Concentration Requirement of glycine as nitrogen source for supporting effective growth of certain marine microplanktonic algae

Eighteen species of marine phytoplankton from 9 algal classes were tested under axenic-culture conditions for their capacity to improve phototrophic-growth performance on glycine with increasing concentration of this amino-acid serving as sole nitrogen source. Whereas all these species showed poor-to-no growth on 0.5 mM glycine, 14 species manifested considerable gain in growth-rate and yield at higher concentration levels. The highest level tested (25 mM) was generally not inhibitory and produced the best yields in these cases. Some species (notably Skeletonema costatum) showed marked reduction in the adaptation-lag period with increased glycine concentration, but Chlamydomonas palla required a very long adaptation period, which was little affected by concentration. Dunaliella tertiolecta, Emiliania huxleyi and Chroomonas salina showed sharp (albeit elevated) concentration thresholds for efficient glycine utilization. Rhodomonas lens and two cyanophycean strains, Agmenellum quadruplicatum and Anacystis marina, appeared incapable of successful growth on glycine at all concentrations tested, while the rhodophyte Porphyridium marinum displayed marginal growth. The results were insufficient to draw taxonomically general conclusions on algal-class potential for glycine utilization, but they showed unequivocally that more than 83% of phytoplankton species from 9 algal classes can utilize glycine for growth if the appropriate substrate concentration is provided.     

Etude des variations du poids sec et de la constitution chimique élémentaire de Tisbe holothuriae (Copepoda: Harpacticoïda) élevé sur différents régimes artificiels

Dry weight and body composition of C, H and N were investigated in male and female Tisbe holothuriae Humes fed 7 artificial compound diets and a living algal diet (Nannochloris sp.) over the whole biological cycle. No correlation was found between the respective proportion of C, H and N in the food and in the copepod body. Food quality had a significant effect on dry weight. Carbon content varied between 35.35 and 42.32% of body dry weight in females, and between 25.10 and 26.84% in males. Nitrogen values were 9.11 to 10.00% and 6.79 to 6.99%, respectively, varying with different diets. The C:N ratio varied between 3.74 and 4.28 in females and between 3.70 and 3.87 in males. Some diets had a significant effect on this ratio. In some experiments, three different temperatures were tested using the same diet. Body dry weight was inversely correlated with temperature, but no clear relation appeared between C:N and temperature. C:N variations were directly related to C concentration and seemed independent of N concentration. It is suggested that C variations correspond to different levels in lipid content under different trophic conditions. The relation between elementary chemical composition and fecundity in T. holothuriae fed different diets is discussed.     

Spawning behaviour,egg and larval development of the myctophid fish Benthosema pterotum

The distribution of eggs and early larval stages of the myctophid fish Benthosema pterotum was studied during three cruises to the Gulf of Oman during January to February 1981 and February 1983. The eggs and yolk sac larvae were identified and described after artificial fertilization on board the Research Vessel Dr. Fridtjof Nansen. The mature fish spawn in the Gulf at 300 to 100 m depths during early night. The eggs and smallest larvae were found at 300 to 200 m depths. The eggs hatch within 12 h at 21°C. Hatching occurs before the slightly bouyant eggs reach the upper 50 m of the water column.     

Collective decisions in ants when foraging under crowded conditions

In this paper we examine the effect of crowding on the selection of a path in the mass-recruiting ant Lasius niger. In our experiment, ants had to go from their nest to a food source by crossing a diamond-shaped bridge, giving the choice between two paths. Two types of bridges were used: the first had two branches of equal length but different width while the second had two branches of different length and width. Experiments at high traffic volume always ended up with the selection of the wider branch, even if it was longer. This result shows that overcrowding on the narrow branch plays an essential role in the mechanism underlying the choice of route in ants. A mathematical model was developed to evaluate the importance of two mechanisms that could account for this result. The first is based on the difference in travel duration between the two paths. The second is based on the repulsive interactions between workers making head-on encounters. The model shows that travel duration per se is not sufficient to explain path choice. Rather, it is the interplay between trail following behaviour and repulsive interactions that allows ants to choose the path that minimizes their travel time. When choosing a path ants thus prefer to trade time against energy. Our results demonstrate that any environmental constraint that alters the dynamics of trail recruitment can lead to the emergence of adaptive foraging decisions without any explicit coding of information by the foragers at the individual level.     

Relationship between body size, provisioning rate, longevity and reproductive success in females of the solitary bee Osmia cornuta

Body size has often been related to reproductive success in bees and wasps. The objective of this 3-year study was to analyze the relationship between nesting female body size, provisioning rate and longevity and their effect on several traits related to parental investment and reproductive success in the solitary bee Osmia cornuta. Body size was not correlated to longevity, and it was only correlated to provisioning rate in the third year (with poor weather conditions during nesting). Variation in fecundity, offspring size and offspring mortality was not well explained by nesting female body size in any of the 3 years. However, in the third year, small females biased their investment toward males, the sex requiring smaller pollen–nectar provisions. Large females were more successful usurpers of other females' nests, but fecundity of usurpers was no higher than fecundity of nonusurpers. Large females were more likely to establish at the release site, probably in relation to size-dependent vigor at emergence. A review of the literature on parental investment in solitary aculeate Hymenoptera showed a stronger relationship between body size and reproductive success in wasps than in bees. In O. cornuta, fecundity was strongly related to longevity and provisioning rate in all 3 years. Offspring size was associated with provisioning rate in 1 year, when females with higher provisioning rates tended to produce larger sons and daughters. Both longevity and provisioning rate appeared to be strongly conditioned by stochastic events.     

