Implications of the feeding current structure of Euchaeta rimana, a carnivorous pelagic copepod, on the spatial orientation of their prey

Many marine planktonic organisms create water currents to entrainand capture food items. Rheotactic prey entrained within thesefeeding currents often exibit escape reactions. If the directionof escape is away from the feeding current, the prey may successfullydeter predation. If the escape is towards the center of thefeeding current, the prey will be re-entrained towards its predatorand remain at risk of predation. The direction of escape isdependent on (i) the ability of the prey to escape in a directiondifferent than its pre-escape orientation and (ii) the orientationcaused by the interaction of the prey's body with the movingfluid. In this study, the change in orientation of Acartia hudsonicanauplii as a result of entrainment within the feeding currentof Euchaeta rimana, a planktonic predatory copepod, was examined,When escaping in still water, A.hudsonica nauplii were ableto vary their pre-escape direction by only 10. This allowsonly a limited ability to escape in a direction different thantheir pre-escape orientation. Analyses of the feeding currentof E.rimana show the flow speed to be most rapid in the centralregion with an exponential decrease in speed distally. In contrast,flow vorticity is minimal in the center of the feeding currentand maximal at 1.75 mm along the antennae. As a result, thedegree of rotation of the prey towards the center of the feedingcurrent shows a strong dependency on the prey's location withinthe feeding current. The feeding current of E.rimana rotatedthe prey 14 when near the center of the flow field and up to160 when located more distal in the feeding current Since theprey's escape abilities cannot compensate for the rotation dueto the flow, this mechanism will maintain the escaping preywithin the feeding current of their predator. Therefore, thefeeding current facilitates predatory copepods in capturingprey by (i) increasing the amount of water which passes overtheir sensors and through their feeding appendages and (ii)controlling the spatial orientation of their prey prior to escape.     

In situ determinations of bacterial selectivity and filtration rates by five cladoceran zooplankters in a hypertrophic subtropical reservoir

Cladoceran in situ feeding rates on natural bacteria labelledwith [methyl-³H] were studied in parallel with feeding ratedeterminations on ¹⁴C-labelled Chlorella in a hypertrophic subtropicalreservoir (Lake Hartbeespoort) through spring and summer (1986/87).Community filtration rates (CFR5) on bacteria and algae weresimilar, but selection for Chlorella (relative to natural bacteria)increased from midsummer in association with declining bacterialdensity and increasing dominance of ‘inedible’ componentsof the natural phytoplankton. Species-specific filtration rates(SSFRs) were determined for Daphnia pulexllongispina, Ceriodaphniareticulata, Diaphanosoma excisum, Bosmina longirostris and Moinamicrura during their respective seasonal occurrence in the studyperiod. SSFRs on algae and bacteria increased with body length(L, mm) in all species apart from Bosmina. Species-specificdifferences in absolute feeding rate (FR, ml animal^–1day^–1), the slope of the FR-L relationship and bacteriaselectivity were evident. The feeding rate of all cladoceranson bacteria is described by the power equation FR 5.231L^1.42FR values on bacteria relative to FR values on algae averaged     

家蚕味觉电生理反应的个体差异

为探讨家蚕Bombyx mori人工饲料饲养发育不齐的生理原因,从同一蚕品种中挑选出对人工饲料摄食性不同的个体,用电生理学方法测定了下颚瘤状体味觉感器对4种代表性物质（蔗糖、肌醇、大豆粉提取物和柠檬酸）的电生理反应。结果表明,栓锥感器Ss-Ⅰ对蔗糖等促食物质的反应以及栓锥感器Ss-Ⅱ对大豆粉提取物等阻食物质的反应,均存在明显的个体差异。在临界浓度下,低摄食性个体的放电脉冲频率显著高于高摄食性个体。说明低摄食性蚕的味觉反应比高摄食性蚕敏感。     

Feeding behaviour of the rotifer Ascomorpha ovalis: functional response, handling time and exploitation of individual Ceratium cells

