A new dimension to hummingbird-flower relationships

The close correspondence between the bills of hummingbirds and the lengths of the flowers they feed from has been interpreted as an example of coadaptation. Observations of birds feeding at flowers longer and shorter than their bills, however, and the lack of experimental evidence for any feeding advantage to short bills, seem to contradict this interpretation. I address this problem by considering a little-studied dimension of floral morphology: corolla diameter. In laboratory experiments on female ruby-throated hummingbirds (Archilochus colubris), probing abilities (maximum extraction depths) increased with increasing corolla diameter. Handling times increased with decreasing corolla diameter, resulting in handling time equivalents, i.e., flowers having the same handling times but different lengths and diameters. Longer-billed birds had greater maximum extraction depths and shorter handling times than shorter-billed birds at all corolla diameters greater than the width of the bill. In contrast, shorter-billed birds made fewer errors inserting their bills into narrow flowers. Hence, differences in bill lengths apparently are associated with trade-offs in foraging abilities, whereby longer-billed birds are able to feed at long flowers and may do so more quickly, whereas shorter-billed birds are able to feed more successfully at narrow flowers.     

Nitrogen stable isotopic composition of leaves and soil: Tropical versus temperate forests

Several lines of evidence suggest that nitrogen in most tropical forests is relatively more available than N in most temperate forests, and even that it may function as an excess nutrient in many tropical forests. If this is correct, tropical forests should have more open N cycles than temperate forests, with both inputs and outputs of N large relative to N cycling within systems. Consequent differences in both the magnitude and the pathways of N loss imply that tropical forests should in general be more¹⁵N enriched than are most temperate forests. In order to test this hypothesis, we compared the nitrogen stable isotopic composition of tree leaves and soils from a variety of tropical and temperate forests. Foliar ¹⁵N values from tropical forests averaged 6.5 higher than from temperate forests. Within the tropics, ecosystems with relatively low N availability (montane forests, forests on sandy soils) were significantly more depleted in¹⁵N than other tropical forests. The average ¹⁵N values for tropical forest soils, either for surface or for depth samples, were almost 8 higher than temperate forest soils. These results provide another line of evidence that N is relatively abundant in many tropical forest ecosystems.     

On the evolution of cicada X host-tree associations in Central America

An hypothesis tout court is proposed to account for the association of cicadas (Homoptera: Cicadidae) with large-sized trees of the family Leguminosae in both climax forest formations and forest remnants in Central America. Based upon extensive field studies of these insects in Costa Rica, final-instar nymphal skins of many genera and species of Neotropical cicadas appear to be aggregated annually around individual large legume trees in a broad range of habitats in Costa Rica, and much of the reproductive behavior of the adult insects is also centered around these trees. A series of testable subhypotheses are generated based largely upon the assumption that cicadas, primarily through egg-placement behavior and nymphal feeding behavior, have coevolved with legume trees in climax forest formations of Central America, and perhaps elsewhere in the Neotropical Region. The root crowns of such trees, with some exceptions, might be optimal feeding sites for cicada nymphs in tropical forests.     

Avian community structure along elevational gradients in the northeastern United States

Summary Breeding birds were censused along four elevational gradients in the Adirondack Mountains, New York, and the Green Mountains, Vermont. The bird communities of the four gradients were basically similar in species composition, richness and amplitude patterns. Three measures of species diversity decreased with increasing elevation. Low-elevation communities contained higher proportions of rare species and the relative abundances conformed to the broken-stick distribution. At higher elevations the communities showed greater dominance and the dominance-diversity curves approached geometric series. The species characteristic of high-elevation communities had the broadest altitudinal distributions.The upper and lower distributional limits of most species were independent of one another except at ecotones where marked changes in vegetation structure occurred. On each mountain, slightly more than half of the species limits coincided with ecotones. This is a significantly greater proportion than has been found in similar studies of tropical forest bird communities. In further contrast to tropical communities, we found no convincing cases of altitudinal competitive exclusion between species. Interspecific competition in the past seems to have been translated primarily into differences in habitat selection by temperate forest birds.Many of the differences between temperate forest breeding bird communities and tropical ones can be understood in terms of the migratory nature of most of the temperate species and the lower species richness in temperature forests.     

