Spatial variability of phytoplankton pigment distributions in the Subtropical South Pacific Ocean: comparison between in situ and predicted data

In the frame of the BIOSOPE cruise in 2004, the spatial distribution and structure of phytoplankton pigments was investigated along a transect crossing the ultra-oligotrophic South Pacific Subtropical Gyre (SPSG) between the Marquesas Archipelago (141° W–8° S) and the Chilean upwelling (73° W–34° S). A High Performance Liquid Chromatography (HPLC) method was improved in order to be able to accurately quantify pigments over such a large range of trophic levels, and especially from strongly oligotrophic conditions. Seven diagnostic pigments were associated to three phytoplankton size classes (pico-, nano and microphytoplankton). The total chlorophyll-α concentrations [TChlα] in surface waters were the lowest measured in the centre of the gyre, reaching 0.017 mg m<sup>−3</sup>. Pigment concentrations at the Deep Chlorophyll Maximum (DCM) were generally 10 fold the surface values. Results were compared to predictions from a global parameterisation based on remotely sensed surface [TChlα]. The agreement between the in situ and predicted data for such contrasting phytoplankton assemblages was generally good: throughout the oligotrophic gyre system, picophytoplankton (prochlorophytes and cyanophytes) and nanophytoplankton were the dominant classes. Relative bacteriochlorophyll-α concentrations varied around 2%. The transition zone between the Marquesas and the SPSG was also well predicted by the model. However, some regional characteristics have been observed where measured and modelled data differ. Amongst these features is the extreme depth of the DCM (180 m) towards the centre of the gyre, the presence of a deep nanoflagellate population beneath the DCM or the presence of a prochlorophyte-enriched population in the formation area of the high salinity South Pacific Tropical Water. A coastal site sampled in the eutrophic upwelling zone, characterised by recently upwelled water, was significantly and unusually enriched in picoeucaryotes, in contrast with an offshore upwelling site where a more typical senescent diatom population prevailed

The "neutral" community structure of planktonic herbivores, tintinnid ciliates of the microzooplankton, across the SE Tropical Pacific Ocean

International audienceAcross a species-rich area, the SE Pacific Ocean, the community characteristics of a group of planktonic herbivores was assessed. A series of 22 stations between the Marquise Islands (7° S 142° W) and the coast of Chile (35° S 73° W) was sampled during the BIOSOPE cruise in 2004. The relationships between taxonomic diversity, morphological diversity, patterns of tintinnid species assemblage, and phytoplankton abundance were examined. Tintinnid community characteristics were estimated from large volume (20–60 l) discrete depth sampling and phytoplankton were characterized based on HPLC pigment signatures. Across the transect, average water column concentrations of tintinnids ranged from 2–40 cells l-1or 8–40 ng C l-1, and were positively related to chlorophyll a concentrations which varied between 0.07–2 µg l-1. Large numbers of tintinnid taxa were found, 18–41 species per station, yielding a total of 149 species. Among stations, morphological and taxonomic diversity metrics co-varied but were not significantly related to phytoplankton diversity estimated using a pigment-based size-diversity metric. Taxonomic diversity of tintinnids, as H' or Fishers' alpha, was inversely related to chlorophyll concentration and positively to the depth of the chlorophyll maximum layer. For each station, species abundance distributions were compared to geometric, log-series and log-normal distributions. For most stations, the observed distribution most closely matched log-series, coherent with the neutral theory of random colonization from a large species pool. Occurrence rates of species were correlated with average abundance rather than specific characteristics of biomass or lorica oral diameter (mouth) size. Among stations, species richness was correlated with both the variety of mouth sizes (lorica oral diameters) as well as numbers of species per mouth size, also consistent with random colonization

Racing performance of the Quarter Horse: genetic parameters, trends and correlation for earnings, best time and time class

The aim of this study was to evaluate the sprint racing performance of Quarter Horses in Brazil. Estimating genetic parameters, trends and correlations were obtained by single- and two-trait analyses using Bayesian inference (earnings to 2 years of equestrian age, best time and time class at distances of 301 m and 402 m). The data comprised a period of 38 equestrian years (1978 to 2015) with 23,482 sprint race records from 5861 animals. The heritability estimates were of low to moderate magnitude, ranging from 0.10 to 0.37 (single-trait) and from 0.15 to 0.41 (two-traits), and the repeatability was 0.31 to 0.46. The additive, residual and phenotypic correlations between earnings to 2 years of equestrian age and the other traits (best time and time class in distances 301 m and 402 m) were high (−0.95, −0.96, 0.69 and 0.92), low (−0.29, −0.37, 0.26 and 0.27) and moderate (−0.41, −0.47, 0.37 and 0.47), respectively. There is a positive genetic trend for all traits considered. However, evaluation of the last 10 equestrian years (2006 to 2015) showed negative trends (genetic loss) and trends close to zero (genetic stagnation). The design of breeding programs using the earnings trait in conjunction with other racing performance traits can enhance changes in the genetic gains as a whole in speed-racing Quarter Horses. These findings suggest that the traits studied should be included in breeding selection programs for racing Quarter Horses.info:eu-repo/semantics/publishedVersio

Approximate Euclidean Steiner trees

An approximate Steiner tree is a Steiner tree on a given set of terminals in Euclidean space such that the angles at the Steiner points are within a specified error e from 120 degrees. This notion arises in numerical approximations of minimum Steiner trees (W. D. Smith, Algorithmica, 7 (1992), 137–177). We investigate the worst-case relative error of the length of an approximate Steiner tree compared to the shortest tree with the same topology. Rubinstein, Weng and Wormald (J. Global Optim. 35 (2006), 573–592) conjectured that this relative error is at most linear in e, independent of the number of terminals. We verify their conjecture for the two-dimensional case as long as the error e is sufficiently small in terms of the number of terminals. We derive a lower bound linear in e for the relative error in the two-dimensional case when e is sufficiently small in terms of the number of terminals. We find improved estimates of the relative error for larger values of e, and calculate exact values in the plane for three and four terminals

Driven Front and Interface of a Fluid-Flow Model in 2+1-Dimensions

Computer simulations are performed to study the motion of the front and the growth of the interface width in a model of fluid flow driven by a biased field in 2+1 dimensions. The initial motion of the front is diffusive, which is followed by a nondiffusive power-law behavior in the long-time regime; the power-law exponent is nonuniversal, varying with the strength of the driven field. The growth of the interface width saturates in the asymptotic time regime. The saturated width W scales with both the driven field B as well as the transverse length L of the sample, leading to a two-parameter scaling W∼L2αBm, where α=1.25 and m=0.17