The planktonic rotifer Ascomorpha ovalis feeds on large dinoflagellates(e.g. Ceratium sp., Peridinium sp.) and is able to extract theircell contents by means of its virgate mastax. This paper presentsthe results of experiments on the feeding behaviour of laboratory-culturedAscomorpha with Cerarium furcoides as food algae. Ascomorphaare three times larger than their prey Ceratium (by volume),but with regard to total length, their prey was even 20% larger.Ascomorpha showed a hyperbolic functional response curve witha plateau of the feeding rate at 8 Ceratium cells animal^–1dar^–1 when concentrations of Ceratium were >100 cellsml^–1. The mean handling time (time for capturing and extractingone Ceratium cell) was 3 min. The shape of the functional responsewas better described by a curvilinear model than by a rectilinearmodel. However, handling times cannot be responsible for this,since they were too short to set limits on ingestion rates.At low food concentrations, encounter rates with prey seemedto limit the feeding rates of Ascomorpha, whereas at mediumto high food concentrations, Satiation effects (lower attackrates) seemed to set limits on the feeding rates. Ascomorphashowed a significant decrease in the exploitation of singleCeratium cells at high prey concentrations. This decrease couldbe explained by a saturation effect in which the partly filledguts of Ascomorpha did not permit the total extraction of thecontents of a Ceratium cell.     

Do transparent exopolymer particles (TEP) inhibit grazing by the euphausiid Euphausia pacifica?

The hypothesis that ubiquitous, sticky transparent exopolymerparticles (TEP) formed from phytoplankton exudates will adhereto and coat the feeding structures of marine zooplankton grazers,and thus depress feeding on phytoplankton, was tested usingthe euphausiid, Euphausia pacifica, as a model organism. Duringtwo feeding experiments, E.pacifica were offered cells of thediatom Thalassiosira weissflogii, TEP, or both TEP and T.weissflogiicells. Ingestion rates on cells were lower in the presence ofTEP. However, contrary to the hypothesis, grazing on cells wasnot inhibited by TEP. Rather, TEP-clusters, aggregates whichformed from TEP and nano-sized particles normally too smallfor the filtering apparatus of E.pacifica to retain, servedas an alternative food source for E.pacifica, reducing theiringestion of cells. These clusters were very similar in formto the TEP actually available to marine grazers in nature. TEP-clusterswere similar to cells in size and food quality, and were grazedat similar rates. When feeding on TEP-clusters, euphausiidsshort circuit the food web by feeding on nano- and picoplanktondirectly, bypassing the microbial loop. Thus, the presence ofTEP appears to enhance, rather than depress, macrozooplanktongrazing.     

Predaceous feeding habits of Limnocalanus macrurus

Limnocalanus macrurus, a large, glacial-relict copepod, hasbeen assumed an omnivore or a herbivore; predaceous habits ofthe species are unknown. The predaceous feeding habits of Limnocalanusfrom Lake Michigan were studied in the laboratory using naturalprey. Predation rates were highest on copepod nauplii. Copepoditesof Diaptomus spp. and Cyclops spp. were preyed upon at lowerrates. Limnocalanus preyed selectively upon nauplii <300µm. Small cyclopoid copepodites (<–750 µm)were also selected over large copepodites. Experiments usingtwo prey types showed that nauplii were selected over all copepodites,and that no selectivity existed for either diaptomid or cyclopoidcopepodites. Predaceous feeding habits began in the fourth copepoditestage of Limnocalanus. Predaceous feeding rates of Limnocalanuschanged seasonally being highest in late spring and autumn andlowest in summer and early winter. Since Limnocalanus also feedson net-phytoplankton, predation rate changes may be relatedto changes in the relative abundance of large phytoplanktonand naupliar prey in nature. Limnocalanus predation may be animportant factor in structuring the zooplankton community. Present address: Great Lakes Research Division, University Michigan,Ann Arbor, MI 48109, USA     

Temporal pattern of feeding response of Chaoborus larvae to starvation

The effect of starvation on the feeding rate of larval Chaoborus(Diptera. Chaoboridae) was investigated using Daphnia roseaas prey. The starvation period varied from 12 h to 22 days.The starved Chaoborus were individually incubated with 10 Daphniaunder controlled light and temperature conditions. Observationswere made on prey mortality every 2 h for the first 12 h andonce after 24 h. Feeding rates gradually increased to a maximumbetween 7–11 days of starvation. After this period, feedingrates declined to previous low levels. Generally, feeding rateswere significantly higher during the first 2–4 h of feeding.Thereafter, feeding rates were lower and exhibited no consistentpattems with length of feeding time.     