Diversity of forest tree species in Yanbaru,the northern part of Okinawa Island

The natural forests of Yanbaru, in the northern part of Okinawa Island, harbor many endemic and endangered birds and mammals, and are dominated by an evergreen oak, Castanopsis sieboldii. The Simpson diversity (D) and equitability index (J) were calculated using survey data on number of stems ( 4.5 cm DBH) of each species found in sample plots.Near-climax old forests (age 50 yr, without pine trees) showed high species diversity of trees, 0.92 ± 0.01 in D and 0.83 ± 0.05 in J for trees of which DBH 4.5 cm, and 0.81 ± 0.04 in D and 0.75 ± 0.05 in J for trees of DBH 10 cm.These high values are comparable to those of tropical rain forests. Although even young forests showed high species diversity, diversity indices tended to increase with forest age.The U.S. Marine Corps leases the eastern half of Yanbaru which contains most of these near-climax forests. Conservation of natural forests in this area is recommended.     

Ecogeographical differentiation of the Submediterranean deciduous forest flora

The deciduous wood flora of southern Europe is characterized as a special nemoral-Submediterranean element. The distribution patterns of some representatives (total ranges and local areas in Roumania) are described and explained by recent climatic conditions. The northern limits of Submediterranean and Submediterranean-middle European deciduous forest taxa exhibit a continuous gradation, but only a few species with a wide ecological amplitude extend into the temperate zone.     

Reversal of a reflex to a single motoneuron in the stick insect Çarausius morosus

In inactive stick insects ramp-wise stretching of the femoral chordotonal organ excites the slow extensor tibiae motoneuron. In active animals the same stimulus decreases the firing rate of this motoneuron. The time-course of increased and decreased activity of this motoneuron can be seen with triangular stimulation.Supported by the Deutsche Forschungsgemeinschaft     

Development and regional differentiation of the European vegetation during the Tertiary

The Tertiary vegetation of Europe evolved from paratropical to warm-temperate and temperate forms in response to a progressive, non-linear, climatic cooling. Its vegetational forms are composed mainly of two separate ecological units: the evergreen, laurophyll paleotropical geoflora and the deciduous, broad-leaved Arctotertiary geoflora. The development of the Tertiary climate and its interaction with the vegetation are convincingly indicated by the geoflora's migration; the changes in its composition; and the development of the Tertiary forest, swamp, and aquatic plant communities. The paleotropical geoflora is characterized in the upper Cretaceous to the upper Miocene by paratropical rain forest, subtropical rain and laurel forests, temperate laurel forests and edaphically-mediated formation of laurel-conifer forests. The Arctotertiary geoflora advanced into Europe in waves since the Paleocene and formed the basis for the Tertiary mixed mesophytic forests. These can be divided into warm-temperate rain forests, oak-hornbeamchestnut or mixed beech-oak-hornbeam forests, and edaphic formations such as bottomland and swamp forests. Beginning in the lower Cretaceous, the hydrophytic vegetation developed independently of the forest vegetation and formed very diverse herbaceous fresh water, swamp, salt water, and coastal formations. Considerable differences in composition allow to separate floral regions and provinces in Eurosiberia. Instead of three ill-defined floral regions in the Paleocene, there are four well-defined floral regions in the Pliocene. A Mediterranean region cannot be recognized, although Mediterranean (eumesogeic) floral elements appear in the Eocene/Oligocene and thereafter. The Mediterranean sclerophyll forests probably arose after the destruction of the laurophyll forests during the Pleistocene.     

