Locomotion in copepods: pattern of movements and energetics of Cyclops

The cost of swimming in copepods has generally been estimated through the application of fluid dynamics theory to data on velocity and acceleration obtained by means of movies. It has also been estimated through the changes in fat content of copepods after sustained swimming (i.e. vertical migration). However, the range of estimated costs of locomotion is exceedingly large (from 0.1% to 95% of total metabolism). This communication studies the pattern of swimming movements and the work done by Cyclops, using high speed cinematographic techniques. The contribution of swimming to the energy expenditure of the individual is estimated, and consideration of the possible role of rubber-like proteins in the cuticle of copepods is made.     

Factors Affecting Swimming Speed in the Rotifer <Emphasis Type="Italic">Brachionus plicatilis</Emphasis>

This study examines the swimming speed in amictic females of Brachionus plicatilis in laboratory cultures. Five different stages were examined: recently hatched females, juveniles, adult non-ovigerous females, ovigerous females with 1 attached egg and ovigerous females with 2 attached eggs. We tested the speed at two temperatures, 15 °C and 25 °C, and two feeding conditions, presence and absence of microalgal cells. An automated motion analysis system was used to measure speed which was then video recorded. Swimming speed (μm s⁻¹) increased with increasing body size. There was a slight decrease in the speed of adult females as the number of attached eggs increased. Swimming activity was higher at 25 °C than at 15 °C and in the absence of food than if microalgae were present. Average values under the different experimental conditions ranged between 500 μm s⁻¹ for the recently hatched and fed females and 1500 μm s⁻¹ for the adult non-ovigerous females in the absence of microalgae. Mass-specific swimming speed decreased with body mass increase.     

The swimming and feeding behavior of Mesocyclops

The swimming and feeding behaviors of Mesocyclops are described from a review of the literature and personal observations.Mesocyclops exhibits considerable behavioral flexibility in response to environmental stimuli. Mesocyclops edax exhibits an increase in horizontal looping behavior at high prey densities, and performs a tight vertical looping behavior in response to the loss of captured prey. Ingestion rates by Mesocyclops are a complex function of prey density, morphology, and behavior in addition to prey size. Vertebrate predators induce a rapid escape response in Mesocyclops and may be responsible at least in part for their extensive diel vertical migrations. The complex behavioral patterns of Mesocyclops suggest that its distribution and abundance in nature will be distinctly nonrandom and influenced as much by its own behavioral responses as by other external physical factors such as water circulation patterns.     

Costs of diving by wing and foot propulsion in a sea duck,the white-winged scoter

Most birds swim underwater by either feet alone or wings alone, but some sea ducks often use both. For white-winged scoters (Melanitta fusca), we measured costs of dives to 2 m with descent by feet only versus wings + feet (only feet are used at the bottom). Dive costs repaid during the recovery period after a dive bout were an important fraction (27–44%) of total dive costs, and removing costs of extraneous surface behaviors increased resolution of differences between dive types. Scoters using wings + feet had 13% shorter descent duration, 18% faster descent speed, 31% fewer strokes/m, and 59% longer bottom duration than with feet only. The cost of time underwater for dives using wings + feet was 32–37% lower than with feet only (P = 0.09 to 0.15). When indirect methods were used to partition descent costs from costs of ascent and bottom phases, using wings + feet lowered descent cost by an estimated 34%. Thus, using wings + feet increases descent speed and lowers descent cost, leaving more time and energy for bottom foraging. For birds in cold water, the large savings may result from both biomechanical and thermoregulatory factors.     