Ingestion and incorporation of freshwater diatoms by Daphnia pulicaria: do morphology and oxylipin production matter?

In order to explain differences in the growth and reproductionof Daphnia pulicaria fed various freshwater diatoms, we measuredingestion rates and carbon incorporation for six cultured diatomspecies: the single-celled Stephanodiscus hantzschii, Stephanodiscusminutulus and Cyclotella meneghiniana, and the colony-formingAsterionella formosa, Fragilaria capucina and Fragilaria sp.Two of the colony-forming species, when damaged, produced polyunsaturatedaldehydes (oxylipins) that have been found to impair the reproductionof marine copepods. We tested two hypotheses: (i) feeding andincorporation rates are affected by diatom morphology; and (ii)polyunsaturated aldehydes act as feeding deterrents. Daphniabody length versus ingestion rate regressions differed for single-celledand colony-forming diatoms. Ingestion rates for single-celleddiatoms showed clear size dependencies and high correlationcoefficients, while the dependency was weak for colony-formingdiatoms and individual variability was high. This differencewas not observed for carbon incorporation rates, which showedlow variability for all diatoms. Asterionella formosa yieldedthe lowest incorporation rates due to low incorporation efficiency,while all other diatoms were incorporated at similar rates.Thus, morphological differences of the diatoms had no effecton carbon uptake by Daphnia. The presence or absence of polyunsaturatedaldehydes did not cause different ingestion rates; hence thealdehydes are not feeding deterrents.     

Capture mechanisms used by the lobate ctenophore, Mnemiopsis leidyi, preying on the copepod Acartia tonsa

Although the lobate ctenophore Mnemiopsis leidyi is an influentialplanktonic predator, the mechanisms enabling it to capture itscharacteristically wide range of prey have not been systematicallyexamined. We recorded interactions between free-swimming M.leidyiand two stages (nauplii, adults) of the calanoid copepod Acartiatonsa in order to determine a mechanistic explanation of thisfeeding process. Prey encounter with Mnemiopsis involved twodifferent processes. The first depended on fluid motions createdby the nearly continuous beating of cilia lining the four auricles.These cilia created a low-velocity flow in which A.tonsa naupliiwere entrained (94% of naupliar encounters) and transportedpast the oral lobes onto the tentillae (oral tentacles). Thenauplii, although capable of rapid escape responses, generallyappeared to be insensitive to the current in which they werecarried. The second process relied upon the collision of swimmingprey with the inner surfaces of the oral lobes and was not obviouslyinfluenced by the auricular feeding currents. Adult A.tonsawere rarely entrained in the auricular flow, but, instead, propelledthemselves into contact with the oral lobes (97% of adult encounters).Both prey capture processes functioned simultaneously. The synergisticfunctioning of these processes probably explains the broad patternsof prey ingestion found by in situ studies of Mnemiopsis feeding.     

Pouncing spider, flying mosquito: blood acquisition increases predation risk in mosquitoes

Female mosquitoes dramatically increase their mass when bloodfeeding on their hosts. Such an increase could impact mosquitomortality risk by reducing escape speed and/or agility. We usedtwo laboratory-based experiments to test this notion. In thefirst, we allowed mature female Anopheles gambiae mosquitoesto feed from 0 to 4 min and then attacked those females withan artificial predator. We videotaped subsequent escape responseof each mosquito. Analysis of those responses clearly demonstratedan inverse relationship between increased mass and escape speed.In the second experiment, we exposed both blood-engorged andunfed A.gambiae females to single zebra spiders (Salticus scenicus)in small plexiglass cages. Here, we focused on mosquito escapesfrom searching and pouncing spiders. We found that engorgedmosquitoes were three times less likely to escape searchingspiders compared to unfed conspecifics. Thus we conclude thatblood feeding has substantial state-dependent risk both at thehost (experiment 1) and after feeding (experiment 2). Such riskcan be extended to a broad range of taxa.     

