Recruitment patterns of decapod crustacean megalopae in a shallow inlet (SW Spain) related to life history strategies

Decapod crustacean megalopae were sampled weekly (spring/neap tides) during late-spring/summer of 1998 by using two planktonic nets located close to the surface and the bottom, at a fixed station in the mouth of the Rı́o San Pedro inlet (SW Spain). Sampling was carried out during 25 h cycles to ascertain the flux of megalopae in relation to the main environmental (diel, tidal, tidal amplitude) cycles. The hypothesis that megalopae of some species may be using tidal-stream transport as a mechanism of re-invading the inlet was tested and the relationship between megalopal behaviour and life history strategy was analysed. In general, the flux of megalopae was higher during spring tides, but such differences were only statistically significant for Pisidia longicornis and Liocarcinus sp.2 due to the considerable interdate variation. With the exception of Macropodia sp., megalopae were more abundant close to the bottom. The diel/tidal flux of most abundant species suggested two different patterns of behaviour: megalopae of Liocarcinus spp., Panopeus africanus, Uca tangeri and Brachynotus sexdentatus seemed to be re-invading the inlet (specially at nocturnal floods), while megalopae of Ilia nucleus, Nepinnotheres pinnotheres and Macropodia sp. may have been just looking for a suitable place for settlement. The first group corresponded to the species whose zoeal development occurs in open sea, and the second one to species that complete their life cycle within the studied system, suggesting a relationship between the duration of the larval phase and the life cycle strategy of the species

Discrimination between disturbed coastal ecosystems by using macrobenthos at different taxonomic levels

The taxonomic level required to detect changes in the macrobenthic communities of disturbed coastal ecosystems was assessed by applying multivariate statistical methods to macrobenthic data. Community data sets were analysed from three estuarine salt marshes on the Gulf of Cadiz (southwest of Iberian Peninsula), affected mainly by agricultural sewage (Barbate River estuary), urban effluents (Cadiz Bay) and mining/industrial sewage (Odiel salt marsh). For both abundance and biomass data, aggregation of macrobenthic densities to Families or Orders did not cause any substantial loss of information, and statistically identical inferences from the macrobenthic community structure could be made, with an obvious saving of time and taxonomic expertise. Aggregating data to Classes or Phyla had some effects on consequent analyses: the more similar communities began to be confounded.Mediante el uso de técnicas multivariantes de análisis de datos se investiga el nivel taxonómico necesario para detectar cambios en la estructura de la comunidad macrobentónica en ecosistemas costeros alterados. Se analizan los datos correspondientes a las comunidades de tres zonas de marismas estuáricas del golfo de Cádiz (suroeste de la península Ibérica) que están sometidas a contaminación principalmente procedente de los cultivos agrícolas (estuario del río Barbate), vertidos urbanos (bahía de Cádiz) y desechos mineros y vertidos industriales (marisma del Odiel). Tanto para la abundancia numérica como para la biomasa, la agregación de las densidades del macrobentos a los niveles de familia u orden no significa una pérdida sustancial de información y se pueden hacer las mismas inferencias estadísticas sobre la estructura de la comunidad, lo que significa un ahorro en tiempo y en la destreza taxonómica requerida. Por el contrario, agregar los datos a los niveles de clase y phylum supone un efecto en los consiguientes análisis: se empiezan a confundir las comunidades con mayor semejanza.Instituto Español de Oceanografí

