Although invasive species are widely recognized as a major threat to marine biodiversity, there has been no quantitative global assessment of their impacts and routes of introduction. Here, we report ...initial results from the first such global assessment. Drawing from over 350 databases and other sources, we synthesized information on 329 marine invasive species, including their distribution, impacts on biodiversity, and introduction pathways. Initial analyses show that only 16% of marine ecoregions have no reported marine invasions, and even that figure may be inflated due to underâreporting. International shipping, followed by aquaculture, represent the major means of introduction. Our geographically referenced and publicly available database provides a framework that can be used to highlight the invasive taxa that are most threatening, as well as to prioritize the invasion pathways that pose the greatest threat.
Understanding and predicting colloid transport and retention in water‐saturated porous media is important for the protection of human and ecological health. Early applications of colloid transport ...research before the 1990s included the removal of pathogens in granular drinking water filters. Since then, interest has expanded significantly to include such areas as source zone protection of drinking water systems and injection of nanometals for contaminated site remediation. This review summarizes predictive tools for colloid transport from the pore to field scales. First, we review experimental breakthrough and retention of colloids under favorable and unfavorable colloid/collector interactions (i.e., no significant and significant colloid‐surface repulsion, respectively). Second, we review the continuum‐scale modeling strategies used to describe observed transport behavior. Third, we review the following two components of colloid filtration theory: (i) mechanistic force/torque balance models of pore‐scale colloid trajectories and (ii) approximating correlation equations used to predict colloid retention. The successes and limitations of these approaches for favorable conditions are summarized, as are recent developments to predict colloid retention under the unfavorable conditions particularly relevant to environmental applications. Fourth, we summarize the influences of physical and chemical heterogeneities on colloid transport and avenues for their prediction. Fifth, we review the upscaling of mechanistic model results to rate constants for use in continuum models of colloid behavior at the column and field scales. Overall, this paper clarifies the foundation for existing knowledge of colloid transport and retention, features recent advances in the field, critically assesses where existing approaches are successful and the limits of their application, and highlights outstanding challenges and future research opportunities. These challenges and opportunities include improving mechanistic descriptions, and subsequent correlation equations, for nanoparticle (i.e., Brownian particle) transport through soil, developing mechanistic descriptions of colloid retention in so‐called “unfavorable” conditions via methods such as the “discrete heterogeneity” approach, and employing imaging techniques such as X‐ray tomography to develop realistic expressions for grain topology and mineral distribution that can aid the development of these mechanistic approaches.
Key Points:
Review of colloid transport in porous media
Discussion of recent advances in understanding of colloid transport
Current colloid transport research needs
It has been more than 30 years since the publication of the new head hypothesis, which proposed that the vertebrate head is an evolutionary novelty resulting from the emergence of neural crest and ...cranial placodes. Neural crest generates the skull and associated connective tissues, whereas placodes produce sensory organs. However, neither crest nor placodes produce head muscles, which are a crucial component of the complex vertebrate head. We discuss emerging evidence for a surprising link between the evolution of head muscles and chambered hearts - both systems arise from a common pool of mesoderm progenitor cells within the cardiopharyngeal field of vertebrate embryos. We consider the origin of this field in non-vertebrate chordates and its evolution in vertebrates.
We present fully covered phased light curves for 56 Jovian Trojan asteroids as observed by the K2 mission of the Kepler space telescope. This set of objects has been monitored during Campaign 6 and ...represents a nearly unbiased subsample of the population of small solar system bodies. We derived precise periods and amplitudes for all Trojans, and found their distributions to be compatible with the previous statistics. We point out, however, that ground-based rotation periods are often unreliable above 20 h, and we find an overabundance of rotation periods above 60 h compared with other minor planet populations. From amplitude analysis we derive a rate of binarity of 20 ± 5%. Our spin rate distribution confirms the previously obtained spin barrier of ~5 h and the corresponding ~0.5 g cm-3 cometary-like density limit, also suggesting a high internal porosity for Jovian Trojans. One of our targets, asteroid 65227 exhibits a double rotation period, which can either be due to binarity or the outcome of a recent collision.
