Fluid mechanosensory stimulation of behaviour from a planktonic marine copepod, Euchaeta rimana Bradford

This research provides the first reported thresholds for thebehavioural response of an individual planktonic copepod. Usinga novel technique to create near-field fluid disturbances, wedirected microlitre volumes of water towards the antennularysetae. In response to an increasing strength of this purelymechanical signal, the animal varied its behaviour from a rapidflick to a capture response and finally an escape reaction.This work provides a basis for addressing the criteria copepodsuse to interpret biologically generated signals to elicit anappropriate behavioural response and offers insight into howthese signals are differentiated from the random fluid motionin their environment.     

Feeding and ovipositing on plants by an omnivorous insect predator

Omnivory (i.e., feeding at more than one trophic level) is common in many ecological communities. To date, most studies of omnivory have focused on systems that include omnivores that feed on several prey items, primarily in aquatic systems. Yet, many terrestrial insect predators feed not only on prey but also on plants. The difference between systems with plant-feeding omnivores and those with exclusively prey-feeding omnivores calls for special attention. The first step towards understanding the interactions between plant-feeding omnivores and their prey is to determine how omnivores respond to variations in plant properties. In this study, I investigated two major aspects of the interactions between the plant-feeding predatory bug Orius insidiosus and four host plants of its prey; the behavioral aspect, in which plants are selected for oviposition and the physiological aspect, in which plants differ in their suitability for the insect's growth, survival, and reproduction. No prey was offered to the omnivore during any of the experiments, but older nymphs and adults were fed prey eggs prior to their use in the experiments. Data show that O. insidiosus females almost completely rejected corn leaves for oviposition; nymph and adult survival was highest on bean; and female fecundity was higher on bean than tomato, pepper or corn foliage. the significance of the apparent ability of O. insidiosus to discriminate among plants and the observed correlation between oviposition preference and offspring performance in bean and in corn is discussed.     

Predator-induced diet vertical migration in a planktonic copepod

Predator evasion is the most commonly hypothesized reason fordiel vertical migrations undertaken by a wide variety of planktonicorganisms in lakes and seas, yet direct evidence remains elusive.We tested the predation hypothesis by exposing enclosed populationsof a marine copepod Acartia hudsonica to caged or free-rangingindividuals of their natural predator, the planktivorous fishGasterosteus aculeatus. After little more than a week, adultcopepods changed their vertical distribution and migration behaviordepending on the presence or absence of predation. Only free-rangingfish induced vertical migration in the copepod population. Cagedfish had no effect, indicating that vertical migration was nota simple chemically mediated response of copepods to the predator.Rather, copepods seemed to react to the presence of predatorsby other means, perhaps visual or mechanical stimuli, and toexhibit a downward escape response which, because encounterswith visually orienting fish occur chiefly in the daytime, effectivelylimited the copepods' occurrence in the upper water column tothe night-time hours. Alternatively, because fish imposed heavymortality on copepods, it is possible that selective predationaltered the proportions of individuals with fixed, geneticallydetermined migration behaviors. We suggest experiments to distinguishthese alternatives.     

Photoreactivation of UV-induced damage to embryos of a planktonic copepod

UV irradiation damaged the embryos of the planktonic copepodCalanus sinicus. The hatching rate was reduced, and the hatchedlarvae were deformed by the UV irradiation at unweighted intensitiessimilar to those occurring naturally. However, the UV-induceddamage was reduced by simultaneous irradiation with the visiblelight from a fluorescent lamp. This photoreactivation may playan important role in reducing the mortality of this speciesin the marine environment.     