The macrobenthic community of the Guadalquivir estuary

The intertidal macrobenthic community of the Guadalquivir estuary (last 50 km) was studied between May 1997 and April 1999 at five sampling sites located to 50, 40, 32, 20 and 8 km from the river mouth. Five monthly replicates were taken at each sampling site by means of an Ekman-Birge grab (15 ˟ 15 cm). A total of 24 taxa were collected but the specific richness increased from the inner (12) to the outer estuary (22). Only four taxa (Oligochaeta; Nereis diversicolor Müller, 1776; Streblospio shrubsolii (Buchanan, 1890) and Corophium orientale Schellenberg, 1928) were considered as constant (present in more than 75 % of the months) for at least one sampling site, while ten were rare (present in less than 12 % of the months) through the estuary. There was a clear dominance of a small number of species, although the dominant taxa changed from one site to another: Oligochaeta at the two inner sites; the amphipod C. orientale at the intermediate site; the polychaetes N. diversicolor and S. shrubsolii at the two outer sites.On average, the macrobenthic density was higher at the most marine site (5 409 indiv ⋅ m-2; 9 118 mg AFDW ⋅ m-2), where numerical abundance showed noticeable seasonal pattern (minimum values in summer and maximum in autumn/winter). In the rest of the estuary, although the community density oscillated over time, a clear seasonal trend was not observed. The spatial and temporal density of dominant taxa seemed to maintain a strong relation with the salinity gradient. The latter showed considerable differences between the first (wet) year and the second (dry) year.As a consequence of the accident occurred in the Aználcollar mine in April 1998, a considerable volume of untreated acid fresh water, with a high content in metals, was released into the estuary. According to the Bray-Curtis similarity index between samples, there were no significant differences in the benthic community of the estuary between the first (before the spill) year and the second (after the spill) year (two-way nested ANOSIM tests; p 0.05 for abundance and biomass data). However, differences were significant (p 0.01) between sampling sites.La comunidad macrobentónica intermareal del estuario del Guadalquivir (últimos 50 km de su cauce principal) fue estudiada entre mayo de 1997 y abril de 1999 mediante la toma mensual de cinco réplicas de sedimento, usando una draga Ekman-Birge (15 x 15 cm), en cinco estaciones de muestreo situadas a 50, 40, 32, 20 y 8 km de la desembocadura.Se han contabilizado 24 taxones diferentes, aumentando la riqueza de especies desde la zona más limnética (12) a la más marina (22). De ellos, sólo cuatro (Oligochaeta; Nereis diversicolor Müller, 1776; Streblospio shrubsolii (Buchanan, 1890) y Corophium orientale Schellenberg, 1928) pueden ser considerados como constantes (presentes en más del 75 % de los meses) en al menos una estación de muestreo, mientras que diez fueron raros (presentes en menos del 12 % de los meses) en todo el estuario. De igual forma, se ha encontrado una fuerte dominancia de un grupo muy reducido de especies, aunque variando los taxones dominantes de unas estaciones de muestreo a otras: Oligochaeta en las dos estaciones más internas, el anfípodo C. orientale en la estación intermedia y los poliquetos N. diversicolor y S. shrubsolii en las estaciones más marinas. Por término medio, la densidad macrobentónica fue más elevada en la estación más marina del estuario (5 409 indiv • m-2; 9 118 mg PSLC • m-2), donde su abundancia numérica mostró un marcado patrón estacional (mínimos en verano y máximos en otoño/invierno). En las restantes estaciones de muestreo, si bien la densidad de la comunidad mostró pronunciadas oscilaciones temporales, no existió un patrón estacional claro, estando estos cambios determinados fundamentalmente por la evolución de las densidades de los correspondientes taxones dominantes. La distribución espacial y, en menor medida, temporal de estos taxones estuvo muy condicionada por el gradiente salino, que mostró una variación considerable entre el primer año (muy lluvioso) y el segundo (seco). Durante la realización del estudio, un volumen considerable de agua dulce ácida con elevado contenido en metales pesados entró en el estuario como consecuencia del accidente minero ocurrido en Aznalcóllar en abril de 1998. De acuerdo con el índice de similitud de Bray-Curtis entre muestras, no existen diferencias significativas (tests ANOSIM encajados de dos vías; p 0,05 para los datos de abundancia y biomasa) en la estructura de la comunidad macrobentónica del estuario entre el primer año (antes del vertido) y el segundo (después del vertido), pero sí (p 0,01) entre las distintas estaciones de muestreo.Instituto Español de Oceanografí

Classical T Tauri stars with VPHAS+ -I : H α and u-band accretion rates in the Lagoon Nebula M8

We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using $ugri$H$\alpha$ photometry from the VPHAS+ survey. Our sample consists of stars displaying H$\alpha$-excess, the intensity of which is used to derive accretion rates. For a subset of 87 stars, the intensity of the $u$-band excess is also used to estimate accretion rates. We find the mean variation in accretion rates measured using H$\alpha$ and $u$-band intensities to be $\sim$ 0.17 dex, agreeing with previous estimates (0.04-0.4 dex) but for a much larger sample. The spatial distribution of CTTS align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. Strong accretors are concentrated spatially, while weak accretors are more distributed. Our results do not support the sequential star forming processes suggested in the literature.Peer reviewe

