Leaf breakdown in an Atlantic Rain Forest stream

The hypothesis of this study was that colonizers in decaying leaf litter prefer native species (Erythrina verna) to exotic ones (Eucalyptus camaldulensis and Protium heptaphyllum). Therefore, native species are expected to show higher breakdown rates, increased biomass, richness and density of invertebrate species, and increased biomass of decomposer fungi. Breakdown of leaf litter from these three species was assessed in an Atlantic Rain Forest stream. Four samples were collected during a period of 90 days and washed on a sieve to separate the invertebrates. Then, a series of leaf disks were cut to determine ash‐free dry mass and fungal biomass, and the remaining material was oven‐dried to determine the dry weight. Eucalyptus camaldulensis and E. verna showed higher breakdown rates than P. heptaphyllum, due to differences in leaf physical and chemical characteristics. The harder detritus (P. heptaphyllum) broke down more slowly than detritus with high concentrations of labile compounds (E. camaldulensis). The density of the invertebrates associated with detritus increased with time. There were no differences in density, taxonomic richness or biomass of invertebrates among the leaf types, which indicated that the invertebrates did not distinguish between exotic and native detritus. Fungal colonization varied among samples; E. camaldulensis showed the lowest ergosterol concentrations, mainly due to a high concentration of total phenolics. The detritus with the highest hardness value was colonized most slowly by fungi. These results showed that leaf breakdown in Atlantic Rain Forest streams could be affected either by changes in riparian vegetation, or by becoming more savanna‐like process due to climate change.     

An Analysis of Clumping in the Soil Amoeba Mayorella palestinensis*

SYNOPSIS. Mayorella palestinensis, a small soil amoeba, clumped during active growth in axenic, fluid culture media. Clumping was not associated with starvation (as in the case of cellular slime molds) or with encystation Hartmannella rhysodes was used as a control amoeba which did not clump to the same extent, but otherwise resembled M. palestinensis. Mixtures of both amoebae formed mixed clumps, without subsequent segregation of amoebae in the clumps. Clumping by M. palestinensis was temperature dependent, localized to the surface of the amoeba and required surface conformation. The requirement for a living system could be separated from the surface specificity of M. palestinensis and satisfied with living amoebae that did not clump by themselves, i.e., H. rhysodes, but did clump with dead M. palestinensis. It is proposed that amoeba-to-amoeba adhesion is similar to foreign substrate adhesion, and that M. palestinensis adheres to itself because its surface is more suitable for adhesion than other surfaces present in the culture. A competition for adhesion exists between surfaces so that clumps can be dissociated by providing a foreign surface that is more suitable for adhesion than the surface of the amoeba.     

Polyamines and Adventitious Root Formation in the Juvenile and Mature Phase of English Ivy

The involvement of polyamines during adventitious root formationwas evaluated using a de-bladed petiole rooting assay for theeasy-to-root juvenile and difficult-to-root mature phase ofEnglish ivy (Hedera helix L.). Auxin (NAA 0.1 mM) stimulatedroot formation in juvenile phase cuttings, but failed to promoterooting in the mature phase. The addition of putrescine, spermineor spennidine (1.0 mM) with or without NAA (0.1 mM) did notaffect the rooting response in either the juvenile or maturephase cuttings. There was a significant increase in endogenouslevels of putrescine and spermidine in NAA-treated cuttings,but the only significant difference between the root formingjuvenile and the non-root forming mature phase cuttings wasan increase in putrescine levels. In NAA-treated juvenile cuttings,the polyamine biosynthesis inhibitor DFMA (1.0 mM) promotedroot formation from 9.2 to 14.5 roots per cutting, while DFMO(1.0 mM) reduced root formation from 9.1 to 1.4 roots per cutting.The promotion of rooting by DFMA was completely reversed byputrescine (1.0 mM), but putrescine, spermine or spermidine(1.0 mM) could not reverse the inhibitory effect of DFMO. NeitherDFMA nor DFMO promoted root formation in mature phase cuttings.DFMA was also added to NAA-treated juvenile petioles at variousstages during the root formation process. DFMA promoted rootingwhen applied during the early stages of root induction (0–3d), but became inhibitory to root formation when applied duringthe organization (6–9 d) or root elongation stages (9–12d). Key words: Hedera helix, organogenesis, root initiation, polyamines, DFMA, DFMO     

The cost of ant attendance and melezitose secretion in the black bean aphid Aphis fabae

1. The aphid Aphis fabae (Scopoli) is facultatively tended by Lasius niger (Linnaeus) ants. Previously, we found that A. fabae colonies can be made up of several clones, and that clones display significant differences in the composition of their honeydew sugars, especially in the amount of the ant attractant sugar melezitose that they produce. 2. These clonal differences could greatly impact the strength of the mutualistic interaction with ants as well as the aphids' fitness. 3. Hence, the aim of this study was to compare the fitness of different A. fabae clones that differed in their melezitose secretion, and whether or not they were tended by ants. 4. Individual fitness indices, colony growth, and alate production of single‐clone aphid colonies were analysed. 5. The results demonstrate that the fitness consequences of ant attendance critically depend on an interaction between levels of melezitose production. In particular, we show that high‐melezitose secreting clones produce fewer alates and hence might have a lower dispersal ability in the presence of ants. 6. Furthermore, these data confirm previous evidence that ant attendance is costly and results in the production of fewer apterae.     