Hydrocarbon contamination decreases mating success in a marine planktonic copepod

The mating behavior and the mating success of copepods rely on chemoreception to locate and track a sexual partner. However, the potential impact of the water-soluble fraction of hydrocarbons on these aspects of copepod reproduction has never been tested despite the widely acknowledged acute chemosensory abilities of copepods. I examined whether three concentrations of the water-soluble fraction of diesel oil (0.01%, 0.1% and 1%) impacts (i) the swimming behavior of both adult males and females of the widespread calanoid copepod Temora longcornis, and (ii) the ability of males to locate, track and mate with females. The three concentrations of the water-soluble fraction of diesel oil (WSF) significantly and non-significantly affect female and male swimming velocities, respectively. In contrast, both the complexity of male and female swimming paths significantly decreased with increasing WSF concentrations, hence suggesting a sex-specific sensitivity to WSF contaminated seawater. In addition, the three WSF concentrations impacted both T. longicornis mating behavior and mating success. Specifically, the ability of males to detect female pheromone trails, to accurately follow trails and to successfully track a female significantly decreased with increasing WSF concentrations. This led to a significant decrease in contact and capture rates from control to WSF contaminated seawater. These results indicate that hydrocarbon contamination of seawater decreases the ability of male copepods to detect and track a female, hence suggest an overall impact on population fitness and dynamics.     

Swimming and feeding behaviour of the planktonic copepod Clausocalanus furcatus

The objective of this study was to quantify motion and feeding behaviour of the small calanoid Clausocalanus furcatus, which is a common and abundant species in oligotrophic environments. Adult females were video recorded at 60 fields s^-1 using video equipment which allowed us to follow each free-swimming individual continuously in 3 1 vessels. At 20C under dark conditions, C.furcatus moved continuously along convoluted small loops at a mean speed of 10 mm s^-1 (corresponding to 10 body lengths s^-1). This motion was occasionally interrupted by sudden somersaulting performed at very high speed (up to 17 mm s^-1). The copepods only occasionally sank. There was no evidence that C.furcatus created feeding currents. Dinoflagellate cells offered as food appeared to be perceived by direct encounter at high speed, being instantaneously captured and ingested or rejected. The capture rates were correlated with the frequency of somersaulting. By moving fast and by associating a high turning rate with a high frequency of crossing the previous tracks, C.furcatus searched 22-26% of the explored volumes. The motion and feeding behaviour of C.furcatus show that the foraging tactic of this species is to explore small volumes of water rapidly. This strategy appears, so far, to be unique among small planktonic copepods.      

Cryptic ecological diversification of a planktonic estuarine copepod, Acartia tonsa

The recent discovery of cryptic species in marine holoplankton, organisms that 'drift' in oceanic currents throughout their life cycle, contrasts with their potential for long-distance passive dispersal and presumably high gene flow. These observations suggest that holoplankton species are adapting to surprisingly small-scale oceanographic features and imply either limited dispersal or strong selection gradients. Acartia tonsa is a widespread and numerically dominant estuarine copepod containing deep mitochondrial lineages within and among populations along the northwestern Atlantic coast. In this study, we intensively investigated A. tonsa populations in Chesapeake Bay with the goals of testing species status for the deep lineages and testing for their association with environmental features over space and time. Phylogenetic analyses of DNA sequences from mitochondrial cytochrome c oxidase I (mtCOI) and the nuclear ribosomal internal transcribed spacer (nITS) resolved two concordant monophyletic clades. Deep divergence between the two clades (13.7% uncorrected sequence divergence for mtCOI and 32.2% for nITS) and genealogical concordance within sympatric populations strongly suggest that the two clades represent reproductively isolated cryptic species. Based on restriction fragment length polymorphisms of mtCOI, representatives from the two clades were found consistently associated with contrasting salinity regimes (oligohaline vs. meso-polyhaline) with an overlap between 2 and 12 PSU in samples from 1995 to 2005. Finding these patterns in one of the best-known estuarine copepods reinforces the conclusion that marine biodiversity is underestimated, not only in terms of species numbers, but also with respect to niche partitioning and the potential importance of ecological divergence in marine holoplankton.     

