Population stability and extinction in a social spider Stegodyphus mimosarum (Araneae: Eresidae)

Nests of social spiders in their natural habitat are clustered and colony clusters may be short-lived. Rapid growth and subsequent extinction of colonies and colony clusters are predicted for social spider populations; however, little quantitative data exist on the longevity of colonies. Furthermore, processes that influence the growth and decline of social spider populations are poorly understood. In this study we followed a population of over 550 nests of S. mimosarum from September 1994 to December 1999 and analysed the changes in relation to abiotic (temperature and rainfall) and biotic (parasitism) factors. We observed two years of apparent population stability (1994–1995), during which nest numbers remained high and constant. This was followed in 1996 by a c. 12% decrease in the numbers of active nests. At the end of 1996 there was a mass dispersal event which was followed in 1997 by a steady decline of the population with no further recovery. Thus, the decline was preceded by dispersal and nest failure, indicating that conditions in the population were unfavourable. The population-wide synchrony of these events reflects the seasonally synchronized development in & mimosarum. However, extrinsic factors related to climate did not explain the extreme events of dispersal and population decline. The potential importance of parasitism, on the one hand, and unknown intrinsic factors on the other, should be considered as alternative explanations that remain to be tested.     

Permeability Changes in Senescing Tissue

Measurements of K⁺ leakage and apparent free space (A.F.S.)to ¹⁴C glycerol and ¹⁴C sucrose indicated permeability changesin senescing Phaseolus multiflorus cotyledons, and Arum maculatumspadix. A.F.S. to glycerol was found to increase in two steps,the first of which took place early in development. A comparativestudy of respiration showed that permeability changes occurbefore any changes in the rate of respiration. They are an earlysign of senescence. The similarity of the increasing changesin leakage of K⁺, A.F.S. to glycerol and sucrose, and permeabilityacross the membrane surrounding the osmotic volume in the twodifferent materials suggests that they are of general occurrence.     

Dispersal history of a spider (Stegodyphus lineatus) across contiguous deserts: vicariance and range expansion

Israel marks a crossroads between three continents encompassing several phytogeographical and zoogeographical zones. In this complex area, the flow of species from different biogeographical regions creates opportunities to study how geographical division and colonization routes affect current distribution and structure of resident populations of organisms associated with desert and arid environments, habitats that may have persisted throughout Pleistocene glacial periods. The present paper analyses the population history of the spider Stegodyphus lineatus in the contiguous Negev and Judean deserts in Israel using allozyme and mtDNA variation. The distinct patterns of variation indicate that Judean and Negev populations are vicariant lineages. The residence time was longer in Judea, where populations were more polymorphic for mtDNA, showed isolation by distance and were less structured than in the Negev. The Negev population, possibly linked to other Mediterranean populations of S. lineatus , consisted of two subdivisions derived from a recent eastward expansion across the central Negev watershed. Despite differences in age and level of structure, all lineages show similar dispersal processes dominated by restricted gene flow. The distribution patterns of allozyme and mtDNA markers are unrelated to geographical patterns of precipitation and vegetation. Rather, they follow large-scale topographic features, namely the water divide between Mediterranean and Afro-Syrian rift drainages and between eastern and western Negev drainages.   © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 739–754.     

RNA Dependent DNA Polymerase in C Type Particles from Normal Rat Thymus Cultures

THE isolation and characterization of C type particles released from normal rat thymus cell cultures has been described^{1, 2}. The detection of RNA dependent DNA polymerase activity in these C type particles is reported here. Some properties of the enzymatic activities found in C type particles isolated from normal rat thymus cultures are described and compared with DNA polymerase found in isolated Moloney leukaemia virus (MLV) particles purified from the growth media of rat thymus cultures infected chronically with MLV². The sensitivity to actinomycin D is different in the two kinds of C type particles, suggesting that the DNA polymerases are not identical.     

Intraspecific variability in egg maturation patterns and associated life‐history trade‐offs in a polyembryonic parasitoid wasp

1. Life‐history theory predicts a trade‐off between the resources allocated to reproduction and those allocated to survival. Early maturation of eggs (pro‐ovigeny) is correlated with small body size and low adult longevity in interspecific comparisons among parasitoids, demonstrating this trade‐off. The handful of studies that have tested for similar correlations within species produced conflicting results. 2. Egg maturation patterns and related life‐history traits were studied in the polyembryonic parasitoid wasp, Copidosoma koehleri (Hymenoptera: Encyrtidae). Although the genus Copidosoma was previously reported to be fully pro‐ovigenic, mean egg loads of host‐deprived females almost doubled within their first 6 days of adulthood. 3. The initial egg‐loads of newly emerged females were determined and age‐specific realised fecundity curves were constructed for their clone‐mate twins. The females' initial egg loads increased with body size, but neither body size nor initial egg load was correlated with longevity and fecundity. 4. The variation in initial egg loads was lowest among clone‐mates, intermediate among non‐clone sisters and highest among non‐sister females. The within‐clone variability indicates environmental influences on egg maturation, while the between‐clone variation may be genetically based. 5. Ovaries of host‐deprived females contained fewer eggs at death (at ～29 days) than on day 6. Their egg loads at death were negatively correlated with life span, consistent with reduced egg production and/or egg resorption. Host deprivation prolonged the wasps' life span, suggesting a survival cost to egg maturation and oviposition. 6. It is concluded that adult fecundity and longevity were not traded off with pre‐adult egg maturation.     

