The life history and vertical distribution of the chaetognath, Sagitta elegans, in Dabob Bay, Washington

Seasonal changes in the population structure and patterns ofvertical distribution and migration of the dominant chaetognath,Sagitta elegans, in a fjord off Puget Sound were determinedwith samples collected at approximately semi-monthly intervalsfrom November 1972 to November 1973. S. elegans bred continuouslyfrom March through August, with major recruitment in June andJuly. Seasonal changes in the vertical distribution of the populationand in the proportion of the population that vertically migratedreflected the stage of maturity and size of the individuals.Small chaetognaths were non-migratory and distributed in thetop 100 m. Stage II individuals were dispersed throughout thewater column; some did migration was evident. Breeding stageswere restricted to a layer between SO and 100 m during the dayand migrated to the surface layer at night, enhancing the probabilityof successful reproduction.     

Studies on Plankton Parasites: III. Examples of the Interaction between Parasitism and other Factors determining the Growth of Diatoms

This paper deals with the interrelations of populations of planktonorganisms and their parasites in two English lakes. The organismsconsidered are diatoms, mainly Asterionella farmosa but alsoTabellaria fenestrata var. asterionelloides, Fragilaria crotonensis,and Melosira italica, with a blue-green Oscillatoria agardhiivar. isothrix. The parasites are the Chytrids Rhizophidium planktonicumon diatoms and R. megarrhizum on Oscillatoria. The parasites may delay the time of maximum algal number ormay decrease the size of the maximum. Generally parasitism ofone alga favoura the development of others. Various other complexitiesarise from the interaction of these factors with nutritionalconditions.     

Composition and seasonality of nocturnal peracarid zooplankton from coastal New Hampshire (USA) waters, 1978-1980

Seasonal changes in the nocturnal peracarid zooplankton froma nearshore area of the Gulf of Maine were studied from January1978 through December 1980 as a requirement of an ecologicalmonitoring program for the Public Service Company of New Hampshire'sSeabrook Generating Stanon. Numerically dominant species includedthe mysids Michteimysis mixta and Neomysis americana. the amphipodsPontogeneia inermis, Themisto gaudichaudi and Monoculodes edwardsi.and the cumaceans Diastylis polita and Lamprops quadriplicata.A general seasonal cycle was documented with a more abundantand speciose assemblage during fall and winter than summer.Peak abundance occurred during spring months prior to emigrationof juvenile M.mixta from the study area. Abiotic and bioticfactors which may affect the structure and composition of thisassemblage are discussed.     

Seasonal variations in copepod size: effects of temperature, food abundance, and vertebrate predation

Seasonal dry weights of female and male Cyclops bicuspidatusthomasi, Diaptomus ashlandi and Diaptomus minutus were studiedin southeastern Lake Michigan during 1975–1981. Smallestanimals occurred during summer and early fall, and largest animalsin winter and spring, a pattern reported for other copepods.The range of weights for the species and sexes decreased fromwinter to summer, and converged in summer to a value of approximately2 µg/animal. Surface water temperature and abundancesof young-of-the-year (YOY) fish were inversely correlated withweights of males and females of the three copepod species. Standingstocks of important phytoplankton groups, especially pennatediatoms and flagellates, were positively correlated with copepodweight. Seasonal change of copepod body size appears to be morethan simply a function of temperature; seasonal predation byYOY fish may be a factor influencing sizes of adult copepods.     

Seasonal patterns in gonad maturation, sex ratio and size in some small, high-latitude copepods: implications for overwintering tactics

Seasonal changes in gonad maturation, sex ratio and size aredescribed for field populations of the marine calanoid copepodsPseudocalanus acuspes (Giesbrecht, 1881) and Acartia longiremisLilljeborg in Balsfjorden, northern Norway. Reproductive populationsof both species were present from March to September. Beginningin August, gonads in P.acuspes late copepodites and A.longiremisadult females switched to an undeveloped resting state. Dormancywas terminated in late winter, several weeks before the vernalbloom. Small samples of Pseudocalanus minutus (Boeck) indicatedboth an earlier induction and termination of the overwinteringphase in this species. Overwintering populations of P.acuspescopepodite stage V were dominated by males, but sex ratios evenedout at the time of spring moulting and mating. Juvenile maleswere larger than the females, except after the vernal bloomand in early summer. The findings are discussed in relationto seasonal life history tactics. ¹Present address: Department of Aquatic Biology, The NorwegianCollege of Fishery Science, University of Tromsø, Dramsveien201B, N-9037 Tromsø, Norway     