Effects of Temperature and Body Size on the Swimming Speed of Larval and Juvenile Atlantic Cod (Gadus Morhua): Implications for Individual-based Modelling

Synopsis The routine swimming speed (S) of three groups of 4, 9 and 32 cm total length (L_T) juvenile cod (Gadus morhua) was quantified in the laboratory at 6 – 10 different temperatures (T) between 3.2 and 16.7°C. At temperatures between 5 and 15°C, mean group S increased exponentially with increasing T (S=a e^bT) and the effect of temperature (b = 0.082, Q₁₀ = 2.27) was not significantly different among the groups (over the 8-fold difference in fish sizes of early- and post-settlement juveniles). Differences in mean S among individuals within each group were quite large (coefficient of variation = 40 – 80%). Swimming data for juveniles and those collected for groups of 0.4, 0.7 and 0.9 cm standard length (L_S) larvae were combined to assess the effect of body size on S. At 8°C, S (mm s⁻¹) increased with L_S (mm) according to: S = 0.26L_S^Φ−5.28L_S⁻¹, where Φ = 1.55L_S^−0.08. Relative S (body lengths s⁻¹) was related to L_S by a dome-shaped relationship having a maximum value (0.49 body lengths s⁻¹) at 18.5 – 19 mm L_S corresponding to the sizes of fish at the end of larval-juvenile metamorphosis. Previous larval cod IBM’s using a cruise-predator mode likely overestimated rates of foraging (prey searching and encounters) by a factor of ~2, whereas foraging rates in pause-travel models are closer to estimates of swimming velocities obtained in this and other laboratory studies.     

Swimming behavior and ultrastructure of sperm of<Emphasis Type="Italic"> Lygodium japonicum</Emphasis> (Pteridophyta)

Swimming behavior of the sperm of Lygodium japonicum (Pteridophyta) and the associated ultrastructure of the flagellar apparatus were studied by video microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The sperm has approximately 70 flagella that emerge from a sinistrally-coiled flagellar apparatus, and swims forward by ciliary beat of these flagella. Backward swimming was not observed even after sperm collided with obstacles. Video microscopy showed that the flagella of the swimming sperm are oriented laterally and oblique-anteriorly. TEM and SEM observations revealed that the basal bodies of these flagella are arranged in at least two rows and oriented in the same directions as observed by video microscopy. These basal bodies (flagella) are categorized into two types according to their orientation: group I (laterally directed) and group II (oblique-anteriorly directed). The directionality of the basal bodies appears to be fixed by electron-dense material around their base. The outer dynein arms of the flagellar axoneme are entirely absent. These morphological characteristics of basal bodies (flagella) may relate to the lack of backward swimming behavior of the sperm. Based on these results, the evolution of swimming behavior in the archegoniates is discussed in connection with lack of backward swimming in a distantly related green alga, Mesostigma viride, and the Streptophyta.     

Ingestion of live filamentous diatoms by the Great Lakes amphipod,Diporeia sp.: a case study of the limited value of gut contents analysis

Individuals of the Great Lakes amphipod, Diporeia sp. (formerly named Pontoporeia hoyi) were collected from a 45-m deep station in southeastern Lake Michigan and isolated in small laboratory feeding vessels at 4 °C, after the animals had voided their guts over a 24-hour period. Over a 20-day period, following introduction of a single ration of live cells of the filamentous diatom, Melosira varians, 9 of 10 animals had ingested this material, and 7 of these 9 individuals had deposited fecal pellets. Subsequent examination of gut contents and fecal pellets showed that although animals had ingested whole algal cells/filaments, little of the material in gut contents or fecal pellets bore any identifiable structural similarity to cells/filaments prior to ingestion. The results suggest that earlier studies of pontoporeiid gut contents may seriously underestimate the importance of algal components in the amphipod's diet and imply that Diporeia sp. growth and production may be more closely linked to primary production than previously thought.     

Dynamics of the contractile system in the pseudopodial tips of normally locomoting amoebae,demonstrated in vivo by video-enhancement

