The balance between photosynthesis and grazing in Antarctic mixotrophic cryptophytes during summer

SUMMARY 1. Grazing and photosynthetic contributions to the carbon balance of planktonic, mixotrophic cryptophytes in Lakes Fryxell and Hoare in the Taylor Valley, Antarctica were measured during November and December 2000.
2. The cryptophytes never became entirely photosynthetic, although carbon derived from grazing decreased in December. Individual grazing rates ranged between 5.28 and 10.08 bacteria cell⁻¹ day⁻¹ in Lake Fryxell and 0.36–11.76 bacteria cell⁻¹ day⁻¹ in Lake Hoare. Grazing rates varied temporally and with depth in the water column. In Lake Fryxell, which is a meromictic lake, highest grazing occurred just above the chemocline. Individual photosynthetic rates ranged from 0.23 to 1.35 pg C cell⁻¹ h⁻¹ in Lake Fryxell and 0.074 to 1.08 pg C cell⁻¹ h⁻¹ in Lake Hoare.
3. Carbon acquisition by the cryptophyte community gained through grazing ranged between 8 and 31% during November in Lake Fryxell, dropping to between 2 and 24% in December. In Lake Hoare grazing contributed 12–21% of the community carbon budget in November and 1–28% in December. Around 4% of the carbon acquired from grazing and photosynthesis was remineralised through respiration.
4. Mixotrophy is probably a major survival strategy for cryptophytes in the extreme lakes of the Dry Valleys, because perennial ice-cover severely limits light penetration to the water column, whereas these phytoflagellates are not normally mixotrophic in lower latitude lakes. The evidence suggests that mixotrophy may be a mechanism for supplementing the carbon budget, as well as a means of acquiring nutrients for growth.     

8 Grazing by heterotrophic nanoflagellates on virus- and bacteria-sized particles in two lakes of different trophy

Although viruses are now widely recognized to infect aquatic bacteria as well as prokaryotic and eukaryotic phytoplankton, our understanding of how they fit into aquatic foodwebs remains still deficient. The present study examined the potential nutritional food source that viral particles represent for natural assemblages of heterotrophic nanoflagellates (HNF). We determined the seasonal and depth-related variability in the grazing activity of HNF on virus- and bacteria-sized particles in the oligomesotrophic Lake Pavin and the eutrophic Lake Aydat. Ingestion rates were determined using 50 and 500 nm diameter fluorescent microspheres. Estimated ingestion rates ranged from 0.01 to 1.7 viruses cell⁻¹·h⁻¹ (Aydat) and from 0.01 to 2 viruses cell⁻¹·h⁻¹ (Pavin). Derived clearance rates for viruses represented 3–5% (Aydat) and 10–12% (Pavin) of those for bacteria. In general, HNF grazing on both viruses and bacteria showed a similar pattern characterized by an apparent decrease in summer followed by autumnal peaks, with lowest values always being recorded in the hypolimnion. Viral production, estimated from the frequency of visibly infected cells (using transmission electronic microscopy), was consumed by HNF at rates averaging 2% (Aydat) and 10% (Pavin). This study suggests that, viruses, which are assumed to correspond to 1×10⁻⁷ ng C/particle, are likely to be of low nutritive value for HNF in both lakes. However, these results imply that HNF grazing may contribute significantly to the removal of viruses in freshwaters, especially in low productive systems.     

Stratification and dynamics of microbial loop communities in Lake Fryxell, Antarctica

