Effect of essential dietary fatty acids on egg production and hatching success of the marine copepod Temora longicornis

The calanoid copepod Temora longicornis and its food (seston of size < 200 μm) was sampled during three successive seasons (2002-04) in the Trondheimsfjord, Central Norway. Egg production (24 h) and hatching success (72 h) was determined by incubation experiments, and the essential fatty acid (EFA) content of their in situ food was analysed. The dominant EFA in the seston were DHA (22:6n-3) and EPA (20:5n-3), whereas ARA (20:4n-6) were present in low quantities. Egg production and hatching success was relatively low during early spring and late autumn (~ 10 eggs female^- 1 day^- 1 and ~ 30%), and relatively high during summer. Spring phytoplankton, dominated by diatoms, contained low amounts of DHA. Dinoflagellates, small flagellates, and ciliates dominated during summer, when a high content of DHA was recorded.The rate of egg production of T. longicornis did not show any relationship with food concentration (r² = 0.003), but was positively correlated to temperature, although not statistically significantly (r² = 0.48, p = 0.05). The quantitative and percent DHA contents of the food was significantly related to the rate of egg production (r² = 0.96 and 0.95, respectively, p < 0.001), but no such relationship were observed for the quantitative or percent content of EPA and ARA in the seston. The egg production of T. longicornis during May-August was 43-47 eggs female^- 1 day^- 1, with dietary DHA contents higher than 7-8 mg DHA g^- 1 DW. Also the hatching success of T. longicornis was positively correlated to the quantitative content of DHA in the diet (r² = 0.88), but hatching was also inversely related to the percentage ARA (r² = 0.84). The maximum hatching success was found when the ARA content was < 0.15% of total fatty acids and the DHA:ARA ratio was > 50. The conclusion that DHA most strongly affected egg production whereas ARA affected hatching, fit well with earlier findings for fish. Our results do not exclude that toxic aldehydes interact with reproduction of calanoid copepods when diatoms are present, but we observed a consistent pattern where dietary DHA and ARA alone explained a majority of the variability in egg production and hatching of T. longicornis.     

Maternal and neonate diatom diets impair development and sex differentiation in the copepod Temora stylifera

Development and sex differentiation in the copepod Temora stylifera was studied in the presence of maternal and larval diets of the diatoms Thalassiosira rotula and Skeletonema marinoi, either provided alone or supplemented with the control dinoflagellate Prorocentrum minimum. Both diatoms had deleterious effects on growth compared to the control when used as pure diets, inducing very low or even zero survival from hatching to adulthood. This effect was deleted when the diet was supplemented with a good food (P. minimum) only in the case of T. rotula. By contrast, with a maternal or larval diet of S. marinoi, nauplii did not pass metamorphosis even when this alga was mixed with P. minimum. Arrested development was not due to lack of feeding since early and late nauplii (NII and NV) ingested all three algae at similar rates when used as single diets, and did not show any preference when the algae were offered as mixtures. Since mortality rates with a mixed diet of S. marinoi + P. minimum were similar or even higher than those obtained with a single diet of S. marinoi, we suggest that this diatom is more toxic than nutritionally deficient for T. stlyfera development. No males were produced in cohorts reared on pure diatom diets or with a mixture of S. marinoi + P. minimum, and intermediate male:female sex ratios were obtained with the mixed T. rotula + P. minimum diet. Possibly some diatoms produce compounds such as oxylipins or new molecules that alter sex differentiation in T. stylifera.     

Effects of estuarine conditions and organic enrichment on the fecundity and hatching success of Acartia clausi in contrasting systems

