Maternal effects, conspecific chemical cues, and switching from parthenogenesis to gametogenesis in the cladoceran Moina macrocopa

The change in reproductive mode from parthenogenesis to gametogenesis in Cladocera is controlled by multiple environmental cues. Maternal effects are involved in the control of reproductive switching. In this study, we estimated the readiness of Moina macrocopa females to change reproduction mode under the effect of conspecific chemicals on maternal and offspring generations. The results demonstrated that information about the chemical environment was not transmitted between generations (none of the females produced diapausing eggs in the control medium irrespective of their mothers' environment). Differences in maternal energetic investments were not significant, hence the maternal environment did not affect the fecundity. However, tested animals adapted to the effect of the diapause inducing factor. When offspring of mothers cultured in crowded water were also cultured in crowded water (the constant effect of conspecific chemicals), they switched less readily to gametogenesis than offsprings of mothers cultured in fresh medium.     

Induction of diapausing amictic eggs in Synchaeta pectinata

Amictic females of a clone of S. pectinata from Star Lake (Norwich, Vermont) may produce diapausing as well as non-diapausing (subitaneous) eggs. The proportion of diapausing eggs produced in cultures was unaffected by temperature (12 vs 19 °C) or rotifer population density (minima of 0.33 vs 3 ind. ml^–1) at 19 °C. However, at 19 °C this proportion was higher in cultures maintained at a low food level suppressing reproduction (5 × 10³ cells ml^–1 Cryptomonas erosa) than in those maintained at a high food level (2 × 10⁴ cells ml^–1); the treatment effect was marginally significant (p=0.067). Consistent with the effect of low food availability, a period of starvation was very effective in inducing the development of diapausing eggs. None of 19 females cultured individually from hatching at 19 °C on C. erosa (2 × 10⁴ cells ml^–1) in 1-ml volumes produced any diapausing eggs in 4 days (0 out of 349 eggs), while 13 out of 16 females subjected to a 15-hour starvation period 6 hours after birth produced one or more diapausing eggs during that time (34% of the 158 eggs produced by the 16 females were diapausing). Diapausing eggs produced and left at 19 °C hatched after 4 to 13 days. Those produced in cultures with a low food level took significantly longer to hatch (9.7 days) than those produced in cultures with a high food level (8.1 days) (p=0.022). In natural communities, S. pectinata should be able to respond directly and rapidly to poor food conditions by producing eggs that undergo an obligatory dormant period before resuming development.     

The Life Histories of Two Temporarily Coexisting,Pond Dwelling Cladocerans

Investigations on the life histories of two cladocerans, Moina brachiata and Daphnia obtusa, in a small, nearly temporary pond in South Germany revealed that M. brachiata is better adapted to fluctuating environmental conditions; the species dominated from May to October. D. obtusa was present in spring and autumn/winter but disappeared completely during the summer months. Both species coexisted for extended periods in spring and autumn; abundance of D. obtusa was generally by an order of magnitute lower. Four periods of low water level were slightly preceded by or coincided with a decrease of clutch size, a decrease of the proportion of egg bearing females indicating that both species suffered from food shortage. Laboratory investigations on life history parameters showed that the two species have different temperature tolerances and preferences. M. brachiata showed its highest reproductive success at 25 and 30°C but died at temperatures <15°C and ≥ 35°C. D. obtusa experienced a broader temperature range (2 to 25°C) but could not withstand temperatures ≥ 30°C. Short term starvation periods (3d) caused the death of M. brachiata females, while D. obtusa soon recovered and reproduced when being refed. M. brachiata is a typical r-species with early reproduction, rapid development, high population growth rates and a high tendency to produce resting eggs; D. obtusa pursues more the concept of k-selection.     