Extraordinary prolongation of the life cycle in a freshwater planktonic copepod

The limnetic copepod Cyclops scutifer Sars shows an extraordinarily prolonged life cycle in a temperate lake near Oslo, Norway. Developmental sequences become one, two, and three years old, and there are circumstantial evidence of a four year old fraction. Prolongation of the cycle is mainly caused by two consecutive periods of diapause, the first as small copepodids during the second winter, the other as large copepodids during the third winter. There is a marked concentration of diapausing individuals in a small area of the bottom at the deepest part of the lake. There is evidence that this concentration is caused by a horizontal migration to areas with optimal oxygen conditions. The adaptive value of a prolongation of the life cycle is assumed to be an increase in the reproductive potential caused by a spreading out of the reproductive period by three year classes succeeding each other throughout the summer.     

Implications of floral resources for predation by an omnivorous lacewing

Understanding the relationship between a predator and its prey requires consideration of the other food resources used by the predator. In the case of true omnivores, these include plant-provided foods such as leaf tissue and nectar. The presence of plant resources can increase or decrease predation depending on the degree to which they are complementary to, or substitutable for, the prey. This has implications for the role of omnivores in biological control and some groups, notably heteropteran bugs and phytoseiid mites, have been studied in this context. However, few experiments have considered the effects of plant resources both on prey consumption by individual omnivores (which have an immediate effect on the prey population) and on attributes such as longevity and fecundity which act over the longer term to affect predation at the population level. In this study, a model system comprising an omnivorous adult lacewing (Micromus tasmaniae), buckwheat flowers and aphid prey was used to investigate how floral resources affected per capita predation rate, longevity and fecundity of the lacewing. Flowers reduced prey consumption. In the absence of prey, longevity was higher for lacewings with flowers than those without. In an experiment where aphids were provided in abundance, lacewing fecundity was unaffected by flowers. However, when aphids were less abundant, providing flowers decreased the pre-oviposition period and increased the daily oviposition rate. The results demonstrate that floral resources can mediate omnivore–prey relationships and that, in the context of biological control, their effects may be either positive or negative.     

Feeding rates of planktonic copepods from a tropical sea

The feeding rates of the marine planktonic copepods, Eucalanus subcrassus Giesbrecht, Tortanus gracilis (Brady), Calanopia elliptica (Dana) (both male and female), Temora turbinata (Dana), and Paracalanus aculeatus Giesbrecht (only female) from tropical inshore waters have been studied. Newly hatched Artemia nauplii (for Eucalanus, Tortanus, and Calanopia), Dunaliella (for Temora), and Skeletonema (for Paracalanus) were used as food.Feeding rates were measured for a single individual through successive incubations once or twice a day until death to determine changes in feeding rate after collection. Copepods survived from a few days to three weeks. In general, feeding rates varied from day to day, but were less variable than the differences between day and night rates. In some cases, feeding rate consistently decreased up to the death of the copepod. Daily ration, estimated in terms of percentage body weight, was in the range of 28–329 ‰ Using the results together with the those of other workers, gives the relation between daily ration (Y, % body weight) and body weight of copepods (X; μg dry weight) at 20 °C as, logY = 2.531?0.377 logX.Copepods given Artemia nauplii as food killed more nauplii than were eaten. This phenomenon, tentatively called ‘over-hunting’, is possibly an important feeding behaviour for carnivorous copepods.     

Glucose metabolism by Lactobacillus divergens

Earlier studies on the fermentation of D-[1-14C]- and D-[3,4-14C]glucose by Lactobacillus divergens showed that lactate was the major fermentation product and that it was probably produced by glycolysis. It was therefore recommend that L. divergens be reclassified as a homofermentative organism. In the present investigation, products of D-[1-14C]-,D-[2-14C]- and D-[3,4-14C]glucose fermented by L. divergens were isolated, and their specific radioactivities and the distribution patterns of radioactivity in their C-atoms were determined. The positional labelling patterns of the fermentation products, their specific radioactivities and their concentrations confirmed that glucose is degraded via the glycolytic pathway. Some secondary decarboxylation/dissimilation of pyruvate to acetate, formate and CO2 was also observed. These results provide conclusive proof that L. divergens is indeed a homofermentative organism. Results obtained with D-[U-14C]glucose showed that approximately three-quarters of the lactate but less than 10% each of the formate and acetate were produced from glucose. The remainder was presumably derived to a varying degree from endogenous non-glucose sources such as fructose and/or amino acids.     