Flower-feeding specialization in wild bee and wasp communities in seasonal neotropical habitats

Summary Flower visitation records were obtained for 192 species of bees and 138 species of wasps in three neotropical habitats. Four indices of feeding specialization were calculated for common species, and similar patterns were observed using each index. Variation in specialization could be attributed to several factors: the habitat and season in which species were found, the degree of sociality of species, and whether species were bees or wasps. Important differences among habitats and seasons were the number of coexisting consumer species and the species richness and phenology of resource plants. Differences in average consumer specialization among habitats and seasons may have been the result of differences in competitive pressures and to a lesser extent, differences in the flowering strategies of local plants. Eusocial bees and wasps were much more generalized in feeding than solitary species, and bees were more generalized than wasps. Bees in these neotropical communities were much less specialized than their north temperate counterparts. This pattern is reflected by the near absence of species that feed at only one or two plant species in Guanacaste, as compared to a very high frequency of these extreme specialist species in north temperate areas. Temperate zone species of bees have less even visitation rates to their resources than tropical bees. Consequently, temperate zone bees are more specialized in both the variety of plant species visited and the dominance of visitation to each set of resource plants. Several hypotheses are examined as possible explanations for this apparent qualitative difference in community structure between neotropical and temperate communities.     

The Salton Sea as critical habitat to migratory and resident waterbirds

Concern about the Salton Sea ecosystem, based on potential impacts of increasing salinity, contaminants, disease outbreaks, and large die-offs of birds, is heightened because of tremendous prior loss and degradation of wetland habitat in western North America. In 1999, we used a variety of survey methods to describe patterns of abundance of birds at the Salton Sea and in adjacent habitats. Our results further documented the great importance of the Salton Sea within the Pacific Flyway to wintering, migratory, and breeding waterbirds. Exclusive of Eared Grebes, we estimated about 187000 individual waterbirds at the Salton Sea in January, 88000 in April, 170000 in August, and 261000 in November. Additional surveys of Eared Grebes in November and December suggested the total population of all waterbirds was about 434000 to 583000 in those months, respectively. We also documented breeding by about 14000 pairs of colonial waterbirds. Waterbirds were particularly concentrated along the northern, southwestern, southern, and southeastern shorelines and river deltas. By contrast, some species of wading birds (Cattle Egret, White-faced Ibis, Sandhill Crane) and shorebirds (Mountain Plover, Whimbrel, Long-billed Curlew) were much more numerous in agricultural fields of the Imperial Valley than in wetland habitats at the Sea. Various studies indicate the Salton Sea is of regional or national importance to pelicans and cormorants, wading birds, waterfowl, shorebirds, and gulls and terns. Important taxa are the Eared Grebe, American White Pelican, Double-crested Cormorant, Cattle Egret, White-faced Ibis, Ruddy Duck, Yuma Clapper Rail, Snowy Plover, Mountain Plover, Gull-billed, Caspian, and Black terns, and Black Skimmer. Proposed restoration projects should be carefully assessed to ensure they do not have unintended impacts and are not placed where large numbers of breeding, roosting, or foraging birds concentrate. Similarly, plans to enhance opportunities for recreation or commerce at the Sea should aim to avoid or minimize disturbance to birds. Future research should focus on filling gaps in knowledge needed to effectively conserve birds at the Salton Sea.     

Common antigenic determinants in the glycoproteins of plants,molluscs and insects

An antiserum raised against -fructosidase isolated from the cell walls of suspension-cultured carrot cells cross-reacts with many plant proteins and hemocyanin ofHelix pomatia. The shared epitope appears to be a small complex glycan with a (1–2)-linked xylose residue attached to the -linked mannose residue of the core of an asparagine-linked oligosaccharide. There is strong cross-reactivity with the proteins of many seed plants, molluscs and insects, and no cross-reactivity with the proteins of fungi, algae, mosses, ferns, or any of the vertebrates tested. Xylose-containing glycans appear to increase the immunogenicity of the proteins to which they are attached, and we suggest that they may be responsible for some allergic responses of people that are repeatedly exposed to plant or insect proteins.     