Summary Behaviour of the membrane and contractile system was directly recorded in the advancing and retracting frontal zones of spontaneously locomoting or stimulated amoebae. The advancing pseudopodial tips alternately slow down and accelerate. In the slowing phase the frontal hyaline caps are flat and compressed by countercontraction of the cortical actin network beneath the leading edge. At this stage the membrane-cytoskeleton complex splits: the detached contractile layer is retracted inwards, and the membrane lifted outwards. The fluid endoplasm fraction is filtered forward through the detached actin network. This results in a local hydrostatic pressure drop, immediately restores the forward flow of endoplasm and initiates the acceleration phase of the leading edge progression. The frontal membrane, temporarily disconnected from the cytoskeletal layer, is free to slide and extend forward, but the new submembrane contractile network is soon repolymerized. In this way, after making one step forward, the frontal zone recovers its former state, and the cycle is then repeated. The cortex disassembly-reassembly cycles at the leading edge are produced every 2 s, on average. Retraction of the frontal contractile layers is part of the general centripetal cortex flow observed during motor functions of amoebae and many other cells, and is therefore associated with various other backward movements observed within and on the surface of advancing frontal zones of amoebae. The backward movement of the contractile cortex is also responsible for the withdrawal of previously advancing pseudopodia, if the detachment of successive contractile sheets from the frontal membrane ceases. It was demonstrated that the action of attractants and repellents is based on the activation or inhibition, respectively, of rhythmic disassembly of the membrane-cytoskeleton complex at the leading edge.     

Microwear, mechanics and the feeding adaptations of Australopithecus africanus

Recent studies of dental microwear and craniofacial mechanics have yielded contradictory interpretations regarding the feeding ecology and adaptations of Australopithecus africanus. As part of this debate, the methods used in the mechanical studies have been criticized. In particular, it has been claimed that finite element analysis has been poorly applied to this research question. This paper responds to some of these mechanical criticisms, highlights limitations of dental microwear analysis, and identifies avenues of future research.     

Feeding activity of Callinectes ornatus Ordway, 1863 and Callinectes danae Smith, 1869 (Crustacea, Brachyura, Portunidae) in Ubatuba, SP, Brazil

The feeding activity along the day cycle and the time consumed for extracellular digestion were evaluated in the portunids C. ornatus and C. danae. Swimming crabs were obtained from trawling in Ubatuba bay, São Paulo, Brazil, during both the rainy and dry seasons. In each season, daily scheduled samples were taken at dawn (±6 h), noon (±12 h), dusk (±18 h) and midnight (±24 h). All individuals were dissected and the degree of stomach replenishment was recorded. In order to estimate the time elapsed for extracellular digestion, crabs were fed, and groups were dissected at 30 min intervals to check the conditions of their stomachs. In general, both species show a higher feeding activity during periods of lower light intensity, as evidenced by an increased percentage of full stomachs in dusk and midnight samples. The obtained results support higher feeding activity at night in these species and indicate short time for extracellular digestion, not exceeding 8 h. Nevertheless, full stomachs were recorded in all sampling schedules. In this case, it should be considered that elimination of certain food items such as fish bones, mollusk shells and carapace fragments of crustaceans could take more time than other items. Additionally, some crab species could require a cycle of cell replacement in the midgut gland epithelium until they can take their next meal.     

Relations of intraspecific variations in fecundity, clutch size, and oviposition frequency to the body size in three species of stoneflies, Sweltsa sp., Isoperla aizuana, and Stavsolus japonicus

Most stoneflies oviposit several times during their adult stage. In this study, the relations among oviposition frequency, the number of eggs per egg mass, and body size were examined in the chloroperlid stonefly Sweltsa sp. and two perlodid stoneflies, Isoperla aizuana and Stavsolus japonicus. It was found that larger individuals tended to oviposit more frequently than smaller ones, but the relation was significant only in Isoperla aizuana. In Sweltsa sp. and Isoperla aizuana, the number of eggs per egg mass was higher for the less-frequently ovipositing individuals than for those ovipositing more frequently, and the number of eggs per egg mass decreased with successive oviposition events. Stavsolus japonicus showed the same tendency but it was not statistically significant.     