The fecundity and hatching success of Acartia clausi were analysed at fixed salinity sites (35, 34 and 33 psu) in two nearby estuaries (Bilbao and Urdaibai, Basque coast, Bay of Biscay) from March to June 1997. Field incubations were conducted to estimate egg production rates and hatching success, and the size of eggs and experimental females measured. Water temperature and dissolved oxygen saturation were also determined, as well as seston samples to quantify food abundance and quality. Between-estuary and within-estuary differences were tested statistically, and correlation and regression analyses were used to determine relationships between reproductive and environmental variables. Egg production rates were higher in the organically enriched estuary of Bilbao; this denoting that food supply controls the fertility of A. clausi in these systems. Temporal patterns of egg production differed between estuaries, and were associated with different nutritional factors in each estuary. Within the salinity range analysed, egg production reached higher values at intermediate salinity (≈34 psu) in both estuaries. This was interpreted as the result of the interaction between the positive effect of food increase, and the negative effect of physicochemical conditions with decreasing salinity. Egg size variations mainly occurred temporally in relation to female size, but no clear trade-off between egg size and egg number was observed in any case. A drop in hatching success in Bilbao, mainly in waters of <34 psu, was related to the oxygen depletion caused by organic pollution. This indicates that organic enrichment in Bilbao has opposite effects on the reproductive success, because it enhances egg production but reduces offspring survival.     

Effects of different diets on the reproduction and naupliar development of the copepod Acartia bifilosa

The influence of diatoms on the reproduction and naupliar development of Acartia bifilosa was investigated under laboratory conditions, comparing initial in situ values and laboratory-food treatments. Egg production by A. bifilosa was significantly reduced by one diatom diet (Phaeodactylum tricornutum: Pt) and by two non-diatom diets (Platymonas subordiformis: Ps and Nannochloropsis oculata: No). It was less affected by the other diatom diet (Skeletonema costatum: Sc) or by two mixed-food treatments (D-mix and DG-mix), composed of two diatoms (Pt, Sc) and four species (Pt, Sc, Ps and No), respectively. The negative effect of Pt was eliminated when adult copepods were offered mixed-food diets. There were no significant differences between the hatching success values observed in filtered seawater and in algal exudates, indicating that diatoms did not produce active dissolved toxic substances under the different food concentrations tested. The mortality rate of nauplii was higher with Pt than the other diets, suggesting that this diatom species had a negative effect on egg production, hatching success and naupliar survival simultaneously. Compared to other diets, No and Pt were not beneficial food sources for reproduction and for female and larval survival.     

New oxylipins produced at the end of a diatom bloom and their effects on copepod reproductive success and gene expression levels

Diatoms are dominant photosynthetic organisms in the world's oceans and are considered essential in the transfer of energy to higher trophic levels. However, these unicellular organisms produce secondary metabolites deriving from the oxidation of fatty acids, collectively termed oxylipins, with negative effects on predators, such as copepods, that feed on them (e.g. reduction in survival, egg production and hatching success) and, indirectly, on higher trophic levels. Here, a multidisciplinary study (oxylipin measurements, copepod fitness, gene expression analyses, chlorophyll distribution, phytoplankton composition, physico-chemical characteristics) was carried out at the end of the spring diatom bloom in April 2011 in the Northern Adriatic Sea (Mediterranean Sea) in order to deeply investigate copepod–diatom interactions, chemical communication and response pathways. The results show that the transect with the lowest phytoplankton abundance had the lowest copepod egg production and hatching success, but the highest oxylipin concentrations. In addition, copepods in both the analyzed transects showed increased expression levels of key stress-related genes (e.g. heat-shock proteins, catalase, glutathione S-transferase, aldehyde dehydrogenase) compared to control laboratory conditions where copepods were fed with the dinoflagellate Prorocentrum minimum which does not produce any oxylipins. New oxylipins that have never been reported before for microalgae are described for the first time, giving new insights into the complex nature of plant–animal signaling and communication pathways at sea. This is also the first study providing insights on the copepod response during a diatom bloom at the molecular level.     

Omnivory in the calanoid copepod Temora longicornis: feeding, egg production and egg hatching rates

