Rothhaupt, 1990. Differences in Particle Size-Dependent Feeding Efficiences of Closely Related Rotifer Species

8/13/2019 Rothhaupt, 1990. Differences in Particle Size-Dependent Feeding Efficiences of Closely Related Rotifer Species.

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Limnol. OctBanogr.. 5(l), 1990, 16-230 1990, by the American Society of Limnology and Oceanography, Inc.

Differences in particle size-dependent feeding efficiencies ofclosely related rotifer speciesKarl 0. RothhauptMax-Planck-Institute of Limnology, Department of Physiological Ecology, P.O. Box 165, D-2320 Plan, FRG

AbstractSize-selective feeding of four Brachionus strains was studied with three experimental setups:selection between polystyrene spheres of different sizes in short-term ( 10 min) feeding experiments,selection between pairs of dual-labeled algal taxa in short-term feeding experiments, and selectionamong three algal taxa in long-term (24 h) feeding experiments. Food size preferences were relatedto body sizes between strains but not within one strain (Brachionus calyciflorus). Brachionusangularis preferred food items


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Brachionus size selectivity 17Table 1. Food algae used in selectivity experiments. ESD is equivalentnumber is from the culture collection at the University of GWingen. spherical diameter (pm); culture

ESD Shape Culture No.Synechococcus elongatusChlorella minutissimaMonoraphidium minutum 23.5

OblongSphericalkcuate 1.80243- 1Chlamydomonas reinhardiiCyclotella meneghinianaChlamydomonas sphaeroidesMicractinium pusillum6 Spherical 11-328.5 Cylindrical 10200la12 Spherical 58.7218 Aggregates 13.81

originally isolated from a lake near Munich(Walz 1983). Brachionus rubens strain F(120-l 80 pm) came from a culture kept atthe University of Frankfurt and was isolatedfrom a pond near Frankfurt (Halbach et al.1983). Brachionus rubens strain B (ZOO-260pm) was isolated from the Grol3er Binnen-see near Plijn. Brachionus calyctflorus (220-285 pm) was hatched from resting eggs thatwere obtained from M. Schliiter. Animalswere maintained in the laboratory in 300-ml Erlenmeyer flasks with modified Chu- 12medium (Miiller 1972). They were fedMonoraphidium (about 2.5 mg C liter-)every 2 d, and medium was renewed every2 weeks. All culturing and experimentationwas done at 20_+ 1C.Food algae (Table 1) -All chlorophytesand the diatom Cyclotella were grown inmodified Chu-12 medium. The blue-greenSynechococcus was cultured in the mediumof OFlaherty and Phinney ( 19 70). Reagent-grade chemicals (Merck) were used through-out. Algae were cultured in continuous lightin chemostats (residence time, - 1.3 d) orin frequently diluted batch cultures.Light extinction (800 nm) of algal cultureswas measured to estimate carbon contentwith previously established calibrationcurves. Carbon content was determined bycombustion and measurement of infraredabsorption (Krambeck et al. 198 1). The ESDof algae was determined with a Coultercounter TA II (140~pm aperture). ESD wastaken as the mode of the size distribution.Selection between polystyrene spheres -Experiments with spheres followed themethods described by DeMott (1986). Ex-periments were run in two parallel jars with20 ml of medium each. Rotifers were fed1 : 1 mixtures of spheres of either Z- and6-pm diameter or 6- and 12qm diameter

(5 X lo3 ml- of each size). Monoraphiumcells were usually present in a concentration10 times higher than the beads ( lo5 cellsml-l). About 50 animals that had beenprefed for at least 1 h at the appropriate cellconcentrations without spheres were pipet-ted into the jars. Feeding time was restrictedto 10 min, which is below gut passage times.Then the animals were collected on 5&msieves, narcotized in carbonated water (30s), and fixed in a Petri dish with a few dropsof formaldehyde (40%). About 20 animalsfrom each jar were transferred to micro-scope slides, and tissues were cleared withtissue solubilizer (Soluene-350, Packard).The number of spheres in the gut was count-ed under a compound microscope. In oneexperiment with B. calyciflorus, the lengthof the lorica was also measured with an ocu-lar micrometer to the nearest 1.5 pm.Long- term feeding experiments-Tubesholding 25 ml of food suspension received125 animals each (four replicates for B. ru-bens, three for B. calycijlorus). Three tubeswithout animals served as controls. Foodsuspensions were Chlamydomonas sphae-roides (0.4 mg C liter-), Monoraphidiumminutum (0.2 mg C liter-l), and Chlorellaminutissima (0.1 mg C liter-l). The tubeswere kept for 24 h in the dark on a rotatingwheel at about 1 rpm. After incubation theanimals were counted and the algae fixedwith Lugols solution. After settling for atleast 24 h in cylindrical chambers (25-mmdiam, 25-ml vol), the algae were countedunder an inverted microscope (Utermohl1958). At least 800 cells of each species werecounted for the small algae; two diametersof the counting chamber for Chlarnydo-monas. Calculation of clearance rates fol-lowed standard procedures (Peters 1984).Dual- label experiments - Two food algae,


