The Challenge of Pneumocystis carinii Culture1

ABSTRACT. Published and unpublished data on the cultivation of P. carinii were reviewed by a panel of investigators convened by the National Institutes of Health. Although several cell culture systems allow propagation of P. carinii for a limited time with modest rates of replication, these have not proved adequate for isolation of P. carinii in sufficient quantity to explore important basic biological investigation. Attempts at cell-free culture have yielded only transient proliferation. Because much of the unsuccessful work on cultivation of the organism has been unpublished, the panel agreed that these data may be useful to other investigators in designing experimental strategies for cultivation. Therefore, the purpose of this report is to make available this information to researchers, lest others unknowingly repeat unsuccessful methods. It is hoped that by documenting the history and the complexities of Pneumocystis culture, renewed interest and efforts will be directed toward this fundamental scientific challenge.     

Density-related foraging behaviour in Closterocerus tricinctus, a parasitoid of the leaf-mining moth, Cameraria hamadryadella

• 1 We examined the foraging behaviour of the parasitoid wasp, Closterocerus tricinctus (Ashmead) (Chalcidoidea: Eulophidae), as it visited larvae of the leaf-mining moth, Cameraria hamadryadella (Lepidoptera: Gracillariidae), in an outbreak population.
• 2 We tracked females of C.tricinctus, recording the time spent searching for mines and handling host larvae. The density of leaf-mines (host larvae) and their condition were recorded for each leaf visited. A subset of leaves visited by C.tricinctus was enclosed in fine mesh bags so that foraging success could be determined by rearing or dissection. The average density of mines and the average leaf-area mined was estimated for a random sample of leaves from each tree.
• 3 The selection of leaves upon which to forage appears to be density-dependent. C.tricinctus visits leaves with leaf-mine densities twice the average, and when switching leaves lands directly on leaf-mines 5 times more often than expected assuming random landings.
• 4 The total time spent foraging on a leaf, the average time spent handling hosts, and the total search time within leaves tend to decline on leaves with many hosts, but the observed declines are not statistically significant.
• 5 The proportion of leaf-mines visited within a leaf is strongly inversely density-dependent. 30% of visits to leaf-mines are re-visits and 29% of handling time is spent re-handling previously visited hosts. Furthermore, only 21% of visits to mines lead to successful parasitism. We suggest that self-interference and the avoidance behaviour of the host may reduce the number of visits of leaf-mines by C.tricinctus within a leaf.
• 6 The effect of the strongly inversely density-dependent foraging investment within leaves is to offset the observed density-dependent pattern of leaf visitation making the overall spatial pattern of visitation by C.tricinctus to mines of C.hamadryadella inversely density-dependent.
• 7 We suggest that the uncertainty of C.tricinctus surviving on multiply mined leaves because of density-dependent host mortality due to intraspecific competition in high-density host populations, the rarity of high-density host populations, and the rarity of multiply-mined leaves in low-density host populations combine to select against an aggregative response within leaves by C.tricinctus.

     

BEHAVIOURAL ADAPTATIONS OF THE WREN (TROGLOD YTES TROGLOD YTES)

• 1 This paper includes observations made and references to relevant literature published since the appearance of The Wren (Armstrong, 1955). It includes comparisons between the Wren's behaviour and that of other birds.
• 2 The Wren is exceptional and perhaps unique in having extended its range in comparatively recent times from North America to Asia, Europe and North Africa. Fossil remains accepted as evidence that it reached Britain some 100000 years ago were wrongly identified.
• 3 The Wren is also exceptional in its adaptability. Behaviour, especially the character of the pair-bond, is related to habitat and foraging opportunities, with polygamy occurring in favourable habitats and monogamy in more marginal areas. This facultative pair-bond is believed to be related primarily to the food supply. The life-style is a complex in which the size of the bird and its territory, nature of the display, song and calls, character of the food supply, structure of the nest, roosting behaviour and other adaptations constitute a delicately integrated complex, in which foraging is probably of primary importance. This principle is applicable to many species.
• 4 Size of population is very variable as numbers are greatly reduced during severe winters but the remnants surviving in prime or ‘refuge’ areas form nuclei enabling the population to expand widely during a series of mild winters, invading marginal areas where the size of territories tends to be smaller when the population reaches a peak.
• 5 Song serves various functions and is partly innate and partly learned. It is readily recognizable throughout the bird's range but local groups utter distinctive songs and there is a tendency for northerly birds to utter longer songs. Individual birds can recognize the songs of neighbours.
• 6 The number of nests built is determined by factors as different as the maturity of the male and the amount of rainfall. The enclosed nest facilitates variability in the pair-bond as a single bird can rear at least some of the young. The complex of behaviour involved, characteristic of a number of tropical species, is further evidence of the Wren's tropical or subtropical antecedents.
• 7 There is variability as to when the eggs are laid, before or after the female's first sortie of the day, and also in the inception and duration of incubation. Published estimates of the incubation period not based on data obtained with automatic recording apparatus can be misleading.
• 8 When his mate disappears, a male who has done little to tend the nestlings may change abruptly to feeding them with extreme diligence, even spending the night in the nest with them. The male visits his nests whether or not they are occupied and is usually aware of the state of affairs at any nest.
• 9 Occasionally a Wren may visit a neighbour's nest and possibly feed the nestlings or a bird of another species may feed young Wrens but there is no evidence that, as happens with some other species, young birds feed nestlings of a later brood. Such ‘altruistic’ behaviour in some species is believed to be advantageous.
• 10 As in many other passerine species there are morning and evening peaks in foraging activity for the nestlings. The number of feeding visits tends to be related to the number of the young as well as to the vigour of their begging.
• 11 Social roosting is a form of behaviour characteristic of some tropical species of wren but which in them has no close relationship to the air temperature. Its persistence in the otherwise asocial Wren enables it to survive the low temperatures of northern winters.