We measured in laboratory experiments the ingestion, egg production and egg hatching rates of female Temora longicornis as a function of diet. The diets consisted of a diatom (Thalassiosira weissflogii), an autotrophic dinoflagellate (Heterocapsa triquetra), and a bacterivorous ciliate (Uronema sp.) given as sole foods, or combinations of these single-food items: diatom+dinoflagellate, diatom+ciliate, dinoflagellate+ciliate, and diatom+ciliate+dinoflagellate. For the three single-item diets, the functional response was similar; i.e., ingestion rate increased linearly with food concentration (food range: ∼25 to ∼600 μg C l⁻¹). When all diets were considered, maximum daily carbon ration (∼70% of body weight) was independent of food type. However, the maximum daily egg production rate (12% of body carbon) was obtained with the diatom diet. For all diets, both ingestion and egg production rates increased with food concentration. Ingestion and egg production rates were affected differently by the interaction of food concentration and food type: at low food concentrations, ingestion rates were highest on diets containing the diatom. At high food concentrations, egg production rates were highest on the two phytoplankter diets and their combination. The presence of the ciliate in the diet did not enhance ingestion rate or egg production. Mixed-food diets did not enhance egg production relative to single-food diets. Hence, dietary diversity did not appear to be particularly advantageous for reproduction. Carbon-specific egg production efficiency (EPE; egg production/ingestion) was independent of food concentration and type, and equaled 9%. Egg hatching success was low (mean<30%) and independent of food concentration and type, and egg production rates. Our results are consistent with previous observations that egg production in T. longicornis is enhanced during diatom blooms. However, the relatively low EPE and egg hatching success suggest that reproduction and recruitment in this study were severely constrained by the biochemical composition of the diet, or the physiological condition of the females towards the end of their season of growth in Long Island Sound.     

Effects of chlorophyll concentration and temperature variation on the reproduction and survival of Temora longicornis (Copepoda, Calanoida) in the Eastern English Channel

The influence of temperature and chlorophyll concentration on egg production, hatching success, female survival and body size of the copepod Temora longicornis was investigated in situ in the coastal waters of the Eastern English Channel. Twenty samples were collected between February and July 2003 three to four times per month. The maximum daily level of egg production of 75.5 eggs female⁻¹ was observed in March, with minima of 10 eggs female⁻¹ in February and July. Between February and March egg production increased with chlorophyll concentration. At the end of March a decrease in egg production corresponded to a strong increase in chlorophyll concentration that indicated a Phaeocystis-dominated bloom. After this period egg production closely followed the temporal variation in chlorophyll concentration with a maximum of 55.3 eggs female⁻¹ in April during a second peak of chlorophyll concentration. Hatching success varied between 60% and 80% and was not influenced by chlorophyll concentration, in situ temperature or any other biological parameter considered in this study. Increases in temperature from February to July paralleled a decrease in body length and an increase in the percentage of spawning females. Mean female survival followed the variation of both temperature and chlorophyll concentration only between April and July. Temperature and chlorophyll concentration affected the reproductive parameters of T. longicornis differently. Female survival and body size were negatively correlated with temperature, while the highest chlorophyll concentrations were not always favourable for egg production. Therefore the quality of food should not be associated with chlorophyll quantity. Furthermore, the maximum values of egg production in this study are the highest recorded for T. longicornis. This study, conducted for the first time in the Eastern English Channel, showed high levels of productivity of T. longicornis despite a decrease of egg production during a Phaeocystis sp. dominated bloom in April.     

Impact of the diatom oxylipin 15S-HEPE on the reproductive success of the copepod Temora stylifera

The copepod Temora stylifera was fed with the pennate diatom Pseudo-nitzschia delicatissima for 15 days. This diatom does not produce polyunsaturated aldehydes (PUAs) but only synthesizes other oxylipins such as the hydroxyacid (5Z,8Z,11Z,13E,15S,17Z)-15-hydroxy-5,8,11,13,17-eicosapentaenoic acid (15S-HEPE). Effects of this monoalgal diet were compared to copepods fed with the PUA-producing diatom Skeletonema marinoi and the control dinoflagellate Prorocentrum minimum which does not produce any oxylipins. Both egg production and hatching success were negatively affected by the two diatoms compared to the control diet. Both diatoms also induced malformations in the offspring, with the number of malformed nauplii increasing dramatically with time. Malformed nauplii were apoptotic (TUNEL-positive) indicating imminent death. In terms of recruitment, only 4 healthy nauplii female⁻¹ day⁻¹ with S. marinoi and 9 healthy nauplii female⁻¹ day⁻¹ with P. delicatissima were produced during the 15-day experimental period. The results indicate that P. delicatissima induced negative effects comparable to those of S. marinoi even though it did not produce PUAs. This is the first study that tests the biological activity of oxylipins other than PUAs on copepod reproduction.     