Sexual reproduction and diapause of Hexarthra sp. (Rotifera) in short-lived ponds in the Chihuahuan Desert

1. In the life cycle of monogonont rotifers it is generally assumed that diapausing eggs invariably hatch into amictic stem females which produce female offspring parthenogenetically. Diapausing eggs are only produced by later generations after sexual reproduction has been induced by environmental cues. 2. We show that populations of an undescribed Hexarthra species inhabiting small temporary ponds in the Chihuahuan Desert deviate from this life cycle pattern. These ponds may dry within days and up to 85% of females were mictic. Females producing male offspring and diapausing eggs were observed 1 or 2 days, respectively, after ponds had filled with water. 3. Under laboratory conditions, 7–46% of females hatching from re‐hydrated sediments were sexual. Male offspring of these females can fertilise other mictic stem females leading to diapausing egg formation. In laboratory experiments, females produced fully developed diapausing eggs within 1.9 days at 20 °C and 1.2 days at 30 °C. 4. In addition, embryonic development time (1.1–0.3 days at temperatures between 12 and 30 °C) and juvenile period (2.1–0.5 days for the same temperature range) are shorter than those of other rotifer species. In short‐lived habitats, the potential for rapid population development and production of new diapausing eggs may be crucial in the long‐term survival of populations.     

Development,Reproduction and Growth Pattern of two Coexisting,Pond Dwelling Cladocerans

Laboratory investigations on life history parameters of 2 coexisting cladocerans (Daphnia obtusa. Moina brachiata) from a nearly temporary pond in South Germany revealed that the species have different temperature tolerances and temperature optima. D. obtusa experienced the highest reproductive success at 15 and 20 °C and was able to survive and to reproduce at 2 °C but died at 30 °C. The reproductive success of M. brachiata was highest at 25 and 30 °C and the species could not withstand temperatures <15 °C and ≥35 °C. At temperatures between approximately 20 and 25 °C, where both cladocerans coexisted in nature, M. brachiata showed a faster population growth due to its approximately twofold higher egg production rates (10–12 eggs female⁻¹ day⁻¹ compared to approximately 5 eggs female⁻¹ day⁻¹ in D. obtusa) and its shorter juvenile development (3.3 and 2.4 days compared to 6.3 and 5.3 days in D. obtusa); M. brachiata needs generally only 3 molts to reach maturity while D. obtusa requires 5–6 molts.     

Fecundity,reproduction, and growth of Moina macrocopa fed different algae

Three micro algae, Ankistrodesmus convolutus, Scenedesmus incrassatulus and Chlorella vulgaris, at three concentrations, were tested as diets for Moina macrocopa. Their effect on reproduction, fecundity, growth and survival was evaluated. All three algae satisfied the nutritional requirements of M. macrocopa, despite their difference in size. The best concentration, expressed in dry weight, was 5 mg l^–1 for all three. Time to first reproduction was 4 days with all diets. Average time between clutches was 33 hours, and maximum number of clutches was 12; the highest average number of offspring per brood was 27. The largest broods were the fourth to sixth, depending on the diet. Ephippium hatching depends on temperature, taking only 24 hours at 30 °C and 48 hours at 27 °C. This species could be an important test organism in aquatic bioassays, and a live food in aquaculture.     

Do Golden Egg Bugs (Phyllomorpha laciniata: Heteroptera, Coreidae) Require Conspecifics for Oviposition?

Golden egg bug (Phyllomorpha laciniata) females lay eggs on the bodies of conspecifics of both sexes. We investigated to what extent reproduction depended on the availability of conspecifics as oviposition substrate and the acceptability of the host plant as an alternative oviposition substrate in the absence of conspecifics. Mated females were placed in experimental enclosures each containing a sprig of fresh host plant. Each experimental female was subjected to one of three treatments: isolated from conspecifics (solitary), paired with another female, or paired with a male. Solitary females laid a few eggs on the host plant but then stopped laying eggs, and solitary females laid significantly fewer eggs than those enclosed with another female or a male. Females enclosed with a male laid no more eggs than those enclosed with a female. When two previously isolated females were later enclosed together, they soon renewed oviposition. Females in nature contained significantly more oviducal eggs than did females that were enclosed with other females for a short period. Thus the availability of suitable conspecifics as oviposition substrate stimulates the deposition of mature eggs, and reproduction depends on the presence of conspecifics of either sex as oviposition substrate.     