Pairing success of male Gammarus lacustris infected by two acanthocephalans: a comparative study

The costs of parasitism to host reproduction can be best assessedusing field studies to determine overall mating success andexperimental studies to examine how parasites may affect matingbehavior. We compared the influence of two parasites, Polymorphusparadoxus and P. marilis (Acanthocephala), on the pairing successof their intermediate host (Gammarus lacustris, Crustacea) inboth the field and laboratory. Parasitism significantly loweredthe pairing success of male gammarids. In the field, P. paradoxus-infectedmales paired significantly less often than P. marilis-infectedor uninfected males. Those infected by P. marilis were alsofound in precopula significandy less often than uninfected ones.In the laboratory, the pairing success of males infected byeither parasite was significantly reduced in both competitiveand noncompetitive situations. As in the field studies, thepairing success of P. paradoxus-infected males was significantlylower than that of P. marilis-infected and uninfected males.Polymorphus marilis-infected males were also outcompeted byuninfected individuals, however, their pairing success improvedwhen alone with a female (noncompetitive experiments). We relatethe differential influence of the two parasites on the pairingsuccess of male gammarids to their effects on the physiologyand behavior of G. lacustris.     

Seasonal variation in the species composition of tintinnid cilates in Hiroshima Bay, the Seto Inland Sea of Japan

Seasonal changes in the species composition of tintinnid ciliateswere examined based on time-series samples taken at 2 week intervalsover a 3 year period in Hiroshima Bay, the Seto Inland Sea ofJapan. The maximum abundance of total tintinnids over the entireperiod was 5.7 x 10³ indi viduals l^– Among 32 speciesidentified, a consistent seasonal occurrence was recognizedin 22 species. The relationships between various environmentalfactors and the abundance of each species of tintinnids wereanalyzed using principal component analysis From this analysis,the abundance of many tintinnids was revealed to be associatedwith temperature, the <20 µm size fraction of chlorophylla and water column stability, but not with the <20 µmsize fraction of chlorophyll a, nor with salinity. From theseresults, tintinnid species were divided into five associationtypes: species whose abundance increased with increasing temperature,decreasing temperature, nanophytoplankton abundance, increasingwater column mixing, or increasing water stratification coupledwith low temperature.     

Glutamine Synthetase Isoenzymes of Striga hermonthica and other Angiosperm Root Parasites

The occurrence of multiple forms of glutamine synthetase inStriga hermonthica and other angiosperm root parasites was investigated.The facultative chlorophyllous parasite Melampyrum arvense exhibitedtwo isoenzymes in leaf tissue, the cytosolic component (GS₁)comprised less than 30% of total glutamine synthetase. In contrastGS₁ was the major component (<70%) in photosynthetic tissueof Striga hermonthica and S. gesnerioides. Only a single isoenzyme(GS₁) was detectable in the achlorophyllous root parasites Orobancheand Lathraea and in non-photosynthetic tissue of S. gesnerioides.The kinetic and physical properties of GS₁ and GS₂ of theseangiosperm parasites were similar to those of the isoenzymesin other non-parasitic angiosperms. Key words: Glutamine synthetase, Angiosperms, Root parasites     

VARIATIONS IN INFESTATIONS OF SIPHONARIA CAPENSIS AND S. CONCINNA(PULMONATA) BY LARVAL TREMATODES IN SOUTHERN AFRICA

The prevalence of digenean trematode parasites in Siphonariacapensis (Pulmonata) was examined in populations from 24 sites,and in S. concinna from 10 sites along the coast of southernAfrica from 1989 to 1991. Sporocysts containing cercariae werefound in the digestive gland of both species. To date, two typesof cercaria have been isolated from S. capensis and one typefrom S. concinna, these types possibly representing three distinctspecies of trematode. In approximately 30% of parasitized S.capensis and 10% of parasitized S. concinna the digestive glandwas completely destroyed. In both species of Siphonaria therewas considerable temporal and spatial variation in parasiteprevalence. At some locations up to 40% of S. capensis wereinfected whereas at others, no parasites were found. Prevalenceof trema-todes in S. concinna rarely exceeded 12%. At severalsites the prevalence of infestation within the limpets increasedwith increasing host size. (Received 8 June 1992; accepted 6 July 1992)     

