Maturing and Coordination of Web-Building Activity

Experiments are reported in which 114 Zygiella x-notata Cl.spiderlings were taken out of the cocoon before the time atwhich they normally left (2 weeks after the second molt); 67were placed on wooden frames and 47 on wire frames. Both groupsbuilt partial, irregular thread-patterns at first, and, as theygrew older, constructed more and more regular geometric orb-webs:the transition can be traced through several stages. The shapeof the web, particularly the presence of the free-sector, wasdependent on the frame; webs built in a circular wire framelacked the free-sector. It is assumed that the accomplishmentof full, regular orb webs is essentially based on the progressivehistological differentiation of the central nervous system inthe spiderlings during the developmental phase under observation;the wire frame could influence the shape of the web throughmaking construction of a retreat difficult.     

蜘蛛位置对成功捕获猎物和球型网图案的影响

静坐在球型网的中心,蜘蛛可能遭受天敌的攻击并暴露在不利的天气条件下,如风和雨。然而,栖居于网的中心使蜘蛛比隐藏在隐蔽场所中的蜘蛛能更迅速地察觉并捕获猎物,这是因为猎物的位置仅能被位于网中心的蜘蛛所确定。对在隐蔽场所中的蜘蛛而言,提高对猎物捕获率的方式之一是尽量减少隐蔽所与网中心的距离。而且,网中心与隐蔽所之间较短的距离使蜘蛛能更迅速地逃离危险境况。我使用既在网中心、又在隐蔽场所的硬类肥蛛(Larinioides sclopetarius Clerck),来检验这两种行为如何影响对猎物的捕获成功率。隐藏在隐蔽场所中的蜘蛛更经常忽略猎物,使猎物也有比较多的逃离机会,这样,与在网中心的蜘蛛相比,猎物的损失率就更高。另外,研究了隐蔽场所的位置对球型网图案的影响。在大多数球型网中,网中心上方的区域比网下方小,丝也比较少,形成了结构不对称的网;隐蔽场所通常在网的上方。当隐蔽场所的位置在实验中被倒转时,就形成了非典型的球型网。最后,L．sclopetarius建造的网有很突出的边缘非对称性,与隐蔽场所相邻的区域面积较小,而远离隐蔽场所的区域面积较大,这也可解释为减少了隐蔽场所和网中心之间的距离[动物学报50(4)：559-565．2004]。     

Phenotypic plasticity of larval retreat design in a net-spinning caddisfly

Larval Macrostemum carolina caddisflies construct silken catchnetswithin protective retreats, often on submerged trees and branches(i.e., snags). In the Savannah River, M. carolina larvae constructthree distinct retreats that differ in the configuration ofthe water entrance hole: (1) at the end of a silken tube, (2)flush with the top of the retreat, and (3) backed by a 180-degreesilken backstop. To identify the proximate mechanism mediatingthis retreat polymorphism, we removed larvae of known phenotypefrom their original retreats and brought them into the laboratory,allowing them to construct new retreats. We found that (1) larvaecan construct more than one type of retreat, so variation inthis behavior is not under strict genetic control; (2) larvaedo not preferentially reconstruct their original retreat design,so these alternative behaviors apparently exhibit little heritability;and (3) larvae primarily construct each phenotype in a particularmicrohabitat (i.e., "tube" and "backstop" retreats are principallyconstructed on the downstream half of the snag, and "flush"retreats on the upstream–bottom quadrant). Therefore,the retreat polymorphism in M. carolina is phenotypically plasticand is controlled by microhabitat location or a correlated environmentalvariable. Most net-spinning caddisflies construct their netsin fairly specific microhabitats. However, behavioral plasticityallows M. carolina larvae to construct retreats all around asnag, thereby reducing potentially intense competition for spacewith other net-spinning caddisflies. Consequently, this maybe the ultimate reason this polymorphism evolved.     

