Influence of diatoms on copepod reproduction. III. Consequences of abnormal oocyte maturation on reproductive factors in <Emphasis Type="Italic">Calanus helgolandicus</Emphasis>

Observations of gonads and oocyte development stages (OS) have been achieved in Calanus helgolandicus females fed different algal diets and starved in filtered sea water under laboratory conditions during 8 days. The effects of 20 diets on egg production rates (EPR), hatching success (HS) and proportion of abnormal larvae (AL, development stages N1-2) were examined. With the control diet Prorocentrum minimum EPR and HS values were high, while AL was very low, coinciding with intact cell structures in oogonia (OO) and normal OS (OS1-OS4). With the other diets, oocyte maturation, EPR, HS and AL patterns were partially or totally impaired. Decrease of EPR coincided with the arrest of OS3 maturation and oocyte degradations, characterised by cell fragmentation, presence of apoptotic bodies in the OS3, degradation of cytoplasm in OS3 and OS4 and consequently the arrest of OS4 formation. These degradations were reversible when females were fed a favourable diet. Results reflect the presence of two distinct inhibitory mechanisms. Inhibition mechanism (1) impairs egg production. It was induced by starvation or by several species belonging to Bacillariophyceae (Chaetoceros calcitrans, Guinardia delicatula, Guinardia striata, Odontella regia, Rhizosolenia setigera, Stephanopyxis turris, Thalassiosira pseudonana) and mixed-diatom assemblages (collected in the field) and to the prymnesiophyte Pavlova lutherii. Remarkably other diatoms like Navicula sp., Nitzschia sp., Skeletonema costatum and Thalassiosira rotula did not induce mechanism (1) Inhibitory mechanism (2) affected exclusively HS and AL and was triggered by species independent of the production of polyunsaturated aldehydes (PUA), which are supposed to have adverse impacts on HS and larval development.     

Double-labelling methods used to diagnose apoptotic and necrotic cell degradations in copepod nauplii

Two double-labelling methods, Tunel+propidium iodide and Annexin V-FITC+propidium iodide, have been tested to diagnose cell degradation processes in N1–N2 nauplius stages produced by spawning females of the copepod Calanus helgolandicus fed either non-toxic (PRO: control) or toxic (TR1) diets under laboratory conditions. Observation of labelled samples with a confocal laser-scanning microscope revealed that the maternal-food effect, following absorption of the toxic diet, induced cell apoptosis and necrosis in 80–100% of the offspring, which sooner or later died. Similar cell damages were also observed in 18–50% of the nauplii produced by females incubated in filtered seawater. Such cell degradation processes and high mortality were not observed in nauplii produced by females fed the non-toxic diet. Our protocols allowed detection of cell degradations before death of unhealthy larvae, preferentially with a confocal microscope or a conventional visible-fluorescent-light microscope.Communicated by O. Kinne, Oldendorf/Luhe     

Adsorption and degradation of the herbicide nicosulfuron in a stagnic Luvisol and Vermic Umbrisol cultivated under conventional or conservation agriculture

Environmental Science and Pollution Research - The main goals of conservation agriculture are to enhance soil fertility and reduce soil degradation, especially through erosion. However,...