High densities of leaf‐tiers in open habitats are explained by host plant architecture

1. Crown architecture remains one of the least studied plant traits that influence plant–herbivore interactions. The hypotheses that dense crown architecture of mountain birches from open habitats favours leaf‐tying caterpillars through bottom‐up and/or top‐down effects associated with high leaf connectivity were tested. 2. Population densities of leaf‐tying herbivores in open (industrial barren and seashore) habitats were three times as high as in the shaded (forest) habitats. An experimental increase in leaf density by branch binding did not affect foliar consumption by free‐living herbivores but increased consumption by leaf‐tiers. 3. The specific leaf weight was lower in shaded habitats and in bound branches, but branch binding did not influence either the foliar concentrations of carbon and nitrogen or the pupal weight of the most abundant leaf‐tier, Carpatolechia proximella Hbn. (Lepidoptera: Gelechiidae). 4. Caterpillars of C. proximella build several shelters during their lifetime and spend a considerable amount of time outside the shelter, where they excrete most of their faeces. In bound branches, caterpillars built new shelters more frequently than in control branches, and consumed less foliar biomass per shelter. 5. Mortality from parasitoids in bound branches was half that in the control, presumably because the complex environment disrupted parasitoid searching behaviour and/or because of lower damage to leaves from which the shelters were built. 6. It is concluded that the crown architecture associated with high leaf connectivity decreases mortality risks from natural enemies both outside and inside the shelter. Compact and dense crowns of host plants may at least partly explain high population densities of leaf‐tiers in open habitats.     

Ribosomal DNA of Leishmania brasiliensis: Number of Ribosomal Copies and Gene Isolation1

ABSTRACT. The DNA content of the hemoflagellate Leishmania brasiliensis. strain Y, has been determined by colorimetric reactions and found to be nearly 0.226 pg/cell. When this DNA is bound to filters and hybridized with labeled rRNA from the same organism, saturation is reached at 0.47% of the DNA, corresponding to an estimated 160 ribosomal gene copies. When the DNA is sheared and centrifuged to equilibrium in CsCl gradients, two major satellites of the main band (p = 1.712 g/cm³) are observed: a heavy one (1.720 g/cm³), which hybridizes with labeled rRNA, and a light one (1.699 g/cm³) with the electron microscopic characteristics of the kinetoplast DNA network.     

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.     

Siphuncular structure in the orders Tarphycerida and Barrandeocerida (Cephalopoda: Nautiloidea)

Abstract: The siphuncular structure is described in two Silurian taxa, Boionautilus tyrannus and Cumingsoceras complanatus, currently placed in the Tarpycerida. Tarphycerids have the Nautilus type of connecting ring that is composed of an outer, thick, spherulitic‐prismatic layer and an inner glycoprotein layer, the latter was destroyed by diagenesis. However, both Silurian specimens have the connecting ring of the calcified‐perforate type, previously known to occur in orthocerids, actinocerids, plectronocerids and now also in barrandeocerids. In this type, the inner layer of the connecting ring is calcified and perforated by pore canals. Boionautilus and Cumingsoceras are therefore classified with barrandeocerids and not with tarphycerids.     

LATE CAMBRIAN PLECTRONOCERID NAUTILOIDS AND THEIR ROLE IN CEPHALOPOD EVOLUTION

Abstract:  Numerous plectronocerid nautiloids appear in the Upper Cambrian of China. We have restudied their siphuncular structure, first described some 20 years ago. The siphuncle is characterized by: (1) long and holochoanitic septal necks dorsally but short and recurved necks laterally and ventrally; (2) strongly expanded connecting rings laterally; (3) two calcified layers in each connecting ring, outer spherulitic-prismatic and inner compact, the latter perforated by numerous pore canals; and (4) highly oblique siphuncular segments. The strongly expanded lateral sides of the connecting rings, together with the highly oblique course of the siphuncular segments, considerably enlarged the surface area of the connecting rings in each chamber, thereby increasing the transport capacity of cameral liquid. Thus, from their first appearance, plectronocerid nautiloids had developed a siphuncle for the replacement of cameral liquid with gases, and this system had a better and a more sophisticated design than that seen in stratigraphically younger nautiloids. However, their small orthoconic or slightly cyrtoconic shells were not well adapted for jet-powered swimming.     