The effect of parental condition on egg-size and reproductive success in short-tailed shearwaters Puffinus tenuirostris

Eggs were exchanged between 50 pairs of shorttailed shearwaters Puffinus tenuirostris on Great Dog Island, Bass Strait, Australia, in an attempt to distinguish the intrinsic effects of egg-size from any effects stemming from differential quality of parental care. At 64 experimental nests, large and small eggs were exchanged whereas at 36 control nests, eggs of equivalent, medium, size were exchanged. Egg-size appeared independent of maternal effects. In both groups, hatching and fledging success were independent both of eggsize and of the body condition of the attending parents. This suggests that breeding success in these birds may be more closely related to the behavioural traits of parents than to physiological factors.     

Seasonal variability in copepod ingestion and egg production on the Faroe shelf

Copepod community ingestion rates of Calanus finmarchicus, Temora longicornis, Acartia longiremis and Pseudocalanus spp., and egg production rates of C. finmarchicus and T. longicornis, were studied in relation to phytoplankton composition, abundance and biomass on the Faroe shelf during a one-year cycle. The phytoplankton community during winter was mainly composed of small flagellates and the copepods of Pseudocalanus spp. As the spring bloom progressed, diatoms increased in abundance and dominated the biomass throughout summer. C. finmarchicus increased in numbers in early spring, while T. longicornis and A. longiremis dominated the community during summer and autumn. While no response in ingestion rates was observed for A. longiremis and Pseudocalanus spp. with increasing diatom biomass, both ingestion rates and egg production of C. finmarchicus and T. longicornis, generally increased, showing a dependence upon diatoms for production. The daily ingestion for C. finmarchicus females was 7% and 22% of body biomass during the pre-bloom and bloom period, respectively, while for T. longicornis females it was 33% and 56% and for A. longiremis females 22% and 33%, respectively. C. finmarchicus accounted for more than 80% of the total copepod ingestion in May, but in mid- and late summer, T. longicornis and A. longiremis dominated, and represented 80–90% of the total copepod ingestion. The proportion of reproductively mature C. finmarchicus increased as the phytoplankton biomass increased. Most of the time there was good agreement between herbivorous ingestion rates and calculated carbon demand for the observed egg production. However, both species showed a peak in egg production prior to the phytoplankton spring-bloom. Handling editor: J. Padisak.     

Interactive effects of time and vegetation on reproduction of redshanks (Tringa totanus) breeding in Wadden Sea salt marshes

As shown for various species, nesting waders are non-randomly distributed on wetlands and preferentially select riparian nest-sites adjacent to limnic or marine waterbodies. Studying the redshank Tringa totanus, we tested the hypotheses that, in a coastal wader species which conceals its clutch in vegetation, predation and hatching success are affected by vegetation zonation, and that breeding in lower salt marsh areas has negative consequences for reproduction. We further predicted effects of timing of breeding and breeding experience/age of adults potentially reflected by egg biometrics both on nest-site selection and reproduction. Effects of vegetation, space, time and individual quality on hatching success of redshanks were studied in the German part of the Wadden Sea. Dominant plant species, vertical vegetation structure and nest concealment varied significantly between nests. Variation in nest concealment was relatively low: about 90% of clutches were classified as being well concealed. This variation was explainable by vegetation structure but not by vegetation composition at the nest-site, distance to shoreline, and time of clutch initiation. Vertical vegetation structure varied by dominant plant species but not by distance to shoreline and time of clutch initiation. Hatching success of clutches was low (10.6%) due to high predation (daily predation rate: 7.4%). Hatching success and duration of clutch survival were negatively and predation positively related to the date of clutch initiation. Furthermore, negative relationships were found between egg size and predation and duration of survival, respectively. We assume that concealed nests, early breeding and breeding experience diminish predation in salt marsh breeding redshanks. Thus, redshank reproduction appears to be affected by interactive effects of timing of breeding and vegetation facilitating early breeding. In contrast to open-nesting species, breeding in riparian habitats next to waterbodies may be disadvantageous for species breeding concealed in vegetation if these are covered by less structured vegetation.     