Testosterone, immunocompetence, and honest sexual signaling in male red grouse

The expression of sexual ornaments has been suggested to reliablyindicate individual quality, such as the ability to cope withparasites and diseases. The Immunocompetence Handicap Hypothesis(IHH) states that testosterone-dependent ornaments honestlysignal such quality because of physiological costs associatedwith testosterone, such as impaired immune function. We testedpredictions of the IHH both correlatively and experimentallyin red grouse Lagopus lagopus scoticus. Male grouse exhibitsupra-orbital red combs whose size is testosterone-dependent.We found that comb size was not correlated to infection intensityby two parasites (coccidia and the nematode Trichostrongylustenuis), but it was significantly positively correlated withcondition and T-cell-mediated immunity (the ability to mounta primary inflammatory response). We manipulated testosteroneby means of implants and re-caught males after a month to investigatethe effects on comb size, condition, immunity, and parasiteload. Males implanted with testosterone had increased comb size,lost more condition, and had lower T-cell-mediated immunitythan control males. Increased testosterone also resulted ina significant increase in coccidia infection intensity but hadno effect on T. tenuis burden. The results are consistent withpredictions of the IHH and suggest that comb size honestly indicatesimmunocompetence and males' ability to cope with certain parasites.Females could thus benefit from choosing mates based on theexpression of this sexual trait.     

The assessment of size variation in Loch Leven phytoplankton: methodology and some of its uses in the study of factors influencing size

The dimensions of individuals of many phytoplankton speciesvary considerably during the population cycle and during long-termsuccession, as well as at any one point in time. Moreover, thetype of size-frequency distribution also fluctuates by being,for example, normal on one occasion and variously departingfrom this condition on another. As a consequence, parametricand many non-parametric methods are of limited value in thestatistical analysis of size data. In this paper the graphical method of Sokal and Rohlf (1969),based on rankits, has been used to assess size spectra of algalplankton. Brief consideration is given to the effects of samplepreservation on algal size, the need for a random choice ofindividuals to be measured, and the size of measuring unit toemploy. Proformas are described which enable the microscopistwithout computer facilities to record measurements in a mannerfacilitating easy tabulation with rankits in readiness for graphing. Seasonal information on size-frequency distributions for a numberof algae are illustrated with rankit-dimension plots. A distinctionis drawn in these results between what are usually normally,or near-normally distributed values, and those showing markeddepartures from the normal distribution. The tendency to follow one or other of these 2 main types ofdistribution appears to be largely a function of the range ofvalues (ratio of maximum to minimum value) in the sample, withthe wider-ranging populations generally departing the most fromthe normal. The orientation of the measured axis with respectto the plane of cell division may also affect the form of theplots, and results must be interpreted with especial care wherethe mono-specificity of the samples is in doubt. Some experimentalresults are described in order to illustrate some uses of therankit graph method in investigating environmental controlsof size. These results indicate also the potential ability thatdense swarms of zooplankton (Daphnia and Cyclops) have for alteringthe length spectra of Oscillatoria and Melosira threads.     

Natural development time of Eodiaptomus japonicus (Copepoda: Calanoida) in Lake Biwa

Seasonal and ontogenetic changes in natural development timewere studied for Eodiaptomus japonicus in Lake Biwa in 1986and 1987. Wild individuals in a certain developmental stagewere collected, fed on natural food and examined until theyhad moulted twice. Natural development times fluctuated irrespectiveof temperature from May to October. Food deficiency delayeddevelopment in all feeding stages, and food availability probablydetermined natural development time. Serious food limitationraised mortality in copepodid stage I. In November developmentwas delayed even with enough food. The development of E.japonicuswas almost isochronal except for a short prefeeding naupliarstage I and a long copepodid stage V.     