Patch exploitation, group foraging, and unequal competitors

Charnov's (1976) marginal value theorem, MVT, addresses howlong a forager should stay in a patch of prey to maximize itsgain. Information-sharing models of group foraging suggest thatindividuals should join groups to improve their patch-findingrate. This is achievable if group members share informationabout the location of food patches. The determinants of theMVT are searching time and cumulative gain against time in apatch, those of the group foraging models are searching time,group size, and individual differences in ability to monopolizethe prey found. After combining the MVT and information-sharingmodels we explore the consequences of unequal competitors (good,G, and poor, P) foraging in groups. Under this domain G andP differ in their accumulated harvest against time in a patch.When the gain function of P is obtained by mere scaling of thatof G, optimal patch residence times for individuals of the twophenotypes do not differ. However, if the gain functions ofG and P cannot be derived from each other by a constant scalingmultiplier, the optimal patch times for G and P are not necessarilythe same. Under these conditions the model suggests that foraginggroups should become assorted by foraging ability.     

Alternative Reproductive Tactics in Spiders

The comparative study of reproduction at the level of populationand individual is a relatively recent development in spiderresearch. Such study is necessary to describe and examine alternativereproductive tactics. Female spider tactics are related to adaptationsfor a carnivorous mode of feeding. Being the larger of the sexes,the female has the alternative of mating with or preying uponattending males. In web building spiders, which are generallysolitary, other female alternatives are related to characteristicsof a web used in prey capture. These alternatives include differentresponses when defending the web, and individually buildingthe web so that it does or does not contact another. Tacticsmay vary in communal species which build a sheet-like structure,as females may remain in the colony or emigrate and establisha small web. Male spiders usually search for females, and matingoccurs on or near a female retreat or web. A male may show differentalternatives in mate searching, demonstrate various courtshipand copulatory tactics, copulate or feed on the female's preywhile she feeds, and guard the female after mating or departand search for another female. Certain characteristics of femalesare related to these male alternatives, these characteristicsbeing: larger size and longer life expectancy as compared withthe male, carnivorous feeding, and sexual receptivity. Maleweb spiders may also use alternatives while defending positionon the female web. These alternatives are related to the designand placement of the web, and occasional web abandonment bythe female. Relevant literature is reviewed and research suggested.     

Food Web Structure in a Harsh Glacier-Fed River

Glacier retreat is occurring across the world, and associated river ecosystems are expected to respond more rapidly than those in flowing waters in other regions. The river environment directly downstream of a glacier snout is characterised by extreme low water temperature and unstable channel sediments but these habitats may become rarer with widespread glacier retreat. In these extreme environments food web dynamics have been little studied, yet they could offer opportunities to test food web theories using highly resolved food webs owing to their low taxonomic richness. This study examined the interactions of macroinvertebrate and diatom taxa in the Ödenwinkelkees river, Austrian central Alps between 2006 and 2011. The webs were characterised by low taxon richness (13–22), highly connected individuals (directed connectance up to 0.19) and short mean food chain length (2.00–2.36). The dominant macroinvertebrates were members of the Chironomidae genus Diamesa and had an omnivorous diet rich in detritus and diatoms as well as other Chironomidae. Simuliidae (typically detritivorous filterers) had a diet rich in diatoms but also showed evidence of predation on Chironomidae larvae. Food webs showed strong species-averaged and individual size structuring but mass-abundance scaling coefficients were larger than those predicted by metabolic theory, perhaps due to a combination of spatial averaging effects of patchily distributed consumers and resources, and/or consumers deriving unquantified resources from microorganisms attached to the large amounts of ingested rock fragments. Comparison of food web structural metrics with those from 62 published river webs suggest these glacier-fed river food web properties were extreme but in line with general food web scaling predictions, a finding which could prove useful to forecast the effects of anticipated future glacier retreat on the structure of aquatic food webs.     