1. Lake Fryxell, situated in the McMurdo Dry Valleys, Antarctica, offers the opportunity to study microbial loop processes in the absence of crustacean zooplankton and other higher organisms. This is the first study of Lake Fryxell to provide detailed temporal and vertical variations of microbial loop organisms.
2. Protozoan communities are concentrated around the chemocline (9–10 m) in Lake Fryxell. Phototrophic nanoflagellates (PNAN), heterotrophic nanoflagellates (HNAN) and ciliates formed deep maxima of 14 580, 694 and 58 cells mL−1 respectively. Although abundance and biomass at the chemocline was high, diversity of protozoa was low, Plagiocampa accounting for> 80% of the total ciliate biomass.
3. In the mixolimnion (4.5–8 m), protozoa were less abundant, but more diverse, with 24 ciliate morphotypes being identified within this region of the water column. Inter-annual variability of protozoan biomass and abundance was greater in the mixolimnion than at the chemocline due to more variable nutrient and prey concentrations.
4. Physicochemical gradients in Lake Fryxell were very stable because the perennial ice cover reduced wind driven currents. As a consequence, ciliate species occurred in distinct depth strata, Monodinium being most abundant directly beneath the ice cover, Askenasia having maximum abundance at 8 m and Plagiocampa dominating ciliate biomass at the chemocline. The lack of vertical mixing reduced seasonal successions of PNAN and ciliate species. Three cryptophyte species dominated the PNAN community at all times (>79% of total biomass).     

Contribution of virus-induced lysis and protozoan grazing to benthic bacterial mortality estimated simultaneously in microcosms

In contrast to the water column, the fate of bacterial production in freshwater sediments is still a matter of debate. Thus, the importance of virus-induced lysis and protozoan grazing of bacteria was investigated for the first time simultaneously in a silty sediment layer of a mesotrophic oxbow lake. Microcosms were installed in the laboratory in order to study the dynamics of these processes over 15 days. All microbial and physicochemical parameters showed acceptable resemblance to field data observed during a concomitant in situ study, and similar conclusions can be drawn with respect to the quantitative impact of viruses and protozoa on the bacterial compartment. Viral decay rates ranged from undetectable to 0.078 h⁻¹ (average, 0.033 h⁻¹), and the control of bacterial production from below the detection limit to 36% (average, 12%). The contribution of virus-induced lysis of bacteria to the dissolved organic matter pool as well as to benthic bacterial nutrition was low. Ingestion rates of protozoan grazers ranged from undetectable to 24.7 bacteria per heterotrophic nanoflagellate (HNF) per hour (average, 4.8 bacteria HNF⁻¹ h⁻¹) and from undetectable to 73.3 bacteria per ciliate per hour (average, 11.2 bacteria ciliate⁻¹ h⁻¹). Heterotrophic nanoflagellate and ciliates together cropped up to 5% (average, 1%) of bacterial production. The viral impact on bacteria prevailed over protozoan grazing by a factor of 2.5–19.9 (average, 9.5). In sum, these factors together removed up to 36% (average, 12%) of bacterial production. The high number of correlations between viral and protozoan parameters is discussed in view of a possible relationship between virus removal and the presence of protozoan grazers.     

Seasonal heterotrophic flagellate and bacterial plankton dynamics in a large oligotrophic lake– Loch Ness, Scotland

1. Bacterial production in the 0–30 m water column of Loch Ness was measured using a dual labelling procedure with [³H] thymidine and [¹⁴C] leucine between May 1993 and June 1994. In most cases the uptake of the two labels did not covary, suggesting unbalanced growth. Rates of bacterial production varied from undetectable to 46.2 μg C l^–1 day^–1. Highest production coincided with the period of highest primary production, but carbon derived from this source was insufficient to meet the bacterial carbon demand, which was met by allochthonous humic inputs to the system.
2. Heterotrophic flagellate (HNAN) grazing rates, measured using fluorescently labelled bacteria, ranged between 10.3 and 24.5 bacteria cell^–1 day^–1 at temperatures between 5 and 15 °C. They removed up to 27% of the bacterial production per day.
3. Heterotrophic flagellate specific growth rates ranged from 0.043 to 0.093 h^–1 between 5 and 15 °C, giving generation times of 7.4–16.1 h.
4. bacterial and HNAN abundances were not coupled, but the highest HNAN grazing impact related to a time of high bacterial productivity.     