Egg production of the copepod Acartia bifilosa in two contrasting European estuaries in relation to seston composition

The egg production of the copepod Acartia bifilosa was measured and related to environmental variables and food availability in two estuaries located in the same biogeographic region (Bay of Biscay) but showing very strong differences in abiotic and biotic features: the Gironde estuary (France) and the estuary of Mundaka (Spain). The study was conducted during the spring-summer-autumn period of 1994. Food availability was evaluated by analysing the chlorophyll a (Chl a), the particulate organic carbon (POC) and the easily extractable macromolecular compounds such as proteins, carbohydrates and lipids of the seston. The egg production of copepods was estimated from field incubations with natural water, and phytoplankton feeding of adult females was estimated by means of the gut fluorescence method. The nutritional environment of the Gironde was characterised by high amounts of suspended particulate matter (SPM) with low food value, emphasising the mainly detrital origin of the organic matter (OM). In Mundaka, the higher contribution of phytoplankton to the seston led to marked increases in particulate food value accounting for up to 35% of organic matter. The weight-specific egg production was found to be sharply higher in Mundaka (ranging from 0.2 to 0.63×10⁻³ day⁻¹) than in the Gironde (ranging from 0 to 0.13×10⁻³ day⁻¹), but the seasonal trend of variations was similar, the highest weight-specific egg production rates occurring in early summer and the lowest in autumn in both estuaries. Egg production was not correlated linearly with temperature since maximal egg production occurred at intermediate temperatures. In Mundaka, the egg production showed a significant positive correlation with the chlorophyll and the Chl/SPM and the POC/SPM ratios. This coupled with higher values of algal food availability (Chl a/SPM: 10 to 1870 μg g⁻¹) and gut fluorescence (between 0.12 and 0.38 ng Chl a Eq ind⁻¹) indicate that a herbivorous diet could cover the energy requirements of A. bifilosa and support egg production. In the Gironde, the algal food availability and the gut fluorescence were lower (Chl a/SPM: 10 to 80 μg g⁻¹; GF: 0.09 and 0.25 ng Chl a Eq ind⁻¹), and the egg production showed significant positive correlation with the particulate food value, suggesting that other sources of carbon rather than phytoplankton were responsible for the observed changes in egg production. Results indicate that the particular seston properties of each system may be responsible for the noticeable differences in A. bifilosa fertility among estuaries.     

Trophic modification of food quality by heterotrophic protists: species-specific effects on copepod egg production and egg hatching

Recent literature suggests that heterotrophic protists could improve the biochemical constituents of poor quality algae for subsequent use by higher trophic levels, a phenomenon dubbed “trophic upgrading”. We conducted experiments to test trophic upgrading effects on the omnivorous calanoid copepod Acartia tonsa. Two heterotrophic protists, Oxyrrhis marina and Gymnodinium dominans, were grown on three algal species of different nutritional qualities: Dunaliella tertiolecta, Isochrysis galbana and Rhodomonas salina. In parallel incubations, the copepods were fed the heterotrophic protists or the algae that the protists grew on. We measured the ingestion rate, egg production rate and egg hatching success of the copepods in each treatment. Comparison of the egg production efficiency (EPE; egg carbon production/carbon ingestion×100%) between parallel diet treatments allowed us to calculate the trophic upgrading index (TUI; ratio of EPE-heterotrophic protist to EPE-alga). The copepods ingested similar amount, or 20-30% more algae than heterotrophic protists. Daily rations ranged 50-122% of body C per day. Copepods feeding on O. marina that grew on D. tertiolecta had higher egg production rate and egg hatching success than copepods feeding on D. tertiolecta directly, and the resultant TUI between the two treatments was 19.7. Similarly, the copepod egg production was improved by G. dominans that grew on D. tertiolecta and the resultant TUI was 23.3. TUI was near 1 between I. galbana treatment and the parallel heterotrophic protist treatments, indicating no or little trophic upgrading effects on the copepod's egg production. However, egg hatching success was significantly lower with G. dominans growing on I. galbana. O. marina that grew on R. salina induced a lower EPE relative to the alga itself, yielding a TUI of less than 1. Biochemical data showed that the heterotrophic protists contained eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) even when they fed on alga that lacked these essential fatty acids, which may explain some of the observed trophic upgrading effects and species-specific differences in our experiments. However, our data also suggested that dietary EPA and DHA could not be the sole factors regulating the copepod's reproductive output, and that egg production and egg hatching appeared to have different nutritional requirements and respond differently to the copepod's diets.     