Nucleolar changes in human phytohaemagglutinin-stimulated lymphocytes

Summary The nucleoli of lymphocytes from circulating peripheral blood and from phytohaemagglutinin (PHA)-stimulated cultures (from 2 h–96 h) were studied using a silver method, RNA-specific fluorescent staining, and electron microscopy of ultrathin sections. In peripheral blood about 75% of the lymphocytes have one ring-shaped nucleolus composed of a distinct fibrillar centre surrounded by a dense pars fibrillaris and little granular material; the remaining lymphocytes showing two or more small ring-shaped nucleoli. With PHA stimulation, the number of cells with several nucleoli increases first (from 2 h–12 h). Next, cells containing one or, at most, two large nucleoli with nucleolonema devoid of fibrillar centers are seen (from 4 h on). 34 h after PHA, nucleoli of the compact type containing one or more fibrillar centres appear and comprise about 60% of the cells after 72 h. The appearance of more than one nucleolus per cell shortly after PHA administration suggests an activation of additional nucleolar organizer regions (NOR), which fuse to form one or two large nucleoli with nucleolonema. These are then transformed into compact nucleoli. The fibrillar centers stain preferentially with silver. They contain nonchromosomal proteins and may serve as stores for nucleolar proteins. The fusion of activated NORs during the first cell cycle explains the relatively high frequency of satellite associations in first mitoses compared to later mitoses after stimulation.     

Yards,corridors, and mosaics: How to burn a boreal forest

Ethnographic studies have established that, until shortly after World War II, Indians in northern Alberta regularly and systematically fired habitats to influence the local distribution and relative abundance of plant and animal resources. In ways similar to what has been reported for hunter-gatherers in other regions, this pyrotechnology contributed to an overall fire mosaic that, in this case, formerly characterized northern boreal forests. Crosscultural comparisons of these practices with those in other parts of North America, as well as in several parts of Australia, illustrate functionally parallel strategies in the ways that hunter- gatherers employed habitat fires, specifically in the maintenance of fire yards and fire corridors in widely separated and different kinds of biological zones.We would like to thank Ross Wein tor his comments and suggestions on this paper, especially his ideas about the characteristics of fire mosaics as they would occur under natural conditions in boreal forests. We are also indebted to several granting agencies for funds that supported our earlier research. They include the Social Sciences and Humanities Research Council, the Museum of Man, Fire Science Center (University of New Brunswick), the Boreal Institute for Northern Studies (University of Alberta), the Australian Institute for Aboriginal Studies, and the Northern Australian Research Unit (Australian National University).     

Disease and illness Distinctions between professional and popular ideas of sickness

The dysfunctional consequences of the Cartesian dichotomy have been enhanced by the power of biomedical technology. Technical virtuosity reifies the mechanical model and widens the gap between what patients seek and doctors provide.Patients suffer illnesses; doctors diagnose and treat diseases. Illnesses are experiences of discontinuities in states of being and perceived role performances. Diseases, in the scientific paradigm of modern medicine, are abnormalities in the function and/or structure of body organs and systems. Traditional healers also redefine illness as disease: because they share symbols and metaphors consonant with lay beliefs, their healing rituals are more responsive to the psychosocial context of illness.Psychiatric disorders offer an illuminating perspective on the basic medical dilemma. The paradigms for psychiatric practice include multiple and ostensibly contradictory models: organic, psychodynamic, behavioural and social. This melange of concepts stems from the fact that the fundamental manifestations of psychosis are disordered behaviours. The psychotic patient remains a person; his self-concept and relationships with others are central to the therapeutic encounter, whatever pharmacological adjuncts are employed.The same truths hold for all patients. The social matrix determines when and how the patient seeks what kind of help, his compliance with the recommended regimen and, to a significant extent, the functional outcome. When physicians dismiss illness because ascertainable disease is absent, they fail to meet their socially assigned responsibility. It is essential to reintegrate scientific and social concepts of disease and illness as a basis for a functional system of medical research and care.Harvard Medical School     

Breeding soybeans for the tropics capable of nodulating effectively with indigenousRhizobium spp.