Bacterivory by starved marine heterotrophic nanoflagellates of two species which feed differently, estimated by uptake of dual radioactive-labelled bacteria

Abstract: The rates of ingestion of bacteria and of accumulation of bacterial biomass by hungry Pteridomonas danica and Paraphysomonas imperforata were measured using dual radioactive-labelled bacteria in experiments lasting 4–8 h. Pteridomonas continuously consumed 4–5 bacteria h⁻¹ throughout experiments lasting 8 h, irrespective of bacterial concentration above a threshold of about 5 × 10⁵ bacteria ml⁻¹, and continued to catch bacteria even below this density. The clearance rate of about 1 nl cell⁻¹ h⁻¹ at higher bacterial concentrations increased three or four times as bacterial numbers fell. Paraphysomonas cells, with only half the biomass of Pteridomonas , ingested up to 10 bacteria h⁻¹ at high bacterial concentrations, and gradually reduced the feeding rate, effectively ceasing to feed at 10⁶ bacteria ml⁻¹; their initial clearance rate of 1–2.5 nl cell⁻¹ h⁻¹ subsequently fell as low as 0.1 nl cell⁻¹ h⁻¹. Estimation of feeding rate by extrapolation from short-term experiments on such flagellates requires extreme caution. These flagellates, starved to levels typical of the natural environment, accumulated ingested bacterial biomass at an efficiency of between 16 and 21%, indicating that in nature they would recycle 80% or more of the nutrients contained in their food.     

Effect of acetate on growth and ammonium uptake in the microalga Scenedesmus obliquus

The effect of acetate on growth and rate of ammonium uptake in Scenedesmus obliquus (UTEX 78) was investigated under light-limiting conditions. Addition of acetate to autotrophic cells with a growth constant of 0.71 day⁻¹ resulted in an increase in the growth rate (mixotrophy, k = 1.3 day⁻¹), and in the presence of acetate, growth occurred in the dark (heterophy, k = 0.44 day⁻¹). The rate of ammonium uptake in autotrophy (17.8 amol cell⁻¹ min⁻¹) was similar to that in heterotrophy (17.4 amol cell⁻¹ min⁻¹) but was 3.7 times lower than that in mixotrophy (65.9 amol cell⁻¹ min⁻¹). In general, mixotrophic cells showed optimum ammonium uptake at the acetate concentration at which they were grown. In autotrophy, uptake of ammonium leveled off at about 12.5 μ M while no saturation was observed in mixotrophic cells. An increase in the rate of uptake of ammonium was observed in autotrophic cells within 1 h after the addition of acetate. The activity of isocitrate lyase (EC 4.1.3.1), a key enzyme for the regulation of the glyoxylate cycle responsible for acetate catabolism, showed a 3.9-fold increase in activity after 24 h in the dark in the presence of acetate. The level of isocitrate lyase activity in cells grown for 24 h in the dark in the presence of 0–20 m M acetate also increased as a function of acetate concentration.     

Heterotrophic bacterioplankton production and grazing mortality rates in an Ethiopian rift-valley lake (Awassa)

SUMMARY. 1. Heterotrophic bacterioplankton growth and production rates were estimated in a tropical lake by various methods. Mean growth rates, determined by tritiated thymidine incoporation into DNA, frequency of dividing cells and increase in cell density varied between 0.013 and 0.014 (with a range of 0.006–0.026) h⁻¹ corresponding to bacterial production of 1.16–1.22 (0.34–3.63) mg C m⁻³ h⁻¹.
2. Heterotrophic bacterial production estimated from oxygen and inorganic carbon consumption in the dark were compared with these values. The oxygen method gave similar results, while values from dark carbon uptake were as much as 2.5 times higher.
3. Although the different estimates of rates of bacterial production showed different patterns, the existence of spatial (vertical) and temporal (diel and seasonal) variation was demonstrated. Bacterial production was 13–41% of the net primary production and 10–30% of gross primary production.
4. Bacterial grazing mortality rate was estimated from size-fractionation and metablic inhibitor experiments. Average grazing rates were between 0.34 and 3.77 mg C m⁻³ h⁻¹ corresponding to 76–120% of the mean bacterial production rate. Organisms 1–12 μm in size, possibly mainly ciliates. were implicated as important bacterial grazers.     