We present the analysis of four first overtone RR Lyrae stars observed with the Kepler space telescope, based on data obtained over nearly 2.5 yr. All four stars are found to be multiperiodic. The ...strongest secondary mode with frequency f... has an amplitude of a few mmag, 20-45 times lower than the main radial mode with frequency f... The two oscillations have a period ratio of P.../P... = 0.612-0.632 that cannot be reproduced by any two radial modes. Thus, the secondary mode is non-radial. Modes yielding similar period ratios have also recently been discovered in other variables of the RRc and RRd types. These objects form a homogenous group and constitute a new class of multimode RR Lyrae pulsators, analogous to a similar class of multimode classical Cepheids in the Magellanic Clouds. Because a secondary mode with P.../P... ~ 0.61 is found in almost every RRc and RRd star observed from space, this form of multiperiodicity must be common. In all four Kepler RRc stars studied, we find subharmonics of f... at ~1/2f... and at ~3/2f... This is a signature of period doubling of the secondary oscillation, and is the first detection of period doubling in RRc stars. The amplitudes and phases of f... and its subharmonics are variable on a time-scale of 10-200 d. The dominant radial mode also shows variations on the same time-scale, but with much smaller amplitude. In three Kepler RRc stars we detect additional periodicities, with amplitudes below 1 mmag, that must correspond to non-radial g-modes. Such modes never before have been observed in RR Lyrae variables. (ProQuest: ... denotes formulae/symbols omitted.)
A detailed analysis is presented of 33 RR Lyrae stars in Pisces observed with the Kepler space telescope over the 8.9-d long K2 Two-Wheel Concept Engineering Test. The sample includes not only ...fundamental-mode and first-overtone (RRab and RRc) stars but the first two double-mode (RRd) stars that Kepler detected and the only modulated first-overtone star ever observed from space so far. The precision of the extracted K2 light curves made it possible to detect low-amplitude additional modes in all subtypes. All RRd and non-modulated RRc stars show the additional mode at P
X
/P
1 ∼ 0.61 that was detected in previous space-based photometric measurements. A periodicity longer than the fundamental mode was tentatively identified in one RRab star that might belong to a gravity mode. We determined the photometric Fe/H values for all fundamental-mode stars and provide the preliminary results of our efforts to fit the double-mode stars with non-linear hydrodynamic pulsation models. The results from this short test run indicate that the K2 mission will be, and has started to be, an ideal tool to expand our knowledge about RR Lyrae stars. As a by-product of the target search and analysis, we identified 165 bona fide double-mode RR Lyrae stars from the Catalina Sky Survey observations throughout the sky, 130 of which are new discoveries.
Context. Because the second reaction wheel failed, a new mission was conceived for the otherwise healthy Kepler space telescope. In the course of the K2 mission, the telescope is staring at the plane ...of the Ecliptic. Thousands of solar system bodies therefore cross the K2 fields and usually cause additional noise in the highly accurate photometric data. Aims. We here follow the principle that some person’s noise is another person’s signal and investigate the possibility of deriving continuous asteroid light curves. This is the first such endeavor. In general, we are interested in the photometric precision that the K2 mission can deliver on moving solar system bodies. In particular, we investigate space photometric optical light curves of main-belt asteroids. Methods. We studied the K2 superstamps that cover the fields of M35, and Neptune together with Nereid, which were observed in the long-cadence mode (29.4 min sampling). Asteroid light curves were generated by applying elongated apertures. We used the Lomb-Scargle method to determine periodicities that are due to rotation. Results. We derived K2 light curves of 924 main-belt asteroids in the M35 field and 96 in the path of Neptune and Nereid. The light curves are quasi-continuous and several days long. K2 observations are sensitive to longer rotational periods than typical ground-based surveys. Rotational periods are derived for 26 main-belt asteroids for the first time. The asteroid sample is dominated by faint objects (>20 mag). Owing to the faintness of the asteroids and the high density of stars in the M35 field, only 4.0% of the asteroids with at least 12 data points show clear periodicities or trends that signal a long rotational period, as opposed to 15.9% in the less crowded Neptune field. We found that the duty cycle of the observations had to reach ~60% to successfully recover rotational periods.