Effect of spatial pattern and microhabitat on pit construction and relocation in Myrmeleon hyalinus (Neuroptera: Myrmeleontidae) larvae

Abstract.  1. In two sets of enclosure experiments, we studied the spatial pattern, relocation rates, pit construction rates, and microhabitat preference of Myrmeleon hyalinus larvae.
2. We showed that M. hyalinus larvae actively prefer shady sites and often relocate to shady areas when exposed to the sun. This behaviour may constitute a life-saving strategy in desert environments.
3. The initial spatial pattern in a cluster of antlion larvae did not affect the final pattern, relocation rate, or the pathway moved while relocating. We interpret this finding to mean that the spatial pattern of M. hyalinus larvae is mainly influenced by factors operating at large time-scales, such as exploitation competition and physical-microclimatological constraints, rather than those operating at shorter time-scales, such as interference competition.
4. In contrast, the likelihood of pit construction was positively correlated with nearest neighbour distance, possibly as a result of interference competition.
5. Pit construction rates were constant throughout the experiment, while relocation rates decreased with time.
6. Contrary to previous studies, we found no correlation between body mass and spatial position inside the cluster, suggesting that these differences are the products of slower processes (e.g. exploitation and body condition).     

Salt activation and inhibition of membrane ATPase from roots of the halophyte Atriplex nummularia

Abstract Salt-stimulated ATPase activity in membrane preparations obtained from roots of Atriplex nummularia Lindl. at pH 5 was not suscep-tible to inhibition by KC1 or NaCl up to 450 mol m-3 but showed a broad peak of activity between 150 and 300 mol m^?3. At pH 8 stimulation occurred at 50 mol m^?3 but concentrations above 100 mol m^?3 depressed activity below the level of the MgATPase activity. By contrast, preparations from roots of Pisum sativum L. at pH 5 showed maximal stimulation at 25 to 50 mol m^?3 of NaCl or KC1; concentrations higher than 150 mol m^?3 depressed activity below that of MgATPase activity. At pH 8 maximal stimulation was observed at 5 to 10 mol m^?3 NaCl or KC1 while the threshold for inhibition was reduced to 15 mol m^?3. With increasing salt concentrations the pH profiles for NaCl stimulation of Atriplex ATPase activity (expressed as the difference between treatment and control) showed a progressive displacement of the apparent optimum towards lower pH. The shift was not apparent when stimulation was expressed as a percentage of MgATPase activity. This shift may be accounted for if NaCl stimulated the monovalent salt-activated ATPase activity but simultaneously inhibited MgATPase activity.     

Species concepts and the determination of historic gene flow patterns in the Eulemur fulvus (Brown Lemur) complex

Eulmur fulvus , a complex comprising six subspecies, is a classic example of species status conferred through evolutionary taxonomy. We used the phylogcnctic species concept as an alternative method to the biological species concept for determining historic patterns of gene flow between the various E. julvus subspecies and for conferring species status. In this paper, we used population aggregation analysis to determine the proper species partitions and cladistic analysis to reconstruct the evolutionary relationships of the different populations in the Eulemur fulvus complex. We sequenced three mtDNA gene regions (d-loop, 12S, and cyt-b) and one nuclear region, casein kinase, for a total of 1247 bases. Through population aggregation analysis, we determined that the E. fulvus complex should be split into three units; one unit supported by six diagnostic sites comprising E.f. albocollans , one unit supported by three diagnostic sites comprising E.f. collaris , and one unit supported by two diagnostic sites comprising the four other subspecies. Although all six subspecies in the E. julvus complex share a common ancestor, we found in our cladistic analysis that E. J. collaris and E. j. albocollans share a common ancestor that more recently split off from the common ancestor of the four other E. fulvus subspecies.     

The Interrelation between the Effects of 2,4-Dinitrophenol and of Substrate Concentration on the Rate of Exogenous Respiration

1. The specific activity of the CO₂ evolved by sunflower hypocotylsegments supplied with labelled glucose or glutamic acid isrelated to the external concentration by a rectangular hyperbolaover a concentration range of approx. 2–60 mM. The overallrespiration rate over this range is approximately 15 per cent.above that of a buffer control, and rises only slightly withincreasing external concentration. 2. The curve for total exogenous substrate respired is alsoclose to a rectangular hyperbola over this concentration range. 3. 2,4-dinitrophenol (DNP) reduces the slope of the hyperbolafor specific activity, but not its maximum value. Increasingthe glucose concentration while maintaining the DNP concentrationconstant reduces the degree of inhibition. 4. The effect of DNP on absolute amount of exogenous substraterespired depends on the external concentration of the substrate.At lower concentrations, absolute exogenous respiration is inhibited:at higher concentrations, it is stimulated. 5. The results have been analysed with the object of determiningwhether the respiratory sites lie in the ‘sugar free space’of the cell. Kinetic analysis indicates (a) that exogenous substratesdo not diffuse to these sites through an appreciable diffusionbarrier; (b) that there is no evidence for an active transportstep; and (c) that the data accord well with the view that exogenoussubstrates diffuse freely to the respiratory sites where theycompete on equal terms with endogenous substrates.