Seasonal fluctuations in fecundity and hatching success in the planktonic copepod Centropages typicus

A mismatch of {small tilde}2–3 months was observed betweenreproductive rates and population abundances in the planktoniccopepod Centropages typicus, with the highest production atrelatively low female abundance and low production at high abundance,during the course of a 2 year study in 1989 and 1990 in neriticwaters of the Gulf of Naples. During this period, egg mortalitywas at times severe, with values as high as 59% in February1989. The seasonal trend in percentage hatching success didnot match seasonal fluctuations in breeding intensity, and wasnot correlated with variations in environmental variables suchas temperature and chlorophyll a. The results of experimentsusing the fluorescent dye Hoechst 33342 showed that unhatchedeggs had been fertilized and that in most cases developmenthad proceeded to an advanced stage before death of the embryo.The causes of high egg mortality are uncertain, but here wegive evidence, for the first time, that egg mortality may notonly be due to infertility caused by failure to remate.     

The mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis

1. Quantitative aspects of the mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis, including duration and frequency of mating, duration of various phases of the oviducal cycle, egg production rate and adult longevity were studied under laboratory conditions. One set of copepods was fed the alga Chlamydomonas reinhardtii whose density was adjusted to 2 × 10⁵ cells mL^?1 (about 10 mg C L^?1), another set was fed a mixed diet consisting of natural plankton (copepod nauplii, small rotifers and large algae) in the size range of 50–150 μm (dry mass approximately 90 mg L^?1). 2. The entire mating process, from the grasping of the female by the male’s right geniculate antennule to the separation of the pair, lasted about 2 min. Spermatophore placement started at about 30 s to 1 min after mating began and took approximately 1 min. Immediately after the spermatophore had been fixed in the female’s genital segment, the pair separated. 3. The total oviducal cycle, including the gravid phase where the female carried ripe oocytes and the non‐gravid phase where the female did not carry ripe oocytes, lasted about 5–6 days. The non‐gravid phase was particularly long; it was longer than the gravid phase and constituted 62–72% of the total cycle. 4. Mating and spermatophore placement usually occurred with gravid females although occasionally (in 30 of 200 observations) spermatophores were attached in the genital segment of non‐gravid females. Generally two to four, but up to seven, spermatophores were observed at a female’s genital segment at the same time. 5. Clutch size, rate of egg production and adult longevity depended on food. When fed on C. reinhardtii, females carried 7–8 eggs clutch^?1, produced a mean of 1.3 clutches and lived 14 days on average. When fed natural mixed food, females carried 10 eggs clutch^?1, produced 5.6 clutches and lived 37 days on average. 6. Removal of males after the first clutch resulted in no further egg production. Re‐mating is necessary in E. gracilis for continuous clutch production and the production of fertile eggs. 7. Mating duration is comparatively short and the non‐gravid phase comparatively long in E. gracilis. This could be an adaption to the life in the pelagic zone of the lake, where fish predators are present. Fish select ovigerous females, pairs in copula and, probably, females with ripe oocytes which make them conspicuous. Thus, a short mating duration and a prolonged period without conspicuous oocytes, can be advantageous.     

Effect of lipid reserves on individual carbon content of two planktonic freshwater copepod species

The effect of the variation of lipid droplet volume on individual carbon content was studied in two species of planktonic freshwater copepods, Eudiaptomus gracilis G.O. Sars and Thermocyclops oithonoides G.O. Sars. It was found, that when a multiple regression of carbon content on prosoma and lipid droplet volume instead of a simple regression of carbon content on prosoma volume was applied, the unexplainied variance of individual carbon content of Eudiaptomus gracilis could be reduced. However, the use of multiple regression on Thermocyclops oithonoides data did not lead to significantly higher coefficient of determination than was obtained by using a simple regression.     

