulae/symbols omitted.)
Facing Extinction in Real Time Wake, David B.
Science (American Association for the Advancement of Science),
03/2012, Volume:
335, Issue:
6072
Journal Article
Peer reviewed
Amphibian populations worldwide are under threat as a result of additive effects of multiple stressors.
A sense of impending doom has enveloped the community of amphibian biologists for more than two ...decades, as evidence has built that the subjects of their research are in severe difficulty. What at first was a puzzle based mainly on anecdotes (
1
) became an evident fact when intensive studies were completed: Throughout the world, amphibians are in decline, and many species—perhaps 40%—face imminent extinction (
2
). Recent studies have elucidated some agents for amphibian losses and projected the likely prospects for amphibian survival across the globe. The picture that emerges is disturbing.
Amphibians Wake, David B.; Koo, Michelle S.
CB/Current biology,
11/2018, Volume:
28, Issue:
21
Journal Article
Peer reviewed
Open access
Since the dawn of history, amphibians have been a part of human culture. Western Europeans built fires for cooking and warmth, adding large logs as needed. What occasionally emerged was astounding: ...large black animals (which had found shelter in the logs) with four legs and a tail, jet black with striking bright yellow spots. These fire salamanders were variously thought to be the product of the fire itself, or, as Aristotle reported, capable of extinguishing fire. Pliny the Elder is said to have tested this idea by throwing a salamander into flames — the salamander died! — nevertheless the association with fire persisted. Pliny perpetuated other fantastical claims, which spread; even Leonardo da Vinci contributed to the legend, and myths from different regions merged — at one point, asbestos was claimed to be salamander wool. Salamanders were attributed great powers; a single salamander upstream was thought to be sufficient to kill an army. King Francis I. of France chose a salamander as his emblem — a powerful symbol, born of fire, filled with poison, immune from burning, and even able to douse flames. Before the emergence of great cities and conurbations, people grew up surrounded by nature. Salamanders and newts, toads and frogs were all part of normal human experience. Myths such as those surrounding the fire salamanders were commonplace. Shakespeare’s witches brewed with an eye of newt and tail of frog. As a child, we raised tadpoles and were taught to shudder at the appearance of a tiger salamander in a root cellar. In general, amphibians are seen as benign and harmless, even helpful as creatures that devour harmful insects and serve as an alternative food source. Thus, it came as a shock to most biologists and to the public at large in the 1980s that amphibians around the world were in decline and that they were at greater risk of extinction as a taxon than any other vertebrate group. A study of every amphibian species known in 2004 showed that on the order of 40% were at high risk of extinction, and by 2008, the decline of amphibians was seen as evidence of an impending sixth mass extinction.
Wake and Koo introduce the biology and diversity of amphibians.
Taxon-based research in evolution permits the development of a multidimensional approach, illustrated here with lessons learned from research on salamanders. The clade is widespread and diverse, yet ...sufficiently small that one can keep all of the species in mind. This facilitates research from diverse perspectives: systematics and phylogenetics, morphology, development, ecology, neurobiology, behavior, and physiology. Different avenues of research offer unique perspectives on how a relatively old vertebrate clade has diversified. An integrated, hierarchically organized, multidimensional program of research on a taxon illuminates many general principles and processes. Among these are the nature of species and homology, adaptation and adaptive radiations, size and shape in relation to issues in organismal integration, ontogeny and development in relation to phylogeny, the ubiquity of homoplasy, ecological niche conservation, species formation, biodiversity, and conservation. Opportunities for future research and threats to the continued existence of salamanders are briefly outlined.
Anura (frogs and toads) constitute over 88% of living amphibian diversity but many important questions about their phylogeny and evolution remain unresolved. For this study, we developed an efficient ...method for sequencing anuran mitochondrial DNAs (mtDNAs) by amplifying the mitochondrial genome in 12 overlapping fragments using frog-specific universal primer sets. Based on this method, we generated 47 nearly complete, new anuran mitochondrial genomes and discovered nine novel gene arrangements. By combining the new data and published anuran mitochondrial genomes, we assembled a large mitogenomic data set (11,007 nt) including 90 frog species, representing 39 of 53 recognized anuran families, to investigate their phylogenetic relationships and evolutionary history. The resulting tree strongly supported a paraphyletic arrangement of archaeobatrachian (=nonneobatrachian) frogs, with Leiopelmatoidea branching first, followed by Discoglossoidea, Pipoidea, and Pelobatoidea. Within Neobatrachia, the South African Heleophrynidae is the sister-taxon to all other neobatrachian frogs and the Seychelles-endemic Sooglossidae is recovered as the sister-taxon to Ranoidea. These phylogenetic relationships agree with many nuclear gene studies. The chronogram derived from two Bayesian relaxed clock methods (MultiDivTime and BEAST) suggests that modern frogs (Anura) originated in the early Triassic about 244 Ma and the appearance of Neobatrachia took place in the late Jurassic about 163 Ma. The initial diversifications of two species-rich superfamilies Hyloidea and Ranoidea commenced 110 and 133 Ma, respectively. These times are older than some other estimates by approximately 30-40 My. Compared with nuclear data, mtDNA produces compatible time estimates for deep nodes (>150 Ma), but apparently older estimates for more shallow nodes. Our study shows that, although it evolves relatively rapidly and behaves much as a single locus, mtDNA performs well for both phylogenetic and divergence time inferences and will provide important reference hypotheses for the phylogeny and evolution of frogs.
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