Studies on functional response and prey selection using zooplankton in the anostracan Chirocephalus diaphanus Prevost, 1803

Freshwater cladocerans and rotifers were used as prey to study functional response and prey selection by adult females of Chirocephalus diaphanus under laboratory conditions. For functional response studies, we offered three rotifer species (Brachionus calyciflorus, B. patulus and Euchlanis dilatata) and three cladoceran species (Alona rectangula, Ceriodaphnia dubia and Moina macrocopa) at various densities ranging from 0.5 to 16 ind. ml^–1. We found increased zooplankton consumption with increasing prey density but beyond 4 ind ml^–1 cladocerans and 8 ind. ml^–1 rotifers, the number of animals eaten plateaued. In general, C. diaphanus consumed fewer large prey (cladocerans) and many more smaller zooplankton (rotifers). For prey selection experiments, we used B. calyciflrous, B. patulus, C. dubia and M. macrocopa, offered at the ratio of two rotifers: one cladoceran and at three prey densities (total zooplankton numbers: 3, 6 and 12 ind. ml^–1). Prey selectivity patterns followed the functional response trends. In general, regardless of prey types, with an increase in the available zooplankton, there was an increase in the number of prey consumed. At any given prey density, C. diaphanus consumed higher numbers of rotifers than cladocerans. Among the prey offered, B. patulus and M. macrocopa were positively selected. Results are discussed in light of possible control of zooplankton by anostracans in temporary ponds.     

Effect of mixed diets (cyanobacteria and green algae) on the population growth of the cladocerans <Emphasis Type="Italic">Ceriodaphnia dubia</Emphasis> and <Emphasis Type="Italic">Moina macrocopa</Emphasis>

Microcystis aeruginosa, a cosmopolitan form, is a colonial cyanobacterium, which is also common in many freshwater bodies in Mexico. In eutrophic water bodies cyanobacteria are often the main phytoplankton that co-exist with cladocerans. We evaluated the effect of mixed diets, comprising 0, 25, 50, 75, and 100% on dry weight basis of M. aeruginosa, and the rest of one of two green algal species (Chlorella vulgaris and Scenedesmus acutus), on the population growth of the cladocerans Ceriodaphnia dubia and Moina macrocopa. Regardless of the share of M. aeruginosa in the mixed diet, C. dubia fed Chlorella had a longer initial lag phase. However, in mixed diet with S. acutus, the lag phase of C. dubia increased with increasing proportion of M. aeruginosa. When raised on 100% M. aeruginosa, the population growth of C. dubia was lowered compared with 100% S. acutus or 100% C. vulgaris. Increased proportion of M. aeruginosa in the mixed diet also resulted in decreased abundance of M. macrocopa. Irrespective of diet type, M. macrocopa had a shorter lag phase than C. dubia. Depending on the diet type, the rate of population increase (r) of C. dubia varied from 0.07 to 0.26 d⁻¹ while that of M. macrocopa was higher (0.14–0.61 d⁻¹). For both cladoceran species, the lower r values were obtained when fed Microcystis. Our study showed that the strain of M. aeruginosa was not highly toxic to cause total elimination of either C. dubia or M. macrocopa. Addition of a green algal component to the diet improved the population growth rates of both cladoceran species.     

Taxonomic Status and Reproduction Dynamics of the Non-Indigenous Cercopagis in the Gulf of Riga (Baltic Sea)

Overwintering population of Cercopagis is represented by resting eggs which hatch generally in May. Although representatives of the first parthenogenetic generation (the spring form individuals) differ morphologically from individuals of the subsequent generations (the summer form individuals) and could be keyed to a separate species – Cercopagis (Apagis) ossiani – our analysis confirm that there is only one Cercopagis species in the Gulf of Riga: Cercopagis pengoi. Notable seasonal dynamics was observed for the gamogenetic mode of reproduction, being strongly associated with the total population density. Gamogenetic females develop since the end of June and reach the maximum absolute abundance in July whereas their proportion is generally the highest in fall. The gamogenetic absolute fecundity drops to the lowest level late July but increased afterwards until the late August. One resting egg was, an average, found in 45.4%, two in 53.4% and three in 1.2% of females. Parthenogenetic fecundity was significantly higher in May–June compared to other months studied. Brood pouch of parthenogenetic females was found to contain 11.6 ± 1.0 and 10.2 ± 0.3 embryos in the spring and summer form individuals, respectively. Variation in the two modes of reproduction and fecundity is probably solely not controlled by temperature, but also by food availability and population density.     