Mechanical determinants of nectar-feeding energetics in butterflies: muscle mechanics,feeding geometry,and functional equivalence

Summary We develop a mechanistic model for nectar feeding in butterflies that integrates the two basic components of the feeding process: the fluid dynamics of nectar flow through the food canal and the contractile mechanics of the muscular, cibarial pump. We use the model to predict the relation between rate of energy intake during feeding and nectar concentration. We then identify nectar concentations that maximize energy intake rates (the optimal concentrations). We illustrate the model using measurements of the food canal and cibarium of Pieris butterflies. The model predicts an overall optimal range of nectar concentration of 31–39% sucrose for butterflies, which is in agreement with previously reported laboratory values. The model also predicts an interaction among the geometries of the food canal, the cibarial cavity, and the cibarial muscles, that allows us to identify the combinations of food canal, cibarium, and muscle dimensions that yield the highest rates of energy intake. Nectar-feeding is functionally equivalent in butterflies and hummingbirds: two physically different feeding mechanisms can yield identical energy intake rates. This equivalence results from a mathematical and physical similarity between quasi-steady-state fluid flow in hummingbrid tongues and the force-velocity characteristics of contracting cibarial muscle in butterflies.     

Feeding preference of the rice stink bug on annual grasses and sedges

Adults of the rice stink bug, Oebalus pugnax (F.), preferred panicles of vasey grass, Paspalum urvillei Steud., over those of 11 species of other grasses and one species of sedge (Cyperus) associated with cultivated rice, Oryza sativa (L.). The number of feeding adults increased approximately 2 times from 1 h post-infestation (PI) to 6 h PI. The number of feeding females was greater than males at 1 h PI but no different at 6 h PI. Both sexes fed significantly (P<0.05) more on O. sativa panicles than on P. urvillei panicles at 6 h PI. Both sexes also fed significantly (P<0.05) more on 28 and 21 cm long O. sativa panicles than on 7 cm long panicles, but no such differences existed in feeding among P. urvillei panicles.

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Résumé Les adultes d'Oebalus pugnax F. ont préféré les panicules de Paspalum urivillei Stend à celles de 11 autres Graminées et 1 Cypéracée associées au riz cultivé, Oryza sativa L. Le nombre d'adultes s'alimentant a cru environ 2 fois de la lère (1P1) à la 6ème (6P1) heure ayant suivi l'infestation. Le nombre de femelles s'alimentant était supérieur à celui des mâles 1 heure après (1P1), mais ne présentait pas de différence 6 h après l'infestation (6P1). Les 2 sexes s'alimentaient significativement plus (P< 0.05) sur les panicules d'O. sativa que sur celles de P. urvillei 6 heures après l'infestation (6P1). Les 2 sexes se sont alimentés significativement plus (P< 0,05) sur des panicules d'O. sativa de 28 et 21 cm que sur ceux de 7 cm, mais aucune différence n'était observée dans l'alimentation sur les panicules de P. urvillei.

     

Regulation by the exogenous polyamine spermidine of Na,K-ATPase activity from the gills of the euryhaline swimming crab Callinectes danae (Brachyura, Portunidae)

Euryhaline crustaceans rarely hyporegulates and employ the driving force of the Na,K-ATPase, located at the basal surface of the gill epithelium, to maintain their hemolymph osmolality within a range compatible with cell function during hyper-regulation. Since polyamine levels increase during the adaptation of crustaceans to hyperosmotic media, we investigate the effect of exogenous polyamines on Na,K-ATPase activity in the posterior gills of Callinectes danae, a euryhaline swimming crab. Polyamine inhibition was dependent on cation concentration, charge and size in the following order: spermine > spermidine > putrescine. Spermidine affected K_0.5 values for Na⁺ with minor alterations in K_0.5 values for K⁺ and NH₄⁺, causing a decrease in maximal velocities under saturating Na⁺, K⁺ and NH₄⁺ concentrations. Phosphorylation measurements in the presence of 20 µM ATP revealed that the Na,K-ATPase possesses a high affinity site for this substrate. In the presence of 10 mM Na⁺, both spermidine and spermine inhibited formation of the phosphoenzyme; however, in the presence of 100 mM Na⁺, the addition of these polyamines allowed accumulation of the phosphoenzyme. The polyamines inhibited pumping activity, both by competing with Na⁺ at the Na⁺-binding site, and by inhibiting enzyme dephosphorylation. These findings suggest that polyamine-induced inhibition of Na,K-ATPase activity may be physiologically relevant during migration to fully marine environments.     

