Partial self‐incompatibility in the polyploid endemic species Scalesia affinis (Asteraceae) from the Galápagos: remnants of a self‐incompatibility system?

Different pollination treatments of capitula were used to examine the breeding system of individuals of the tetraploid endemic species Scalesia affinis from the Galápagos Islands. All types of crossings resulted in approximately 35 achenes per capitulum, but in actively and passively self-pollinated capitula these were mostly without embryos. Among self-pollinated individuals a large variation was found in the production of embryos. Some individuals failed completely to set filled achenes while others produced few or many. Additionally, we found a clear difference in female phenology of florets in self-pollinated capitula compared with florets in cross-pollinated capitula. Female florets in self-pollinated capitula remained receptive for longer time. These results suggest that Scalesia affinis is partly self-incompatible. Outcrossing is assured by the endemic carpenter bee, Xylocopa darwini , which proved to be an important pollinator of Scalesia affinis . Nevertheless, geitonogamy seemed to be considerable in the focal population, for which reason open pollinated capitula produced fewer achenes than controlled outcrossed capitula.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 93–101.     

Atypical Granules in the Eyes of the White Mutant of Drosophila melanogaster Are Lysosome-Related Organelles

In the pigment cells of the white mutant of Drosophila melanogaster, as described earlier, two types of abnormal granules are found by conventional electron microscopy. However, both types of abnormal granules, in addition to those in pigment cell invaginations, are also present in the cytoplasm of the photoreceptor cells. Three enzymes (acid phosphatase, peroxidase, and tyrosinase) are localized within the eyes of wild type and white mutant Drosophila melanogaster by electron microscopy. Peroxidase activity is present in lamellar bodies close to the rhabdomeral microvilli of both fly types. However the organelles containing peroxidase activity are 6-fold more frequent in the wild type than in the mutant. Acid phosphatase is present in lamellar bodies between and at the bases of the rhabdomeral microvilli of the wild type, as well as in ommochrome granules of the photoreceptor cells. In the white mutant, however, acid phosphatase was located in electron lucent vacuoles in the cytoplasm of the receptor cells. These acid phosphatase-positive vacuoles also contained both types of abnormal granules. The latter result indicates that abnormal granules in the receptor cells originate from lysosomal degradation and that targeting of lysosomal enzymes is altered in the white mutant. Due to the tyrosinase activity in the hemolymph of flies, the extracellular spaces are electron dense after DOPA incubation. Since some abnormal granules within the photoreceptor cells are not surrounded by an extracellular space, they can be assumed to originate within the photoreceptor cells.     

Juvenile survival of a planktonic insect: effects of food limitation and predation

• 1 An experiment was conducted to investigate potential impacts of food limitation and copepod predation on juvenile survival of Chaoborus purtctipennis. We tested the hypotheses that: (i) juvenile survival of Chaoborus is influenced more by copepod predation than by starvation in a productive environment, and (ii) food limitation and predation interact to affect survival.
• 2 Effects of food concentration (approximately 800, 1400 and 2300 microzooplankton 1-^?1) and predator density (0, 1 and 2 Mesocydops edax 1-^?1) on Chaoborus development and survival were evaluated using a 3 × 3 factorial design. Jars containing lake water, the appropriate food and predator treatments, and two Chaoborus (<12h old) were rotated on a plankton wheel at 25°C. Survival and developmental stage were monitored daily until all individuals had either died or moulted to instar II.
• 3 Predation by Mesocydops was the major source of mortality, causing 87.5% of Chaoborus deaths over all treatments. Chaoborus mortality was significantly higher in treatments with Mesocydops (67–100%) than in predator-free treatment (0–13%).
• 4 Development time was significantly longer in the low-density food treatment than in the highest food treatment.
• 5 No significant interaction between food limitation and predation was detected.
• 6 These results suggest that predation by copepods may limit recruitment of juvenile Chaoborus in productive lakes.

     

Sex ratios in field populations of Epidinocarsis lopezi, an exotic parasitoid of the cassava mealybug, in Africa

Abstract.

• 1 In cassava fields in Africa, population sex ratios of Epidinocarsis fopezi vaned from 0.44 (males to total parasitoids) at low host densities to highly male-biased ratios of 0.70 at high host densities.
• 2 This variability is caused by the difference in allocation of sons and daughters to hosts of different sizes, through the following mechanisms: (a) small, i.e. second instar, hosts are mainly used for the production of male offspring, whereas in large, i.e. third instar, hosts a variable, female-biased sex ratio is produced; (b) E.fopezi does not selectively oviposit into large hosts but always accepts both small and large hosts for oviposition upon encountering; (c) in the field, this parasitoid is time-limited, and not egg-limited. On the basis of an optimal diet model, such general host acceptance is shown to be the best strategy.
• 3 Thus, sex ratio increases with host density for three reasons: the proportion of small hosts encountered in the field increases with increasing host density, small hosts are used for male production, and hosts are always accepted when encountered.

     

Bromine, Bromophenols and Floridorubin in the Red Alga Lenormandia prolifera

The pigment floridorunin was localized to the cuticle of the red alga Lenormandia prolifera (C. Ag.) J. Agardh by x-ray micro-analysis in Ihe transmission electron microscope and by its colour reactions in the light microscope. The pigment was set free from the cell wall by a pectinase. Bromine was also identified in the chloro-plasts. the middle lamellae, the intercellulars and the pore plugs of the alga. The content of bromophenols in the alga increases with increasing age. The cell walls of old plants are stratified and their outer parts are apparently shed. The bromophenols could have a function as regulators of the epiphytes or the shedding of parts of the outer cell wall.     