Sexual harassment in live-bearing fishes (Poeciliidae): comparing courting and noncourting species

Sexual harassment by males has been reported from several live-bearingfishes (Poeciliidae) and has been shown to inflict costs onfemales. For example, poeciliid females have reduced feedingopportunities when accompanied by a male because females dedicateattention to avoiding male copulation attempts. Poeciliid speciesdiffer considerably in male mating behavior, such as the presenceor absence of courtship. Courting males display in front ofthe females, but males attempting to sneak-copulate approachfemales from behind, that is, in the blind portion of theirvisual field, and force copulations, which can be viewed asa male persistence trait. We predicted that poeciliid femalesneed to be more vigilant in the presence of noncourting males,and costs of harassment by noncourting males might be stronger.In a comparative approach we examined the costs of male sexualharassment for females as reduced feeding time in 9 speciesof live-bearing fishes, including courting (Poecilia latipinna,Poecilia reticulata, Xiphophorus cortezi, Xiphophorus variatus)and noncourting species (Poecilia mexicana [surface- and cave-dwellingform], Poecilia orri, Gambusia affinis, Gambusia geiseri, Heterandriaformosa). In all species examined except for the cave form ofP. mexicana, focal females spent significantly less time feedingin the presence of a male than when together with another female.The time females spent feeding was found to significantly declinewith increasing male mating activity (sum of all sexual behaviors),but there was no support for the idea that females would spendmore time feeding in the presence of courting males comparedwith noncourting ones.     

Filtering rates on natural bacteria by Daphnia longispina and Eodiaptomus japonicus in Lake Biwa

Filtering rates on [³H]thymidine-labelled natural unattachedbacteria and that on [¹⁴C]bicarbonate-labelled natural planktonwhich pass through the 25 µm-mesh-size screen were measuredfor Daphnia longispina and Eodiaptomus japonicus in Lake Biwa.Errors associated with the radioisotope technique, i.e the lossof labels after feeding trials and the self-absorption of thebeta emittance of ³H, were checked and corrected for the calculationof the filtering rates. It was suggested that Daphnia collectsbacteria efficiently, although the efficiency is somewhat variabledepending on food particle composition (i.e. presence and absenceof larger particles) and feeding condition (i.e. animal densityand physical disturbance). By contrast, copepodites of Eodiaptomuswere suggested to be less efficient bacteria feeders. Food resourceexploitation strategies of these two co-existing zooplanktersare discussed.     

Hormonal Control of Molting and Reproduction in Ticks

SYNOPSIS. Among ticks there are two developmental and threereproductive patterns that correlate with taxonomic groupings(Argasidae, prostriate and metastriate Ixodidae). Feeding isa prerequisite for molting; feeding and mating are necessaryfor reproduction in all except a few parthenogenetic species.Growth and development in ticks and other chelicerates appearto be controlled by molting hormones (ecdysteroids), as theyare in insects and crustaceans. Ecdysone and 20-hydroxyecdysoneappear to be present in most or all of the major cheliceratetaxa. Epidermis is the site of ecdysone production and fat bodythe site of 20-hydroxylation in the argasid Ornithodoros parkeri,as is probably the case in all ticks. Ecdysteroids influenceearly stages of spermatogenesis by stimulation of DNA synthesisin spermatocytes, but controls for later stages of meiosis areunknown. A polypeptide (12,000 daltons) from male genital accessoryglands stimulates capacitation (maturation) of spermatids intosperm at the time of spermatid transfer to females. Knowledgeof control of egg development and oviposition is incomplete.Stimuli from the synganglion are necessary for completion ofoogenesis and two synganglial factors have been proposed. AnEgg Development Stimulation Factor (EDSF) in O. parkeri is synthesizedand/or released three to six days after feeding. VitellogenesisInducing Factor (VIF) in O. moubata is synthesized and/ or releasedwithin one hour after feeding. The VIF is hypothesized to impactan unidentified tissue which in turn produces a Fat Body StimulationFactor (FSF) that stimulates fat body to synthesize vitellogenin(Vg). Roles of ecdysteroids and juvenile hormones during eggdevelopment and oviposition are unclear.     

