Settlement pattern and survival of a shell-infesting sabellid polychaete,Terebrasabella heterouncinata,on South African abalone,Haliotis midae,fed two diets

This study tested whether abalone diet influences larval settlement success of the shell-dwelling sabellid polychaete Terebrasabella heterouncinata and their survival over the first 96h after settlement on host abalone. Shell area preferences of the sabellid were also investigated. Abalone diet (fresh kelp, Ecklonia maxima or Abfeed?) did not affect sabellid settlement success (F_1,30 = 1.05; p <= 0.31). There were significant differences in settlement between shell regions, with the highest number of sabellids settling near the respiratory pores (F_2,30 = 61.0; p < 0.001). Percentage occupation rate of tubes 96h after settlement did not differ between dietary treatments. There were no significant interactions between diet and shell region for sabellid settlement (F_2,30 = 0.77, p = 0.69) and tube formation (F_2,30 = 1.02, p = 0.67) or for the percentage occupation rate of the tubes (F_9,180 = 0.11, p = 0.73). Thus, infestation intensity in relation to shell region can be estimated independent of abalone diet. For treatment purposes, total settlement after 36 days of exposure can be used to identify the shell areas on which most sabellids will be found.     

IMGT standardized criteria for statistical analysis of immunoglobulin V-REGION amino acid properties

IMGT, the international ImMunoGeneTics information system(R) (http://imgt.cines.fr) is a high-quality integrated information system specializing in immunoglobulins (IG), T cell receptors (TR) and major histocompatibility complex (MHC) of human and other vertebrates. IMGT comprises IMGT/LIGM-DB, the comprehensive database of IG and TR sequences from human and other vertebrates (76 846 sequences in September 2003). In order to define the IMGT criteria necessary for standardized statistical analyses, the sequences of the IG variable regions (V-REGIONs) from productively rearranged human IG heavy (IGH) and IG light kappa (IGK) and lambda (IGL) chains were extracted from IMGT/LIGM-DB. The framework amino acid positions of 2474 V-REGIONs (1360 IGHV, 585 IGKV, 529 IGLV) were numbered according to the IMGT unique numbering. Two statistical methods (correspondence analysis and hierarchic classification) were used to analyze the 237 framework positions (80 for IGHV, 79 for IGKV, 78 for IGLV), for three properties (hydropathy, volume and chemical characteristics) of the 20 common amino acids. Results of the analyses are shown as standardized two-dimensional representations, designated as IMGT Colliers de Perles statistical profiles. They provide a characterization of the amino acid properties at each framework position of the expressed IG V-REGIONs, and a visualization of the resemblances and differences between heavy and light, and between kappa and lambda sequences. The standardized criteria defined in this paper, amino acid positions and property classes, will be useful to study the mutations and allele polymorphisms, to establish correlations between amino acids in the IG and TR protein three-dimensional structures and to extract new knowledge from V-like domains of chains, other than IG and TR, belonging to the immunoglobulin superfamily.     

The predatory impact of invasive alien smallmouth bass,Micropterus dolomieu (Teleostei: Centrarchidae), on indigenous fishes in a Cape Floristic Region mountain stream

Fish populations in the Rondegat River, a mountain stream in the Olifants-Doring system in the Cape Floristic Region, South Africa were surveyed to assess the impact of predatory alien invasive smallmouth bass Micropterus dolomieu (Lacepède) on the indigenous fishes. This was the first such attempt to quantify the predatory impacts of M. dolomieu within this region. The Rondegat River is home to five species of indigenous fish and is partially invaded by M. dolomieu, which has penetrated the lower river up to a waterfall barrier. Seasonal surveys were conducted at five sites above, and five below, the waterfall. Physical habitat was measured at each site. Four of the five indigenous fish species were absent at bass-invaded sites. Labeobarbus capensis (Smith), while still present below the waterfall, appeared to have suffered a near-total loss of post-spawning recruits. Analyses of physical habitat quality failed to explain the loss of indigenous fish below the waterfall, although sedimentation may have increased the vulnerability of the catfish Austroglanis gilli (Barnard) to M. dolomieu predation by obliterating benthic cover. Consequently, predation by M. dolomieu was presumed to be the critical mechanism explaining the loss of indigenous fishes in the lower Rondegat River.     

