Germination ecology of drupelets of the fig (Ficus carica L.)

Abiotic and biotic factors and their effects on germination of fig drupelets were studied. The drupelets germinated between 10^oC and 30^oC.Constant humidity was necessary for germination and frequent drying out of the substrate was unfavourable. Total darkness for the whole duration of the experiments had a slighly negative effect on germination. The fastest germination occurred at constant humidity and an alternating temperature of 20/30^oC with exposure to light for 8 hours (at the higher temperature) and to darkness for 16 hours (at the lower temperature).Natural or artificial removal of drupelets from the syconium guaranteed a high germination percentage, whereas no germination occurred in drupelets left inside the syconium. Hence birds and mammals act as dispersal agents and mediators of germination. As they eat pieces of fig syconium, they free the drupelets from the flesh, eliminating the effect of inhibitors and/or microenvironments with high osmotic pressure inside the syconium. These findings support the hypothesis that germination occurs in autumn or spring depending on the climatic zone in which the species grows.     

Development of Plastids in Pollen and Tapetum of Rye-grass, Lolium perenne L

Proplastids of both tapetal cells and microsporocytes were presentearly in anther development. Tapetal proplastids differentiated—probablyinto elaioplasts—at late microspore stage. The tapetalcytoplasm was completely resorbed by early tricellular pollenstage. Microspore proplastids differentiated into amyloplastsat early bicellular stage, and were present in both vegetativeand generative cells. In the generative cell, the amyloplastswere ephemeral and apparently degenerated within autophagicvacuoles. Plastids were absent from sperm cells. Vegetativecell amyloplasts increased in number apparently by fission suchthat one amyloplast produced one amyloplast and one proplastidper division. Mature pollen grains were estimated to containbetween 550 and 820 amyloplasts with only one starch granuleper plastid. Elaioplasts, amyloplasts, plastid division, plastid differentiation, starch granules, autophagy, Lolium perenne, Poaceae, rye-grass     

Development and Ultrastructure of Cucurbita pepo Nectaries of Male Flowers

The development of the nectary of the male flower ofCucurbitapepo L. was studied from 5d before to 2d after anthesis. Thenectary consists of parenchyma that stores starch in the presecretorystages, and epidermis. An hour before nectar secretion begins,the starch is hydrolyzed. The nectar exudes from the stomataand forms a continuous layer on the nectary surface. Duringanthesis the nectar may all be collected by pollinators or someor all of it may remain in the nectary and be successively resorbed.The nectary parenchyma stores material for synthesizing thesugar component of nectar and stores similar material againafter nectar resorption. It is also responsible for nectar productionand secretion. The epidermis is actively involved in the reabsorptionprocess. The resorption of nectar is a phenomenon that allowsthe plant to recover invested energy. Few observations on thisphenomenon have hitherto been published. Amyloplasts; Cucurbita pepo L.; courgette; nectaries; Nectar resorption; plastid; secretion; starch     

The smell of danger: chemical recognition of fish predators by the invasive crayfish Procambarus clarkii

1. Since avoiding predation can compromise animal fitness, prey are expected to respond to different predator species with an intensity appropriate to the level of risk. In fresh waters, the threat of predation is typically assessed by chemical cues, in particular by odours released by either injured/disturbed conspecifics (conspecific alarm odour) or predators (predator odours). Here, we used the most widely distributed crayfish in the world, the invasive North American Procambarus clarkii, to investigate the relative effectiveness of odours emitted by fish predators compared with conspecific alarm odour. We also tested whether P. clarkii is able to discriminate between fish predators of which it has ‘experience’ (either recent, via introduction to the same water body, or old, by sharing a native range), as well as between fish predators that pose low or high risk. 2. The study was carried out on introduced populations of P. clarkii from two sites, characterised by different fish assemblages: the Malewa River (a tributary of Lake Naivasha, Kenya) and Lake Trasimeno (Italy). Laboratory experiments consisted of three sequential phases (‘water’, ‘food’ and ‘smell’ phases) and five treatments. Treatments differed in the odour presented during the smell phase, i.e. no odour (plain water) and odours from either injured conspecifics or three fish species per site. Crayfish from the Malewa River population were confronted with the odours of largemouth bass (Micropterus salmoides), common carp (Cyprinus carpio) and tilapia (Tilapia zillii) (all introduced to Lake Naivasha but absent from the Malewa River), and those from the Lake Trasimeno population with the odours of the introduced largemouth bass and carp and the native chub (Squalius cephalus). Largemouth bass is the only predator that imposes a high risk to crayfish, and it also shares its native range with P. clarkii. We analysed the time spent by crayfish feeding, in locomotion and in adopting a raised or lowered posture. A reduction in the time spent feeding and in locomotion, and an increase in the time spent in the lowered posture were considered to indicate alarm. 3. Crayfish from both populations responded with a more pronounced reduction in feeding to conspecific alarm odour rather than to predator odours. Crayfish from the Malewa River reacted with the same intensity to the odours of the three fish species tested, whereas, in Lake Trasimeno, the odour of largemouth bass was significantly more threatening than the odours of the other two species. 4. Procambarus clarkii seems to perceive a general fish odour that alerts it to possible predation risk without the need of either a direct recent experience or via sharing a common native range. However, where they coexist with fish, crayfish become able to distinguish among species, adapting the intensity of their response to the effective risk. Our results confirm the relatively high learning capacity of P. clarkii reported in previous studies and suggest the existence of mechanisms that make predator recognition particularly efficient in this extraordinarily successful invader.     