Abrupt change in primary productivity in a littoral zone of Lake Biwa with the development of a filamentous green-algal community

1. Some characteristics of the photosynthesis and primary production of benthic and planktonic algal communities were investigated in a littoral zone covered with gravel in the north basin of Lake Biwa, paying special attention to the recent development of filamentous green algae (FGA) in the benthic algal community.
2. P_max (maximum gross photosynthesis rate) values of the benthic algal community (0.1–1.2 mg C mg chl. a ⁻¹ h⁻¹) obtained from photosynthesis–irradiance (P–I) curves were lower than those of the planktonic algal community (2.4–11.5 mg C mg chl. a ⁻¹ h⁻¹). This is apparently a result of the high degree of self shading in the benthic algal community and its low turnover as compared with that of the planktonic algal community.
3. Relatively high I_k values (150–200 μmol photon m⁻² s⁻¹) were observed in the benthic algal community only in June–July when a FGA, Spirogyra sp., was abundant. This reflected a photosynthetic characteristic of the Spirogyra itself, in which photosynthesis was saturated at high light intensity.
4. The FGA community established in the layer between planktonic and sessile (benthic algae except for FGA) algal communities. It brought about extraordinarily high organic matter production in the littoral zone at the expense of production in the sessile algal community.     

Flagellate nutritional versatility as a key to survival in two contrasting Antarctic saline lakes

1. Seasonal patterns of grazing and photosynthesis were investigated in two saline Antarctic lakes (Highway and Ace) in the Vestfold Hills (68°S). The phototrophic nanoflagellate (PNAN) community was dominated by Pyramimonas gelidicola and two morphological forms of a cryptophyte species that occurred throughout the year. Both species were mixotrophic on bacteria, and in Highway Lake they also exploited dissolved organic carbon as determined by the uptake of fluorescently labelled dextrans. 2. Clearance rates ranged between 0.02 and 0.21 nL h^?1 cell^?1 in Ace Lake and 0.004–1.05 nL h^?1 cell^?1 in Highway Lake. On occasion cryptophyte grazing equalled that of the heterotrophic nanoflagellates (HNAN). 3. Photosynthetic rates showed similar trends in both lakes, but there were differences in chlorophyll a specific rates and photosynthetic efficiency, probably related to the meromictic characteristic of Ace Lake. Primary production was measurable in winter and peaked in summer following the maxima of mixotroph grazing. 4. The HNAN community of Highway Lake achieved clearance rates of 0.02–1.80 nL h^?1 cell^?1 and removing between 50 and 693 ng bacterial carbon L^?1 day^?1, with highest impact in winter when HNAN were most abundant. The HNAN also ingested fluorescently labelled dextrans showing a preference for 4 and 500 kDa molecules. The more diverse HNAN community of Ace Lake had lower clearance rates (0.04–0.37 nL h^?1 cell^?1) and exerted a lower grazing pressure on bacterioplankton. In Highway Lake, where the HNAN community was dominated by the choanoflagellate Diaphanoeca grandis, there was a significant correlation between mean cell volume and clearance rate. 5. The major feature was that the microbial plankton functioned throughout the year by employing nutritional versatility.     

Lactic acid production by Lactobacillus delbrueckii in a dual reactor system using packed bed biofilm reactor

Aims:  An integrated dual reactor system for continuous production of lactic acid by Lactobacillus delbrueckii using biofilms developed on reticulated polyurethane foam (PUF) is demonstrated.
Methods and Results:  Lactobacillus delbrueckii was immobilized on PUF, packed in a bioreactor and used in lactic acid fermentation. The rate of lactic acid production was significantly high with a volumetric productivity of 5 g l⁻¹ h⁻¹ over extended period of time. When coupled to a bioreactor, the system could be operated as dual reactor for over 1000 h continuously without augmentation of inoculum and no compromise on productivity.
Conclusions:  Polyurethane foams offer an excellent support for biofilm formation.
Significance and Impact of the Study:  The system was very robust and could be operated for prolonged period at a volumetric productivity of 4–6 g l⁻¹ h⁻¹.     