Untangling the Tangle-Web: Web Construction Behavior of the Comb-Footed Spider Steatoda triangulosa and Comments on Phylogenetic Implications (Araneae: Theridiidae)

Theridiidae typically construct a three-dimensional web often described as irregular. The web consists of a supporting structure and lines under tension termed gumfooted lines. We used automated methods to observe web construction in the theridiid Steatoda triangulosa under laboratory conditions. Web construction lasted several nights. After orientation, spiders built a three-dimensional structure of several threads radiating sideways and downward from the retreat. To build gumfooted lines, they started from the retreat, moved along a structural thread, then dropped down to attach the thread to the lower substrate. On returning, they coated the lowest part of the thread with viscid silk before moving up along the same thread back to the structural thread. They then continued moving along the same structural thread to drop down again to build the next gumfooted line. This behavior was continued until the spiders had built a series of gumfooted lines (a bout). There were regular intervals between the construction of two bouts. Thus, a single web included many bouts built in different stages. We show that gumfooted lines are not homologues to sticky web elements of orb-weavers and present new synapomorphic characters that support the monophyly of Theridiidae + Nesticidae and the monophyly of araneoid sheet web weavers. Further, the time allocation pattern for different behavioral stages and the fine structure of a gumfooted line are presented.     

Previous foraging success influences web building in the spider Stegodyphus lineatus (Eresidae)

Stegodyphus lineatus (Eresidae) is a desert spider that buildsan aerial capture web on bushes in the Negev desert in southernIsrael. Web building for spiders is costly in energy, time,and risk of predation. Spiders should trade-off these costswith the benefits in terms of prey capture. We tested the hypothesisthat the previous foraging success of the spider influencesthe effort invested in foraging. Specifically, we asked whetheran increase in food intake causes spiders to reduce web renewalactivity and web size. Alternatively, time constraints on foragingand development, resulting from a short growing season, couldinduce spiders to continue foraging even when supplemented withprey. The cost of web building was measured as time and massloss. To build an average size web (about 150 cm²), we calculatedthat a spider requires 6 h and that spiders lose 3%-7% of their weight.In field experiments, spiders responded differently to food supplementationin 2 different years. In 1994, they improved their condition comparedto individuals whose webs were removed to reduce foraging opportunitiesand compared to control spiders. In 1995, spiders tested earlier inthe season than the previous year did not improve their conditionin response to prey supplementation. Nonetheless, in both years, food-supplementedspiders built significantly smaller webs than food-deprived andcontrol spiders. This result was confirmed in a laboratory experiment whereprey intake was controlled. We conclude that for S. lineatus immediateforaging risks outweigh the potential time constraints on foraging.     

The benefits of stealing from a predator: foraging rates, predation risk, and intraspecific aggression in the kleptoparasitic spider Argyrodes antipodiana

In the trade-off between food and safety, the role of aggressiveintraspecific interactions has not been extensively examined.Here I present information on this system using a kleptoparasiticspider, Argyrodts antipodiana, and its host spider and potentialpredator, Eriophora pustulosa. A. antipodiana can feed eitherat a potentially dangerous site (the hub of its host's web withthe host), or at a relatively safe site (on food bundles aroundthe edge of the host's web). I found that A. antipodiana cangain food very quickly when feeding with the host, apparentlyby exploiting the host's ability to digest the prey. Thus A.antipodiana follows predictions based on foraging models inthat it accepts a higher predation risk at the hub because ofthe higher food payoff. A. antipodiana also aggressively competesfor access to more food. However, aggressive competition increasesthe predation risk from the host, especially at tile hub wherethe host is very close. Consequently, A. antipodiana modifiesits level of intraspecific aggressiveness in accordance withits position on the web: at the hub, where the cost of aggressionis high (due to predation risk), A. antipodiana reduces itsaggressiveness, but it is aggressive away from the hub whencompeting for food bundles. The ability of A. antipodiana tochange interaction intensity as a function of its position onthe web enables it to exploit a rich, but risky, food sourceand provides a new angle for examining food and safety tradeoffs in light of intraspecific competition for food     