Size specific demography of three species of Anastrepha fruit flies

Individuals of three Anastrepha species: A. obliqua, A. ludens, and A. serpentina (Diptera: Tephritidae), were sorted according to pupal weight in cohorts of large and small flies. Demographic parameters and reproductive patterns and heterogeneity were determined for each cohort. Large flies of the three species presented greater expectation of life and gross fecundity rates. A. ludens was the species with the longest life span (expectation of life of large adults was 110 days) and the greatest gross fecundity rates (1597 eggs/female for the large flies). While, A. obliqua had the shortest mean age of reproduction (33 days), and the greatest daily egg production (14 eggs/female/day). Net fecundity was similar in these two. A. serpentina had lower fecundity rates.Reproductive information for each size and each species include: age-by-parity relations, fraction of sexually mature life in which females lay eggs, and frequency distribution of individual egg production. Results demonstrate that even under constant laboratory conditions and using standard artificial hosts, there is a great deal of life history variation among these Anastrepha species and among other tephritid fruit flies.     

Life cycle and mating behavior of <Emphasis Type="Italic">Helicotylenchus multicinctus</Emphasis> (Nematoda: Hoplolaimidae) on excised <Emphasis Type="Italic">Musa cavendishii</Emphasis> roots

The life cycle and mating behavior of Helicotylenchus multicinctus (Nematoda: Hoplolaimidae) were observed in vitro on excised roots of Musa cavendishii in gnotobiotic culture. Eggs hatched into juveniles whose appearance and structure were similar to those of the adults. Juveniles grew in size and each juvenile stage was terminated by a molt. H. multicinctus had four juvenile stages. The first molt occurred outside the egg shortly after hatching. After the final molt the juveniles differentiated into adult males and females. Mating was required for reproduction. After mating, fertilized females began to lay eggs. The life cycle from second stage juvenile to second stage juvenile was completed in 39 days.     

Reproductive Parameters of Female<Emphasis Type="Italic">Pan paniscus</Emphasis> and <Emphasis Type="Italic">P. troglodytes</Emphasis>: Quality versus Quantity

We investigated intra- and interspecific differences in life history and reproductive parameters in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). We compare the parameters of wild and captive females in order to shed light on the influence of habitat or specific differences or both on reproduction. We present new and additional information on reproductive parameters from captive bonobos and chimpanzees. Captive chimpanzees birth more live offspring and have a shorter interbirth interval, but experience higher infant mortality than captive bonobos. Although captive bonobo females tend to start reproduction at a younger age than chimpanzees, this is effectively only so for wild-born females of both species. Ultimately both species reach the same rate of production of offspring surviving to 5 yr. These results contrast with data from the wild. Wild bonobos tend to have higher reproductive success, a higher fertility rate and a shorter interbirth interval than wild chimpanzees. Reproduction is similar for wild and captive bonobos, which suggests that they are producing at their maximum under both conditions. Overall captive chimpanzees perform better than their wild conspecifics, probably because of lower feeding competition. Infant survival is the only specific difference not affected by captivity. Bonobo infants survive better, which suggests that chimpanzee infants are more at risk. We argue that the interspecific variation in reproductive parameters in captivity is related to the different influence of captivity on reproduction and different pressures of external sources of infant and juvenile mortality.     

The Insect Growth Regulator Pyriproxyfen Terminates Egg Diapause in the Asian Tiger Mosquito,Aedes albopictus

The Asian tiger mosquito, Aedes albopictus, is a highly invasive mosquito species that transmits chikungunya and dengue. This species overwinters as diapausing eggs in temperate climates. Early diapause termination may be a beneficial strategy for winter mosquito control; however, a mechanism to terminate the diapause process using chemicals is not known. We tested the hypothesis that a hormonal imbalance caused by the administration of juvenile hormone analog would terminate egg diapause in A. albopictus. We tested the insect growth regulator pyriproxyfen on all developmental stages to identify a susceptible stage for diapause termination. We found that pyriproxyfen treatment of mosquito eggs terminated embryonic diapause. The highest rates of diapause termination were recorded in newly deposited (78.9%) and fully embryonated (74.7%) eggs at 0.1 and 1 ppm, respectively. Hatching was completed earlier in newly deposited eggs (25–30 days) compared to fully embryonated eggs (71–80 days). The combined mortality from premature diapause termination and ovicidal activity was 98.2% in newly deposited and >98.9% in fully embryonated eggs at 1 ppm. The control diapause eggs did not hatch under diapausing conditions. Pyriproxyfen exposure to larvae, pupae and adults did not prevent the females from ovipositing diapausing eggs. There was no effect of pyriproxyfen on diapausing egg embryonic developmental time. We also observed mortality in diapausing eggs laid by females exposed to pyriproxyfen immediately after blood feeding. There was no mortality in eggs laid by females that survived larval and pupal exposures. In conclusion, diapausing eggs were the more susceptible to pyriproxyfen diapause termination compared to other life stages. This is the first report of diapause termination in A. albopictus with a juvenile hormone analog. We believe our findings will be useful in developing a new control strategy against overwintering mosquito populations.     