We present a detailed analysis of the bright Cepheid-type variable star V1154 Cygni using 4 yr of continuous observations by the Kepler space telescope. We detected 28 frequencies using the standard ...Fourier transform method. We identified modulation of the main pulsation frequency and its harmonics with a period of ~159 d. This modulation is also present in the Fourier parameters of the light curve and the O - C diagram. We detected another modulation with a period of about 1160 d. The star also shows significant power in the low-frequency region that we identified as granulation noise. The effective time-scale of the granulation agrees with the extrapolated scalings of red giant stars. Non-detection of solar-like oscillations indicates that the pulsation inhibits other oscillations. We obtained new radial velocity observations that are in a perfect agreement with previous years data, suggesting that there is no high-mass star companion of V1154 Cygni. Finally, we discuss the possible origin of the detected frequency modulations.
ABSTRACT
The question of how tetrapod limbs evolved from fins is one of the great puzzles of evolutionary biology. While palaeontologists, developmental biologists, and geneticists have made great ...strides in explaining the origin and early evolution of limb skeletal structures, that of the muscles remains largely unknown. The main reason is the lack of consensus about appendicular muscle homology between the closest living relatives of early tetrapods: lobe‐finned fish and crown tetrapods. In the light of a recent study of these homologies, we re‐examined osteological correlates of muscle attachment in the pectoral girdle, humerus, radius, and ulna of early tetrapods and their close relatives. Twenty‐nine extinct and six extant sarcopterygians were included in a meta‐analysis using information from the literature and from original specimens, when possible. We analysed these osteological correlates using parsimony‐based character optimization in order to reconstruct muscle anatomy in ancestral lobe‐finned fish, tetrapodomorph fish, stem tetrapods, and crown tetrapods. Our synthesis revealed that many tetrapod shoulder muscles probably were already present in tetrapodomorph fish, while most of the more‐distal appendicular muscles either arose later from largely undifferentiated dorsal and ventral muscle masses or did not leave clear correlates of attachment in these taxa. Based on this review and meta‐analysis, we postulate a stepwise sequence of specific appendicular muscle acquisitions, splits, and fusions that led from the ancestral sarcopterygian pectoral fin to the ancestral tetrapod forelimb. This sequence largely agrees with previous hypotheses based on palaeontological and comparative work, but it is much more comprehensive in terms of both muscles and taxa. Combined with existing information about the skeletal system, our new synthesis helps to illuminate the genetic, developmental, morphological, functional, and ecological changes that were key components of the fins‐to‐limbs transition.
Since the early 1900s, researchers have attempted to unravel the origin and evolution of tetrapod limb muscles using a combination of comparative anatomy, phylogeny, and development. The methods for ...reconstructing soft tissues in extinct animals have been refined over time as our ability to determine muscle homology and phylogenetic relationships between tetrapods has improved. Since many muscles do not leave osteological correlates, muscle reconstruction in extinct animals is largely based on anatomy and development in extant animals. While muscle anatomy in extant tetrapods is quite conservative, the homologies of certain muscles between taxonomic groups are still uncertain. Comparative developmental studies can help to resolve these controversies, as well as revealing general patterns of muscle morphogenesis across tetrapod groups. We review the methods, results, and controversies in the muscle reconstructions of early members of the amniote, mammalian, and lissamphibian lineages, including recent attempts to reconstruct limb muscles in members of the tetrapod stem group. We also review the contribution of recent comparative developmental studies toward understanding the evolution of tetrapod limb muscles, including morphogenic gradients, the origin of paired fins, and the evolution of morphological complexity. Finally, we discuss the role of broad, comparative myological studies as part of an integrative research program on vertebrate evolutionary biology.
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