Harvester ants modify seed rain using nest vegetation and granivory

1. In annual plant communities, the seed bank determines each generation's potential emergence and any factor that influences it could alter community structure. Harvester ants are common seed predators that may cause seed sources and seed rain composition to vary. 2. In semi‐arid shrubland of the Negev desert of Israel, we hypothesised that the positive effects of dense vegetation on nests of the harvester ant Messor ebeninus Sant. would outweigh reduction by granivory. 3. To test whether nests were seed sources, we removed vegetation on 10 of 20 sampled nests prior to seeding. We tested the interaction between seed sources and granivory by locating seed traps at three locations: nests, foraging trails, and unvisited areas. Trapped seeds were recorded during spring and summer dispersal. Plant recruitment from the altered seed bank was recorded the following spring. 4. During April, seeds were more abundant near nests than the other locations and at uncut compared with cut nests. Foraging trails had fewer species and higher equitability compared with nests or unvisited areas. May and June to August had highest species richness at nests, but richness of cut and uncut nests were similar. Ordination of plant recruitment showed slightly lower vegetation community variation by diminished species in the cut seed bank. 5. While intact nest vegetation initially had high abundance of locally deposited seeds, it apparently blocked wind‐dispersed seeds later in the summer. Conversely, granivory reduced seed species richness only on trails and decreased dominance structure by preferential removal of some species.     

Population Dynamics of Marine Copepods: The Importance of Photoperiodism

SYNOPSIS. Biological oceanographers have traditionally emphasizedfood and temperature as the most important factors governingthe population dynamics of marine copepods. This paper addressesthe importance of light and light-dark periods as stimuli forthe induction of specific biological processes and activities.Attention is focused on photoperiodic control of dormancy andvertical migration, and the rhythmic expression of daily functionssuch as the timing of feeding and egg-laying. Emphasis is placedon relating the genetic basis of photoperiodically determinedresponses and activity rhythms to the population dynamics, ecologyand evolution of marine copepods, and the maintenance of diversezooplankton communities.     

Microelectrode Experiments with Potato Cells: A Reinterpretation of the Experimental Findings

The conclusions of Macklon and Macdonald (1967) concerning theuptake of chloride at low temperatures by potato cells havebeen reinterpreted. It is believed that the lack of agreementbetween their experimental result and what is expected fromconventional electrochemical theory of the passive movementof ions into plant cells is due to the fact that electrodesinserted into potato cells only detect the potential acrossthe plasmalemma.     

Resistance to Didymella applanata in red raspberry and some related species

When raspberry canes were inoculated in summer with a mycelial inoculum of Didymella applanata resistant genotypes developed relatively small lesions which produced few fruiting bodies in the following spring. Scores of the frequency of these fruiting bodies provided the best discrimination between genotypes. Very strong resistance was found in R. pileatus, R. occidentalis and R. coreanus and in hybrids of these species with red raspberry. Hybrids with R. crataegifolius were less resistant. Resistance was also found in Malling 1473/35, a derivative of red raspberry cv. Chief, and in red raspberry segregates with gene H which determines cane pubescence. Both the expression of resistance and the ranking of resistance sources for their resistance was similar for D. applanata to that reported for Botrytis cinerea.     

Evolution of a Neuropeptide Family: Gonadotropin-Releasing Hormone

SYNOPSIS. Gonadotropin-releasing hormone (GnRH), a small peptidein the brain, is essential for reproduction. It is now clearthat GnRH is part of a family of closely related molecules.The primary structure has been identified for 4 GnRH molecules:mammalian, chicken I, chicken II and salmon. During evolutionthe molecule has been conserved in length, terminal amino acidstructure, 70–90% of amino acid sequence and the His²Trp³residues,residues, which are important in the release of gonadotropin.Alterations have occurred in positions 5, 7 and 8, regions thoughtto be involved in receptor binding. The receptors for GnRH haveapparently evolved also in that the mammalian and avian receptorsvary considerably in their ability to bind different GnRH molecules.Other GnRH family members have been distinguished indirectlyby chromatographic or immunological means; 3 different GnRH-likemolecules are present, respectively, in lamprey, sturgeon andsalmon (a second form). Several GnRH-like molecules includingthose in chondrichthyes have not yet been distinguished fromthe proposed salmon II molecule. The lamprey GnRH-like moleculemay be a nodal point inthe analysis of the ancestral molecule;hagfish do not contain a detectable GnRH molecule. The elucidationof the GnRH precursor molecule in human placenta showed thepresence of a 53-amino-acid gene-related peptide of unknownfunction, but did not reveal the basis for expression of multipleGnRH forms in many nonmammalian species. GnRH has a varietyof novel functions in addition to release of gonadotropin fromthe pituitary. During evolution certain functions such as thosein the retina and sympathetic ganglia have apparently disappearedin amniotes, but GnRH placental functions have appeared in mammals.     

The Effect of Ions on Growth and Leaf Succulence of Atriplex hortensis var. cupreata

When plants of Atriplex hortensis var. cupreata were grown insolutions containing at least 100 mmoll^–1 of various saltsit was found that sodium was the ion most effective in stimulatingleaf succulence, irrespective of whether the anion was chloride,bromide or sulphate. Potassium was the next most effective ion.Magnesium and calcium were without effect. Dry weight productioncould be greatly reduced by sodium and potassium but stimulatedby magnesium. The results are compared with those previouslyreported for C₄ species of Atriplex.