Dietary neutral lipid level and source in Senegalese sole (Solea senegalensis) larvae: effect on growth, lipid metabolism and digestive capacity

Contrary to larval essential fatty acid (EFA) requirements, the effect of dietary neutral lipid supply has been little investigated in marine fish larvae. The present work investigates the effect of feeding Senegalese sole larvae on Artemia enriched with higher or lower doses of lipid emulsion. Two lipid sources - soybean oil and fish oil - were compared. From 16 days after hatching (DAH) onwards, larvae were fed one of four experimental treatments: Artemia enriched on a high or low dose of soybean oil emulsion (HS and LS) or Artemia enriched on a high or low dose of fish oil emulsion (HF and LF). In terms of growth, the dietary lipid level did not have a significant effect while the soybean oil treatments induced a lower growth than the fish oil-enriched Artemia. The fatty acid (FA) composition of the larvae closely reflected the dietary quantitative and qualitative FA profile. Only slight dietary effects were noted in the activity of trypsin, lipase and alkaline phosphatase. A higher amount of lipid droplets was noticeable in the posterior intestine epithelia and in the hepatocytes of larvae fed Artemia enriched with higher lipid doses, while LS-Artemia induced the lower lipid accumulation on the basal zone of the enterocytes, in accordance with the lowest total lipid level measured in this treatment. These results suggest an important effect of dietary total lipid level on lipid accumulation in the enterocytes and on FA absorption. At 33 DAH a tube feeding trial was conducted with 14C-labelled oleic acid (OA) or triolein (TRI), showing that the lower accumulation of lipid droplets in the larvae fed LS was associated with a significantly higher absorption and retention in the gut and body tissues of the TRI label. For OA no significant differences between treatments were found. TRI label was considerably more evacuated than OA, indicating that sole larvae may have a lower capacity to incorporate a triacylglycerol, which needs to be digested. Finally, OA appears to be preferentially utilized for energy production, accumulating more in larval tissues when absorbed in higher amounts.     

Identification and characterization of the new bacillus thuringiensis serovars pirenaica (serotype H57) and iberica (serotype H59)

Two new Bacillus thuringiensis strains have been classified by the H antigen of the cells and differentiated by their morphological, biochemical and molecular characteristics. The flagellar agglutination showed that both strains bore specific H antigens which allowed their classification as the new serotypes H57 and H59. The serovar names proposed for the type strains characterized in this work are B. thuringiensis ser. pirenaica, for the H serotype 57, and B. thuringiensis ser. iberica, for the H serotype 59. Further characterization of these strains, by means of SDS-PAGE, Western inmunodetection, plasmid profile and cry -gene identification by polymerase chain reaction, confirmed the originality of the two novel serotypes. Toxicity tests carried out against several insect species, belonging to the orders Lepidoptera, Diptera and Coleoptera, showed no detectable insecticidal activity for either of the B. thuringiensis strains.     

Sedentary life style of Neotropical sedge wrens promotes song imitation

To what extent has the style of song development among songbirds coevolved with other life history strategies? Among Cistothorus wrens in North America, it seems that sedentary or site-faithful habits of marsh wrens, C. palustris, favour song imitation, but seminomadic habits of sedge wrens, C. platensis, favour song improvisation, whereby each male generates a large but unique song repertoire. In this study, we tested whether more sedentary populations of sedge wrens in the Neotropics would imitate songs. At our primary study site near Cartago, Costa Rica, breeding birds were colour-banded during 1995 and 1996, and follow-up surveys revealed that the birds remained at this site the year round. Extensive tape recording and analysis of songs showed that males had large song repertoires (200-300+ songs), and that many songs were shared among neighbouring males. In addition, males only 27 km distant, at La Pastora, used different songs. Furthermore, matched countersinging, in which two males answer each other with identical song types, was recorded near Brasilia, in Brazil. The sharing of songs among permanent neighbours, microgeographical variation in song, and matched countersinging can be achieved only through song imitation, thus revealing a striking difference in the style of song development among different populations of the sedge wren. In the Neotropics, having predictable neighbours throughout life appears to have favoured song imitation, so that individuals can interact using a common, learned code typical of the local population; among more mobile populations in North America, however, individuals improvise large repertoires of species-typical songs, thereby enabling singing males to communicate with any individual, no matter what the population of origin. Strategies of song development must correlate with life history features, and further surveys are needed to make sense of the great diversity of singing behaviours among songbirds. Copyright 1999 The Association for the Study of Animal Behaviour.     

Potential of the Bacillus thuringiensis Toxin Reservoir for the Control of Lobesia botrana (Lepidoptera: Tortricidae), a Major Pest of Grape Plants

The potential of Bacillus thuringiensis Cry proteins to control the grape pest Lobesia botrana was explored by testing first-instar larvae with Cry proteins belonging to the Cry1, Cry2, and Cry9 groups selected for their documented activities against Lepidoptera. Cry9Ca, a toxin from B. thuringiensis, was the protein most toxic to L. botrana larvae, followed in decreasing order by Cry2Ab, Cry1Ab, Cry2Aa, and Cry1Ia7, with 50% lethal concentration values of 0.09, 0.1, 1.4, 3.2, and 8.5 μg/ml of diet, respectively. In contrast, Cry1Fa and Cry1JA were not active at the assayed concentration (100 μg/ml). In vitro binding and competition experiments showed that none of the toxins tested (Cry1Ia, Cry2Aa, Cry2Ab, and Cry9C) shared binding sites with Cry1Ab. We conclude that either Cry1Ia or Cry9C could be used in combination with Cry1Ab to control this pest, either as the active components of B. thuringiensis sprays or expressed together in transgenic plants.     

