Growth and reproduction of the mosquitofish,Gambusia affinis,in relation to temperature and ration level: consequences for life history

The allocation of energy to growth and reproduction, in relation to temperature and food availability, was investigated in laboratory experiments with the mosquitofish,Gambusia affinis. At constant temperature of 20, 25 and 30°C and ad libitum feeding, specific growth rates increased with increasing temperature at 1.7, 3.1 and 3.4% dry mass day⁻¹, respectively. Growth rates in a cycling temperature regime (20–30°C, ) were faster than in a 25°C constant temperature. As temperature increased from 20 to 30°C, mean age at first reproduction decreased from 191 to 56 days and brood size and mass of offspring increased significantly. Interbrood interval was also temperature dependent; estimates at 25 and 30°C for females >1000 mg were 22.6 and 18.6 days, respectively. Interbrood interval could not be calculated at 20°C. Although fitness was highest at 30°C, females at 25°C invested a greater proportion of surplus energy (growth and reproduction) to reproduction (38%) than at 20 (17%) or 30°C (36%) during the 32-week study. Fish at cooler temperatures began reproduction at a smaller size. Where rations were controlled at low, medium, and ad libitum levels, somatic and gonadal growth increased with increasing temperatures and food availability. The proportion of energy invested in reproduction was highest at 25°C for each comparable ration level. Calculated energy budgets indicated that over the 10-week study, 17–22% of the food energy was invested in growth, 0–7% in reproduction, and 75–83% in respiration and excretory losses, depending on feeding and temperature conditions.     

Species-specific effects of bombesin on gastric emptying and neurohypophyseal secretion

Previous reports have demonstrated that systemic injection of cholecystokinin (CCK) in rats produces dose-related decreases in food intake, increases in neurohypophyseal secretion of oxytocin (OT), and decreases in gastric emptying. The present studies determined whether systemic injection of bombesin (BBS), another peptide that potently reduces food intake in rats, had similar effects on OT secretion and gastric emptying. Although BBS produces a dose-dependent inhibition of food intake, even very high doses did not significantly affect plasma OT levels and only slightly decreased rates of gastric emptying. Consequently, despite their similar inhibitory effects on food intake, BBS does not appear to activate the same network of central nervous system pathways as does CCK in rats. However, parallel studies in monkeys demonstrated that systemic injection of BBS was effective in stimulating neurohypophyseal secretion of vasopressin rather than OT, in a pattern both qualitatively and quantitatively analogous to the effects of CCK in this species. Together with previous findings that BBS more potently inhibits gastric emptying in primates than in rats, these results therefore also suggest the presence of significant species differences in the central mechanisms by which BBS acts to reduce food intake.     

Calcium-Independent Release of Acetylcholine from Electric Organ Synaptosomes and Its Changes by Depolarization and Cholinergic Drugs

Chemiluminescent detection was applied to measure the continuous spontaneous Ca2+-independent liberation of acetylcholine (ACh) from Torpedo electric organ synaptosomes. Differentiation between the release of ACh and choline was achieved by inhibiting cholinesterases with phospholine, and a way to quantify the continuous release was devised. The method permitted measurements during short time intervals from minute amounts of tissue and without an accumulation of ACh in the medium. Synaptosomes continuously liberated small amounts of ACh during incubations in the presence of 3 mM K+ and in the absence of Ca2+. The spontaneous liberation of ACh was similar both quantitatively and qualitatively at pH values of 8.6 and 7.8. It was unaltered by MgCl2 (10.4 mM), 2-(4-phenylpiperidino)cyclohexanol (10 microM), ouabain (104 microM), atropine (10 microM), and valinomycin (102 nM). Carbamoylcholine brought about a decrease, which could be partially reversed by atropine. The Ca2+-independent output of ACh was increased considerably when the concentration of K+ ions was raised (eightfold at 103 and 35-fold at 203 mM K+). Carbamoylcholine (104 microM) blocked the increase in ACh release produced by high K+; this effect of carbamoylcholine was not reversed by atropine (10 microM). When Ca2+ was added to synaptosomes depolarized by a high concentration of K+, the amount of ACh released during the first 1-3 min after the addition of Ca2+ was at least 20 times higher than in the absence of Ca2+, but the release returned rapidly to predepolarization values. Similarly high values of ACh release could be achieved by adding Ca2+ plus the ionophore A23187 and even higher values by adding Ca2+ plus gramicidin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Calcium-Dependent Evoked Release of N[3H]Acetylaspartylglutamate from the Optic Pathway

N-Acetylaspartylglutamate (NAAG) is a neuropeptide localized to several putative glutamatergic neuronal systems, including the rodent optic pathway. To determine whether the peptide is released by depolarization, the superior colliculus of the rat was perfused with 2 microCi of [3H]NAAG, then with Krebs-bicarbonate buffer for 1 h, using a microdialysis system. Subsequently, 10-min fractions were collected and analyzed by HPLC for [3H]NAAG. Addition of 100 microM veratridine resulted in a several-fold increase in the evoked release of [3H]NAAG that was virtually abolished by coperfusion with Ca2+-free Krebs buffer containing 1 mM EGTA. When [3H]glutamate was used as the precursor, veratridine depolarization resulted in only an 80% increase in the release of [3H]NAAG. Prior enucleation of the right eye reduced the spontaneous release of [3H]NAAG by 50%, and the veratridine-evoked release by greater than 85%, from the left superior colliculus. These results suggest that NAAG is released upon depolarization and may serve as a neurotransmitter/neuromodulator in the optic tract.     

Book Review

Book Reviewin this Article:
Diabetic Neuropathy edited by P. J. Dyck, P. K. Thomas, A. K. Asbury, A. I. Winegrad, and D. Porte, Jr.     