The comparative study of the predatory behaviour of Myrmarachne, ant-like jumping spiders (Araneae: Salticidae)

The predatory behaviour of 31 species of Myrmarachne , ant-like salticids, was studied in the laboratory and the field. The ant-like morphology and locomotion of these spiders appears to function primarily in Batesian mimicry. No evidence was found of Myrmarachne feeding on ants. However, predatory sequences were found to differ considerably from those typical of salticids. Instead of stalking and leaping on prey, Myrmarachne lunged at prey from close range. Myrmarachne used its legs I to tap prey before lunging, another unusual behaviour for a salticid. Myrmarachne fed on a wide range of arthropod prey in nature and the laboratory, but appears to be especially efficient at catching moths. Also, Myrmarachne tends to open up, or enter into, other spiders' nests and eat other spiders' eggs. Myrmarachne males were less efficient than females, in laboratory tests, at catching various types of arthropod prey, but they appear to be as efficient as females at oophagy. Myrmarachne tend to use webs of other spiders as nest sites, but no evidence was found of Myrmarachne preying on spiders in webs. It appears that the unusual features of Myrmarachne's predatory and nesting behaviour are important in enabling these spiders to preserve their ant-like appearance.     

Decay and composition of the hemichordate Rhabdopleura: implications for the taphonomy of graptolites

Although the graptolites lacked biomineralised tissue, their skeletons are abundantly preserved in deeper-water mudstones. Decay experiments and observations on the closely related living hemichordate Rhabdopleura demonstrate that the periderm and stolon are highly resistant to decay, remaining intact for months, whereas the zooids are unrecognizable within days. The extreme rarity of the preservation of traces of the zooids in graptoloids reflects their planktic lifestyle; the zooids had normally decayed before burial. Curie-point-gas-chromatography (Py-GC) and Curie-point-gas-chromatography-mass spectrometry (Py-GC-MS) of the periderm of Rhabdopleura confirms that proteinaceous organic matter is a major constituent. Ultrastructurally preserved graptolite periderm (Ordovician, Oklahoma; Silurian, Arctic Canada), on the other hand, is a highly altered kerogen-like substance rich in aliphatic biomacromolecules. The composition of the preserved graptolite periderm reflects diagenetic replacement by components probably mainly derived from algal cell walls.     

Arabidopsis thaliana ASN2 encoding asparagine synthetase is involved in the control of nitrogen assimilation and export during vegetative growth

We investigated the function of ASN2, one of the three genes encoding asparagine synthetase (EC 6.3.5.4), which is the most highly expressed in vegetative leaves of Arabidopsis thaliana. Expression of ASN2 and parallel higher asparagine content in darkness suggest that leaf metabolism involves ASN2 for asparagine synthesis. In asn2‐1 knockout and asn2‐2 knockdown lines, ASN2 disruption caused a defective growth phenotype and ammonium accumulation. The asn2 mutant leaves displayed a depleted asparagine and an accumulation of alanine, GABA, pyruvate and fumarate, indicating an alanine formation from pyruvate through the GABA shunt to consume excess ammonium in the absence of asparagine synthesis. By contrast, asparagine did not contribute to photorespiratory nitrogen recycle as photosynthetic net CO₂ assimilation was not significantly different between lines under both 21 and 2% O₂. ASN2 was found in phloem companion cells by in situ hybridization and immunolocalization. Moreover, lack of asparagine in asn2 phloem sap and lowered ¹⁵N flux to sinks, accompanied by the delayed yellowing (senescence) of asn2 leaves, in the absence of asparagine support a specific role of asparagine in phloem loading and nitrogen reallocation. We conclude that ASN2 is essential for nitrogen assimilation, distribution and remobilization (via the phloem) within the plant.     

The systematic significance of morphological and anatomical variation in fruits of Crotalaria and related genera of tribe Crotalarieae (Fabaceae)

The phylogenetic and taxonomic significance of morphological and anatomical trends in fruits of tribe Crotalarieae has been evaluated, with emphasis on the genus Crotalaria and its seemingly distinctive, inflated and balloon‐shaped pods. In addition to the normal explosive dehiscence as a means of dispersal, several genera (including Crotalaria) show independent evolution of modifications apparently adapted for dispersal by wind, water and gravity. Transverse sections were made of mature pods of 142 species from the 12 currently recognized genera of Crotalarieae. The taxa differ in the orientation of the fibres (related to dehiscence or non‐dehiscence), the overall thickness of the fruit wall, the relative proportions of the pericarp layers, the degree of lignification and the presence or absence of trichomes. Three basic pericarp types can be distinguished: type I, with one, two or three zones of various numbers of cell layers of fibres (almost all genera); type II, with a single cell layer of fibres (only in Rothia, Robynsiophyton, Lebeckia and Lotononis sections Listia and Leobordea); and type III, with one zone of several cell layers of gelatinous fibres and multicellular trichomes associated with the endocarp (only in some species of Calobota and Wiborgiella). Considerable variation was encountered in the tribe, but Crotalaria appears to be rather uniform, with type I predominating. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 165 , 84–106.