Feeding selectivity of a tropical Chaoborus population

SUMMARY. The Chaoborus population of Lake Lanao, Philippines, was sampled weekly over a 65-week period. Specimens representing all four instars, all times of the year, and two points in the daily migration cycle were dissected for determination of gut contents. Major items in the diet of Lanao Chaoborus include Bosmina, Diaphanosoma, and the copepodid and adult stages of cyclopoid and calanoid copepods. Items that are available but seldom eaten include nauplii and rotifiers except Keratella. Feeding rate averages 2.5% of body weight per day in instars 3–4. Predator size affects but does not fully explain prey selection. Electivity values are much higher for Bosmina and Diaphanosoma than for copepods, even though these food items overlap in size. Bosmina, which has the highest electivity value of any prey, is virtually identical in size to the calanoid nauplius, which has one of the lowest electivity values. This and other similar data suggest that prey of the same size differ greatly in palatability or vulnerability. There is a marked variation in feeding rate and food composition from day to night. The smallest Chaoborus feed more during the day than at night, but the opposite is true for Chaoborus of moderate to large size. Large Chaoborus switch from a daytime emphasis on copepod copepodids and adults to a nighttime emphasis on Cladocera. Diurnal variation between instars in food composition cannot be explained simply on the basis of the vertical distributions of predators and prey. An interaction of vertical distribution with prey density and predator selectivity does explain the overall Chaoborus feeding pattern, however. During the day, larger Chaoborus move deep into the water column where food is scarce. Their daytime feeding rate is lower due to low prey density at great depths. Low prey density is partially compensated by relaxation of preference. At night, upward migration of large Chaoborus into an area of high prey density permits a resumption of marked selectivity and high feeding rates. Small Chaoborus do not descend deep into the water column during the day, as their lower hunting efficiency apparently requires higher food density and use of visual cues to sustain adequate feeding rates. Prey density thus affects both the vertical distribution and feeding selectivity of the Chaoborus population.     

Differential use of food resources by the instars of Chaoborus punctipennis

SUMMARY. 1. Differential use of food resources by instars I-1V of Chaoborus punctipennis was examined in a mesotrophic New Hampshire lake during midsummer when all instars coexisted. Diet composition and prey preference were quantified first, at night when all instars were feeding at the same depth, and second, during the day when the early instars (I-II) and instar III were segregated by depth. Relative abundance, per cent biomass, and per cent frequency of occurrence of soft and hard-bodied rotifers, flagellated phytoplankton, protozoans, and crustaceans in C. punctipennis diets were quantified using crop content analyses. 2. All four instars ingested large, flagellated phytoplankton (mainly Dinobryon and Ceratium). This unexpected result suggests that the effects of phytoplankton on Chaoborus growth and survival should be investigated. All instars also consumed rotifers (mainly Kellicottia, Gastropus, Polyarthra), but only instars III and IV fed upon crustaceans (mainly Daphnia, Bosmina and Diaphanosoma). Small rotifers (Gastropus spp., Keratella cochlearis, Trichocerca similis) occurred more frequently and were more abundant in early instar diets than late instar (III and IV) diets, whereas large rotifers (Asplanchna priodonta and Keratella crassa) were eaten only by instars III and IV. Zooplankton with gelatinous sheaths (e.g. Ascomorpha, Collotheca and Holopedium) were rarely ingested. 3. Developmental increase in gape diameter of C. punctipennis seemed to be the major proximate mechanism causing dietary differences among instars. Body widths of hard-bodied prey in C. punctipennis crops were always less than gape diameter. The relationship between prey body width and Chaoborus gape diameter, coupled with knowledge of prey escape behaviour, should be useful for predicting the presence of hard-bodied prey taxa in diets of other Chaoborus species. 4. All four instars of C. punctipennis selected soft-bodied, or weakly loricate, rotifer prey over crustaceans and phytoplankton. Early instars preferred the small rotifer T. similis and the protozoan Difflugia sp. to other rotifers and phytoplankton when feeding in the epilimnion or thermocline during the day or night. Late instars positively selected the rotifer, Asplanchna. Prey value (prey weight ingested per unit handling     