Comparison of biological and demographic parameters forMononychellus progresivus andOligonychus gossypii on cassava: influence of temperature

The effect of five constant temperatures (16, 22, 26, 31 and 36°C) on biological (survival and duration of developmental stages, fecundity and longevity of females, sex-ratio) and demographic parameters (R _o , G, r _m and λ) of the two main phytophagous mites that attack cassava in Africa,Mononychellus progresivus Doreste andOligonychus gossypii (Zacher), was studied in the laboratory. Experiments were performed simultaneously on the two mite species reared on the same cassava variety (1M20) under controlled conditions: 70±10% r.h. and 12L∶12D. The lower thermal threshold was 13°C forM. progresivus and 11°C forO. gossypii. Both species developed in the range from 22 to 36°C. The shortest development time was obtained at 31°C for both species; it was 7.2 days forM. progresivus and 8.2 days forO. gossypii. Maximum fecundity of both species was recorded at 26°C with 42.1 eggs forM. progresivus and 36.3 eggs forO. gossypii The highest intrinsic rate of increase (r _m ) was obtained at 31°C for both species with 0.289 and 0.214 forM. progresivus andO. gossypii, respectively.     

Development and reproductive capacity of the predatory mite <Emphasis Type="Italic">Parasitus consanguineus</Emphasis> (Acari: Parasitidae) reared on the larval stages of <Emphasis Type="Italic">Megaselia halterata</Emphasis> and <Emphasis Type="Italic">Lycoriella ingenua</Emphasis>

Development and reproduction of the predatory mite Parasitus consanguineus Oudemans et Voigts (Acari: Parasitidae) reared on a diet of first and second instars of Megaselia halterata (Diptera: Phoridae) or Lycoriella ingenua (Diptera: Sciaridae) were studied. Mites were allowed to feed on these diets until death. The developmental time of immature stages of P. consanguineus was significantly longer when reared on L. ingenua than on M. halterata larvae (8.3 vs. 7.9 days, respectively). Survival to adulthood of P. consanguineus reared on L. ingenua or M. halterata larvae was 63 and 49%, and mite fecundity was 17.8 and 12.3 eggs/female, respectively. Adult females reared on L. ingenua lived on average 6.9 days, whereas those reared on M. halterata lived for 5.7 days. Mite survival, female longevity and fecundity were significantly different among the two diet types.     

Interpopulation variation in Chrysoperla carnea reproduction: implications for mass-rearing and storage

To determine whether diverse populations and biotypes of Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) can be mass-produced and stored under uniform conditions, we assessed reproduction in five North American populations, four from the carnea biotype and one from the mohave biotype. Non-diapause adults from the carnea biotype varied significantly in only one aspect of reproduction, viz., the preoviposition period, whereas the duration and rate of oviposition, as well as fecundity, did not vary significantly. Relative to the carnea populations, the mohave population typically had delayed oviposition and a lower rate of oviposition; however, its oviposition period was long, and thus its fecundity differed only from that of the most productive carnea populations.The shelf-life (= survival during storage, and subsequent survival and reproduction after storage) was evaluated for four populations of the carnea biotype. Survival of diapausing adults during the first 18 weeks of storage was high among all four populations; adults from three populations also showed high survival after 35 weeks of storage. A high incidence of females from all four populations laid some fertile eggs after being stored for up to 31 weeks or longer. After six or more weeks of storage, average fecundity was high and ranged from 400–900 eggs/female. Duration of storage (up to 39 weeks) was a significant determinant of fecundity in two of the four populations.In practice, diverse populations of C. carnea can be efficiently mass-produced (with or without storage) under uniform conditions in the insectary. Thus, the choice of which populations to mass-produce and use in augmentation can be based primarily on the characteristics (e.g., climate, habitat, crop) of the intended area of release, rather than on considerations concerning mass-rearing.     