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Brachionus size selectivity 19

6-- 4-

; 2-Jz 0 .Tg 12-- lo-3 8-w 6- +5 :-w O H-l

Brachionusangularis

Brachionus ru bensStrain F

Brachionuscalycif lorus "0 0.5 1 1.5 2.5

DIAMETERFig. 2. Clearance rates for different sizes of poly-styrene spheres, calculated from the selectivity exper-iments in Fig. 1 (mean rS1 SD).

experiments with B. rubens strain F, selec-tivities between 6- and 12-pm spheres re-mained unchanged without algae and in thepresence of different densities of Monora-phidium (Table 2). In another experiment,6-pm beads were used as a tracer to es-timate clearance and ingestion rates at dif-ferent concentrations of Monoraphidium.Algal cell densities were 10 times higher than

Table 2. Brachionus rubens strain F. Selectivity be-tween 6- and 12-brn polystyrene spheres n media with-out algae and in different concentrations Monoraphi-dium. (n = No. of animals).

No. of ingestedMonoraphidium Spheres spheres(mg C (cells ml liter-l) ml-l) (per si7e) n 6m 12crm D,0 0 104 22 337 4 0.9760.1 2x lo4 10 32 59 3 0.90333 58 2 0.93348 81 4 0.9060.5 105 5x103 27 279 8 0.94433 339 16 0.91038 355 15 0.9592.5 5x105 5~10~ 36 39 1 0.95061 82 1 0.97639 63 1 0.969

0 0.5 1 1.5 2.5FOOD CONCENTRATION (mg C liter)

Fig. 3. Clearance and ingestion rates of Brachionusrubens on Monoraphidium, determined with 6-pmspheres as tracers. Lines are rates determined in ra-diotracer experiments (Rothhaupt 1990). Short dash-es-Monoraphidium (3.5~pm ESD); long dashes-Chlamydomonas reinhardii (6-pm ESD).

the concentration of spheres. Clearance andingestion rates were comparable to resultswith radiolabeled algae (Fig. 3).Long- term feeding experiments - In theseexperiments the algae were chosen to besimilar in size to the beads. Monoraphidiumwas chosen for the medium size because itsdistinct shape facilitates microscopic iden-tification. Brachionus rubens strain F andB. calyciflorus had similar particle size-de-pendent clearance rates on the algae as theyhad in the experiments involving plasticspheres (Fig. 4). Again, B. calycijlorus in-gested the biggest food item most efficiently,whereas B. rubens strain F had highest clear-


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20 Rothhaupt- 12-i-L: 108,7cl 6

- Brachionus rubens- StrainF

8 125 10

2 6w 46 20 i Cm. Mm.

Fig. 4. Clearance rates from long-term feeding ex-periments with three algae offered simultaneously (meank I SD). C.m.-Chlorella minutissima (2-pm ESD);M.m.- Monoraphidium minutum (3.5~pm ESD); C.S.Chlamydomonas sphaeroides (12~pm ESD).ante rates on the medium-sized alga (cf. Fig.2).Dual-label experiments- Among the sev-en food algae (Table I), the most rapidlyingested proved to be Monoraphidium (ESD= 3.5 blrn) for B. angularis, Chlamydomonasreinhardii (ESD = 6 grn) for both B. rubensstrains, and Cyclotella meneghiniana (ESD= 8.5 pm) for B. calyciflorus. All other algaewere offered in pairwise comparison withthem. The results show (Fig. 5) that B. an-gularis most efficiently ingested algae


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Brachionus size selectivity 21Table 3. Selectivilies between 6- and 12-pm beads and ingestion rates of four size classes of Brachionuscu/~@Zoru~ lorica length). Ingestion rates are expressed as the sum of the relative volumes of ingested spheres(6-pm spheres: volume = 1; 12-pm spheres: volume = 8). Number of animals (n) is not identical for selectivitiesand ingestion rates, because no D, can be calculated for animals that did not ingest any beads. Only the biggestsize class has a significantly higher ingestion rate (Tukeys multiple range test. P -=z0.05).