Some factors affecting the respiration of some aquatic plants

Summary The oxygen consumption of four aquatic plants has been determined at various concentrations of dissolved oxygen and at three different temperatures.Oxygen consumption rates (mg oxygen/g dry weight per hr) at 20°C in air-saturated water were Berula erecta, 1.25; Callitriche obtusangula, 2.8; Hippuris vulgaris, 1.96; and Ranunculus pseudofluitans, 1.90.Oxygen consumption rates increased with increase in dissolved-oxygen concentration within the experimental limits of 1.2–17 p.p.m. dissolved oxygen. The relation of oxygen consumption to this range of oxygen concentrations can be described by the empirical equation R = aC ^b. Increase of temperature has been shown to increase the rates of oxygen consumption. Q₁₀ values ranging from 1.32 to 3.48 have been obtained.     

Energetic costs of prey ingestion in a scincid lizard,Scincella lateralis

Summary The relative importance of aerobic and anaerobic metabolism during feeding was investigated in the ground skink, Scincella lateralis. Animals were fed crickets of three different sizes relative to body mass (5, 10, and 15% of body mass). Oxygen consumption and lactic acid production of animals during feeding were compared with those of animals at rest and when exercising intensely. Oxygen consumption was higher in feeding and exercising animals than in those at rest. Rates of oxygen consumption of animals consuming prey of 5 and 10% of body mass were not significantly different from each other, but were lower than rates of animals consuming prey of 15% of body mass. Lactic acid concentrations in feeding animals increased with increasing prey size. Concentrations in resting and feeding animals were not different, but those of exercising animals were significantly higher. These data suggest that, despite a positive correlation between prey size and lactic acid concentration, anaerobiosis is relatively unimportant in the support of prey handling for Scincella lateralis. The energetic requirements of feeding in this species are met largely by increased aerobic metabolism.     

Age-specific Chaoborus predation on rotifer prey

SUMMARY. 1. This is the first study to examine predator-prey interactions between Chaoborm instars and rotifer prey. The predatory behaviour of instars I–III of Chaoborus pimctipennis and the diet selectivity of instars I—IV feeding on rotifers were examined in the laboratory. Prey used in direct observations of predatory behaviour included a variety of rotifers (Symhacta pectlnata, S. ohUmga, Polyarthra remata, Asplanchna girodi, Keratella crassa, spined and unspined forms of Keratella cochlearis) and two crustaceans (Bosmitia longirostris, Mesocyclops edax nauplii. 2. In general, strike efficiencies (percentage of strikes resulting in inges- tion) increased in successive instars I—III. Early instar (I and II) strike efficiencies were low when compared with other invertebrate predators. For a given instar. mean prey handling times varied among prey species more than strike efficiencies. Mean handling times for small, soft-bodied rotifers were lowest and those for wide, hard-bodied prey were highest. 3. Instar I exhibited significantly greater selectivity for the small, soft- bodied S. obUmga than for the larger S. pectinata, hard-bodied K. crassa, and spined and unspined forms of K. cochlearis. Instars II—IV positively selected both the large and small Symhaeta species over all Keratella species. The relationship between Chaobortts selectivity and prey value (weight of prey per unit handling time) can be described by a power function. Ingestion rates of rotifers by older instars (III and IV) are among the highest reported for invertebrate predators. 4. Rotifer vulnerability to Chaoborus predation probably depended on rotifer cuticle texture, body width, and hydrodynamic disturbances. Spined rotifers were not necessarily protected from Chaoborus predation because Chaohorus can manipulate and swallow them. Giguere et al.'s 1982) encounter rate model must be modified to predict encounter rates of slow-moving rotifer prey with Chaohorus.     

Respiratory metabolism of the soft tick,Ornithodoros turicata (Dugès)

The rate of oxygen consumption was investigated in fed larval, nymphal and adult Ornithodoros turicata ticks and in starved nymphal and adult ticks. Oxygen consumption rate of fed adult ticks increased with increasing temperature. The metabolic rate of adult ticks was affected by starvation whereby starved adult ticks showed a significantly lower oxygen consumption than their fed counterparts. The oxygen consumption rate of fed female ticks was significantly higher than that of fed males but, there was no significant difference between the oxygen consumption rates of starved female versus starved male ticks. Oxygen consumption of fed larvae was significantly greater than those of fed first through third instar nymphs. Fed and starved nymphal ticks as well as fed adult ticks ventilated continuously. In contrast, starved adults ventilated discontinuously. The ability to reduce metabolic rate, plus the capability to ventilate discontinuously allow O. turicata adults to cope with prolonged starvation.     