Effects of beta-cyclodextrin-dextran polymer on stability properties of trypsin

Dextran modified with the mono-6-pentylene-diamino-6-deoxy-beta-cyclodextrin derivative was evaluated as a thermoprotectant additive for trypsin. The optimum temperature for trypsin activity was increased by 7 degrees C in the presence of this polymer. The enzyme thermostability was increased from 48.5 to 64 degrees C over 10 min of incubation, and the activation free energy of thermoinactivation at 50 degrees C was increased by 4.1 kJ/mol in the presence of the additive. Trypsin was 6-fold more resistant to autolytic inactivation at alkaline pH in the presence of the polymer.     

Fixed contributions designs vs. minimization of global coancestry to control inbreeding in small populations

Populations with small census sizes are at risk because of the loss of genetic variability and the increase of inbreeding and its harmful consequences. For situations with different numbers of males and females, several hierarchical designs have been proposed to control inbreeding through the fixation of individuals' contributions. An alternative method, based on the minimization of global coancestry, has been proposed to determine contributions as to yield of the lowest levels of inbreeding in the population. We use computer simulations to assess the relative efficiency of the different methods. The results show that minimizing the global coancestry leads to equal or lower levels of inbreeding in the short and medium term, although one of the hierarchical designs provides lower asymptotic inbreeding rates and, thus, less net inbreeding in the long term. We also investigate the performance of the alternative methods against departures from the ideal conditions, such as inbred or differentially related base individuals and random failures in the expected contributions. The method of minimization of global coancestry turns out to be more flexible and robust under these realistic situations.     

The Bacillus subtilis acyl lipid desaturase is a delta5 desaturase

Bacillus subtilis was recently reported to synthesize unsaturated fatty acids (UFAs) with a double bond at positions delta5, delta7, and delta9 (M. H. Weber, W. Klein, L. Muller, U. M. Niess, and M. A. Marahiel, Mol. Microbiol. 39:1321-1329, 2001). Since this finding would have considerable importance in the double-bond positional specificity displayed by the B. subtilis acyl lipid desaturase, we have attempted to confirm this observation. We report that the double bond of UFAs synthesized by B. subtilis is located exclusively at the delta5 position, regardless of the growth temperature and the length chain of the fatty acids.     

Predominance of vanA genotype among vancomycin-resistant Enterococcus isolates from poultry and swine in Costa Rica

The use of avoparcin as a growth promoter is considered to have selected for vancomycin-resistant enterococci (VRE). In Costa Rica, the use of avoparcin for poultry and swine was intensive until the product was withdrawn from the market in 2000. We evaluated the presence of VRE in poultry, swine, and cattle fecal samples obtained during 1998 and 1999. A total of 185 VRE isolates were recovered from 116 out of 893 samples. Enterococcus faecium was the most frequently isolated species (50.8%), being predominant among poultry (71.6%) and swine (37.7%) isolates, but it was not recovered from the bovine samples. The second-most-frequently-isolated species from poultry and swine, respectively, were E. durans (23.2%) and E. faecalis (21.7%). E. casseliflavus was the only species obtained from bovine samples, but it was not found among the avian isolates. An evident predominance of the vanA determinant among vancomycin-resistant enterococcal species from poultry and swine, but not from cattle, was observed and was similar to the situation in European countries before avoparcin was forbidden. The diversity of the vanA determinant in the isolates was assessed by detection of the IS1251 insertion in the vanSH intergenic region and of the IS1476 insertion in the vanXY intergenic region. However, in none of the 154 vanA+ isolates recovered in this study were those insertions detected.     

Nonallopatric and parallel origin of local reproductive barriers between two snail ecotypes

Theory suggests that speciation is possible without physical isolation of populations (hereafter, nonallopatric speciation), but recent nonallopatric models need the support of irrefutable empirical examples. We collected snails (Littorina saxatilis) from three areas on the NW coast of Spain to investigate the population genetic structure of two ecotypes. Earlier studies suggest that these ecotypes may represent incipient species: a large, thick-shelled 'RB' ecotype living among the barnacles in the upper intertidal zone and a small, thin-shelled 'SU' ecotype living among the mussels in the lower intertidal zone only 10-30 m away. The two ecotypes overlap and hybridize in a midshore zone only 1-3 m wide. Three different types of molecular markers [allozymes, mitochondrial DNA (mtDNA) and microsatellites] consistently indicated partial reproductive isolation between the RB and the SU ecotypes at a particular site. However, each ecotype was related more closely to the other ecotype from the same site than to the same ecotype from another site further along the Galician coast (25-77 km away). These findings supported earlier results based solely on allozyme variation and we could now reject the possibility that selection produced these patterns. The patterns of genetic variation supported a nonallopatric model in which the ecotypes are formed independently at each site by parallel evolution and where the reproductive barriers are a byproduct of divergent selection for body size. We argue that neither our laboratory hybridization experiments nor our molecular data are compatible with a model based on allopatric ecotype formation, secondary overlap and introgression.