The Intracellular Location of Particulate-Bound Polyphenol Oxidase in Avocado Mesocarp

Polyphenol oxidase of avocado mesocarp exists in a supernatant and a participate fraction. Isolation conditions were sought where maximal polyphenol oxidase activity could be retained in the particulate fraction. More polyphenol oxidase was associated with the 270–2000 g pellet than with the 2000–12,000 g pellet. Analysis of the particulate polyphenol oxidase on linear sucrose density gradient revealed two relatively heavy peaks. The data showed that the major part of polyphenol oxidase was not a constituent of chloroplasts, chromoplasts or mitochondria. The closeness of the positions of polyphenol oxidase and of catalase in both the green and the yellow zones of the mesocarp established that most of the particulate polyphenol oxidase of avocado is associated with microbodies.     

The species of Myochrous Erichson (Coleoptera: Chrysomelidae) occurring in Central America

Myochrous femoralis Jacoby is redescribed and a species from Nicaragua is described as new. A new key is given to the 12 species of Myochrous known from Central America. A list of Jacoby's type-material of this group is included and lectotypes are designated where necessary.     

Stem canker (Rhizoctonia solani) on five early and seven maincrop potato cultivars I. Infection of shoots, stolons and tubers

In 1983 and 1984, potato seed tubers of five early and seven maincrop cultivars were inoculated with cultures of Rhizoctonia soluni during planting to simulate severe seed infection. Shoot and stolon infection was assessed in June-August and black scurf on tubers recorded after harvest in October. Almost all shoots of all cultivars had stem canker in both years and disease on shoots, stolons and tubers was more severe in 1984 than in 1983. In 1983 similar amounts of disease developed on all early cultivars and between 11% (Ulster Sceptre) and 32% (Maris Peer) shoots were pruned off. Maris Peer had a stem canker score lower than other cultivars in 1984 but more than half the shoots were pruned off. Shoot pruning on Estima, Ulster Prince and Ulster Sceptre was more common on plants from sprouted than non-sprouted seed. Between 30 and 50% of stolons were pruned off. After harvest in 1985, black scurf was least prevalent on Arran Comet and Maris Peer tubers and in 1984 on Arran Comet and Estima tubers from non-sprouted seed. Of the maincrop cultivars, King Edward plants from sprouted seed had many shoots pruned off in both years. Shoot pruning was also prevalent on Maris Piper and Pentland Squire plants from non-sprouted seed. Record had fewest pruned shoots and stolons and the lowest stem canker score. The disease was more severe on Pentland Crown and Maris Piper plants from non-sprouted than sprouted seed. Black scurf was most common on Cara and King Edward tubers in 1983 and on King Edward and Record tubers in 1984. In both years few shoots but many tubers were infected on plants from non-inoculated seed and the significance of this is discussed.     

Ecological Bases of Hormone--Behavior Interactions: The "Emergency Life History Stage"

SYNOPSIS. Superimposed upon seasonal changes in morphology,physiology and behavior, are facultative responses to unpredictableevents known as labile (i.e., short-lived) perturbation factors(LPFs). These responses include behavioral and physiologicalchanges that enhance survival and collectively make up the "emergency"life history stage. There is considerable evidence that glucocorticosteroids,and other hormones in the hypothalamo—pituitary—adrenal(HPA) cascade, initiate and orchestrate the emergency life historystage within minutes to hours. This stage has a number of sub—stagesthat promote survival and avoid potential deleterious effectsof stress that may result from chronically elevated levels ofcirculating glucocorticosteroids over days and weeks. Thesesub—stages may include: redirection of behavior from anormal life history stage to increased foraging, irruptivetypemigration during the day, enhanced restfulness at night, andelevated gluconeogenesis. Once the perturbation passes, glucocorticosteroidsmay also promote recovery. Additional evidence from birds indicatesthat glucocorticosteroid responses to a standardized capture,handling and restraint protocol are modulated both on seasonaland individual levels. Field work reveals that these changesin responsiveness to LPFs have ecological bases, such as reproductivestate, body condition etc., that in turn indicate differenthormonal control mechanisms in the HPA cascade.