Predation of cockles (Cerastoderma edule) by the whelk (Buccinum undatum) under laboratory conditions

The feeding rate and behaviour of whelks (Buccinum undatum)offered cockles (Cerastoderma edule) in laboratory experimentswere examined. When presented with cockles in a range of sizes(10–40 mm), 14 B. undatum (34.6–88.3 mm),held individually in aquaria, consumed a wide size range ofcockles. Small whelks (<40 mm) consumed cockles (<23 mm),whereas large whelks, (>60 mm) ate a greater numberof larger cockles (>30 mm) and a wider size range ofcockles (12–40 mm) than smaller whelks. The majority(90%) of the shells of the predated cockles were undamaged andthe few (<10%) that were damaged showed only slight abrasionsto the anterior and posterior shell margin. Filmed observationsof B. undatum feeding on C. edule showed a method of attackthat has not previously been reported and involved the use ofthe whelk's foot to asphyxiate the cockle or to pull the shellvalves apart. No filmed evidence was found for the previouslyreported shell ‘wedging’ technique for prising openthe closed shell valves of C. edule, although 10% of the shellsof consumed cockles in feeding experiments had damaged shellmargins. (Received 4 April 2007; accepted 30 June 2007)     

The feeding strategies of two large marine copepods

We compared the feeding behaviour of the two copepods Paraeuchaetanorvegica and Chiridius armatus, allowing them to prey on othercalanoids in small-scale laboratory experiments. Several differenceswere found. When fed either live, free-swimming or dead, non-movingprey, P.norvegica seemed unable to locate the dead prey itemswhile C.armatus foraged heavily on them. When starved, P.norvegicaincreased its feeding rate while C.armatus reduced its feedingafter an initial increase. None of the predators changed theirfeeding rates when exposed to light. Nighttime versus daytimefeeding was tested only with P.norvegcia, which seemed to possessan endogenous feeding rhythm with increased rates at night.Chiridius armatus infected with epizooic ciliates appeared tohave increased feeding rates.     

Lipids in Acanthodiaptomus denticomis during starvation and fed on three different algae

Variations in the levels of triglycerides, wax esters and polarlipids were determined in adults of the calanoid copepod Acanthodiaptomusdenticornis when freshly caught, starved or fed on the followingalgae: Anabaena spiroides, Cyclotella pseudostelligera and Pediastrumduplex. Over 7 days starvation, triglycerides and wax esterswere almost entirely used up by the copepods. Subsequent feedingover 20 days partially restored triglycerides but restored onlya relatively small fraction (<20%) of wax esters in the animals.Differences in the lipid restoration were found: the restoredtriglyceride level was higher in animals feeding on Cyclotellapseudostelligera or Pediastrum duplex than in those feedingon Anabaena spiroides. Fatty acid composition of neutral lipidswas closely linked to fatty acid composition of algae. The resultssuggest that lipid and fatty acid contents of Acanthodiaptomusdenticornis are good indices of the copepod's nutritional statusand short-term (0–20 days) feeding history.     

SOME OBSERVATIONS ON THE DIET AND DISTRIBUTION OF NUDIBRANCHS AT SIGNY ISLAND, ANTARCTICA

Observations were made on the diet and distribution of eightspecies of nudibranchs found in Borge Bay, Signy Island, Antarctica.Specimens from seven sites were examined in situ on four separateoccasions during 1992 and 1993 using SCUBA. A small collectionfor identification was also made Six of the eight species presentwere identified, and the first ecological data for at leastone species (Charcotia granulosa) were recorded. Notaeolidiagigas was feeding principally on hydroids of the genus Tubulariaover the entire depth range surveyed (3–36 m), and wasmost abundant in shallow water, whereas Truomella belli wasonly found at deeper sites, mostly on an octocoral of the genusAscolepis. Charcoaa granulosa and Pseudotritoma gracilidensappeared to be specialist bryozoan feeders and, as has beenfound at other locations, Austrodoris kerguelenesis specialisedon the demosponge Dendnlla antarcnca. Two unidentified aeolidspecies occurred almost entirely on particular hydroids andthe prey of Tritonia antarctica was not apparent. The physicalsize of Antarctic nudibranchs may have important implicationsto the type of prey and feeding strategy used by different species. (Received 11 May 1995; accepted 3 December 1995)     