SEASONAL CHANGES IN THE BIOCHEMICAL COMPOSITION OF A TROPICAL INTERTIDAL PROSOBRANCH MORULA GRANULATA (DUCLOS)

Seasonal changes in total carbohydrates, glycogen, free sugars,proteins, TNPS and lipids, were studied in different body components(foot, gonad-digestive gland complex and viscera) of Morulagranulata from January to December 1982. All biochemical constituentsshowed a progressive increase during May–October and adecrease during November–April; some exhibited a secondaryJanuary peak. These changes were correlated to the reproductivecycle and feeding of the animal. Utilisation of lipids was greaterduring the reproductive season indicating a ‘lipid-oriented’ metabolism. Seasonal changes in the water content offoot, gonad-digestive complexand viscera were also reported.The results are discussed in relation to other observationson gastropods and other molluscs. (Received 24 May 1984;     

Differential effects of a parasite on ornamental structures based on melanins and carotenoids

Models of sexual selection predict that ornamental colorationshould be affected by parasites in order to serve as honestsignals. Animals are commonly infested by a range of parasitespecies and often simultaneously display several ornaments.Thus the specific effect of a given parasite on ornaments isimportant for the understanding of the signal. Here we investigateexperimentally the effect of an ectoparasite on carotenoid-and melanin-based traits in breeding great tits Parus major.In the experiment, nests were either infested with hen fleas,Ceratophyllus gallinae, or kept free of parasites. The colorof the two traits and the size of the melanin-based breaststripe were assessed both in the year of experimental parasiteinfestation and during the following breeding season, afterthe annual molt. The size of the breast stripe of infested malesand females significantly decreased, but increased significantlyin uninfested males and females. The blackness of the breaststripe and the carotenoid-based plumage coloration was unaffected.Our experiment demonstrates that the size of the melanin-basedbreast stripe of adults depends on parasite infestation, suggestingthat the trait can serve as an honest signal of previous parasite exposure.     

Egg production of individual copepods of Acartia grani Sars from coastal waters: seasonal and diel variability

Seasonal and diel fecundity patterns of adult Acartia granifemales from a coastal area of Malaga Bay (south of Spain) werestudied between spring and autumn 1990. Copepod egg productionwas measured in situ by short-term (     

The effect of container size on the feeding rate of Heterocope septentrionalis, a freshwater predaceous copepod

The feeding rates of freshwater predaceous copepods have beenmeasured many times using enclosure experiments. Typically theseexperiments involve enclosing a known number of zooplanklonprey with a known number of predaceous copepods and determiningthe number of prey remaining after a set length of time. Variousfactors such as prey species and size have been shown to influencethe feeding rate of copepods. However, little attention hasbeen paid to the influence that container size may have on feedingrates. Using previously published data and some new data itwas found that container size has a major impact on the feedingrate of Heterocope septentrionalis, a predaceous freshwatercopepod common in North American arctic waters. In experimentswith Daphnia puiex, where container size varied from 0.3 to54 l (180 times), the measured feeding rate coefficient variedfrom –0.04 to –1.7 (42.5 times). Other prey speciesshowed similar changes, but the vulnerability of particularprey species to Heterocope predation remained consistent acrossthis range of expenmental containers. The reason for the containereffect is not known, but it is postulated that edge avoidanceby Heterocope may account for the observed change in feedingrate.     

Parasite-induced change in host behavior of a freshwater snail: parasitic manipulation or byproduct of infection?