Nonvisual feeding in a visual planktivore,Xenomelaniris venezuelae

Summary Studies of the diel feeding patterns of the planktivorous fish, Xenomelaniris venezuelae, in Lake Valencia, Venezuela, revealed that, although the fish is primarily a diurnal feeder, it consumes substantial numbers of Chaoborus larvae and pupae at night. A number of fish species are known which feed on plankton at night, but these fish are filter feeders and their diets largely consist of relatively small, nonevasive prey. Chaoborus, however, is large and agile. Predation by Xenomelaniris in the dark was also studied experimentally. Captured fish were placed in completely darkened aquaria with zooplankton from Lake Valencia. After several hours the plankton was removed and examined for evidence of feeding. The fish were found to consume Chaoborus pupae and fourth instar larvae but not other types of prey. The mode of feeding by Xenomelaniris in the dark is unknown.     

Skeleton weight-free oxygen consumption related to adaptations to environment and habits of six crustacean species

• 1.1. Oxygen consumption in six crustacean species from the continental shelf of the NW Gulf of Mexico was related to the ash free weight per dry weight (afdw) gram of the tissue excluding the exoskeleton, suggesting a close relationship to their life strategies.
• 2.2. Dry weight exoskeleton proportion varied among species, with highest values recorded in callapid brachyuran crab species (46.8–52.5%) against the values recorded in portunid crab (45.8–48%) and the shrimp species (26.7–35.7%).
• 3.3. Oxygen consumption was related to afdw in each species according to the expression y = ax^b, with b values ranging from 0.68 to 2.92.
• 4.4. Rates of oxygen consumption per afdw/dw were larger in shrimps than in portunids and callapids, and was related to the morphophysiology and lifestyle of six species described; the former as the morphological design of the exoskeleton versus the muscle content in the species and the latter as the activity rate in the environment.
• 5.5. The oxygen extraction efficiency, calculated from oxygen consumption, was higher in the eurytopic species Penaeus aztecus and Callinecies similis than in species restricted to the marine environment, hence considered as a response to environmental fluctuations.

     

Feeding and bioturbation effects of the sand dollar Peronella lesueuri (L. Agassiz, 1841) (Echinodermata) on microphytobenthos and sediment fluxes

Respiration and excretion rates of a key bioturbating species, the sand dollar Peronella lesueuri, were measured in mesocosms at three different temperatures. Benthic oxygen and nutrient fluxes were additionally measured at winter and summer temperatures to assess the impact of P. lesueuri on ecosystem processes. Oxygen consumption by sand dollars increased significantly with wet weight at all three temperatures 16, 19, and 23 °C. Ammonia release also increased with body weight. The weight vs. oxygen uptake relationship was similar at 19 and 23 °C but oxygen uptake was significantly reduced at the lower exposure temperature. The bioturbation caused by sand dollar P. lesueuri reduced the photosynthetic rate of the microphytobenthos (MPBs) but had a much smaller and less obvious effect on nutrient fluxes across the sediment–water interface.     

Water balance of over-wintering beetles in relation to strategies for cold tolerance