Timing and success of reproductive stages in the seagrass Zostera noltii

The timing and success of sexual reproduction of the seagrass Zostera noltii was investigated at the Ria Formosa lagoon, Portugal. Thirty plants were tagged and monitored individually through time to determine in situ the development time of each maturation stage, from the emergence of the flowers to the production of seeds. The overall process of flowering and fruiting lasted 47 ± 4 days, during which formation and maturation of the fruits was the most time-consuming stage (27 ± 2 days). Spathe success, i.e. the percentage of spathes that produced seeds, was 22 ± 4% while spathe mortality was 34 ± 6%. A considerable percentage of spathes (37 ± 7%) was lost through leaf detachment, but some of these may still add to the reproductive success of the species by contributing to the species recruitment within the source meadow or elsewhere. Meadow seed production (MSP) of Z. noltii was estimated to be 312 ± 66 seeds m⁻², whereas the potential seed production of the studied meadow was 2623 seeds m⁻². Under laboratory conditions, 70% of Z. noltii seeds germinated within 26 days, but only 10% reached the seedling stage due to the high mortality of germlings. Fertility, defined as the probability of a seed to originate a new plant, was estimated to be 14 × 10⁻⁴, which is higher than what is expected for most seagrasses.     

Male reproductive success in the domestic cat (Felis catus L.): A case history

The domestic cat shows a great variability in different life history traits like its social organization, ranging from a solitary life to living in large social groups depending on environmental conditions. Until now, the mating system has not been shown to vary between populations and was described as promiscuous. Here we present data on the reproductive success of a male, which clearly show that monopolization of females by males is possible in this species.     

The effect of food limitation on gonad development and egg production of the planktonic copepod Calanus finmarchicus

Calanus finmarchicus, one of the dominant copepods species of the North Atlantic, often encounters low food concentration or quality during the reproductive period; however, our knowledge on the effect of these conditions on reproduction processes is scarce. The present study combines experiments with histological observations to describe the response of C. finmarchicus to limited food focussing on (1) oocyte maturation processes, (2) gonad morphology, (3) egg production rates as a function of spawning frequency and clutch size, and (4) the fuelling of egg production by measuring carbon and nitrogen content of the females. In the laboratory, C. finmarchicus females were exposed to 0, 10, 50, 150 or >300 μg C l⁻¹ for several days. To account for food quality and season, reproductive activity was compared in April and July 1999 between females feeding on diatoms or dinoflagellates. The effect of feeding history was studied in February with females fed and starving prior to the experiment. Feeding conditions had severe effects on oocyte maturation process. Hence, egg production varied significantly with food concentration and quality, season and feeding history due to variation in both clutch size and spawning frequency. Clutch size differed by a factor of 2-4 between food limited and well fed females, and is thus an important parameter for modelling egg production. Changes in clutch size were related to changes of the number of maturing oocytes in the females gonads indicating that the latter can be used to precise the prediction of egg production from preserved samples. The proportion of females carrying at least some mature oocytes was relatively high at low food availability. Apparently, these females used internal body reserves as the carbon and nitrogen content decreased significantly under these conditions. These results indicate that C. finmarchicus embarks on the strategy to enable reproduction in all or many females of a population at low rates when feeding conditions are unfavourable.     