The mechanisms of interference competition: two experiments on foraging waders

Models of population dynamics that include interference competitionhave often been applied to foraging waders and less so to otherforagers, even though these models are, in principle, generallyapplicable. At present, however, it is still unclear whetherinterference competition is of importance for foraging waders.To support this idea experimental evidence and knowledge ofthe mechanisms underlying interference effects are required.We experimentally determined the relationship between foragerdensity and foraging success in two wader species: the red knot(Calidris canutus) and the ruddy turnstone (Arenaria interpres).With each of the two species, we conducted an experiment consistingof 300 one-min trials. In these trials we scored the behaviorand the foraging success of focal individuals at specific combinationsof bird and prey density. Irrespective of prey density, individualsof both species discovered fewer prey items at higher bird densities.Despite this, only in turnstones did intake rates decline withincreasing bird density. Knots compensated for a lower prey-discoveryrate by rejecting fewer prey items at higher bird densities.In knots, bird density had a complex, nonmonotonic effect onthe time spent vigilant and searching. In turnstones the maineffect of increased bird density was a reduction in the prey-encounterrate, that is, the reward per unit search time. Effects on thetime spent vigilant and the time spent searching were less pronouncedthan in knots. Thus, the mechanistic basis of the effects ofbird density was complex for each of the two species and differedbetween them.     

Webs of theridiid spiders: construction, structure and evolution

Understanding the web construction behaviour of theridiid (comb-footed) spiders is fundamental to formulating specific evolutionary hypotheses and predictions regarding the reduction of orb-webs. We describe for the first time in detail the web construction behaviour of Achaearanea tepidariorum , Latrodectus geometricus , Theridion sisyphium and T. varians as well as webs of a range of other theridiids. In our survey we distinguish four major web types. Among webs with gumfooted lines, we distinguish between webs with a central retreat ( Achaearanea -type) and those with a peripheral retreat ( Latrodectus -type). Among webs without gumfooted lines, we distinguish between those which contain viscid silk ( Theridion -type) and those with a sheet-like structure, which do not ( Coleosoma -type). Theridiid gumfoot-webs consist of frame lines that anchor them to surroundings and support threads which possess viscid silk. Building of gumfooted lines constitutes a unique stereotyped behaviour and is most probably homologous for Nesticidae and Theridiidae. Webs remained in place for extended periods and were expanded and repaired, but no regular pattern of replacement was observed. We suggest that the cost of producing and maintaining viscid silk might have led to web reduction, at least in theridiids.  © 2003 The Linnean Society of London. Biological Journal of the Linnean Society , 2003, 78 , 293−305.     

Song matching, overlapping, and switching in the banded wren: the sender's perspective

Interpreting receiver responses to on-territory playback ofaggressive signals is problematic. One solution is to combinesuch receiver-perspective experiments with a sender-perspectiveexperiment that allows subjects to demonstrate how their choiceof singing strategies is associated with their approach behavior.Here we report the results of a sender-perspective study onthe banded wren (Thryothorus pleurostictus) and combine informationon context and results of previous receiver-perspective experimentsto clarify function. Territorial males were presented with a5-min playback consisting of song types present in their repertoire.We assessed the degree to which the subjects' song-matchingrate, overlapping rate, and song-type versatility were correlatedwith their approach latency, closeness of approach, latencyto first retreat, and time spent close to the speaker. Maleage, breeding stage, and features of the playback stimuli werealso considered. Song matching was associated with rapid andclose approach, consistent with the receiver-perspective interpretationof type matching as a conventional signal of aggressive motivation.Overlapping was associated with earlier retreat and togetherwith the aversive receiver response to our previous overlappingplayback experiment suggests that overlapping is a defensivewithdrawal signal. High versatility was associated with slowerfirst retreat from the speaker and high levels of reciprocalmatching between subject and playback. Males with fledglingssang with particularly low versatility and approached the speakeraggressively, whereas males with nestlings overlapped more andretreated quickly. Finally, older males matched more but overlappedless.     