Prey Preference by the StinkbugPerillus bioculatus,a Predator of the Colorado Potato Beetle

Perillus bioculatus(F.) is sometimes considered a generalist but has most often been recorded as predator of Colorado potato beetle (CPB),Leptinotarsa decemlineata.(Say). This study was designed to analyze prey selection inP. bioculatuswith respect to factors that may lead to specialization. To establish if parental prey determines preference in na?&#x0308;ve progeny, prey selection experiments were conducted with the CPB and two unusual prey, the yellow mealwormTenebrio molitor(L.) and the house cricketAcheta domesticus(L.). Na?&#x0308;ve nymphs reared from yellow mealworm-fed parents in the absence of contact with the CPB initiated feeding more frequently on CPB (81.4%) than on cricket prey (69.6%) (P = 0.038), suggesting genetically inheritable preference for CPB. Progeny from CPBfed parents initiated feeding more frequently on CPB prey (93.3%) than on yellow mealworm prey (76.6%) (P = 0.0001), but progeny from yellow mealwormfed parents initiated feeding on yellow mealworm prey as frequently (89.2%) as on CPB (95.0%) (P = 0.613). Similarly, progeny from CPB-fed parents established proboscis contact more frequently on CPB (39.2%) than on house cricket prey (25.0%) (P = 0.008), whereas those from cricket-fed parents probed house cricket prey as frequently (12.5%) as CPB prey (15.4%) (P = 0.416). Results confirm specialization ofP. bioculatustoward CPB or related prey and suggest genetically inheritable as well as maternally reinforcible affinity toward CPB prey. However, affinity of na?&#x0308;ve nymphs for the CPB can be lowered by rearing parents on alternative prey, increasing their chances of survival when alternative prey must be relied upon.     

Dietary self-selection for vitamins and lipid by larvae of the corn earworm, Heliothis zea

Last instar larvae of the corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), require lipid and certain vitamins in their diet in order to complete larval development. When experimental larvae were offered two nutritionally incomplete diets, each lacking a different one of the requirements, they invariably ate from both diets, self-selecting a mixture that was nutritionally superior to either diet alone.

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Résumé Les chenilles de dernier stade d' H. zea (Boddie) (Lep.:Noctuidae) ont besoin de lipides et de certaines vitamines dans leur régime alimentaire, probablement parce qu'elles n'en contiennent pas assez provenant des stades précédents. Quand deux régimes incomplete ont été fournis aux chenilles (chacun privé différemment de l'un de ces consituants: lipide, chlorure de choline ou un ensemble de vitamines), elles ont consommé systématiquement des deux régimes et autosélectionné un aliment de qualité supèrieure à celle de chaque régime séparément. D'un autre côté, les chenilles témoins à qui on a offert deux régimes identiques et nutritionnellement complets, ont choisi apparemment leur aliment au hasard, et presque la moitié d'entre elles ont consommé exclusivement on presque exclusivement l'un des régimes, tandis que l'autre moitié a choise exclusivement or presque exclusivement l'autre.

     

A phylogenetic analysis of the myxobacteria Myxococcus fulvus,Stigmatella aurantiaca,Cystobacter fuscus,Sorangium cellulosum and Nannocystis exedens

Five representatives of the order Myxobacterales were characterized by oligonucleotide cataloguing of their 16S ribosomal RNA to determine their phylogenetic relationship to one another and to other gliding and non-gliding Gram-negative bacteria. Myxococcus fulvus, Stigmatella aurantiaca and Cystobacter fuscus are highly related, while Sorangium cellulosum and Nannocystis exedens are clearly separated from each other and from the former organisms. All myxobacteria are members of one line of descent, which is specifically related to the broad groups of non-sulphur and sulphur purple bacteria and their non-phototrophic relatives. Myxobacteria are distantly related to Cytophaga johnsonae, which stands completely isolated at present.     