The vapour pressure of the haemolymph of a supercooled insect is higher than the vapour pressure of the haemolymph of a frozen insect at the same temperature. The aim of the study was to see whether this may affect the water loss of freeze-avoiding and freezetolerant, over-wintering beetles. The rates of water loss were determined on freeze-tolerant Pytho depressus larvae and Upis ceramboides adults. Within each species one group was kept supercooled whereas another group was frozen. All groups were incubated at-5°C. Both species displayed significantly lower rates of water loss when they were frozen than when they were supercooled. Values of respiratory rate and water loss of freeze-avoiding and freeze-tolerant species were compared to corresponding values of desert beetles. The results indicate that the freeze-avoiding species have lower rates of cuticular water loss than freeze-tolerant species. This indicates that the freeze-avoiding species have developed more efficient water-saving mechanisms than freeze-tolerant species. The reason for this may be that the haemolymph in frozen animals will be in vapour pressure equlibrium with the ice in the hibernaculum and thus there is no danger of desiccation during winter. The supercooled insects will have a vapour pressure of the haemolymph that is higher than the vapour pressure of water in the surrounding air and will thus lose water.Abbreviations BW body weight - BW_i initial body weight - BW_t body weight at time t - P vapour pressure difference between the water in the haemolymph and the water in the air - DWL_t dry weight loss at time t - M _w rate of metabolic water production - MF_w mol fraction of water, in the haemolymph - MO₂ rate of oxygen consumption - Osm osmolality of the haemolymph - P _a vapour pressure of water in the air - P _h vapour pressure of water in the haemolymph - P _w vapour pressure of pure water - Q a constant (2,02 1 oxygen per g fat metabolized) relating oxygen consumption to dry weight loss when fat is metabolized - R a constant (1,89 1 oxygen per g water produced) relating metabolic water production to oxygen consumption when fat is metabolized - R _dwl rate of dry weight loss - RH relative humidity of the air - RWC_i initial relative water content measured by weighing - RWC_t relative water content at time t - STP standard temperature and pressure     

Increase in respiratory rate during feeding in larvae of the armyworm, Spodoptera exempta

Oxygen consumption was measured in fifth and sixth instar larvae of Spodoptera exempta (Walker) (Lepidoptera, Noctuidae) at 25d?C using Warburg manometry. The mean rate of oxygen consumption while feeding on maize or sorghum leaves was approximately twice that at rest. The increment in oxygen consumption attributable to feeding was 583±207 μlg-¹ h-^l (mean±95% confidence limits) or, for maize, 6.1±3.5 μl O₂ per mg of leaf eaten.     

THE OXYGEN CONSUMPTION OF LUMINOUS BACTERIA

Oxygen consumption of luminous bacteria determined by the Thunberg micro respirometer and by the time which elapses before the luminescence of an emulsion of luminous bacteria in sea water begins to dim, when over 99 per cent of the dissolved oxygen has been consumed, agree exactly. Average values for oxygen consumption at an average temperature of 21.5°C. are 4.26 x 10^–11 mg. O₂ per bacterium; 2.5 x 10⁴ mg. per kilo and 5.6 mg. O₂ per sq. m. of bacterial surface. The only correct comparison of the oxygen consumption of different organisms or tissues is in terms of oxygen used per unit weight with a sufficient oxygen tension so that oxygen consumption is independent of oxygen tension. Measurement of the oxygen concentration which just allows full luminescence, compared with a calculation of the oxygen concentration at the surface of a bacterial cell just necessary to allow the observed respiration throughout all parts of the cell, indicates that oxygen must diffuse into the bacterium much more slowly than through gelatin or connective tissue but not as slowly as through chitin.     

Oxygen consumption and ammonia excretion rates in Octopus maya,loligo forbesi and Lolliguncula brevis (Mollusca: Cephalopoda)

Oxygen consumption and ammonia excretion rates were investigated in young Octopus maya (hatching to 139 days old; 0.11–81.23 g wet body weight, BW; 22.5–23.9°C), young squids of Loligo forbesi (hatching to 45 days old; 9.4–115.3 mg BW; 12.3–13.1°C) and young squids of Lolliguncula brevis (2.00–39.98 g BW; 23.8–24.7°C). Except at hatching, oxygen consumption and ammonia excretion rates on an individual basis (M) of these three cephalopods increased linearly with increasing body weight (BW) expressed as M = aBW^b . Values of b for oxygen consumption were 0.900, 0.910 and 0.848 and for ammonia excretion were 0.744, 0.809 and 0.751 for O. maya, L. forbesi and L. brevis, respectively. Among the three species the value a varied widely, while b was similar for both oxygen consumption and ammonia excretion rates. Based upon these data, metabolism for hatchlings of O. maya and L. forbesi was estimated to be relatively lower than that of older juveniles. The O/N ratios for hatchlings of O. maya and L. forbesi were relatively high and indicate an apparent dependence upon lipids in the immediate post‐hatching period, followed by standard protein energy utilization thereafter.     

