Resource dynamic plays a key role in regional fluctuations of the spruce bark beetles Ips typographus

Abstract 1 We analysed time series of spruce bark beetles (N_t) caught in pheromone traps from 1979 to 2000 in approximately 100 localities throughout south‐east Norway. 2 The analysis was performed at two spatial scales (whole area and 12 subregions), and included additional analyses of the time‐series sequences before and after a large windfelling (1987) that appeared to induce a shift in the dynamics. 3 Regression of R_t (logarithmic per‐capita growth rate) on N_{t ? d} indicated that the endogenous dynamics were dominated by lag 1 density dependence. This was particularly so in the sequence after the large windfelling (R² = 0.79), probably due to intraspecific competition for breeding substrate. 4 The sequence before the windfelling (1979–1987) was declining without significant density dependence. We suggest this to be a transition period, reflecting a drop in carrying capacity due to depletion of susceptible trees during the preceding outbreak period (1970s) and a drop in beetle number to below the density required to kill trees. 5 Windfelling (W_{t ? 1}) appears to be an important predictor of the dynamics; however, it was difficult to evaluate the statistical significance of this factor due to only one large windfall event. 6 The weak influence of drought stress (D_{t ? 1}) could be due to the absence of severe drought periods within the time series.     

A Dominant-Negative Mutant of rab5 Inhibits Infection of Cells by Foot-and-Mouth Disease Virus: Implications for Virus Entry

Foot-and-mouth disease virus (FMDV) can use a number of different integrins (αvβ1, αvβ3, αvβ6, and αvβ8) as receptors to initiate infection. Infection mediated by αvβ6 is known to occur by clathrin-mediated endocytosis and is dependent on the acidic pH within endosomes. On internalization, virus is detected rapidly in early endosomes (EE) and subsequently in perinuclear recycling endosomes (PNRE), but not in late endosomal compartments. Due to the extreme sensitivity of FMDV to acidic pH, it is thought that EE can provide a pH low enough for infection to occur; however, definitive proof that infection takes place from within these compartments is still lacking. Here we have investigated the intracellular transport steps required for FMDV infection of IBRS-2 cells, which express αvβ8 as their FMDV receptor. These experiments confirmed that FMDV infection mediated by αvβ8 is also dependent on clathrin-mediate endocytosis and an acidic pH within endosomes. Also, the effect on FMDV infection of dominant-negative (DN) mutants of cellular rab proteins that regulate endosomal traffic was examined. Expression of DN rab5 reduced the number of FMDV-infected cells by 80%, while expression of DN rab4 or DN rab7 had virtually no effect on infection. Expression of DN rab11 inhibited infection by FMDV, albeit to a small extent (∼35%). These results demonstrate that FMDV infection takes place predominantly from within EE and does not require virus trafficking to the late endosomal compartments. However, our results suggest that infection may not be exclusive to EE and that a small amount of infection could occur from within PNRE.Foot-and-mouth disease virus (FMDV) is a member of the Aphthovirus genus of the family Picornaviridae and the etiological agent responsible for FMD, an economically important and severe vesicular condition of cloven-hoofed animals, including cattle, pigs, sheep, and goats (2). The mature virus particle consists of a positive-sense single-stranded RNA genome (vRNA) enclosed within a nonenveloped icosahedral capsid formed from 60 copies each of four virus-encoded proteins, VP1 to VP4 (1).The initial stage of FMDV infection is virus binding to cell surface integrins via a highly conserved RGD motif located on the GH loop of VP1. A number of different species of RGD-binding integrins (αvβ1, αvβ3, αvβ6, and αvβ8) have been reported to serve as receptors for FMDV (5, 23-26). Using pharmacological and dominant-negative (DN) inhibitors of specific endocytic pathways in combination with immunofluorescence confocal microscopy, the cell entry pathway used by FMDV has been determined for αvβ6-expressing cells (6, 36). These studies established that infection occurs by clathrin-mediated endocytosis and is dependent on the acidic pH within endosomes, which serves as the trigger for capsid disassembly and translocation of the vRNA across the endosomal membrane into the cytosol. Internalized virus was detected rapidly in early endosomes (EE) and subsequently in perinuclear recycling endosomes (PNRE), but not in late endosomes (LE) or lysosomes (Lys) (the late endosomal compartments). Due to the extreme sensitivity of FMDV to acidic pH (15), it is thought that EE can provide a pH low enough for virus disassembly to occur; however, definitive proof that infection takes place from within EE is still lacking. For example, the possibility cannot be excluded that a productive infection requires virus transport to late endosomal compartments, where, following capsid disassembly and viral genome transfer into the cytosol, the capsid proteins are rapidly degraded.rab proteins control multiple membrane trafficking events in the cell. They are members of the ras superfamily of small GTP-binding proteins and cycle between active GTP- and inactive GDP-bound states (22, 38, 39, 47, 50). Conversion between these states is regulated by guanine nucleotide exchange factors, which stimulate the binding of GTP, and GTPase-activating proteins that which accelerate GTP hydrolysis. Activated rab proteins are recruited onto membrane-bounded compartments where they regulate many steps of vesicle trafficking, including vesicle budding, movement, tethering, and fusion (35, 61). Each rab is recruited to a specific compartment and functions through interactions with specific effectors that mediate the downstream rab-associated functions (39). In mammalian cells, at least 12 rab proteins that regulate trafficking through the endosomal pathway have been identified (27). Of these, rab4, rab5, rab7, and rab11 play major roles in endocytic vesicle trafficking. rab5 is present on EE and regulates transport of incoming endocytic vesicles from the plasma membrane (PM) to EE and homotypic EE fusion events (3, 8, 10, 20, 30, 44, 52). Both rab4 and rab11 are regulators of receptor recycling from EE back to the PM (34); rab4 is localized primarily to EE and regulates rapid recycling directly back to the PM (16, 45, 48, 51, 56), and rab11 is localized primarily to the PNRE and regulates a slower recycling pathway through these compartments (21, 43, 54, 60). In addition rab11 also regulates membrane traffic from endocytic recycling compartments to the trans-Golgi network (55). rab7 is located primarily on LE and regulates traffic from EE to LE and between LE and Lys (7, 9, 18, 32, 40, 58, 59). The unique targeting of rab proteins to distinct cellular compartments and their specificity as regulators of vesicular trafficking has made them important tools for studying endocytosis. For example, expression of DN or constitutively active mutants of rab proteins that regulate endosomal traffic has been used to identify the intracellular transport steps that are required for infection by a number of different viruses (13, 14, 28, 31, 41, 42, 49, 53, 57, 59).Here we have investigated the intracellular transport steps required for FMDV infection using porcine IBRS-2 cells, which are derived from a natural host of FMDV. IBRS-2 cells use αvβ8, and not αvβ6, as the major FMDV receptor (11). Our initial experiments confirmed that FMDV infection mediated by αvβ8 is dependent on clathrin-mediated endocytosis and on an acidic pH within endosomes. The effect on FMDV infection within IBRS-2 cells of DN mutants of cellular rab proteins that regulate endosomal traffic was examined. These experiments show that rab5 is needed for FMDV infection, as expression of DN rab5 reduced the number of FMDV-infected cells by ∼80%. In contrast, expression of either DN rab4 or DN rab7 had virtually no effect on infection. Expression of DN rab11 inhibited infection by FMDV, albeit to a small extent (∼35%). These results demonstrate that FMDV infection takes place predominantly from within EE and does not require virus trafficking to the late endosomal compartments. However, our results suggest that infection may not be exclusive to EE and that a small amount of infection could occur from within PNRE.     