Modelling physico-chemical factors affecting occurrences of a non-indigenous planktonic copepod in northeast Pacific estuaries

Estuarine ecosystems along the Pacific coast of North America are vulnerable to invasions by non-indigenous planktonic copepods, with documented invasions by at least nine species introduced via ship’s ballast. One of these, the calanoid copepod Pseudodiaptomus inopinus, now occurs in a relatively wide geographical area in coastal estuaries of Washington and Oregon States. Although it appears to be well established in the region, plankton surveys conducted in 1992, 1996, 2000, and 2004 in estuaries from southern Vancouver Island in British Columbia, Canada, to northern California, United States indicate that it has not expanded its range. This static distribution suggests that P. inopinus has reached a distributional limit, and it may thus be a good organism for applying models for predicting planktonic invasions, by characterizing estuaries with and without populations of the copepod. In this study, we applied both parametric, linear (discriminant function analysis, logistic regression) and nonparametric, non-linear (classification trees) techniques to develop models for occurrence of P. inopinus, to identify parameters that may lead to successful invasions and to identify specific estuaries or regions that might be at risk of invasion by this species. Both model types had similar results, identifying relatively simple salinity- and stratification-based models as good predictors of P. inopinus. While different models selected slightly different sets of variables and thresholds, all models identified relatively low salinity and stratification of water column temperature and salinity as important predictors of P. inopinus presence. The models also identified several “false positives” that mainly occurred in more inland waters of Puget Sound—estuaries that did not have P. inopinus, but had the conditions that support it, and which may be at risk for future invasions by this species.     

Food-specific spatial memory biases in an omnivorous bird

The tendency of nectarivorous birds to perform better on tasks requiring them to avoid previously rewarding locations (to win-shift) than to return to them (win-stay) has been explained as an adaptation to the depleting nature of nectar. This interpretation relies on the previously untested assumption that the win-shift tendency is not associated with food types possessing a different distribution. To test this assumption, we examined the specificity of this bias to different food types in an omnivorous honeyeater, the noisy miner (Manorina melanocephala). As predicted, we found that the win-shift bias was sensitive to foraging context, manifesting only in association with foraging for nectar, not with foraging for invertebrates.     

Acanthodiaptomus denticornis another omnivorous calanoid copepod: description of its mouth appendages and feeding experiments on animal prey

The mouthpart morphology of the freshwater calanoid copepod Acanthodiaptomus denticornis was examined with optical microscopy. The mouthparts have sharp teeth and stout appendages with clawlike setae, typical of omnivorous calanoid mouthpart morphology. Observation of the buccal aperture with Scanning Electron Microscopy shows a large opening permitting feeding on prey as large as Keratella cochlearis. These observations agree with our feeding experiments which show that A. denticornis feed on K. cochlearis.     

Egg production of the marine,planktonic copepod,Calanus pacificus Brodsky: Laboratory observations

When acclimated to a continuous, superabundant food supply and constant temperature, Calanus pacificus Brodsky females produce eggs at a weight-specific rate ranging from 0.13 · day^?1 at 8°C to 0.21 · day^?1 at 15°C. Maximum weight-specific egg production rates do not change with seasonal changes in female body size. The relationship between egg production rate and food concentration is hyperbolic, with threshold and critical concentrations that are high relative to other species for which data are available. Food concentration and temperature influence spawning frequency (i.e., the time required for oocytes to mature) much more than the number of eggs in a single spawning event (i.e., clutch size). Clutch size is significantly related to female body size.     

The effect of reproductive condition on egg production rates in the planktonic copepod Centropages typicus

Centropages typicus females oscillated between a dark, ripestage of oogenesis and a light, unripe stage of primary oocytes.The number of eggs released after 24 h under different experimentalconditions was strongly dependent on the reproductive statusof females at the time of incubation.