Annual dynamics of the abundance of fish larvae and its relationship with hydrological variation in the Pearl River

We studied daily periodicity, taxonomic composition and annual variation of fish larvae abundance from a survey of the Zhaoqing section of the Pearl River over a 3-year period, 2006–2008, and collected 52 species, in eight families and 16 orders. The fish larval samples were numerically dominated by six species, Barbel Chub (Squaliobarbus curriculus) 33.1%, Black Guangdong Bream (Megalobrama hoffmanni) 20.6%, Yellowfin (Xenocypris argentea) 15.4%, Mud Carp (Cirrhina molitorella) 10%, Common Sawbelly (Hemiculter leucisculus) 4.3%, and Freshwater Bream (Parabramis pekinensis) 3.1%. These six species accounted for 86.5% of total numbers. Black Carp (Mylopharyngodon piceus), Grass Carp (Ctenopharyngodon idellus), Silver Carp (Hypophthalmichthys molitrix) and Bighead Carp (Aristichthys nobilis) are four of the most economically important fish species in China, and accounted for approximately 4.6% of the total. When compared with historical records from 1931, there are obvious changes in the fish larvae community. Chinese Sturgeon (Acipenser sinensis), Seasonal Shad (Macrura reevesi) and Long Spiky-head Carp (Luciobrama macrocephalus) populations have disappeared and there are also decreases in several other economically important fish populations. We observed a delay in spawning time of Black Carp, Grass Carp, Silver Carp and Bighead Carp, which may be the result of the hydrological regime change in the Pearl River. We used canonical correspondence analysis (CCA) and cross-covariance function (CCF) to analyze the relationship between fish larvae and environmental variables. Our results clearly show that discharge affects the majority of fish larvae, with the various species having different responses. Larval abundances of 15 species such as Black Carp, Grass Carp, Silver Carp, Bighead Carp, Mud Carp and Black Guangdong Bream are significantly and positively related to the discharge. Other species such as Chinese Noodlefish (Leucosoma chinensis) and Rhinogobius olivaceus are negatively related to the discharge. Abundances of larval Mosquitofish (Gambusia affinis), Common Carp (Cyprinus carpio) and Eleotris oxycephala were not related to the discharge. As most economic fish species are affected by discharge, we also conclude that changes of hydrological regime, mainly caused by river damming, will result in the decline of fisheries resources in the Pearl River. The findings of this study have important implications for our ability to model the responses of fish larvae to environmental flows for the purpose of river regulation.     

The evolution of skeletal muscle performance: gene duplication and divergence of human sarcomeric α‐actinins

In humans, there are two skeletal muscle α‐actinins, encoded by ACTN2 and ACTN3, and the ACTN3 genotype is associated with human athletic performance. Remarkably, approximately 1 billion people worldwide are deficient in α‐actinin‐3 due to the common ACTN3 R577X polymorphism. The α‐actinins are an ancient family of actin‐binding proteins with structural, signalling and metabolic functions. The skeletal muscle α‐actinins diverged ～250–300 million years ago, and ACTN3 has since developed restricted expression in fast muscle fibres. Despite ACTN2 and ACTN3 retaining considerable sequence similarity, it is likely that following duplication there was a divergence in function explaining why α‐actinin‐2 cannot completely compensate for the absence of α‐actinin‐3. This paper focuses on the role of skeletal muscle α‐actinins, and how possible changes in functions between these duplicates fit in the context of gene duplication paradigms.     