Effect of the epizoic rotifer Brachionus rubens on the population growth of three cladoceran species

Using population densities and growth rates as criteria, we studied interactions between the epizoic rotifer Brachionus rubens and each of three cladoceran species differing in size and reproductive rates — Daphnia carinata, Moina macrocopa and Ceriodaphnia rigaudi. In all mixed — species experiments, B. rubens existed in both the epizoic mode, attached to the cladoceran host, and in the free-swimming mode. Rotifer population growth rates were significantly depressed in the presence of M. macrocopa, presumably as a consequence of exploitative and interference competition. The largest cladoceran, D. carinata probably did not suppress B. rubens, because the epizoic component of the rotifer population escaped from the deleterious effects of mechanical interference. Peak population numbers and initial population growth rates reached by all three cladocerans were lower in the presence of B. rubens, probably because of the adverse effects of the epizoic infestation, which was maximal on D. carinata and least on C. rigaudi. In mixed-species cultures of D. carinata and M. macrocopa, the presence of B. rubens helped D. carinata coexist with M. macrocopa, which otherwise would have suppressed the Daphnia.     

Reproduction of Meloidogyne javanica on Plant Roots Genetically Transformed by Agrobacterium rhizogenes

Reproduction of Meloidogyne javanica was compared on several Agrobacterium rhizogenes-transformed root cultures under monoxenic conditions. M. javanica reproduced on all transformed roots tested; however, more females and eggs were obtained on potato and South Australian Early Dwarf Red tomato than on bindweed, Tropic tomato, lima bean, or carrot. Roots that grew at moderate rates into the agar and produced many secondary roots supported the highest reproduction. Numbers of females produced in cultures of transformed potato roots increased with increasing nematode inoculum levels, whether inoculum was dispersed eggs or juveniles. Females appeared smaller, produced fewer eggs, and were found in coalesced galls at the higher inoculum levels. The ratio between the final and initial population decreased sharply as the juvenile inoculum increased. The second-stage juvenile was preferred to dispersed eggs or egg masses for inoculation of tissue culture systems because quantity and viability of inoculum were easily assessed. Meloidogyne javanica reared on transformed root cultures were able to complete their life cycles on new transformed root cultures or greenhouse tomato plants.     

Ontogenetic Shifts in the Ability of the Cladoceran,Moina macrocopa Straus and Ceriodaphnia cornuta Sars to Utilize Ciliated Protists as Food Source

The ontogenetic diet shifts and age specific ability of the two cladoceran species Moina macrocopa and Ceriodaphnia cornuta to derive energy from ciliated protists have been investigated in laboratory. The postembryonic developmental rates and life table demography (longevity, age and size at first reproduction, fecundity and intrinsic rate of natural increase) of the cladocerans have been elucidated on algae (Chlorella vulgaris) and the ciliated protists (Tetrahymena pyriformis, Colpoda (c.f.) steini) as food. For either of the cladoceran, the somatic growth rate and average body size at first reproduction were higher with algal diet. During initial stages of development (0–5 days), either cladoceran realized higher rate of somatic growth on algal diet, subsequently ciliated protists supported significantly higher growth rate than the alga. Algal and ciliate diets did not differ in maximum body size (C. cornuta: 539–554 μm; M. macrocopa: 1274.8–1309 μm) reached by either of the cladocerans. The maximum body sizes were larger than size at first reproduction with either of the ciliated protists, however, with algal diet the maximum body sizes did not differ from the size at first reproduction in each case. In case of C. cornuta the generation time (20.5 ± 0.3 days on ciliate; 15.6 ± 0.17 days on algal diet), reproductive rates (net reproductive rate: 20.05 ± 3.2 on ciliate; 15.5 ± 1.2 on algal diet), and average life expectancy at hatching (27 ± 0.8 days on ciliate; 22.7 ± 0.71 days on alga) were higher, whereas the size at first reproduction (482 μm on ciliate; 521 μm on alga) was smaller with the ciliate than with an algal diet. The algal and the ciliate diets did not differ in survival (life expectancy at hatching: 9.2 ± 0.7 days) and fecundity (NRR: 23.6 ± 2.4) for M. macrocopa. The two ciliates used in the experiment did not differ in their performance as food source for either cladoceran species. Our results suggest that both the cladoceran species are able to utilize smaller ciliate (e.g., T. pyriformis, C. (c.f.) steini) as food; however with differential ability to derive energy from the ciliate diet and this ability is size and age structured in both cases. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)