Summary Most soybean varieties fail to nodulate effectively in tropical soils unless inoculated with a competitive strain ofRhizobium japonicum. Developing countries in the tropics, with few exceptions, lack inoculant industries to produce and distribute viable inoculants to small farmers and extension programs to teach them to use inoculant. Several soybean genotypes have been identified that nodulate effectively with many strains of the cowpea inoculation group which is ubiquitous in tropical soils of Africa. Soybean genotypes that nodulate and grow well without inoculant application are called promiscuous. Methodologies for incorporation of the promiscuity character into high-yielding backgrounds are discussed.Supported in part by grant 05-0560 from United Nations Development Program to the International Institute of Tropical Agriculture.     

Verhaltensontogenese der Habitatwahl beim Teichrohrs?nger (Acrocephalus scirpaceus)

Zusammenfassung In Anpassung an seinen aus vertikalen Vegetationsstrukturen zusammengesetzten Lebensraum besitzt der Teichrohrsänger die beste morphologische Ausstattung aller sechs mitteleuropäischer Rohrsängerarten für Vertikalklettern. An jungen Teichrohrsängern wurde überprüft, ob frühkindliche Erfahrungen auf verschiedenen Sitzstangen (auf senkrechten=K_s, senkrechten und waagerechten=K_m, waagerechten=V_w und waagerechten Sitzstangen mit Futter belohnt=V_w+) die spätere Wahl dieser Strukturelemente beeinflussen. Die lokomotorische Aktivität der vier Aufzuchtsgruppen wurde im Zweifachwahlversuch (horizontale gegen vertikale Sitzstangen) getestet. Mit Ausnahme der auf senkrechten Sitzstangen aufgezogenen Vögel (K_s), deren Wahlverhalten gleichverteilt war (Abb. 2), bevorzugten alle anderen Gruppen das vertikale Testsubstrat (Abb. 2 und 3). Auch die Belohnung mit Futter als positiver Verstärker der Horizontalelemente (V_w+) machte diese nur wenig attraktiver (Tab. 1). Alle Gruppen nutzten während der Testperiode das vertikale Substrat zunehmend stärker (Tab. 1). Die Zunahme rührte bei den Vögeln der beiden Kontrollgruppen (K_s und K_m) und der Versuchsgruppe waagerecht (V_w) alleine von der Erfahrung in der Versuchssituation her (Tab. 2). Die Nutzung vertikaler bzw. horizontaler Strukturelemente durch junge Teichrohrsänger wird somit bestimmt durch: 1. eine angeborene Präferenz für das artgemäße Substrat, 2. einen Novitätseffekt, bedingt durch die Aufzuchterfahrung (Wahlverhalten der K_s-Gruppe, Abb. 2), 3. Eigenerfahrung bei der Nutzung verschiedener Substrate im Versuch. Zusätzliche Wahlversuche später im Jahr (Oktober bis Dezember) mit denselben Versuchsvögeln zeigten keine Änderungen in der Substratwahl (Abb. 4).

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Ontogeny of habitat choice in the Reed Warbler (Acrocephalus scirpaceus)

Summary The Reed Warbler shows the most specialized morphological traits for vertical climbing among the six central EuropeanAcrocephalus species. We consider this as an adaptation to the vertical structures in its habitat. In experiments with young Reed Warblers I tested whether early experience with different perches has an influence on the choice of these structures later on in life. Locomotory activity of the following groups was tested in double choice experiments (horizontal versus vertical perches):Control group vertical (K_s): raised on vertical perches, Control group mixed habitat (K_m): raised on vertical and horizontal perches, Test group horizontal (V_w): raised on horizontal perches, Test group horizontal, plus rewards (V_w+): raised on horizontal perches and additional feeders attached to the bars. With the exception of Control group vertical (K_s) which shows no choice preference (Fig. 2) all other birds prefered the vertical test substrate (Fig. 2 and 3). Even the reward (food) as a positive reinforcement of horizontal elements had little effect on their attractiveness (Tab. 1). An increase in the choice of the vertical substrate could be observed throughout the 3-day test period in all groups (Tab. 1). This increase was only due to the experience in the test situation for the birds in both control groups (K_s and K_m) and the Test group horizontal (V_w) (Tab. 2). Therefore the use of vertical or horizontal structures in Reed Warblers is determind by: 1. An innate preference for species-specific substrate, 2. Novelty due to early experience (choice behaviour of Control group vertical, Fig. 2), 3. Experience while using different substrates (experience in the test situation) which optimizes substrate choice according to proprioceptive learning. Additional choice experiments with the same test birds later on in the year (October to December) revealed the same results. Therefore it seems unlikely that there exists a preprogrammed change in substrate choice in the course of a year (Fig. 4). Although choice experiments of this kind can only include a limited part of the habitat-scheme, they are useful experimental designs for investigating specialized species whose habitats can be simulated closely in the laboratory.

