Population history in social spiders repeated: colony structure and lineage evolution in Stegodyphus mimosarum (Eresidae)

Social cooperative spiders from diverse taxonomic families share life-history and demographic traits, including highly inbred colony structure. The combination of traits suggests constrained pathways for social evolution in spiders. The genus Stegodyphus has three independently evolved social species, which can be used as replicate samples to analyse population constraints in evolutionary time. We tested colony structure and population history of the social S. mimosarum from South and East Africa using mitochondrial DNA variation, and we compared the results to published data for the independently evolved social congener S. dumicola . S. mimosarum had many and diverse haplotypes (5–7% sequence divergence for ND1) but colonies were monomorphic and genealogically similar haplotypes occurred in abutting regions. These findings are nearly identical to results for S. dumicola and imply similar colony-level processes over evolutionary time in independently evolved social species. These population dynamics are discussed with respect to the apparent lack of cladogenesis in social spiders.     

Crystalline arrays of ribosomes in isolated pea chloroplasts

Abstract Transmission electron microscopy of chloroplasts isolated by osmotic lysis of pea leaf protoplasts has revealed crystalline arrays of ribosomal particles associated with the thylakoid membranes. Optical diffraction techniques have established the crystallinity of the arrays and an image-enhancement technique has given an indication of ribosomal macrostructure. A model of crystal-packing is presented. This apparently artefactual induction of ribosome crystals should provide a valuable approach towards the elucidation of the details of the structure of chloroplast ribosomes.     

Experiments on the control capacity of stomata of Picea abies (L.) Karst. after fumigation with ozone and in environmentally damaged material

Abstract. With the aid of specifically designed potometer experiments, it is shown that, after ozone fumigation, twigs transpiring in gas exchange chambers show poor water balance in decreasing humidity. The quotient of water uptake to water loss never falls below 0.9 in healthy material because of the control capacity of the stomata. In twigs from a tree fumigated with ozone irregular and delayed stomatal closure results in values of < 0.5 or even lower, depending on the degree of damage. As a result, in dry air, the transpiration rates of fumigated twigs often fall far below those of the control material, even if they were higher than the latter in humid air. In analogous experiments, the difference in behaviour between twigs of densely ('healthy') and sparsely needled ('damaged') trees from the natural stand is comparable to the difference between controls and ozone-fumigated trees in most respects. In soil that is more or less dried out and after the best possible saturation of the twigs during the night, the transpiration rates of fumigated trees increase fairly strongly in the humid chamber air at dawn, but finally decrease more or less suddenly to lower values than in the controls. The results are placed in the context of the basic research on plant water relations and compared with histological changes in the stomatal apparatus after a period of fumigation as described earlier. Therefore, long-term effects of pollution can be explained as a specific distrubance of hydroregulation.