Bumble bee workers drift to conspecific nests at field scales

1. Workers in several bee species travel to conspecific nests (‘drifting’), enter them, and produce male offspring inside them, so acting as intra‐specific social parasites. This adds a new dimension to bees' reproductive behaviour and spatial ecology, but the extent to which drifting occurs over field scales, i.e. at natural nest densities in field conditions, has been unclear. 2. Using the bumble bee Bombus terrestris (Linnaeus) as a model system, we sought to determine rates of worker drifting at field scales and the frequency of potential drifter workers in wild nests. 3. A field experiment with 27 colonies showed that workers travelled to, and became accepted in, conspecific nests that were up to 60 m away, although the number of accepted drifter workers within nests fell significantly with distance. The rate at which nests were entered by drifters was relatively high and significantly exceeded the rate at which drifters became accepted. 4. Microsatellite genotyping of eight field‐collected nests from Greater London, U.K., showed that a low frequency (3%) of workers were not full sisters of nestmate workers and hence were likely to have been drifter workers. 5. It is therefore concluded that workers can drift to conspecific nests over field scales and confirmed that successful drifting occurs in natural populations. Drifting appears to be a natural but low‐frequency behaviour permitting B. terrestris workers to gain direct fitness.     

Herpetomonas roitmani (Fiorini et al., 1989) N. Comb.: A Trypanosomatid with a Bacterium-like Endosymbiont in the Cytoplasm

The trypanosomatid previously described as Crithidia roitmani is characterized here at the ultrastructural and biochemical levels. The data indicates that the parasite belongs to the Herpetomonas genus, and we therefore suggest the flagellate to be denominated as Herpetomonas roitmani n. comb. Cladistic analysis of isoenzyme data generated by eight different enzymes showed that the parasite presented a distinct banding pattern and could be grouped with some Herpetomonas spp., but not with Crithidia spp., used as reference strains. Accordingly, when the parasites were grown for longer periods in Roitman's defined medium, expontaneous differentiation from promastigotes to opisthomastigotes (typical of the Herpetomonas genus) occurred. Transmission electron microscopy revealed the presence of bacterium-like endosymbionts in the cytoplasm of all evolutive forms of the parasite. All morphological alterations characteristic of endosymbiont-bearing trypanosomatids could be observed.     

Isolation and characterization of eight dinucleotide microsatellite loci from two closely related clupeid species (Alosa alosa and A. fallax)

Eight dinucleotide microsatellite loci were developed through an enrichment protocol for allis shad (Alosa alosa) and twaite shad (A. fallax). Cross‐species amplification was successful for all loci isolated. The number of alleles per locus ranged from three to nine for A. alosa and from two to seven for A. fallax, while the observed heterozygosity ranged from 0.267 to 0.926 and from 0.240 to 0.727, respectively. These markers will constitute useful tools for studies of population structure and gene flow between two closely related hybridizing species.     

Membrane-Associated Polysaccharides Composition, Nutritional Requirements and Cell Differentiation in Herpetomonas roitmani: Influence of the Endosymbiont

Herpetomonas roitmani , a trypanosomatid containing a bacterial endosymbiont, was cured by high doses of chloramphenicol. Wild-type and cured flagellates were compared as to polysaccharide composition, nutritional requirements and cellular differentiation. Fucose (18.0%), xylose (15.7%), mannose (38.9%), galactose (10.8%), glucose (16.4%) and inositol (< 1.0%) were identified as polysaccharide components of cured H. roitmani as assessed by gas-liquid chromatography. However, the wild-type strain displayed a markedly different sugar profile, in that xylose was absent and inositol preferentially synthesized, whereas the other monosaccharide components remained unchanged. Variations in nutritional pattern also occurred between both strains. The bacterial endosymbiont seems to provide the flagellates with nutritional factors, including usual amino acids, vitamins, purine (as adenine) and hemin. The process of cell differentiation was also significantly influenced by the endosymbiont. Opisthomastigote forms predominate (72.0%) in cured as compared with wild-type H. roitmani (37.0%).     

How Plants Cope with Water Stress in the Field? Photosynthesis and Growth

Plants are often subjected to periods of soil and atmosphericwater deficit during their life cycle. The frequency of suchphenomena is likely to increase in the future even outside today’sarid/semi-arid regions. Plant responses to water scarcity arecomplex, involving deleterious and/or adaptive changes, andunder field conditions these responses can be synergisticallyor antagonistically modified by the superimposition of otherstresses. This complexity is illustrated using examples of woodyand herbaceous species mostly from Mediterranean-type ecosystems,with strategies ranging from drought-avoidance, as in winter/springannuals or in deep-rooted perennials, to the stress resistanceof sclerophylls. Differences among species that can be tracedto different capacities for water acquisition, rather than todifferences in metabolism at a given water status, are described.Changes in the root : shoot ratio or the temporaryaccumulation of reserves in the stem are accompanied by alterationsin nitrogen and carbon metabolism, the fine regulation of whichis still largely unknown. At the leaf level, the dissipationof excitation energy through processes other than photosyntheticC-metabolism is an important defence mechanism under conditionsof water stress and is accompanied by down-regulation of photochemistryand, in the longer term, of carbon metabolism.