Length (pm)141-168171-19s20 l-22823 l-285

4 Ingestion raten Estimate SE n Estimate SE

24 -0.222 0.133 25 62.6 11.958 -0.349 0.060 74 60.2 6.627 -0.111 . 0.115 33 60.8 12.317 -0.376 0.130 17 139.0 18.9I;= 1.471; 3, 122 df P = 0.226 F = 7.738; 3, 145 df P < 0.001

turn (ESD = 3.5 pm) and is the superiorcompetitor, reaching a given populationgrowth rate at lower food concentrationswhen this alga is fed. The same is true forB. calyciflorus with C. sphaeroides (ESD =12 pm) as food. Using Tilmans (1982)graphical method, I predicted coexistenceor extinction of one or both species fromthe supplied concentrations of both foods.The predictions were tested in semicontin-uous laboratory experiments at two dilutionrates (equivalent to experimentally imposedmortality rates) with six different foodpreparations. There was a high degree ofcorrespondence between prediction and ex-periment: the outcome of exploitative com-petition was correctly predicted by the mod-el in 11 of 12 cases.In contrast to the pattern between species,selectivities do not change significantly withbody size within B. calyciflorus. This pat-tern may be due to eutelic body growth inrotifers. There are no more cell divisionsafter hatching from the egg (Ruttner-Kolis-ko 1972) and it may be that the cilia andcirri, constituting the feeding apparatus onthe corona, do not grow isometrically withbody size.Very small particles generally are ingestedwith low efficiency. The relative clearanceefficiency for the smallest food alga tested(Synechococcus, ESD = 1 pm) is highest forB. angularis ( Wsyn = 0.494&O. 119) andlowest for B. calyciflorus ( WSYn =0.043 kO.0 12). Synechococcus is large rel-ative to field bacteria. It thus may be con-cluded that Brachionus species are not sig-nificant grazers on unattached bacteria orphototrophic picoplankton. Low ingestion

rates on bacteria-sized particles have beenreported for B. rubens (Pilarska 1977) andfor B. calyciflorus (Starkweather et al. 1979;Seaman et al. 1986).Brachionus ingests inert particles if theyare of the appropriate size (DeMott 1986).There are differences in selectivity, how-ever, between polystyrene spheres and algaeof similar sizes: Brachionus angularis didnot ingest any 12-pm beads, but algae ofthis size were still ingested, although withlow efficiency (WChla 12= 0.197+0.137 forC. sphaeroides); B. rubens strain F selectedmore strongly against 12-pm spheres (012= -0.938kO.03) than against C. sphae-roides in dual-label experiments (&hla 12=-0.225-1-0.136) and in long-term feedingexperiments (&hl a 12= -0.65620.03); B.rubens strain B selected against 12-ymsphercs, whereas algae from 3.5 to 12-pmESD were ingested equally well in radiotra-cer experiments. In all these cases, particlesare near the upper food size limit, and thedifferences may be due to different size-fre-quency distributions of algae and spheres.The modes of the size distributions of algaeand spheres are identical, but algal cell sizeshave broader variances, extending intosmaller and more ingestible size classes Fig.6). Another explanation may be the differ-ent texture of particles. It is possible thathard spheres cannot be ingested if they arebigger than the mouth opening, but thatsofter and more flexible algae of the samesize can still be eaten. Hard, artificial par-ticles like plastic or glass spheres seem tobe unsuitable to estimate the maximal sizeof ingestible natural food (Nadin-Hurley andDuncan 1976).


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22 Rothhaupt8060 60

3 6 9 12 3 6 9 12CHANNEL No.Fig. 6, Comparison of the size distributions of Chlamydomonas reinhardii (left) and of Chlamydomonassphaeroides (right) with polystyrene spheres of similar sizes. Measurements were done with a Coulter counter.Algae--@; spheres-O.

In conclusion, the experiments reportedhere confirm the view that apart from par-ticle size, Brachionus spp. have a generalist,poorly discriminating feeding mode. Simi-lar to other rotifer genera (Gilbert and Bog-dan 1984; Bogdan and Gilbert 1987), par-ticle size-dependent ingestion efficienciesmay differ significantly between species orstrains. Ingestion efficiency is not constantover the range of ingestible particle sizeswithin one species Particle size is thus animportant feature of food quality. When-ever functional or numerical responses ofBrachionus species are determined andcompared, the results may depend cruciallyon the size of the food items used. This factis important in determining the trophic roleof Brachionus species in nature and aqua-culture.ReferencesBOGDAN, K. G., AND J. J. GILBERT. 1987. Quanti-tative comparison of food niches in some fresh-water zooplankton. A multi-tracer-cell approach.0ec:ologia 72: 33 l-340.DEMO-IT, W. R. 1986. The role of taste in food se-lection by freshwater zooplankton. Oecologia 69:334-340.-. 1988. Discrimination between algae and ar-tific:ial particles by freshwater and marine cope-pods. Limnol. Oceanogr. 33: 397-408.EDMONI)SON, W. T. 1965. Reproductive rate ofplanktonic rotifers as related to food and temper-ature in nature. Ecol. Monogr. 31: 6 l-l 11.GILBERT, J. J., AND K. G. BOGDAN. 1984. Rotifergrazing: In situ studies on selectivity and rates, p.97-l 33. Zn Trophic interactions within aquaticecosystems. AAAS Select. Symp. 85. Westview.HALBACH, U.,M. SIEBERT, M. WE:STERMAYER,AND C.