Feedback structures of northern small rodent populations

Regular oscillations of northern small rodents (lemmings, voles and mice) have fascinated ecologists for decades. In particular, cycles exhibited by Fennoscandian voles have inspired population ecologists to propose several hypotheses for their underlying causes. Although there is now some agreement that the interaction with specialist predators is involved, many aspects remain enigmatic, one being the precise ecological mechanism involved in the first-order feedback effect (i.e. direct density dependence). In this paper we evaluate the relative importance of first and second-order negative feedback on small rodent dynamics in 64 data sets, assess the evidence of non-linearity in the feedback structure, and look for similarities and/or differences between species and places. A clear feature of our analysis was the highly consistent pattern of first-order dynamics across species and locations, suggesting the importance of intra-specific interactions independent of local environmental conditions. Second-order feedback generally showed a large degree of variation and appears to be strongly dependent on environmental conditions and locality. There seems to be no consistent latitudinal pattern or non-linearity in the feedback responses. We conclude that northern small rodent populations are basically regulated by both highly consistent first-order feedback (e.g. intra-specific competition, functional responses of generalist predators) and less consistent, site-specific second-order effects (e.g. numerical responses of specialist predators or food plants).     

Elastic fibers in the anulus fibrosus of the dog intervertebral disc

A light microscopic investigation of the anulus fibrosus in cervical intervertebral discs of the dog was conducted to ascertain the arrangement and distribution of elastic fibers. Elastic fibers were observed in all lamellae of the anulus fibrosus. However, collagenous fibers were the predominant type of connective tissue fiber, and elastic fibers were randomly dispersed among them. Intralamellar (collagenous and elastic) fibers were vertically and obliquely oriented in both superficial and deep lamellae of the anulus fibrosus. All intralamellar fibers were densely and regularly arranged in superficial lamellae, but they were more loosely organized in deep lamellae. A narrow border of interlamellar, elastic fibers was observed between broader, contiguous lamellae in the superficial zone of the anulus fibrosus. Interlamellar elastic fibers wer vertically and obliquely arranged in superficial lamellae; however, they were radially oriented in deep lamellae. The deepest lamella of the anulus fibrosus consisted of a loose, three-dimensional network of intermeshing collagenous and elastic fibers. These observations suggest that elastic fibers are integral components of the articular and shock absorption mechanisms of the anulus fibrosus, and the cervical intervertebral disc of the dog is a suitable model for experimental investigation of the role of elastic fibers in intervertebral disc herniation.     

Guinea-pig Vocalizations: Their Structure,Causation and Function

Feeding, mating behaviour, communication, breeding biology, and development of Pipa carvalhoi are described. Like in other species of the genus Pipa, the eggs are laid onto the ♀ back during several turnovers, and this behaviour cau be observed even in the absence of ♂♂ Acoustic communication involves a mating call and a combat call. The biology and behaviour of Pipa carvalhoi are compared to that of other pipid frogs, and it is suggested that the specialized breeding biology of the genus Pipa evolved as an adaptation to the life in small ponds and ditches which are rich in nutrients but poor in oxygen.