Importance of Nutrient Competition and Allelopathic Effects in Suppression of the Green Alga Scenedesmus obliquus by the Macrophytes Chara, Elodea and Myriophyllum

Possible allelopathic effects of substances released from the macrophytes Chara globularis, Elodea canadensis, Myriophyllum spicatum on the common green alga Scenedesmus obliquus were tested in the laboratory with plastic plants and untreated medium as controls. A two-phase approach was used in which first the effects of physical presence of plants was studied (phase I) followed by the effects of plant culture filtrates (phase II). In the presence of plastic plants growth was reduced only marginally, but strong growth inhibition of Scenedesmus occurred in the physical presence of all macrophytes. In contrast, filtrates from Chara had no growth inhibitory effect on Scenedesmus. Myriophyllum filtrate reduced particle-based growth rate by 7% compared to filtration controls, while Elodea culture filtrate reduced volume-based growth by 12%, chlorophyll-based growth by 28% and particle-based growth by 15%. Photosystem II-efficiency of Scenedesmus was reduced in all three macrophyte treatments in phase I, but not in filtrates from macrophyte cultures (phase II). Thus, while enzyme activity or other physiological aspects may have been affected, the current study yielded no proof for allelopathically active compounds being directed at photosynthesis. Mean particle volume (MPV) of Scenedesmus was not influenced by macrophyte exudates and cultures remained dominated by unicells. The strong growth inhibitory effects found for Scenedesmus in the physical presence of macrophytes, but not in plastic controls, and no or weaker response in nutrient-enriched filtrates, suggest nutrient competition was a more powerful driving factor than allelochemicals. However, the experimental design does not exclude disappearance of allelochemicals during the filtration process.     

Morphological and molecular diversity of the monocercomonadid genera Monocercomonas, Hexamastix, and Honigbergiella gen. nov

The family Monocercomonadidae (Parabasala, Trichomonadida) is characterized by the absence of a costa and in most species also of an undulating membrane; both of which are typical structures of trichomonadids. We have examined 25 isolates of Monocercomonadidae species by sequencing of the SSU rDNA and the ITS region and by light and transmission electron microscopy. The isolates formed three distinct phylogenetically unrelated clades: (1) Monocercomonas colubrorum, (2) Monocercomonas ruminantium together with a strain ATCC 50321 designated as Pseudotrichomonas keilini, and (3) Hexamastix. Twenty isolates of Monocercomonas colubrorum split into three clades with no host-specificity. The morphological differences among clades were insufficient to classify them as a separate species. Non-monophyly of the cattle commensal Monocercomonas ruminantium with the type species Monocercomonas colubrorum and absence of Pseudotrichomonas characters in the free-living strain ATCC 50321 led to their reclassification into a new genus (Honigbergiella gen. nov.). The close relationship of these strains indicates a recent switch between a free-living habit and endobiosis. Two strains of Hexamastix represented different species -Hexamastix kirbyi Honigberg 1955 and Hexamastix mitis sp. nov. Polyphyly of the Monocercomonadidae confirmed that the absence of a costa and an undulating membrane are not taxonomically significant characters and were probably secondarily lost in some or all clades. Our observations, however, indicated that other characters - infrakinetosomal body, comb-like structure, marginal lamella, and the type of axostyle - are fully consistent with the position of Monocercomonadidae species in the parabasalian tree and are, therefore, reasonable taxonomic characters.     

Feeding preferences and their modification in early and late instar larvae of the bagworm,Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae)

Feeding preferences in naive first instar and penultimate-final instar bagworm (Thyridopteryx ephemeraeformis)larvae were investigated using two choice tests. Naive first instar larvae showed a general (though not exclusive) preference for black willow (Salix nigra)over other hosts tested, regardless of the host of origin. Penultimate-final instar larvae showed strong preferences for the previous rearing host, suggesting induction of host preference; there was no evidence of host origin effects. The ability to discriminate among hosts is important if it is actually used to make host choices based on host quality. In bagworms, where host choices (if any) must be made by larvae in habitats where several hosts are often present, host discriminatory ability is likely important.