WISSEL. 1983. POpUkitiOII eCOlOgy of rotifers asa bioassay tool for ecotoxicological tests in aquaticenvironments. Ecotoxicol. Environ. Safety 7: 484-513.HUTCHINSON, G. E. 1965. The ecological theater andthe evolutionary play. Yale..fAcOEIs, J. 1974. Quantitative measurement of foodselection. A modification of the forage ratio andIvlevs electivity index. Oecologia 14: 4 13-4 17.KRAMBECK, H.J., W. LAMPERT, AND H. BREDE. 1981.Messung geringer Mengen von partikularem Koh-lenstoff in natiirlichen GewHssem.GIT Fachz. Lab.25: 1009-1012.LAMPERT, W. [ED.]. 1985. Food limitation and thestructure of zooplankton communities. Ergeb.Limnol. 21.~ AND B. E. TAYLOR. 1985. Zooplankton graz-ing in a eutrophic lake: Implications of diel verticalmigration. Ecology 66: 68-82.MILLER, H. 1972. Wachstum und Phosphatbedarfvon Nitzschia actinastroides (Lemm.) v. Goor ins atischer und homokontinuierlicher Kultur unterPhosphatlimitierung. Arch. Hydrobiol. Suppl. 38,p. 399-484.NADIN-HURLEY, C. M., AND A. DUNCAN. 1976. Acomparison of daphnid gut particles with the ses-ton present in two Tharnes reservoirs throughoutthe season. Freshwater Biol. 6: 109-123.O'FLAHER-IY, L.M., AND H.K. PHINNEY. 1970. Re-quirements for the maintenance and growth ofI Aphanizomenon j7os-aquae in culture. J. Phycol.6: 95-97.PETERS,R. H. 1984. Methods for the study of feeding,grazing, and assimilation by zooplankton, p. 336-412. In J. A. Downing and F. H. R igler [eds.], Amanual on methods fo r the assessment of second-ary productivity in fresh waters, 2nd ed. IBPHandbook 17. Blackwell.RLARSKA, J. 1977. Eco-physiological studies onBrachionus rubens Ehrbg. (Rotatoria). 1. Food se-lectivity and feeding rate. Pol. Arch. Hydrobiol.24: 3 19-328.ROIHHAUPT, . 0. 1988. E4echanistic resource com-petition theory applied to laboratory experimentswith zooplankton. NatLlre 333: 660-662.


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Brachionus size selectivity 23-. 1990. Changes of the functional responses ofthe rotifers Brachionus rubens and Brachionus ca-IyciJlorus with particle sizes. Limnol. Oceanogr.35: 24-32.RUTTNER-KOLISKO, A. 1972. Rotatoria. Die Binnen-

gewasser 26: 99-234.SEAMAN, M. T., M. GOPHEN, B. Z. CAVARI, AND B.f&OULAY. 1986. Brachionus calyciflorus Pallasas agent for the removal ofE. coli in sewage ponds.Hydrobiologia 135: 55-60.STARKWEATHER,P.L.,J.J. GILBERT,AND T.M. FROST.1979. Bacterial feeding by the rotifer Brachionuscalyciflorus: Clearance and ingestion rates, behav-ior and population dynamics. Oecologia 44: 26-30.

TILMAN, D. 1982. Resource competition and com-munity structure. Princeton.UTERM~HL, H. 1958. Zur Vervollkommnung derquantitativen Phytoplankton-Methodik. Mitt. Int.Ver. Theor. Angew. Limnol. 9. 38 p.VANDERPLOEG, H. A., AND D. SCAVIA. 1979. Calcu-lation and use of selectivi ty coefficients of feeding:Zooplankton grazing. Ecol. Model. 7: 135-149.WALZ, N. 1983. Continuous culture of the pelagicrotifers Keratella cochlearis and Brachionus an-gularis. Arch. Hydrobiol. 98: 70-92.

Submitted: 8 February 1989Accepted: 7 June 1989Revised: 3 October 1989

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Rothhaupt, 1990. Differences in Particle Size-Dependent Feeding Efficiences of Closely Related Rotifer Species