Wasp Attacks and Spider Defence in the Orb Weaving Species <Emphasis Type="Italic">Zygiella x-notata</Emphasis>

Predator–prey relationships are generally based on arm-race. Wasps and spiders are both predators, which could be potential prey for each other. The orb weaver spider Zygiella x-notata is sometimes a prey for the wasp Vespula germanica. We observed the wasp hunting behaviour under natural conditions, and we tested the influence of the spider’s behaviour on the wasp attack success. Wasps were active predators during the reproductive period of the spider. Results showed that wasps located more easily male spiders than females particularly when they were engaged in mate guarding. Female location depended on the presence of a web, but also of prey or prey remains in the web. On the other hand, their location depend neither on the characteristics and the position of the retreat in the environment nor on the size of the web. After location, males were more often captured than females whatever their behaviour (mate guarding or not). Presence of prey remains or prey in the web did not increase the risk for the spider to be captured. There was also no influence of the retreat’s characteristics or of its position in the habitat on the risk for the spider to be captured; but wasp successful attacks were less numerous when silk was present around the entrance of the retreat or when the spider was completely inside. As prey and prey remains favoured location of spiders by the wasps, we tested spider web cleaning behaviour as a response to wasp predatory pressure. By throwing small polystyrene pellets in the webs, we observed that more 80% of the spiders rejected the pellets in less than one minute. Our data indicated that wasps were significant predators of Z. x-notata and wasp attack could have been a selective pressure that had favoured spider defensive behaviours such as web cleaning.     

Hunting Behavior in the Ctenizidae

The most primitive way of hunting in Mygalomorph spiders seemsto be the free roaming and catching of encountered prey Theraphosidae.The trap-door spiders Ctenizidae, Actinopodidae and Barychelidawhich are entirely sedentary, lie in wait behind the trap-doorand leap at prey that happens to pass close to the door. Somespecies spin radial silk threads outside the door which functionas stumbleor signal-lines, and some Australian species use grassblades and other litter in the same way. A further evolutionarystep leads to species which do not build a trap-door but crowntheir burrow by a funnel-shaped web. The Dipluridae finallyare real web-builders, which depend on a sheet-web to catchtheir prey. Generally they do not dig a burrow but hide in asmall retreat from which a funnel-web leads to the net. With a few exceptions Ctenizidae are entirely nocturnal. Theirrhythm of activity has been analyzed. The "Zeitgeber" is thedaylight during the last half hour before sunset. Most trapdoorspiders never leave their burrow during their whole life. Theyneed three to four years from hatching to become adults. Adultmales die during or at the end of the restricted mating-season;they take no food when adult. Females, which undergo post-adultmolts, can probably live for 15–20 years. Nemesia caementaria, like most other species, hunts during thewhole night. The mean time of activity is about Si/o hours,consisting of periods of lying in wait and periods of intermediaterests. The spiders make an average of three leaps per nightto catch a prey, but only about 10% of all bounds are successful.A hungry animal, lurking in vain, shows unmotivated leaps. The effects of light, moisture, and temperature on hunting activityare analyzed. Ctenizidae hunt during autumn, winter, and springbut interrupt their activity in summer for an estivation whichlasts usually two months. The females of some species capture the male after mating andeat him; others never attack him. This difference in behaviorlias repercussions on reproduction. Among certain species the young nymphs of the third instar refuseall food until they have made their own burrow and can huntby themselves. The young of other species stay with the motherfor one year and leave her at the fifth or sixth instar to maketheir own burrow. The young of Nemesia caementaria can remainin the burrow of the mother until they are almost adult, i.e.,for two or three years, and feed on the prey the mother hascaught. The behavior of Ctenizidae can be grouped. Some species lurkbehind the closed or almost closed trap-door. Another groupopens the trap-door and puts the pedipalpi and the two anteriorpairs of legs radially out onto the rim of the burrow, whilethe cephalothorax is hidden behind the trap-door. A third groupspins threads of silk radially about the entrance and uses themas signal-lines. A fourth group can come out and pursue theprey, then drags it to the trap-door and into the burrow. The nature of the prey depends on the bio tope. The Ctenizidaefeed almost exclusively on insects, mainly ants and beetles;in the laboratory crickets are accepted as prey. Ctenizidae have no tarsal organ. They have different types oftrichobothria, transversal and longitudinal slit-organs, andlyriform organs. With these three kinds of sense-organs, thefunctions of which are not clearly understood, the trap-doorspiders are able to perceive the approach of prey, to judgeits distance from the trap-door, and to locate it in direction.They seem to have an organ of smell, since certain groups ofinsects are repulsive to them. Sight is not used for hunting.     