Prelaying maternal condition modifies the association between egg mass and T cell-mediated immunity in kestrels

Theoretical models of parental care predict differential allocation in relation to the expected fitness of the offspring. As birds must allocate all the resources required for embryonic development in self-contained packages, maternal egg allocation takes a central role in avian life histories. It is predicted that mothers can influence offspring performance by varying the size or composition of their eggs. In this context, T cell-mediated immune response has been revealed as a valuable tool to evaluate fledgling fitness. However, little is known about its relationships to egg mass. I describe a negative association between egg mass and cellular immune response in Eurasian kestrel nestlings (Falco tinnunculus) throughout 3 years. To explore how environmental conditions could mediate this relationship, I experimentally supplied food to females before egg formation in the third study year. I found that this relationship turned to positive in food-supplied females without any effect on egg size. This result shows that environmental conditions before egg formation mediate the relationship between egg mass and future immune response of the nestlings. I suggest that females may be constrained in improving the future immune response of their offspring due to resource allocation trade-offs determined by their pre-laying condition.     

The two reindeer parasites,Hypoderma tarandi andCephenemyia trompe (Oestridae), have evolved similar olfactory receptor abilities to volatiles from their common host

Summary Using the linked gas chromatographical/electroantennogram (GC/EAG) technique it was revealed that the reindeer warble fly (H. tarandi) was specifically able to sense the same components from reindeer interdigital pheromone gland as the reindeer nose bot fly (C. trompe) another reindeer endoparasite. These two species belong to the same family (Oestridae), but different subfamilies, and the evolution towards an endoparasitic life cycle is thought to have been independent. The development of olfactory abilities to find reindeer from long distances is hypothesized to have taken place through convergent evolution or exists because of their common ancestry.     

What describes fecundity of Capitella sp. 1 better: macro- or micronutrient availability?

During a preliminary set of experiments (April 1987). I measured short-term (20 d) reproductive responses of laboratory-cultured Capitella sp. 1 at 20°C, at four daily ration levels (0.26 to 2.60 mg of organic nitrogen per bowl), and for four food types: Gerber's mixed cereals, Ulva sp., diatoms, and Tetramen fish food. Average female body size, number of fertile segments, and fecundity were significantly affected both by food type and food ration. Average fecundities ranged from 21 (Gerber, 0.26 mg N d^-1) to 448.3 eggs per female (Tetramen, 2.60 mg N d^-1). During a second set of experiments (May 1987), I measured the reproductive response of laboratory-cultured Capitella sp. 1 at 20°C at six ration levels of spring and summer sediment-trap material collected in the Patuxent Estuary, Maryland, USA. Worms raised on these two diets failed to reproduce during the period of this experiment. I used simple and miltiple linear-regression models to describe relationships between fecundity and daily rations and macro- (dry wt, C, N) and micronutrients (essential amino- and essential fatty acids). These models were carried out on three data sets corresponding to either 4 or 6 food types. The results suggest that different nutritional factors may be limiting for different foods. However micronutrients and especially essential amino acids probably more aptly describe nutritional limitation of reproduction in Capitella sp. 1.     

Ladybird defence alkaloids: Structural,chemotaxonomic and biosynthetic aspects (Col.: Coccinellidae)

Summary The defensive mechanisms which protect ladybird beetles (Coccinellidae) against predators are reviewed. Besides behavioural mechanisms, such as thanatosis and reflex bleeding, chemical defence mechanisms are playing a prevalent role. Indeed, ladybirds are protected not only by their smell, but also by repulsive alkaloids, most of which are considered to be of autogenous origin. In a few cases, dietarily-acquired substances are also involved. Particular emphasis is laid on the repellent alkaloids which are contained in the haemolymph of many species. The structures of 34 nitrogen-containing compounds isolated so far are presented, and their distribution within the family is discussed in the light of the most widely accepted classification of these beetles. To conclude, the mode of release of the alkaloids, their variation through the life cycle and their repellent and toxic properties are discussed, as well as the few biosynthetic data yet available.     

Causative species of diarrhetic shellfish poisoning (DSP) in Norway

This study was performed at Vikane in the Sognefjord, Norway, from September 1987 to October 1988 on the blue musselMytilus edulis collected monthly at three different depths (3 to 6, 6 to 8 and 8 to 12 m). Cell numbers of three species ofDinophysis from mussel digestive glands and in seawater were counted for each specimen. Multivariable statistical methods were used to detect annual cycles of phytoplankton abundance in the fjord and to examine the contribution of each species to toxification of mussels. Cluster analysis and principal component analysis indicated the following results: (1) an annual cycle and an inter-specific association of threeDinophysis species populations were pointed out.D. acuta andD. norvegica were well associated over the entire period of this study, and exhibited an autumnal peak.D. acuminata was dissociated from these species and reached its maximum abundance between spring and early summer. (2) The threeDinophysis species induced toxicity in the blue mussels in different manners.D. acuta andD. norvegica were responsible for high autumnal toxicity, andD. acuminata for the spring peak. (3) A long persistence of diarrhetic shellfish poisoning (DSP) in blue mussels (from April to February), and a depth gradient of toxicity were observed — the toxicity value in the upper layer being double those of other depths.