Optimal foraging and ontogeny; food selection by Haplochromis piceatus

Summary We examined the influence of satiation level, prey density and light intensity on food uptake rate through the ontogeny of Haplochromis piceatus. Prey handling in the buccal cavity was found to be the main factor limiting prey uptake rate under light circumstances and at a sufficiently high prey density. Food uptake rate per unit body weight of different sizes of H. piceatus was equal when feeding on Chaoborus but decreased with increasing fish size when feeding on Daphnia magna. In choice experiments with Chaoborus and D. magna, prey selection by H. piceatus of all sizes was according to the predictions based on Charnov's 1976 model.     

Temperature-dependent energetics of Chaoborus populations: hypothesis for anomalous distributions in the great lakes of East Africa

Chaoborus, the phantom midge (Insecta, Diptera, Chaoboridae), has a widespread distribution, commonly occurring in lakes and ponds all over the world. In the great lakes region of East Africa Chaoborus is present in Lakes Victoria, Albert, Edward, Malawi and George, but absent from Lakes Tanganyika, Kivu and Turkana. Tropical lakes typically have water temperatures in the range of 22–26 °C year round. Lakes Tanganyika and Kivu have only 20% of their bottom sediments oxygenated during full circulation, contrary to 95–100% in all of the other lakes, excluding Lake Malawi (45%) (Hecky & Kling, 1987). Planktivorous fish are present in all lakes (Lehman, 1995). We hypothesized that the absence of Chaoborus larvae from some lakes of East Africa may be the result of interaction among high temperatures, low oxygen levels, and fish predation.We developed a model to estimate energetic costs for Chaoborus larvae at temperatures greater than 14 °C. We hoped to shed light on the bioenergetics of Chaoborus populations, and the possibility that extant distributions of Chaoborus larvae are the result of energetic constraints.We found that relative respiratory and growth costs of Chaoborus larvae are highest in the early stages of development. We estimated that non-feeding instar I larvae living in 25 °C water will starve to death in less than one day. It is possible that Chaoborus populations are prevented from establishing in certain areas because high energetic costs condemn young larvae to death by either predation or starvation.     

Habitat segregation and interactive effects of multiple predators on a prey assemblage

1. In a field experiment we examined the interactive effects of two common predators of zooplankton, bluegill sunfish (Lepomis macrochirus) and Chaoborus spp. on the growth rate and habitat use of three congeneric prey species (Daphnia). Bluegill and Chaoborus both consume Daphnia, but bluegill also prey on Chaoborus. The prey species, Daphnia pulicaria, D. rosea and D. retrocurva, differed in body size and vertical distribution. We expected the largest species, D. pulicaria, to be most vulnerable to fish predation and the smallest species, D. retrocurva, to be most vulnerable to Chaoborus predation. 2. As we expected, the population growth rate of D. pulicaria was significantly reduced by fish. However, Chaoborus also significantly reduced the growth rate of this species. No significant interaction effect was detected, indicating that the effect of these predators was additive. The growth rates of D. rosea and D. retrocurva were significantly reduced by Chaoborus, but a significant interaction effect indicated that the effect of Chaoborus was stronger in the absence of fish than when fish were present. Therefore the impact of Chaoborus and fish on D. rosea and D. retrocurva was non-additive. The interactive effect of the two predators on D. retrocurva was greater in magnitude than on D. rosea. 3. In the absence of predators, the three Daphnia species showed no differences in mean habitat depth between day and night. Both predators significantly affected diel habitat use of D. pulicaria and D. rosea. Fish caused both of these Daphnia species to move deeper during the day, whereas Chaoborus caused Daphnia to move into shallower water at night. Daphnia retrocurva tended to migrate upwards at night in all predator treatments, but no significant differences in migration were observed among the predator treatments. The effects of predators on habitat use were not interactive for any prey species. 4. Our results suggest that body size, habitat use and the diel migratory response to predators are important factors mediating the interactive effects of multiple predator types on zooplankton.     