Variable Mutation Rates as an Adaptive Strategy in Replicator Populations

For evolving populations of replicators, there is much evidence that the effect of mutations on fitness depends on the degree of adaptation to the selective pressures at play. In optimized populations, most mutations have deleterious effects, such that low mutation rates are favoured. In contrast to this, in populations thriving in changing environments a larger fraction of mutations have beneficial effects, providing the diversity necessary to adapt to new conditions. What is more, non-adapted populations occasionally benefit from an increase in the mutation rate. Therefore, there is no optimal universal value of the mutation rate and species attempt to adjust it to their momentary adaptive needs. In this work we have used stationary populations of RNA molecules evolving in silico to investigate the relationship between the degree of adaptation of an optimized population and the value of the mutation rate promoting maximal adaptation in a short time to a new selective pressure. Our results show that this value can significantly differ from the optimal value at mutation-selection equilibrium, being strongly influenced by the structure of the population when the adaptive process begins. In the short-term, highly optimized populations containing little variability respond better to environmental changes upon an increase of the mutation rate, whereas populations with a lower degree of optimization but higher variability benefit from reducing the mutation rate to adapt rapidly. These findings show a good agreement with the behaviour exhibited by actual organisms that replicate their genomes under broadly different mutation rates

Infidelity of SARS-CoV Nsp14-Exonuclease Mutant Virus Replication Is Revealed by Complete Genome Sequencing

Most RNA viruses lack the mechanisms to recognize and correct mutations that arise during genome replication, resulting in quasispecies diversity that is required for pathogenesis and adaptation. However, it is not known how viruses encoding large viral RNA genomes such as the Coronaviridae (26 to 32 kb) balance the requirements for genome stability and quasispecies diversity. Further, the limits of replication infidelity during replication of large RNA genomes and how decreased fidelity impacts virus fitness over time are not known. Our previous work demonstrated that genetic inactivation of the coronavirus exoribonuclease (ExoN) in nonstructural protein 14 (nsp14) of murine hepatitis virus results in a 15-fold decrease in replication fidelity. However, it is not known whether nsp14-ExoN is required for replication fidelity of all coronaviruses, nor the impact of decreased fidelity on genome diversity and fitness during replication and passage. We report here the engineering and recovery of nsp14-ExoN mutant viruses of severe acute respiratory syndrome coronavirus (SARS-CoV) that have stable growth defects and demonstrate a 21-fold increase in mutation frequency during replication in culture. Analysis of complete genome sequences from SARS-ExoN mutant viral clones revealed unique mutation sets in every genome examined from the same round of replication and a total of 100 unique mutations across the genome. Using novel bioinformatic tools and deep sequencing across the full-length genome following 10 population passages in vitro, we demonstrate retention of ExoN mutations and continued increased diversity and mutational load compared to wild-type SARS-CoV. The results define a novel genetic and bioinformatics model for introduction and identification of multi-allelic mutations in replication competent viruses that will be powerful tools for testing the effects of decreased fidelity and increased quasispecies diversity on viral replication, pathogenesis, and evolution

Does Mutational Robustness Inhibit Extinction by Lethal Mutagenesis in Viral Populations?

Lethal mutagenesis is a promising new antiviral therapy that kills a virus by raising its mutation rate. One potential shortcoming of lethal mutagenesis is that viruses may resist the treatment by evolving genomes with increased robustness to mutations. Here, we investigate to what extent mutational robustness can inhibit extinction by lethal mutagenesis in viruses, using both simple toy models and more biophysically realistic models based on RNA secondary-structure folding. We show that although the evolution of greater robustness may be promoted by increasing the mutation rate of a viral population, such evolution is unlikely to greatly increase the mutation rate required for certain extinction. Using an analytic multi-type branching process model, we investigate whether the evolution of robustness can be relevant on the time scales on which extinction takes place. We find that the evolution of robustness matters only when initial viral population sizes are small and deleterious mutation rates are only slightly above the level at which extinction can occur. The stochastic calculations are in good agreement with simulations of self-replicating RNA sequences that have to fold into a specific secondary structure to reproduce. We conclude that the evolution of mutational robustness is in most cases unlikely to prevent the extinction of viruses by lethal mutagenesis

New insights into the neolithisation process in southwest Europe according to spatial density analysis from calibrated radiocarbon dates

The agricultural way of life spreads throughout Europe via two main routes: the Danube corridor and the Mediterranean basin. Current archaeological literature describes the arrival to the Western Mediterranean as a rapid process which involves both demic and cultural models, and in this regard, the dispersal movement has been investigated using mathematical models, where the key factors are time and space. In this work, we have created a compilation of all available radiocarbon dates for the whole of Iberia, in order to draw a chronological series of maps to illustrate temporal and spatial patterns in the neolithisation process. The maps were prepared by calculating the calibrated 14C date probability density curves, as a proxy to show the spatial dynamics of the last hunter-gatherers and first farmers. Several scholars have pointed out problems linked with the variability of samples, such as the overrepresentation of some sites, the degree of regional research, the nature of the dated samples and above all the archaeological context, but we are confident that the selected dates, after applying some filters and statistical protocols, constitute a good way to approach settlement spatial patterns in Iberia at the time of the neolithisation process