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1.
A mismatch of {small tilde}23 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. 相似文献
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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. 相似文献
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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. 相似文献
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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. 相似文献
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Microsetella norvegica is a widely distributed marine planktonicharpacticoid copepod, which is poorly known from the biologicalpoint of view. We investigated the seasonal population dynamicsandproduction of M. norvegica in the central part of the InlandSea of Japan. It occurred throughout the year, whilst its reproductionwas confined to the warm season between May and November. Theproportion of ovigerous females, which carry a single egg sac,was low (mean: 23.1%) in August and September, and high (53.6%)in October. Their brood size attained a maximum (mean: 15.8eggs per sac) in July and August and declined gradually to 6.2eggs in November. Duration time from egg laying to moultingto adulthood was temperature-dependent; it was 31.9 and 14.3days at 20 and 27°C, respectively, under excess food conditionsin the laboratory. An enormously high population abundance (7.32x 104 individuals m-3), which accounted for 86.5% of the totalcopepods, and biomass (69.6 mg C m-3) gave an annual maximumproduction rate of 4.90 mg C m-3 day-1) in October. Naupliiand copepodites disappeared in December, and the overwinteringpopulation was represented by adults, mainly large females.Associations of M. norvegica with marine snow aggregates, whichhave often been found in oligotrophic waters, were not observedin the food-rich environment of the Inland Sea of Japan. 相似文献
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Jeffrey A. Runge 《Journal of experimental marine biology and ecology》1984,74(1):53-66
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. 相似文献
7.
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. 相似文献
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Kåre Elgmork 《Ecography》1981,4(4):278-290
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. 相似文献
9.
Omnivorousness in marine planktonic copepods 总被引:6,自引:0,他引:6
Adult females of Centropages furcatus and Temora stylifera hadsignificantly different feeding behaviours. At equal averagefood concentrations, C. furcatus ingested more nauplii of thecalanoid copepod Pseudodiaptomus coronatus and fewer diatomsthan T. stylifera. At 20°C and 2.0 µg of nitrogen.1.1.1of each food source, C. furcatus ingested 17.2% and 4.4% ofits body nitrogen daily as nauplii and diatoms, respectively.Ingestion rates of the same food sources by T. stylifera were5.1% and 14.5%, respectively. At the environmental concentrationssimulated in these experiments, the presence of diatoms didnot affect the ingestion of nauplii nor did the presence ofnauplii affect diatom ingestion. The behaviour of predator andanimal prey largely dictates the types and quantities of preyingested. 相似文献
10.
Priority effects occur when a species or genotype with earlier arrival has an advantage such that its relative abundance in the community or population is increased compared with later-arriving species. Few studies have dealt with this concept in the context of within-species competition. Skeletonema marinoi is a marine diatom that shows a high degree of genetic differentiation between populations over small geographical distances. To test whether historical events such as priority effects may have been important in inducing these patterns of population differentiation, we performed microcosm experiments with successive inoculation of different S. marinoi strains. Our results show that even in the absence of a numerical advantage, significant priority effects were evident. We propose that priority effects may be an important mechanism in initiating population genetic differentiation. 相似文献
11.
Nancy H. Marcus 《Journal of experimental marine biology and ecology》1985,91(3):263-269
Daily pattern of egg release has been studied in the marine calanoid copepod, Labidocera aestiva (Wheeler) under cycling light-dark (12L-12D, 12D-12L) conditions, and constant light (24L) or darkness (24D). Under cycling conditions maximum egg release occurred during the dark phase. Rhythmic spawning was also evident under 24D, but not under 24L. The results suggest that the pattern of nocturnal egg release is regulated by an endogenous rhythm entrained by light. 相似文献
12.
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. 相似文献
13.
The marine bacterium L.16.1 (Alcaligenes sp.) grows preferentially on alkanes (C10 to C18) with a very high growth yield (98 per cent); optimal growth depends strictly on the presence of a well-defined NaCl concentration (100 mM). Our strain is constitutive for the enzymatic systems responsible for the oxidation of alkanes to fatty acids, i.e. NADH-dependent hydroxylase, alcohol and aldehyde dehydrogenases, the latter of which located at the cytoplasmic membrane level. The aerobic oxidation of primary alcohols by particulate extracts prepared in the presence of 400 mM NaCl is NAD+-dependent (Km = 0.082 mM, Vmax = 238 with decanol). With extracts prepared in the absence of NaCl, Vmax undergoes a very strong decrease. On the contrary , the NAD+ (P)+-dependent oxidation of aldehydes is carried out anaerobically by the same extracts irrespective of the presence or the absence of added Na+ in the solutions used for the preparation of these extracts. A possible explanation for our results could be that Na+ acts on the enzymatic systems for which the maintenance of the membrane integrity is essential. This interpretation is consistent with the slowing down of the growth speed accompanying the decrease of NaCl concentration in the growth medium. With regard to alcohol and aldehyde-dehydrogenases, it is noteworthy that these enzymes behave like similar enzymatic activities induced by alkanes in other microorganisms. 相似文献
14.
Bollens Stephen M.; Frost Bruce W.; Cordell Jeffery R. 《Journal of plankton research》1994,16(5):555-564
Recent experimental evidence in both marine and freshwater systemsindicates that predators can induce vertical migration behaviorin individual zooplankters, yet the specific cues by which zooplankterssense their predators appear to vary. In situ manipulation experimentswere carried out with enclosed populations of the marine planktoniccopepod Acartia hudsonica to re-examine the potential role ofchemical cues in the behavior of A.hudsonica, and to test explicitlyfor the role of mechanical or visual stimuli in triggering verticalmigration behavior in this species. Adult female copepods wereinduced to vertically migrate (descend) when exposed to fishmimics during the day, but no such response occurred when thecopepods were exposed to Fish mimics during the night. Moreover,copepods exhibited no changes in vertical distribution whenexposed to water which, having recently held a natural predator(the threespine stickleback, Gasterosteus aculeatus), was presumedto be laden with predator-produced chemical exudates. Predator-mediatedmechanical or visual cues, or a hierarchy of both, are responsiblefor eliciting vertical migration behavior in adult female A.hudsonica.These results, together with those of other investigations demonstratingthe inducing role of chemical exudates, indicate that the stimulieliciting vertical migration in zooplankton can be expectedto vary between species. 相似文献
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The ingestion preferences of planktonic protozoa influence the structure and succession of microbial communities and thus biogeochemical cycling within aquatic environments. Some predatory ciliates and flagellates are reported to switch to cannibalism when no suitable non-self prey items are available for consumption. However, the importance of cannibalism as a survival strategy, and its ubiquity within the planktonic protozoa is not known. We report the first attempt to quantify cannibalism in a phagotrophic marine dinoflagellate (Oxyrrhis marina). Cannibalistic Oxyrrhis cells seldom comprised >2% of any experimental population, including those in which all non-self prey items had been grazed to extinction. Such 'prey-deplete' cultures became dominated by homogeneous populations of highly motile Oxyrrhis that were morphologically unable (too similar in size) to cannibalise. That cannibalism can only occur when 'victim' and 'cannibal' cell size-classes of sufficient difference collide, suggests that cannibalism may be of limited use as a long-term survival strategy in phagotrophic protozoa. 相似文献
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