Influence of selected factors on the dietary compositions of three targeted and co‐occurring temperate species of reef fishes: implications for food partitioning

The dietary compositions of three medium to large targeted fish species, which co‐occur over reefs in temperate waters of south‐western Australia, were determined. These data were then used to ascertain statistically the extent to which body size, season and habitat influence the diets of these species and the degree to which food resources were partitioned among and within those species, and thus reduced the potential of interspecific and intraspecific competition. On the west coast, Bodianus frenchii (Labridae) and Epinephelides armatus (Serranidae) spent their whole life over prominent limestone reefs, as did Glaucosoma hebraicum (Glaucosomatidae) in all but juvenile life, when it lived over low‐relief, limestone substrata. The dietary composition of each species changed with increasing body size, which, in G. hebraicum, was particularly pronounced at c. 300 mm total length (L_T) and therefore at the size when this species shifts habitat. When the three species co‐occurred over the same reefs, their dietary compositions were significantly different, with that of B. frenchii being by far the most discrete, reflecting a far greater contribution by sedentary taxa. Thus, the diet of B. frenchii was distinguished from those of the other two species in containing substantial volumes of bivalve and gastropod molluscs and echinoid echinoderms and essentially no teleosts. Although the diets of G. hebraicum and particularly E. armatus were dominated by teleosts, and especially for larger individuals, the former species ingested greater volumes of cephalopods and small crustaceans. The pointed jaws of B. frenchii, with their forwardly directed and interlocking anterior incisors, are ideally adapted for biting and retaining their invertebrate prey, which are attached to or reside within reef crevices. In contrast, the mouths of G. hebraicum and E. armatus are broader and rounder and contain numerous small, slender and inward‐pointing teeth. These teeth, in conjunction with prominent backward‐curved canines in E. armatus, facilitate the capture and retention of fish prey. Observations in situ indicate that G. hebraicum is a suction feeder, while E. armatus is predominantly a ram feeder. Although reef environments on the west and south coasts differ, the diet of B. frenchii on these coasts differed only slightly. Interspecific differences in diet, combined with size‐related changes in dietary compositions and the occupation of different habitats by juvenile and adult G. hebraicum, reduce the potential for competition for food resources among and within B. frenchii, G. hebraicum and E. armatus and thus helps facilitate the coexistence of these species which historically have been abundant over reefs in south‐western Australia.
     

Mutations in BICD2 Cause Dominant Congenital Spinal Muscular Atrophy and Hereditary Spastic Paraplegia

Dominant congenital spinal muscular atrophy (DCSMA) is a disorder of developing anterior horn cells and shows lower-limb predominance and clinical overlap with hereditary spastic paraplegia (HSP), a lower-limb-predominant disorder of corticospinal motor neurons. We have identified four mutations in bicaudal D homolog 2 (Drosophila) (BICD2) in six kindreds affected by DCSMA, DCSMA with upper motor neuron features, or HSP. BICD2 encodes BICD2, a key adaptor protein that interacts with the dynein-dynactin motor complex, which facilitates trafficking of cellular cargos that are critical to motor neuron development and maintenance. We demonstrate that mutations resulting in amino acid substitutions in two binding regions of BICD2 increase its binding affinity for the cytoplasmic dynein-dynactin complex, which might result in the perturbation of BICD2-dynein-dynactin-mediated trafficking, and impair neurite outgrowth. These findings provide insight into the mechanism underlying both the static and the slowly progressive clinical features and the motor neuron pathology that characterize BICD2-associated diseases, and underscore the importance of the dynein-dynactin transport pathway in the development and survival of both lower and upper motor neurons.     

Life history of the riverine cyprinid Henicorhynchus siamensis (Sauvage, 1881) in a small reservoir

The riverine species, Henicorhynchus siamensis (Sauvage 1881), is an important source of protein and an economical fish for the rural population of inland Indochina. Investigated in the present study were the reproductive feeding aspects and growth of H. siamensis living in a lake system. The gonadosomatic index peaked in August, which was delayed compared to river fish, and individuals took 1.5 years to attain the length of 50% maturity (about 200 mm). Stomach contents were dominated by phytoplankton and showed considerable seasonal variation. Asymptotic length of H. siamensis was 264.2 mm, with a 0.75 year^?1 growth coefficient and slower growth during the winter. The role of the flood pulse as a major influence on the life history of the fish is also discussed.     