苏云金杆菌δ-内毒素、芽孢及苏云金素A对棉铃虫毒性及拒食性的比较

苏云金杆菌库斯塔克变种HD-1的晶体蛋白与芽孢、HD-1无晶体突变株(Cry-)的芽孢以及苏云金素A对棉铃虫Helicoverpa armigera毒性和拒食性的比较研究显示,HD-1晶体蛋白对棉铃虫的杀虫毒力高, 拒食作用强; HD-1芽孢对棉铃虫具有一定的杀虫活性和生长抑制作用, 并有很强的拒食作用; HD-1无晶体突变株(Cry-)芽孢对棉铃虫无毒也无拒食作用;苏云金素A对棉铃虫的生长发育有极显著的抑制作用, 但对棉铃虫无拒食作用,由此证明晶体蛋白是苏云金杆菌杀虫活性和拒食作用的主要来源。苏云金素A与苏云金杆菌芽孢晶体混合物一起使用, 可使棉铃虫的死亡率显著提高。     

Pigment ingestion and egg production rates of the calanoid copepod Temora longicornisr. implications for gut pigment loss and omnivorous feeding

We examined the relationship between egg production rate (E)and pigment ingestion rate (I, from gut content corrected for33% loss) for adult female Temora longicornis in Long IslandSound on 47 occasions. Linear regression of E on I [both variablesexpressed in mass of nitrogen (N) female^–1 day^–1]was: E_N = 0.0016 + 0.770 x I_N. The slope, 0.77, is the apparentgross efficiency of egg production, equivalent to the grossgrowth efficiency (GGE) assuming that females partition allnitrogen for growth into egg production. Published work suggeststhat a GGE of 0.37 would be expected for herbivorous copepods.The discrepancy between the expected value of 0.37 and observedvalue of 0.77 could result from unquantified losses of gut pigmentor because T.longicomis ingested a significant amount of nitrogenby feeding as a carnivore. We suggest that if T.longicomis femalesderive all of their nitrogen for growth by feeding on phytoplankton,and if no correction for pigment loss is employed, then thegut pigment method underestimates pigment ingestion by no morethan a factor of two.     

Suspension feeding and kleptoparasitism within the genus Trichotropis (Gastropoda: Capulidae)

The marine gastropod Trichotropis cancellata is a facultativekleptoparasite, either suspension feeding or parasitically stealingfood from tube-dwelling polychaete worms. To determine whetherconclusions drawn from long-term studies in the San Juan Islands,Washington, about the relative importance of suspension feedingand kleptoparasitism can be applied generally to T. cancellataacross its biogeographic range, I expanded earlier studies toAlaska and British Columbia. Kleptoparasitism is pervasive throughoutthe range of T. cancellata, occurring with equal frequency throughoutthe areas studied. The average density and size of worm hostsare relatively constant across this range. Snail and worm densitiesare not significantly correlated at the larger scale of site(averaged over nearby sampling locations clustered around acity), but are correlated at the smaller local scale (withina sampling location). Larger worms do not support more snails.The abundance of uninfected worm hosts is usually not limiting,except potentially in some sampling locations in southwest Alaskawhere the use of a novel host (a holothurian) may be the resultof low densities of uninfected worms. Additionally, I documentedthe feeding behaviours of other trichotropid species in theseregions. Trichotropis conica is the second confirmed kleptoparasitewithin the genus Trichotropis, with kleptoparasitism as frequentin this species as in T. cancellata. Like T. cancellata, allsizes observed of T. conica are kleptoparasites. On the otherhand, Trichotropis insignis is an obligate suspension feeder.Further studies are needed to determine exactly how many timesthis behaviour has arisen and been lost in Capulidae and relatedfamilies. (Received 31 May 2007; accepted 19 October 2007)