SEASONAL VARIATION IN METABOLIC FUNCTIONS OF BRAMBLINGS

Seasonal variation in the rate of oxygen consumption during rest at different test temperatures and in the respiratory quotient (RQ) was observed in male Bramblings Fringilla montifringilla which had been caught as immature birds during autumn migration and kept under outdoor conditions for one year. Resting oxygen consumption measured from +31^o to – 4^oC during one night was significantly lower in late April and October (migratory seasons) as compared to the preceding and the following December. Because of marked seasonal changes in body weight, the significance of differences in metabolic rate between different seasons was largely dependent on the manner of expressing the rate of oxygen consumption, either per bird or as the 0–67 power of body weight (“surface coefficient”). The lower resting rate of oxygen consumption during the migratory seasons was interpreted as one possible factor responsible for allowing fat deposition by reducing total energy expenditure. This modification occurred only in birds kept under quasi-natural conditions outdoors and not in birds which were kept in cages under constant conditions of light and temperature in the laboratory.     

Oxygen consumption of gestating femaleSebastes schlegeli: Estimating the reproductive costs of livebearing

Synopsis During gestation, live-bearing fishes incur physiological energy costs, including provision of energy and respiratory gases to the developing embryos and removal of waste products. Fecundity in the genusSebastes is high, and the ovaries represent a significant portion of the weight of gestating females. In this study, we compare oxygen consumption of gestating females with non-gestating females and males of kurosoi,Sebastes schlegeli, to estimate these costs. Oxygen consumption by pregnant females is significantly higher than that of males and immature females at similar sizes and weights. We estimate that a 1.5 kg gestating female consumes 68% more oxygen than a non-gestating fish during the 51.5-day period of gestation. Such an increase in oxygen consumption rates may have important implications to the metabolic scope of gestating alone, suggesting that costs of increased gill ventilation, ionic and osmotic regulation and cardiac output are relatively high. Such energetic costs represent a quantifiable expense of the viviparous mode of reproduction inSebastes as compared with oviparous species.     

Chronic Application of MTII in a Rat Model of Obesity Results in Sustained Weight Loss

Objective: To examine the effects of a cafeteria diet and a chronic treatment with melanocortin agonist (MTII) on mature weight-stable female rats. Research Methods and Procedures: Ex-breeder Chbb:Thom rats (350 to 400 g) were divided into two groups: highly palatable food (HPF) and normal rat chow (RC). Both groups had ab libitum access to rat chow. The HPF group had access to chocolate bars, cookies, cheese, and nuts (∼20 g/d). After 21 days, the rats in each group were then divided into control and treated groups. Mini-pumps delivering saline or MTII (1 mg/kg per day) for minimally 28 days were implanted. Oxygen consumption was measured for 17 days in a second group of rats implanted with mini-pumps containing MTII (1 mg/kg per day) or saline. Results: HPF rats ate less (<50%) rat chow than RC rats. After 20 days, the HPF group had reached a plateau and weighed significantly more (p < 0.005) than the RC group (411.7 ± 9.3 g; n = 17 vs. 365.1 ± 9.4 g; n = 16). HPF rats and RC rats receiving MTII reduced their pellet intake and body weight in the initial 2 weeks of treatment (day 14, RC-saline: −1.6 ± 1.8 g; RC-MTII, −22.5 ± 3.7 g; HPF-saline, −7.1 ± 1.7 g; HPF-MTII, −30.7 ± 4.8 g). Subsequently, pellet intake returned to pre-implantation values, although body weights remained reduced in both HPF and RC groups. Oxygen consumption was increased in rats treated with MTII. Discussion: This suggests that MTII initially reduced body weight by limiting food intake; however, maintenance of weight is most likely due to increased energy expenditure under conditions of normal and highly palatable diets in mature animals.     

Effect of reproductive state and body size on food consumption in captive Galago senegalensis braccatus

Measurements of food consumption for different types of foods were made for seven Galago senegalensis braccatus. Differences because of reproductive state in females and body size were found. Lactating females consumed more food in total and had greater energy and protein intake than they did during other reproductive states. Near-term pregnant females consumed less food, energy, and protein than they did during other reproductive states. Body size affected food intake, with smaller animals ingesting more per unit metabolic weight than larger subjects.