Speciation and adaptive radiation of subterranean mole rats, Spalax ehrenbergi superspecies, in Jordan

The major initial mechanism of speciation in subterranean blind mole rats, Spalacidae, is chromosomal, primarily through Robertsonian rearrangements. Here we highlight another scenario of chromosomal rearrangement leading to ecological speciation and adaptive radiation apparently initiated by pericentric inversions and genie divergence to different ecologies in mole rats in Jordan. We analysed karyotype, allozyme, size and ecological diversity across the range of mole rats in Jordan from mesic Irbid in the north to xeric Wadi Musa (Petra region) in the south, a transect of 250 km. We examined mole rats for chromosome ( N =71), size ( N =76), and allozyme ( N =67) diversities, encoded by 32 loci, in 12 populations of the Spalax ehrenbetgi superspecies in Jordan. By a combination of chromosome morphology, genetic distance, body size and ecogeography, we identified four new putative biological species. All species (except two animals in Madaba) share 2 n = 60 but vary in chromosome morphology, caused by pericentric inversions and/or centromeric shifts. The 'north Moav' species is karyotypically polymorphic for 2 n (2 n = 60; including locally also two animals with 2 n = 62). The distribution of the four species is associated with ecogeographical different domains and climatic diversity. Genetic diversity indices were low, but like chromosome arms (NFa) were positively correlated with aridity stress. Discriminant analysis correctly classified 91% of the individuals into the four species utilizing combinatorially chromosome, allozyme and size diversities. It is hypothesized that mole rat evolution underground is intimately associated with climatic diversity stress above ground.     

Analysis of Genetic Diversity at the arom Locus in Isolates of Pneumocystis carinii

ABSTRACT. The DNA sequences of a portion of the 5-enolpyruvyl shikimate phosphate synthase domain of the arom gene, encoding the pentafunctional AROM protein, were determined from isolates of Pneumocystis carinii from five mammalian host species (rat, human, ferret, rabbit and mouse). High levels of genetic divergence were found among P. carinii derived from different hosts species, 7–22% at the DNA sequence level, and 7–26% at the derived amino acid sequence level. Two separate and distinct sequences were isolated from infected ferret lungs. Low levels of divergence were seen in human-derived organisms.     

CONSUMER ACCEPTABILITY OF VEGETABLE SOUPS

The aim of this study was to investigate whether product label information “produced with organic ingredients” and “stabilization technology” affects consumer acceptability of vegetable soups. Three focus group interviews were preliminarily conducted in order to gain information about the appropriate terminology to use in the next consumer test. In all, 109 subjects were recruited by means of a background questionnaire. They were then divided into three groups according to age, gender and soup preference. Each group evaluated three different types of soup in two phases, first blind and then with information. At the end of the second phase, the participants filled in a conjoint analysis questionnaire. The results demonstrated that if consumers were informed that soup is prepared with organic ingredients, they would improve their acceptability scores, whatever the soup type. Stabilization technology information had no effect. Conjoint results revealed that consumers appreciate soups made with organic legumes and cereals and without seasoning. However, differences among subgroups were found.     

Macro-alga population shows low but significant heterogeneity in developmental instability with no detectable association with individual fitness

We studied among-individual variation in developmental instability (DI) and fitness-related parameters in 80 individual plants of Fucus vesiculosus (Phaeophyta). To minimize differential environmental effects, plants were sampled from one environmentally homogenous population. DI was measured as fluctuating asymmetry (FA) of four bilaterally symmetric traits (branch length, receptacle length and width, and bladder width) for an average total of 30 structures per individual. FA levels varied significantly among individual plants, consistent with a coefficient of variation of 0.12 for organism-wide DI or 0.13–0.21 for trait-specific DI. These values are lower than estimates for other organisms, suggesting that the genetic heterogeneity in DI was low. The data provide some evidence for organism-wide DI, but simulations show that organism-wide and trait-specific variation cannot be conclusively separated. Growth rate of branch tips was determined experimentally, demonstrating significant variation among individuals. FA was not significantly correlated with growth rate or with morphological variables associated with fecundity, age, size, and health. At the same time, the signs of all the correlation coefficients were consistent with the expectation of a negative relationship between DI and fitness. The simulations indicated that the correlation between FA and the underlying DI was comparatively strong (high hypothetical repeatability), implying that the lack of significant associations between FA and fitness variables reflected a weak relationship between DI and these fitness parameters. This weak relationship may be related to the low amount of DI variation in the study population.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 277–286.