Heterostyly and gene-flow in Menyanthes trifoliata L. (Menyanthaceae)

NIC LUGHADHA, E. M. & PARNELL, J. A. N., 1989. Heterostyly and gene-flow in Menyanthes trifoliata L. (Menyanthaceae). Menyanthes trifoliata is shown to be a self-incompatible heterostylous species with a suite of associated pollen and gynoecium dimorphisms. These features may promote legitimate pollination. Analysis of a natural population showed substantial pollen inviability, a preponderance of illegitimate pollen on stigmas and a possible asymmetry of pollen flow. Mean pollen travel was estimated as 2.6 m by counting legitimate grains on stigmas whose distance from the nearest source of legitimate pollen was known. Direct field and laboratory measurement indicated mean seed travel of <0.2m. The density of flowering spikes varied greatly within the studied colony of Menyanthes , with a mean of 0.93 m^-2. Using suitable corrections the genetically effective density was estimated as between 0.04 and 4.4 m^-2. Crossing experiments indicated that Menyanthes is fully outcrossed (r=1). The neighbourhood area was estimated as 10–15 m² while neighbourhood size ranged from less than one to sixty-five. Some published neighbourhood estimates are revised with the results for Menyanthes being at the lower end of the range. If the genetically effective density were estimated more accurately, neighbourhood estimates would likely be lower still. It is concluded that what is generally referred to as a population of Menyanthes , may actually represent many evolutionary units.     

Variation in nectar–sugar profile of Anchusa and allied genera (Boraginaceae)

The nectar–sugar profile (fructose, glucose and sucrose) of 14 species of Anchusa and five members of the allied genera Anchusella, Cynoglottis, Hormuzakia and Lycopsis (Boraginaceae: tribe Boragineae) was determined. Most of the species examined (c. 74%) produce sucrose‐dominant nectar, whereas the remaining taxa produce sucrose‐rich nectars. Little variation in nectar–sugar composition was found in some species, even when sampling was repeated in different years and/or localities. Average sucrose concentration was 57.75% (coefficient of variation 19.1%). The only floral morphological character that was correlated with the nectar–sugar profile is the length of the corolla tube, as taxa with relatively long floral tubes produce nectar with lower glucose concentrations. The flowering period is also related to sugar composition, as nectar of late‐flowering species contains lower sucrose concentrations. However, small differences in sugar profiles do not reflect phylogenetic relationships based on molecular studies. It would appear that dry habitats and time of flowering are the main determinants of nectar–sugar composition in the genus Anchusa sensu lato. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 616–627.     

Large-scale climatic signatures in lakes across Europe: a meta-analysis

Recent studies have highlighted the impact of the winter North Atlantic Oscillation (NAO) on water temperature, ice conditions, and spring plankton phenology in specific lakes and regions in Europe. Here, we use meta-analysis techniques to test whether 18 lakes in northern, western, and central Europe respond coherently to winter climate forcing, and to assess the persistence of the winter climate signal in physical, chemical, and biological variables during the year. A meta-analysis approach was chosen because we wished to emphasize the overall coherence pattern rather than individual lake responses. A particular strength of our approach is that time-series from each of the 18 lakes were subjected to the same robust statistical analysis covering the same 23-year period. Although the strongest overall coherence in response to the winter NAO was exhibited by lake water temperatures, a strong, coherent response was also exhibited by concentrations of soluble reactive phosphorus and soluble reactive silicate, most likely as a result of the coherent response exhibited by the spring phytoplankton bloom. Lake nitrate concentrations showed significant coherence in winter. With the exception of the cyanobacterial biomass in summer, phytoplankton biomass in all seasons was unrelated to the winter NAO. A strong coherence in the abundance of daphnids during spring can most likely be attributed to coherence in daphnid phenology. A strong coherence in the summer abundance of the cyclopoid copepods may have been related to a coherent change in their emergence from resting stages. We discuss the complex nature of the potential mechanisms that drive the observed changes.     

Influence of temperature and rainfall on fruit and seed production of Arbutus unedo L.

Correlations were found between certain climatic parameters and fresh weight, dry weight and seed number of the fruit of Arbutus unedo L. In five stations in central Italy. Temperature and rainfall were found to affect fruit production. For the parameters fresh weight and number of seeds, the first months of development were important and fresh weight was also influenced by rainfall in the last monthS. Dry weight did not show statistically significant correlation with any one of the considered parameterS. However, the pattern of temperature and rainfall over the 12-month period of fruit ripening determined the characteristics of the fruit.     

A Note on Bile Acids Transformations by Strains of Bifidobacterium

The hydrolysis of sodium taurocholate and glycocholate was a common feature among 52 strains from 14 species belonging to the genus Bifidobacterium. Forty-eight strains were able to hydrolyse both these conjugated bile acids, yet four strains failed to split the amide bond of either. Twenty-eight strains were checked for the ability to transform sodium cholate, chenodeoxycholate, deoxycholate and lithocholate; only 13 of these strains formed minimal quantities of monochetoderivatives from cholic acid, while none of them was able to transform the other tested bile acids.     

Scanning Electron Microscopy Analysis of Exine Patterns in Cultivars of Olive (Olea europaea L.)

Scanning electron microscope analysis of exine patterns in thepollen of nine cultivars of the olive tree (Olea europaea L.)has revealed specific differences between them. The differencesinclude variation in size, form and profile of the meshes andin the thickness of the muri. Every cultivar possesses its ownmorphological characteristics which are constant and are foundin successive years. Olea europaea L, olive, pollen, exine patterns