Germination of the Spores and Development of Primary and Secondary Protonema of Funaria hygrometrica

Abstract

1. The primary protonema of Funaria hygrometrica, cultivated on Knop's or Marchal's agar in the light, proved to consist of filaments with much chlorophyll, a hyaline membrane, perpendicular cross-walls and branches equal to the main filament (chloronema). These filaments grow on the surface of the agar, the branches may also grow vertically. Sometimes filaments with less chlorophyll occur immediately after the germination. The caulonema described by Sironval has not been observed. Thus the rhizoid-like forms mentioned in the literature should more likely be considered as a result of external conditions (see Schoene, Bauer, Heitz and Fitting). Therefore it remains doubtful if a distinction between rhizoids and chloronema on the primary protonema is of any importance as it is impossible to give a good definition of either form.

At the base of moss plants main filaments with brown membranes, oblique septa and without chlorophyll may develop (rhizoids). They grow on the surface or within the agar. In F. hygrometrica especially, the stem seems to influence the occurrence of these rhizoids. The main filaments form buds on the basal cell of the branches and thus serve for vegetative reproduction. The branches show the characteristics of the chloronema. This is contrary to the conclusion of Westerdijk that rhizoids would pass into chloronema only when they are damaged or when the growth of the end bud of the plant is inhibited. At the base of the plant, moreover, little ramified, short branches with oblique septa appear which do not produce buds.

2. Branches may develop in the first growth stages of the primary protonema at any point of the cells. One single cell of a main filament can produce none, one, or more than one branch. Later the branches appear immediately behind the acroscopic cross-wall except in a few cases. Each cell then produces one branch.

3. Buds always develop at the basal cell of a primary branch of a green main filament or of a rhizoid derived from a moss plant.

4. In two ways the protonema may fall into pieces, which can develop into new main filaments:

(a) By forming brood cells; rounded cells which get detached by splitting of the septum. This phenomenon is very frequent. Contrary to Servettaz's opinion it seems to occur particularly under unfavourable conditions.

(b) By forming special cells, tmemata, whose walls are rent. These occur on the primary protonema contrary to the observations of Correns and Bauer, but they are much less frequent than the brood cells. No observations have been made on the circumstances of their occurrence.     

Reorganization of the DNA-nuclear matrix interactions in a 210 kb genomic region centered on c-myc after DNA replication in vivo

In the interphase nucleus of metazoan cells DNA is organized in supercoiled loops anchored to a nuclear matrix (NM). DNA loops are operationally classified in structural and facultative. Varied evidence indicates that DNA replication occurs in replication foci organized upon the NM and that structural DNA loops may correspond to the replicons in vivo. In normal rat liver the hepatocytes are arrested in G0 but synchronously re-enter the cell cycle after partial-hepatectomy leading to liver regeneration. Using this model we have previously determined that the DNA loops corresponding to a gene-rich genomic region move in a sequential fashion towards the NM during replication and then return to their original configuration in newly quiescent cells, once liver regeneration has been achieved. In the present work we determined the organization into structural DNA loops of a gene-poor region centered on c-myc and tracked-down its movement at the peak of S phase and after the return to cellular quiescence during and after liver regeneration. The results confirmed that looped DNA moves towards the NM during replication but in this case the configuration of the gene-poor region into DNA loops becomes reorganized and after replication only the loop containing c-myc resembles the original in the control G0 hepatocytes. Our results suggest that the local chromatin configuration around potentially active genes constraints the formation of specific structural DNA loops after DNA replication, while in non-coding regions the structural DNA loops are only loosely determined after DNA replication by structural constraints that modulate the DNA-NM interactions.