     

Cytokinesis in the green alga Eremosphaera viridis: Plasmalemma formation from “open membranes”

Summary Cytokinesis in the unicellular chlorococcalean alga Eremosphaera viridis de Bary has been investigated by electron microscopy of thin sections. The new plasmalemmata of the daughter cells in this organism form centrifugally within a phycoplast. Unlike other cell division systems each new plasmalemma is formed, not by the fusion of vesicles, but rather by the fusion of open membranes which are characteristically heavily stained. Measurements of these open membranes reveal that they are 11 nm thick with a central 4,5 nm unstained portion. The possible origin of these open membranes as burst-open vesicles has been suggested from the presence of intensely straining vesicles in the vicinity of the cell equator. Calculations of vesicle and open membrane surface areas support this contention.     

Are the funnel-canal organs the “campaniform sensilla” of the shore crab Carcinus maenas (Crustacea,Decapoda)?

Summary The topography of the funnel-canal organs of Carcinus maenas (Decapoda, Crustacea) and their stimulus-receiving cuticular and sensory apparatus were studied in the light and electron microscopes.About 4000 funnel-canal organs are situated within the exoskeleton of Carcinus. Almost all of them are on the distal segments of the walking legs, in particular on the epicuticular cap at the tip of the dactyl. They were not found to be arranged in groups or sensilla fields, and no sex-specific differences were observed.Characteristic features of the funnel-canal organs are as follows: (a) There is a terminal pore (0.5×0.8 m diameter) in the cuticle, at the tip of a small projection. It is closed by a plug of electron-dense material. (b) The terminal sections of the dendrites are enclosed in a dendritic sheath up to ca. 10 m below the pore. (c) The dendrites, 3–24 in number, end below the plug; none of the dendrites exhibits a tubular body; two of the dendrites are distinguished from the others by the greater number of microtubules in their outer segments.The structural characteristics, in particular the gustatory pore and the number of dendrites, are typical of bimodal receptors in arthropods. In such receptors, as in the contact chemoreceptors of insects and arachnids, mechano-and chemosensitive sensory cells are combined.This interpretation of the function of the funnel-canal organs is supported by electrophysiological data of other authors.The morphological parameters we find for the funnelcanal organs, in comparison with those of insect campaniform sensilla, provide clear evidence against the reclassification of the funnel-canal organs as crustacean campaniform organs proposed by Shelton and Laverack (1968).Supported by the Deutsche Forschungsgemeinschaft (W.G., SFB 45/A1)We thank Professor Dr. F.G. Barth for valuable discussion and Mr. K. Grommet for drawing the Figs. 1 and 6c     

DNA homology and adsorption specificity of Pseudomonas aeruginosa virulent bacteriophages

Summary The DNA homology and adsorption specificity of newly isolated virulent bacteriophages of P. aeruginosa have been studied. On the basis of this analysis all phages were divided into four groups: k, m, mnP78-like and mnF82-like bacteriophages. DNA's of k as well as m phages were shown to possess different restriction patterns although they have an extensive homology. Unlike other groups, k phages were characterized by the presence of T4 DNA ligase-repaired, single-chain breaks.Abbreviations kbp kilobase pairs - EM electron microscopy