Survey of wound-induced ethylene production by excised root segments

Ethylene production was measured from excised 10-mm apical and subapical root segments from 50 cultivars in 19 species of 7 families. Monocotyledonous species tended to have much lower rates of ethylene production than dicotyledonous species. Ethylene production was generally higher in apical root segments than in subapical segments within 1 h of wounding. However, cultivars of Cucumis melo , C. sativus , Helianthus annuus , Hibiscus esculentus , and Zea mays had higher rates of ethylene production from subapical segments. In apical root segments, Phaseolus aureus cv. Berken had the highest ethylene production rate (76.7 ηl g⁻¹ h⁻¹), while Zea mays cv. Silver Queen had the lowest rate (0.6 ηl g⁻¹ h⁻¹). In subapical root segments, Cucumis sativus cv. Armenian had the highest rate (55.7 ηl g⁻¹ h⁻¹), while Zea mays cv. Silver Queen again had the lowest rate (0.6 ηl g⁻¹ h⁻¹). The many different responses in magnitude and kinetics of wound-induced ethylene production among the species, cultivars and tissues should provide interesting and useful systems with which to study wound responses and induced ethylene production.     

Mixotrophy in the phototrophic harmful alga Cochlodinium polykrikoides (Dinophycean): prey species, the effects of prey concentration, and grazing impact

We first reported here that the harmful alga Cochlodinium polykrikoides, which had been previously known as an autotrophic dinoflagellate, was a mixotrophic species. We investigated the kinds of prey species and the effects of the prey concentration on the growth and ingestion rates of C. polykrikoides when feeding on an unidentified cryptophyte species (Equivalent Spherical Diameter, ESD = 5.6 microm). We also calculated grazing coefficients by combining field data on abundances of C. polykrikoides and co-occurring cryptophytes with laboratory data on ingestion rates obtained in the present study. Cocholdinium polykrikoides fed on prey cells by engulfing the prey through the sulcus. Among the phytoplankton prey offered, C. polykrikoides ingested small phytoplankton species that had ESD's < or = 11 microm (e.g. the prymnesiophyte Isochrysis galbana, an unidentified cryptophyte, the cryptophyte Rhodomonas salina, the raphidophyte Heterosigma akashiwo, and the dinoflagellate Amphidinium carterae). It did not feed on larger phytoplankton species that had ESD's > or = 12 microm (e.g. the dinoflagellates Heterocapsa triquetra, Prorocentrum minimum, Scrippsiella sp., Alexandrium tamarense, Prorocentrum micans, Gymnodinium catenatum, Akashiwo sanguinea, and Lingulodinium polyedrum). Specific growth rates of C. polykrikoides on a cryptophyte increased with increasing mean prey concentration, with saturation at a mean prey concentration of approximately 270 ng C ml(-1) (i.e. 15,900 cells ml(-1)). The maximum specific growth rate (mixotrophic growth) of C. polykrikoides on a cryptophyte was 0.324 d(-1), under a 14:10 h light-dark cycle of 50 microE m(-2) s(-1), while its growth rate (phototrophic growth) under the same light conditions without added prey was 0.166 d(-1). Maximum ingestion and clearance rates of C. polykrikoides on a cryptophyte were 0.16 ng C grazer(-1)d(-1) (9.4 cells grazer(-1)d(-1)) and 0.33 microl grazer(-1)h(-1), respectively. Calculated grazing coefficients by C. polykrikoides on cryptophytes were 0.001-0.745 h(-1) (i.e. 0.1-53% of cryptophyte populations were removed by a C. polykrikoides population in 1 h). The results of the present study suggest that C. polykrikoides sometimes has a considerable grazing impact on populations of cryptophytes.     