Various Aspects of the Biology of Agelena consociata Denis when Bred in the Laboratory

SYNOPSIS. Agelena consociata Denis, which Chauvin discoveredin Gabon, when put in a laboratory, weaves nests which are 2m² and consist of three different parts: shelters, a web, andvertical threads used as a snare. The snare stops insects intheir flight and causes them to fall into the web which thespiders use as their hunting field. These spiders have a nocturnalactivity which can be divided into two successive periods: afirst stage during which the spiders weave vertical threads,and a second stage of general activity. Hunting and eating are done in common. These activities andthe relations between the individuals which they involve, showin a definite way the social characteristics of these spiders. Eating favors an exchange of chemical substance between theindividuals, but we have not been able to determine the exactpart played by such an exchange. As study proceeds, we shall try to make clear the relationshipsbetween the individuals inside the society. We shall analyzegroup effects on physiology and behavior, comparing them tothose found for Agelena labyrinthica.     

Photoperiod and Reproduction in Lobsters (Homarus)

SYNOPSIS. Photoperiodic control of lobster (Homarus) ovipositionranges from none in the European species (H. gammarus) to atwo-phase requirement in some populations of H. americanus.In the inshore population from Massachusetts two to three monthsof shortday photoperiod appear necessary to condition the ovaryfor final vitellogenesis following long-day onset (LDO). Thestimulus of LDO is only effective near the time of molt. Ifmolt follows LDO within 120 days, egg extrusion follows themolt in about 80 days. If LDO follows the molt, extrusion occursin about 125 days. Extrusion delayed in this way delays thefollowing molt, which is also delayed by the retention of eggson the pleopods. In lobsters from Prince Edward Island the photoperiodic responseseen at laboratory temperatures (ca. 14°C) appears to besubordinated to a response to other cues, probably temperature,when females are held on a near-natural temperature regime withwinter minimum of 2°C characteristic of inshore environments.H. americanus from the migratory outer continental shelf populationexperience winter temperatures rarely lower than 8°C andprobably require photoperiodic control to initiate migrationas well as vitellogenesis. The photoperiodic response may haveoriginated in offshore populations during the Pleistocene andspread to more northerly inshore areas as habitat opened afterthe retreat of the continental ice sheet.     

Sea ice phenology and timing of primary production pulses in the Arctic Ocean

Arctic organisms are adapted to the strong seasonality of environmental forcing. A small timing mismatch between biological processes and the environment could potentially have significant consequences for the entire food web. Climate warming causes shrinking ice coverage and earlier ice retreat in the Arctic, which is likely to change the timing of primary production. In this study, we test predictions on the interactions among sea ice phenology and production timing of ice algae and pelagic phytoplankton. We do so using the following (1) a synthesis of available satellite observation data; and (2) the application of a coupled ice‐ocean ecosystem model. The data and model results suggest that, over a large portion of the Arctic marginal seas, the timing variability in ice retreat at a specific location has a strong impact on the timing variability in pelagic phytoplankton peaks, but weak or no impact on the timing of ice‐algae peaks in those regions. The model predicts latitudinal and regional differences in the timing of ice algae biomass peak (varying from April to May) and the time lags between ice algae and pelagic phytoplankton peaks (varying from 45 to 90 days). The correlation between the time lag and ice retreat is significant in areas where ice retreat has no significant impact on ice‐algae peak timing, suggesting that changes in pelagic phytoplankton peak timing control the variability in time lags. Phenological variability in primary production is likely to have consequences for higher trophic levels, particularly for the zooplankton grazers, whose main food source is composed of the dually pulsed algae production of the Arctic.     