Host behavioral changes due to parasitism are often assumedto be adaptations of the parasite. However, behavioral effectsof parasites may be a generalized response to parasitism andonly coincidentally beneficial for parasite transmission. Forthis reason, alternatives to the manipulation hypothesis shouldbe tested. Previous work demonstrated that the trematode parasiteMicrophallus sp. influences the behavior of the snail Potamopyrgusantipodarum in a way that may increase the probability of transmission.Here I report work conducted to test alternatives to the manipulationhypothesis. In a field study, the effect of Microphallus onbehavior was compared to that of two other castrating parasitegroups to determine if the behavioral change is simply a byproductof parasitism. Also, the foraging behaviors of infected anduninfected snails were examined in the presence and absenceof food resources to determine if the hunger level of Microphallus-infectedsnails could account for the parasite-induced behavioral change.First, Microphallus-infected snails were found on top of rocksduring the day less often than the two other parasite groups. Thisevidence suggests that the behavioral change caused by Microphallusis specific to Microphallus-infected snails. Second, Microphallus-infectedsnails responded to the lack of food differently from uninfectedsnails. Uninfected snails retreated to safer positions underrocks when the food source was removed from the top of the rocks,while Microphallus-infected snails remained on top of the rockswhere the risk of consumption by the final host is greater.Taken together with previous studies, these results suggestthat infection by Microphallus results in behavior that enhancesparasite transmission.     

Elevated spring testosterone increases parasite intensity in male red grouse

The expression of testosterone-dependent sexual traits mightsignal the ability of their bearers to cope with parasite infections.According to the immunocompetence handicap hypothesis (IHH),such signals would be honest because physiological costs oftestosterone, such as a reduced ability to control parasiteinfections, would prevent cheating. We tested whether testosteronewould affect the outcome of a standardized parasite challengein red grouse, using a main parasite of the species, the nematodeTrichostrongylus tenuis. We caught males in spring, removedtheir nematode parasites, and implanted them with testosteroneor empty implants, as controls. After 1 month, they were reinfectedwith a standard dose of infective T. tenuis parasites. Whenchallenged, testosterone males had relatively less globulinrelative to albumin plasma proteins than control males, an indicationthat they had experienced increased physiological stress. Testosterone-treatedmales had significantly more T. tenuis parasites than controlsin the next autumn and also had more coccidia and lost moreweight than controls. Testosterone-treated males neverthelessbenefited from their elevated spring testosterone: they hadbigger sexual ornaments than controls both in spring and autumn,and they tended to have a higher pairing and breeding successthan controls. Our results supported the IHH in showing thatelevated testosterone impaired the ability of males to copewith a standardized challenge by a dominant parasite. Testosteronethus plays a key role in mediating trade-offs between reproductiveactivities and parasite defense, and testosterone-dependentcomb size might honestly signal the ability of red grouse tocontrol T. tenuis infection.     

Egg production and hatching success in the calanoid copepods Calanus helgolandicus and Calanus finmarchicus in the North Sea from March to September 2001

Spatial and seasonal egg production rates (E_r) and egg hatchingsuccess in the copepods Calanus finmarchicus and Calanus helgolandicuswere measured in the North Sea from March to September. Foodavailability was monitored by chlorophyll and protist concentrationsand three size fractions of seston fatty acids. Seasonal andspatial distribution and production differed between the species.Calanus finmarchicus was found only offshore of the 50-m isobath,with decreasing E_r (37–28 eggs female^–1 day^–1)from March to July. Calanus helgolandicus had two abundancepeaks, in spring and autumn, with a low in May during whichtime the highest E_r were observed (38 eggs female^–1 day^–1).At other times, E_r in C. helgolandicus remained lower than inC. finmarchicus (     

Photosynthesis and primary production of Microcystis aeruginosa Kutz. in Lake Kasumigaura

Seasonal changes in the photosynthesis and primary productionof Microcystis aeruginosa Kütz. were investigated in LakeKasumigaura during 1981–1982. Microcystis always showeda light-saturated photosynthesis-light curve. Both P_max andthe initial slope of the photosynthesis-light curve of Microcystisin early summer were very high, so it was concluded that Microcystisutilized both low and high light intensities efficiently. TheP_max of Microcystis was found to be a function of the watertemperature except in August and September. The linear regressionon the temperature-P_max relationship discontinued at 11°C,where the P_max value dropped; Microcystis did not photosynthesizebelow 4°C. The initial slope of the curve was also descendingbelow 11°C. It is suggested that Microcystis changes itsphysiological properties below 11°C. The highest value ofgross production calculated for M. aeruginosa was 5.4 gC m^–2d^–1 in July; the annual gross production was estimatedto be 300 gC m^–2year^–1 (i.e., 40% of the total primaryproduction in this lake).