Water‐based measurement of rainbow trout melatonin

Melatonin (MLT) was isolated from water samples using solid phase extraction cartridges and measured by radioimmunoassay. In tanks of rainbow trout Oncorhynchus mykiss , concentrations of MLT in water increased rapidly from <0·1 ng l⁻¹ in the light phase to 0·7 ng l⁻¹ in the dark giving calculated release rates of <1 ng kg⁻¹ h⁻¹ and 15 ng kg⁻¹ h⁻¹, respectively. This cycle in water MLT values corresponds to reported changes in plasma MLT concentrations. The colour of the tanks and a daytime acute handling stress did not affect concentrations of MLT in either the light or dark phase.     

The relative importance of algae and bacteria as food for Daphnia longispina (Cladocera) in a polyhumic lake

SUMMARY. 1. Grazing on algae and bacteria by the planktonic cladoceran, Daphnia longispina , was studied in a small polyhumic lake with low phytoplankton primary production in southern Finland.
2. D. longispina filtered algae at average rates of 0.09-0.82 ml ind⁻¹ h⁻¹. The filtering rates on bacteria were 26-92% of those on algae in parallel experiments.
3. From June to August algae, including mixotrophic and heterotrophic forms, comprised 56-93% of the food ingested by D. longispina. In mid-September and early October, when the Daphnia population was declining and the algal biomass was low, bacteria comprised 73% and 55% respectively of the food of Daphnia.
4. For D. longispina , an energy pathway via bacteria and bactivorous flagellates is probably a more important link to allochthonous organic matter than direct utilization of epilimnetic bacteria.     

Long-term effects of successive Ca(OH)2 and CaCO3 treatments on the water quality of two eutrophic hardwater lakes

1. Whole-lake experiments were conducted in two hardwater lakes (Halfmoon and Figure Eight) in Alberta, Canada, to investigate the effectiveness of repeated lime (slaked lime: Ca(OH)₂ and/or calcite: CaCO₃) treatments (5–78 mg L^–1) for up to 7 years.
2. Randomized intervention analysis of intersystem differences between the experimental and three reference lakes demonstrated a decline in euphotic total phosphorus and chlorophyll a concentrations in the experimental lakes after repeated lime treatments.
3. After the second lime application to Halfmoon Lake, mean winter total phosphorus release rates (TPRR) decreased to < 1 mg m^–2 day^–1 compared with 3.6 mg m^–2 day^–1 during the winter after initial treatment. In the final year of lime application, mean summer TPRR decreased to 4.5 mg m^–2 day^–1 compared with 7.6 mg m^–2 day^–1 in the pre-treatment year.
4. Mean macrophyte biomass declined and species composition was altered at 1 and 2 m depths in Figure Eight Lake during lime application. Over the first 6 years of treatment, macrophyte biomass at 2 m declined by 95% compared with concentrations recorded during the initial treatment year. In the last year of the study, macrophyte biomass at 2 m reached initial treatment concentrations, which coincided with the greatest water transparency. Over the treatment period, macrophyte species shifted from floating to rooted plants.
5. Multiple lime applications can improve water quality in eutrophic hardwater lakes for periods of up to 7 years.     

Fed-batch culture of Candida guilliermondii FTI 20037 for xylitol production from sugar cane bagasse hydrolysate

A fed-batch culture system was used to study xylitol production by Candida guilliermondii FTI 20037 in a synthetic and a sugar cane bagasse hydrolysate medium. The values achieved for xylitol yield and volumetric productivity were, respectively, 0 · 84 g g⁻¹ and 0 · 64 g l⁻¹ h⁻¹ using the synthetic medium and 0 · 78 g g⁻¹ and 0 · 62 g l⁻¹ h⁻¹ using the hydrolysate medium.     