Harvest rates and foraging strategies in Negev Desert gerbils

We examined the foraging strategy and quantified the foragingtraits of two nocturnal rodent species, Allenby's gerbil (Gerbillusallenbyi) and the greater Egyptian sand gerbil (Gerbillus pyramidum).In the laboratory, both species used two distinct foragingstrategies: either they immediately consumed seeds found ina patch (seed tray); or they collected and delivered the seedsto their nest box for later consumption. Moreover, we founda transition in foraging strategy among individual G. allenbyi under laboratory conditions; they all began by consuming theseeds on the tray and, after 7 days on average, switched tothe collecting strategy. By contrast, in the field both speciesused only one foraging strategy; they collected and deliveredthe seeds to their burrow or to surface caches for later consumption.Furthermore, G. allenbyi and G. pyramidum collected seeds atsignificantly higher rates in the field than in the laboratorybecause the seed encounter rates for both species were higherin the field. This suggests that in natural conditions, probablyinvolving predation risk and competitive pressure, gerbilsmust respond in two ways: (1) they must choose a foraging strategythat reduces predation risk by minimizing time spent feedingoutside their burrows; and (2) they must forage more efficiently.In the field, seed handling time of the larger species, G. pyramidum, was shorter than that of the smaller one, G. allenbyi.This difference may give G. pyramidum an advantage when resourcelevels are high and when most of a forager's time is spent handling seeds rather than searching for more seeds. Additionally,our field study showed that the seed encounter rate of G. allenbyiwas higher than that of G. pyramidum. This difference may giveG. allenbyi an advantage when resource levels are low and whensearching occupies most of the forager's time. The differentadvantages that each species has over the other, under differentconditions, may well be factors promoting their coexistenceover a wide range of resource densities.     

LEPSCAN--a web server for searching latent periodicity in DNA sequences

A web server for searching latent periodicity based on the method of modified profile analysis has been developed. This method allows searching latent periodicity in presence of insertions and deletions. During searching process, the periodicity classes are used which were found by us earlier for various groups of organisms. Period length belongs to the range 2-20 nt, not including the triplet periodicity. The results obtained are subjected to various filtration steps to ensure their statistical significance. Availability: The use of web server is free for non-commercial users. No registration is required. URL of the server is http://victoria.biengi.ac.ru/lepscan. Current software version is 1.06.     

Chemical composition and biomass parameters of a population of Craspedacusta sowerbii Lank1880 (Cnidaria: Limnomedusa)

Until now, very little information about the ecology of thefreshwater jellyfish, Craspedacusta sowerbii, has been available.Although many publications deal with Craspedacusta, most ofthem contain only observations. Detailed analyses are rare.In this study, investigations on size-dependent fresh and dryweights, and carbon, nitrogen and phosphorus, are presented.The water content of the medusae ranged between 96.74 and 99.87%.Fresh and dry weights ranged from 0.06 to 331.86mg FW ind.^0–1and 0.01 to 2.50 mg DW ind.^–1, respectively. The molarC:N:P relationship was calculated as 39:9:1. The C:P ratio waslow in contrast to other freshwater zooplankton species, andimplied a high demand for P. A comparison with the C:P stoichiometryof their prey indicates the possibility of P limitation of Craspedacustaat a gross growth efficiency above 25%. The results are discussedin relation to medusae abundance, bioaccumulation and theirimpact on food web structure.