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| Author(s): |
Denise Loli
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2008-06-18 |
| Examining board members: |
Jose Eduardo Pereira Wilken Bicudo;
José Guilherme de Souza Chaui Mattos Berlinck;
Ana Maria Landeira Fernandez;
Fernando Ribeiro Gomes;
Gisele Akemi Oda
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| Advisor: | Jose Eduardo Pereira Wilken Bicudo |
| Abstract | |
In eusocial insects, such as stingless bees, the control of nest conditions and maintenance of the colonial microclimate are important to brood incubation, development of eggs, larvae and pupae, and survival of the colony. One of the main thermoregulatory mechanisms to control nest temperature is the microhabitat selection to build the nest, such as tree holes, characteristic of the stingless bee Melipona quadrifasciata, the biological system chosen for this study. In addition to the behavioral mechanisms involved in thermoregulation, physiological mechanisms underlying thermogenesis are also found in Hymenoptera, such as futile cycles (in bumblebees) and shivering thermogenesis. Thermogenesis in bees is detected mainly during brood incubation, social interactions and pre-flight warming; additional possible physiological mechanisms have not yet been investigated with enough detail. Biogenic amines, especially octopamine, play important physiological roles in bees. Although octopamine and norepinephrine are chemically not identical, it appears that octopaminergic systems of invertebrates and noradrenergic systems of vertebrates are homologous. Oral treatment with beta-blockers can cause hypothermia, leading to the hypothesis that an octopaminergic pathway involved in bee energetics and thermogenesis might exist. The main aspects investigated in the present study are the colonial thermoregulation, the energetics of individual bees, and the mechanisms associated with thermogenesis in M. quadrifasciata. With regards to the colonial thermoregulation, temperature and humidity, time series were recorded inside and outside the nest, in two colonial compartments, i.e., brood and pots. In addition, flight activity was also recorded. Flight activity time series presented similar periodicities in both ambient and brood series. In closed colonies, maintained under constant conditions, the brood time series presented periodicities close to 24h and 12h, suggesting endogenous aspects and rhythm. Another goal of this study was to characterizing the effects of the light-dark cycles and ambient temperatures. This was achieved using intermittent respirometry, and the effects of the light-dark cycles at 28°C (normal photoperiod, inverted photoperiod, constant light and constant dark) on metabolic rate (MR), and the effects of different temperatures (10 40°C) on MR and respiratory quotient (RQ) were measured. The different light-dark cycles affected the MR under normal photoperiod and constant light. Two \"platforms,\" with low MR values were detected between 19h and 5h. When the photoperiod was inverted, lower values were recorded in the dark phase, between 6h and 18h, resulting in an inverted pattern of MR, thus suggesting an exogenous response to photoperiodic changes. Between 7h and 17h59, in the light phase, metabolic rate did not change significantly. The temperature has a significant effect on MR and RQ of the foragers, and reduced values at 10, 35 and 40°C were detected. Between 15 and 30°C no significant differences were detected. In the third part of this work the aim was to verify the time-dependent effects of beta-blockers (Alprenolol and Mianserina) on MR and thoracic temperature of foragers, and to verify whether octopamine and methoprene (analogous to juvenile hormone) compensate the effects of beta-blockers. Alterations of substrates oxidation, considering the RQ and the activity (Vmax) of specific enzymes, such as hexokinase, trehalase, HOAD and glycogen phosphorylase, were also investigated. Treatments with blockers caused alterations in the RQ and in the enzyme activities of hexokinase, HOAD and glycogen phosphorylase. The reduced values of thoracic temperature in foragers treated with Alprenolol suggests the involvement of octopaminergic pathways in thermogenesis; however, it is not yet known if such effects are due to interferences in the heat production and/or represent a by-product of a reduced metabolic rate. At the colonial level, nests treated with blockers presented colonial time series periodicities more similar to the ambient humidity series than to the ambient temperature series, suggesting therefore that the responses to ambient temperature are reduced. These results do not prove that mechanisms of nonshivering thermogenesis are present in bees, involving both octopamin and juvenile hormone, but they can indicate possible involvements of these substances in metabolic rate, energetics and fuel utilization. Under a comparative approach, one can suggest similarities between the effects caused by modifications in the noradrenergic and octopaminergic pathways on the energetics and thermogenesis of M. quadrifasciata. The results, however, do not prove such hypothesis, but they suggest an octopaminergic influence on both metabolic rate and thoracic temperature of M. quadrifasciata foragers. (AU) | |