How can the functional reponse best be determined?

Summary We evaluated three methods for the analysis of functional response data by asking whether a given method could discriminate among functional responses and whether it could accurately identify regions of positive density-dependent predation. We evaluated comparative curve fitting with foraging models, linear least-squares analysis using the angular transformation, and logit analysis. Using data from nature and simulations, we found that the analyses of predation rates with the angular transformation and logit analysis were best at consistently determining the true functional response, i.e. the model used to generate simulated data. These methods also produced the most accurate estimates of the true regions of density dependence. Of these two methods, functional response data best fulfill the assumptions of logit analysis. Angularly transformed predation rates only approximate the assumptions of linear leastsquares analysis for predation rates between 0.1 and 0.9. Lack-of-fit statistics can reveal inadequate fit of a model to a data set where simple regression statistics might erroneously suggest a good match.     

Consequences of a mixed reproductive system in the hog peanut,Amphicarpaea bracteata, (Fabaceae)

Summary The forest annual, Amphicarpaea bracteata L. can reproduce via aerial chasmogamous, aerial cleistogamous, and subterranean cleistogamous flowers. Both plant size and light intensity influenced the utilization of the three modes of reproduction. chasmogamous and aerial cleistogamous flower number and the ratio of chasmogamous flowers to the total number of aerial flowers increased with plant size. The latter demonstrated a shift to xenogamy and outbreeding in larger plants. Light intensity indirectly influenced reproductive modes through its infuence on plant size. Seed set by both types of aerial flowers was low and unrelated to plant size. Subterranean seed number and the total dry weight of subterranean seeds per plant increased with size. The subterranean seeds of Amphicarpaea bracteata are thirty-four times larger than the aerial seeds (fresh weight). Under field conditions, subterranean seeds had greater germination after one year than acrial seeds. The plants arising from subterranean seeds were significantly larger and more fecund than those from aerial seeds. Seeds produced by aerial cleistogamous, hand selfpollinated chasmogamous, and naturally pollinated chasmogamous flowers had equivalent germination rates and produced plants of equal size and fecundity. This suggests that the outbred progeny from chasmogamous flowers have no advantage over the inbred progeny from aerial cleistogamous flowers.     

Glutamate Oxidation by Soybean Cotyledon and Leaf Mitochondria

Mitochondria purified from cotyledons of soybean seedlings fiveto ten days old have the capacity to rapidly oxidize glutamate(measured as glutamate dependent oxygen consumption). This capacitywas greatest at ten days after planting but was very low priorto emergence of cotyledons from the vermiculite and during senescence.Solubilized glutamate dehydrogenase activity, on the other hand,was substantial at two days after planting, peaked at sevendays, then declined and rose again during senescence. It issuggested that mitochondrial glutamate oxidation plays a rolein reserve mobilization and amino acid metabolism during seedlinggrowth. Leaf mitochondria and those from senescing cotyledonscould not sustain rapid rates of glutamate oxidation despiteready oxidation of other substrates and high solubilized glutamatedehydrogenase activity, suggesting an alternative role for theenzyme in these tissues. Possible controlling factors are discussed. ² Present address, Garvan Institute, Darlinghurst, N. S. W.,Australia. ³ Permanent address, Department de Biologia Vegetal, Facultatde Biologia, Universitat de Barcelona, Barcelona, Spain. (Received May 6, 1988; Accepted August 3, 1988)     

Production and Characterization of Monoclonal Antibodies to Wall-Localized Peroxidases from Corn Seedlings

A library of 22 hybridomas, which make antibodies to soluble wall antigens from the coleoptiles and primary leaves of etiolated corn (Zea mays L.) seedlings, was raised and cloned three times by limit dilution to assure monoclonal growth and stability. Two of these hybridomas made immunoglobulin G antibodies, designated mWP3 and mWP19, which both effectively immunoprecipitated peroxidase activity from crude and partially purified preparations of wall peroxidases. Direct peroxidase-binding assays revealed that both antibodies bound enzymes with peroxidase activity. As judged by immunoblot analyses, mWP3 recognized a M_r 98,000 wall peroxidase with an isoelectric point near 4.2, and mWP19 recognized a M_r 58,000 wall peroxidase. Immunogold localization studies showed both peroxidases are predominately in cell walls.     

Induction by antimycin A of cyanide-resistant respiration in heterotrophic Euglena gracilis: Effects of growth,respiration and protein biosynthesis

The addition of antimycin A during the logarithmic phase of growth of heterotrophic Euglena gracilis cultures (in lactate or glucose medium) was immediately followed by decreased respiration and a cessation of grwoth. Induced cyanideresistent respiration appeared 5 h after the addition of the inhibitor then the cells started to grow again and could be cultured in the presence of antimycin A. Thus the cells exhibited a cyanide-and antimycin-resistant respiration which was, in addition, sensitive to salicylhydroxamic acid and propylgallate. Antimycin-adapted Euglena and control cells were compared for their biomass production and protein synthesis. The difference in growth yield between control and antimycin-adapted cells was not as high as would be expected if only the first phosphorylation site of the normal respiratory chain was active in the presence of antimycin A. Furthermore, the ability to incorporate labelled valine into proteins, under resting-cell conditions, was not changed. Strong correlations were established between the effects of respiratory effectors on O₂ consumption and valine incorporation. These results suggest that sufficient energy for protein synthesis and growth is provided by the operation of the cyanide-resistant respiratory pathway in antimycin-adapted Euglena.Abbreviations DNP dinitrophenol - PG propylgallate - SHAM salicylhydroxamic acid