     

New Step in Transmitter Release at the Myoneural Junction

QUANTAL release of acetylcholine from vesicles in the presynaptic terminals of neuromuscular synapses is well established^1–3, even if some doubts persist⁴. The mechanism by which acetylcholine (or any other transmitter at other synapses) is transferred from the vesicles into the synaptic gap, however, is unknown. A calcium influx into the terminal is associated with release of transmitter⁵, as is an electrical field change⁶.     

Energy Budgets of Ectothennic Vertebrates

Ecological energetics provides a unifying focus for ecologicalstudies. Heat energy budget analysis is used to predict thebody temperatures of animals and their microclimatic requirements.Climate space diagrams, transient energybalance models and operativeenvironmental temperature models predict daily and seasonalactivity patterns, predator—prey interactions and energyrequirements of vertebrate ectotherms. Food energy budget (resourceallocation) models are used toinvestigate the life history processesof fish, amphibians and reptiles. Heat energy budgets and foodenergy budgets interact through their effects on body temperatureand metabolism. Coupled heat, food and mass balance equationscan serve as aunified energy budget model and are useful indetermining limits on the energy available to an animal forgrowth and reproduction. Bioenergetic models have been successfullyapplied to some reptiles and fish. Complete energy budgets arenow needed for other ectothermic vertebrates.     

Afrochlus Freeman: an African gondwanan midge and the phylogeny of the Podonominae (Diptera: Chironomidae)

The immature stages and male adult of Afrochlus harrisoni Freeman are described for the first time, from the type locality, a granite outcrop in Zimbabwe. A phylogenetic position within the subfamily Podonominae as sister to South African-western/central Australian genus Archaeochlus Brundin, suggested in 1966 by Brundin from the adult female alone, is confirmed by cladistic analysis of all life history stages combined. Within the Podonominae, the tribes Boreochlini and Podonomini erected by Brundin are monophyletic only if Trichotanypus Kieffer is transferred from the former to the latter. Little or none of the structure provided by the combined evidence from all stages is retrieved by cladistic analyses of characters derived solely from the adult stage. The implications of erection of monotypic genera for adult-only taxa are discussed.     

Massive mortality of aspen following severe drought along the southern edge of the Canadian boreal forest

Drought‐induced, regional‐scale dieback of forests has emerged as a global concern that is expected to escalate under model projections of climate change. Since 2000, drought of unusual severity, extent, and duration has affected large areas of western North America, leading to regional‐scale dieback of forests in the southwestern US. We report on drought impacts on forests in a region farther north, encompassing the transition between boreal forest and prairie in western Canada. A central question is the significance of drought as an agent of large‐scale tree mortality and its potential future impact on carbon cycling in this cold region. We used a combination of plot‐based, meteorological, and remote sensing measures to map and quantify aboveground, dead biomass of trembling aspen (Populus tremuloides Michx.) across an 11.5 Mha survey area where drought was exceptionally severe during 2001–2002. Within this area, a satellite‐based land cover map showed that aspen‐dominated broadleaf forests occupied 2.3 Mha. Aerial surveys revealed extensive patches of severe mortality (>55%) resembling the impacts of fire. Dead aboveground biomass was estimated at 45 Mt, representing 20% of the total aboveground biomass, based on a spatial interpolation of plot‐based measurements. Spatial variation in percentage dead biomass showed a moderately strong correlation with drought severity. In the prairie‐like, southern half of the study area where the drought was most severe, 35% of aspen biomass was dead, compared with an estimated 7% dead biomass in the absence of drought. Drought led to an estimated 29 Mt increase in dead biomass across the survey area, corresponding to 14 Mt of potential future carbon emissions following decomposition. Many recent, comparable episodes of drought‐induced forest dieback have been reported from around the world, which points to an emerging need for multiscale monitoring approaches to quantify drought effects on woody biomass and carbon cycling across large areas.