Design of superior spider silk: from nanostructure to mechanical properties

Spider dragline silk is of practical interest because of its excellent mechanical properties. However, the structure of this material is still largely unknown. In this article, we report what we believe is a new model of the hierarchical structure of silk based on scanning electron microscope and atomic force microscope images. This hierarchical structure includes beta-sheet, polypeptide chain network, and silk fibril. It turns out that an exceptionally high strength of the spider dragline silk can be obtained by decreasing the size of the crystalline nodes in the polypeptide chain network while increasing the degree of orientation of the crystalline nodes. Based on this understanding, how the reeling speed affects mechanical properties of spider dragline silk can be understood properly. Hopefully, the understanding obtained in this study will shed light on the formation of spider silk, and consequently, on the principles for the design of ultrastrong silk.     

Are protein complexes made of cores,modules and attachments?

It has recently been proposed by Gavin et al. (Nature 2006, 440, 631-636) that protein complexes in the cell exist in different forms. The proteins within each complex were proposed to exist as three different classes, being core, module or attachment proteins. This study investigates whether the core-module-attachment classification of proteins within each complex is supported by other high-throughput protein data. Core proteins were found to have lower abundance, and shorter half-life as compared to attachment proteins, whilst the abundance and half-life of core and module proteins were similar. When the cell was perturbed, core proteins had smaller changes in abundance as compared to module and attachment proteins. Comparisons between six different pairwise interaction types of core, module and attachment proteins within a complex showed interaction types involving core or module proteins were more likely to be mediated by domain-domain interactions (DDIs) than interaction types involving attachment proteins. Interaction types that involve attachment proteins had a relatively higher ratio of abundance and ratio of half-life. So we conclude that, the core, module and attachment model of protein complexes is supported by data from these proteomic scale datasets, and describe a model for a typical protein complex that considers the above results.     

Distribution of zooplankton community in Mediterranean-climate lakes

The sometimes sharp thermal variations and irregular precipitations and force concentrated over short periods characterize the Mediterranean climate. The structure of the zooplanktonic settlement was analyzed during one year in three Algerian reservoirs (lakes) with different geographical and climatic situation, in relation to abiotic factors (temperature, dissolved oxygen, pH, suspended matter, carbonates, nitrogenized and phosphorated nutritive salts). A canonical correspondence analysis was used to estimate the influence of the abiotic factors on the temporal distribution.The studied lakes are located, on the one hand, in northern Algeria, in a sub-humid area (Lake Boukourdane) and, on the other hand, in the South of the country, in the arid region (Foum El Ghorza and Djorf Torba). Analysis of the environmental parameters indicates that there is a seasonal variation in the three reservoirs. In Lake Foum El Ghorza, the temperature and hydrology variations, linked with the arid climate, affects the concentration of dissolved oxygen, which strongly decreases (1.5 mg/l), involving a pH reduction; suspended matters are sometimes high, coming from the stripped catchment area, causing a turbidity in this not very deep lake. The study of the distribution of the species allowed us to highlight a seasonal temporal variation. Lake Boukourdane, in the sub-humid zone, has an increased specific richness (SR=13). The various species evolve in alternation during the annual cycle. The representative species of this lake is Copidodiaptomus numidicus, characteristic of the rainy and endemic zone of the western Mediterranean; it is dominant (67%) in the spring. The Stenothermal species Diaphanosoma brachyurum, endemic of hot waters, is common to the two lakes; it evolves particularly in the summer (51.3%) at Boukourdane, whereas it is perennial and dominant (55%) in the spring at Djorf Torba. The specific richness is lower in Djorf Torba (SR=7) and in Foum El Ghorza (SR=6). The species collected in these two lakes are common and cosmopolitan, but they are adapted to the extreme conditions of the arid climate. Nevertheless, the species evolving in Lake Foum El Ghorza have undergone a significant decline, which has reduced the number of species and their density in the summer-autumn period. Thus, we can say that in the studied lakes, the hydrological factors and the temperature related to the Mediterranean climate would be two of the principal causes of the temporal distribution of the species. To cite this article: M. Cherbi et al., C. R. Biologies 331 (2008).