Movement herkogamy in Kosteletzkya virginica: Effect on reproductive success and contribution to pollen receipt and reproductive assurance

Herkogamy may act as a mechanism to reduce interference between the reproductive functions of female and male organs, but too great a distance between stigmas and anthers may also decrease the outcross pollen transfer and male and female fitness. Our goal was to quantify the effect of movement herkogamy in Kosteletzkya virginica on reproductive success and its contribution to pollen receipt and reproductive assurance. Field investigations and hand-pollination experiments were performed to test: (1) the relationship between herkogamy before curvature of un-pollinated lobes and reproductive success under pollinator exclusion; (2) the contribution of movement herkogamy to pollen receipt; and (3) the relationship between pollen load and seed set. We noted that variation in herkogamy before curvature of un-pollinated lobes did not affect the outcome of autogamous self-pollination measured by fruit set and mean number of seeds per fruit. Under natural conditions, 39% of pollen grains deposited per flower were from autogamous self-pollination via movement herkogamy resulting in contact between anthers and stigmas. The relationship between the amount of pollen grains and the number of seeds per capsule was highly significant. Flowers producing four or five seeds received more pollen grains than those producing only one seed. Our data provides experimental evidence that movement herkogamy, which decreases the separation between anthers and stigmas and results in delayed self-pollination, contributes to pollen receipt and further enhances seed set when pollinators are scarce or absent.     

Nucleic acid indices of egg production in the tropical copepod Acartia sinjiensis

Two experiments were conducted to evaluate the effects of food and temperature on the nucleic acid content and egg production (and their relationship) of the tropical copepod Acartia sinjiensis. Experiment 1 evaluated the effect of food quality (as different algae species) on the relationship between nucleic acid content and egg production. In Experiment 2, the main and interaction effects of food type, food concentration and temperature on the total, Carbon and Nitrogen specific egg production and nucleic acid indices were evaluated in a factorial experimental design. Food quality, concentration and temperature significantly affected the nucleic acid content, egg production rate and the nucleic acid-egg production relationship of A. sinjiensis. RNA indices were correlated with egg production in females fed Pavlova salina, Tetraselmis chuii and Chaetoceros muelleri, but not in females fed Isochrysis aff. galbana. The slopes of the linear regressions of RNA indices as predictors of egg production were similar in females fed different algae species, suggesting that the slope of these relationships might be independent of food quality. The DNA content of females was significantly affected by food and temperature, suggesting that it is not a good index of cell number in this species. Nevertheless, the RNA:DNA ratio was as good a predictor of egg production as total RNA content. Egg production showed a weakly positive correlation with temperature. On the other hand, total, C- and N-specific nucleic acid indices had a strong negative correlation with temperature. In addition, temperature had a non linear effect on the slopes of the regression lines of RNA content and RNA:DNA ratio as predictors of egg production—slopes were similar at 25 °C and 30 °C, but significantly lower at 20 °C. Furthermore, the predictability of egg production was improved when the interaction term of nucleic acid indices with temperature was used instead of the nucleic acid indices alone in linear regression models. Our results suggest food quality has a limited influence on the nucleic acid-egg production relationship, and that temperature should be accounted for in models using nucleic acid indices as predictors of egg production in A. sinjiensis.     

Mapping glycoconjugate-mediated interactions of marine Bacteroidetes with diatoms

The degradation of diatoms is mainly catalyzed by Bacteroidetes and this process is of global relevance for the carbon cycle. In this study, a combination of catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) and fluorescent lectin binding analysis (FLBA) was used to identify and map glycoconjugates involved in the specific interactions of Bacteroidetes and diatoms, as well as detritus, at the coastal marine site Helgoland Roads (German Bight, North Sea). The study probed both the presence of lectin-specific extracellular polymeric substances (EPS) of Bacteroidetes for cell attachment and that of glycoconjugates on diatoms with respect to binding sites for Bacteroidetes. Members of the clades Polaribacter and Ulvibacter were shown to form microcolonies within aggregates for which FLBA indicated the presence of galactose containing slime. Polaribacter spp. was shown to bind specifically to the setae of the abundant diatom Chaetoceros spp., and the setae were stained with fucose-specific lectins. In contrast, Ulvibacter spp. attached to diatoms of the genus Asterionella which bound, among others, the mannose-specific lectin PSA. The newly developed CARD-FISH/FLBA protocol was limited to the glycoconjugates that persisted after the initial CARD-FISH procedure. The differential attachment of bacteroidetal clades to diatoms and their discrete staining by FLBA provided evidence for the essential role that formation and recognition of glycoconjugates play in the interaction of bacteria with phytoplankton.