Protozoan growth rates in Antarctic lakes

The growth rates of heterotrophic nanoflagellates (HNAN), mixotrophic cryptophytes, dinoflagellates and ciliates in field assemblages from Ace Lake in the Vestfold Hills (eastern Antarctica) and Lakes Fryxell and Hoare (McMurdo Dry Valleys, western Antarctica), were determined during the austral summers of 1996/1997 and 1997/1998. The response of the nanoflagellates to temperature differed between lakes in eastern and western Antarctica. In Ace Lake the available bacterial food resources had little impact on growth rate, while temperature imposed an impact, whereas in Lake Hoare increased bacterial food resources elicited an increase in growth rate. However, the incorporation of published data from across Antarctica showed that temperature had the greater effect, but that growth is probably controlled by a suite of factors not solely related to bacterial food resources and temperature. Dinoflagellates had relatively high specific growth rates (0.0057–0.384 h⁻¹), which were comparable to Antarctic lake ciliates and to dinoflagellates from warmer, lower latitude locations. Temperature did not appear to impose any significant impact on growth rates. Mixotrophic cryptophytes in Lake Hoare had lower specific growth rates than HNAN (0.0029–0.0059 h⁻¹ and 0.0056–0.0127 h⁻¹, respectively). They showed a marked seasonal variation in growth rate, which was probably related to photosynthetically active radiation under the ice at different depths in the water column. Ciliates' growth rates showed no relationship between food supply and mean cell volume, but did show a response to temperature. Specific growth rates ranged between 0.0033 and 0.150 h⁻¹ for heterotrophic ciliates, 0.0143 h⁻¹ for a mixotrophic Plagiocampa species and 0.0075 h⁻¹ for the entirely autotrophic ciliate, Mesodinium rubrum. The data indicated that the scope for growth among planktonic Protozoa living in oligotrophic, cold extreme lake ecosystems is limited. These organisms are likely to suffer prolonged physiological stress, which may account for the highly variable growth rates seen within and between Antarctic lakes. Accepted: 7 December 1999     

Relationships between bone growth rate, body mass and resting metabolic rate in growing amniotes: a phylogenetic approach

We explored the factors that explain the variation in resting metabolic rates (RMR) in growing amniotes by using the phylogenetic comparative method. For this, we measured raw RMR (mL O₂ h⁻¹), body mass, body mass growth rate, and periosteal bone growth rate in a sample of 44 growing individuals belonging to 13 species of amniotes. We performed variation partitioning analyses, which showed that phylogeny explains a significant fraction of the variation of mass-specific RMR (mL O₂ h⁻¹ g⁻¹), and that the cost of growth is much higher than the cost of maintenance. Moreover, we tested the hypothesis of the independence of energy allocation, and found that maintenance metabolism and growth rates are not significantly related. Finally, we calculated the statistical parameters of the relationship between geometry-corrected RMR (mL O₂ h⁻¹ g^−0.67) and bone growth rate. This relationship could potentially be used in palaeobiology to infer RMR from bone tissue samples of fossil species by assuming Amprino's rule (according to which bone tissue types reflect bone growth rates). These estimates would be especially interesting for Mesozoic non-avian theropod dinosaurs and Permian and Triassic therapsids to investigate, respectively, the origin of avian and mammalian endothermy.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 63–76.     

Ammonium and phosphate regenerationby the zooplankton of an Amazon floodplain lake

SUMMARY. 1. Regeneration of ammonium and phosphate by macro-zooplankton (Cladocera. adult copepods. and copepodites) was measured in Lake Calado. an Amazon floodplain lake, Macrozooplanktonabundances ranged between 1×10⁴ and 3×10⁵ individuals m⁻².
2. Phosphate regeneration ranged from 0.2 to 1.3 μ mol PO₄ m⁻² b⁻¹at station 1. located 2 km from the Solimoes River, and from 1.6 to8.3 μ mol PO₄ m⁻² h ⁻¹ at station 3, located 7 km from the SolimoesRiver. Ammonium regeneration at stations 1 and 3 ranged from 1.7 to11.9 and from 13.4 to 77.2 μ mol NH₄ m⁻² h⁻¹. respectively.
3. Zooplankton regenerated ammonium and phosphate at similarrates during rising and falling waier. Regeneration by macrozooplankton was low compared to other tropical lakes and compared to microbesand microzooplankton in Lake Calado.