The differences in potential reproductive rate between the sexescan be used to predict the operational sex ratio and the patternsand intensity of mating competition and hence sexual selectionin a population. This article describes how one environmentalcomponent, temperature, affects potential reproductive ratesof the two sexes in the paternally brooding, sex-role reversedpipefish (Syngnathus typhle). Males brooded embryos much longer(on average 58 days) in cold water (about 10°C) than inwarmer water (35 days at about 15°C). As a consequence,the potential reproductive rate (number of eggs brooded perday) of males was significantly higher in warm water. In females,however, potential reproductive rate, i.e., number of eggs producedper day given an unlimited access to mates, was not significantlydifferent between temperatures. In both sexes, potential reproductiverate was positively related to body size. At both temperatures,females had the potential to reproduce faster than males. Asa result, the operational sex ratio will become female biasedand sex-roles reversed, as is the case in this species. Sincetemperature differently influenced the potential reproductiverates of males and females, with the sexual difference largerat lower temperatures, more intense female-female competitionis predicted at low temperatures. 相似文献
The energetic adaptations of non-breeding Tengmalm's owls (Aegolius funereus) to temperature and fasting were studied during the birds' autumnal irruptions in western Finland. Allometric analysis (including literature data and two larger owl species measured in this study) indicates that the basal metabolic rate of owls is below the mean level of non-passerine birds. However, the basal metabolic rate of the 130-g Tengmalm's owl (1.13 W) is higher than in other owls of similar size. This is probably related to its northern distribution and nomadic life history. Relative to its size, Tengmalm's owl has excellent cold resistance due to effective insulation (lower critical temperature +10°C, minimum conductance 0.19 mW·cm-2·°C-1). Radiotelemetric measurements of body temperature showed that the level of body temperature is lower than for birds in general (39.4°C at zero activity) and that the amplitude of the diurnal cycle is also low (0.2–0.6°C). In contrast to many other small birds, Tengmalm's owls do not enter hypothermia during a 5-day fast at thermoneutrality or in cold. Moreover, while the metabolic rate per bird shows the expected mass-dependent decrease, the mass-specific rate decreases only slightly during the fast. In line with this, there was no decrease in the plasma triiodothyronine concentration during the fast in the owl, whereas a dramtic drop was observed in the pigeon and Japanese quail that were used as a reference. Despite this, the owl has an excellent capacity for fasting because of its ability to accumulate extensive fat depots and its low overall metabolic rate. Fasting reduced evaporative water loss to 50% of that in the fed state. Calculations show that the oxygen consumption observed in fasting birds would involve a production of metabolic water barely sufficient to compensate for evaporative water loss. The threat of dehydration may thus set a limit to the decrease in metabolic rate in fasting owls (owls rely totally on water either ingested with food or produced metabolically). We conclude that the metabolic strategy in Tengmalm's owl is largely dictated by an evolutionary pressure for fasting endurance. With the restrictions set by small body size and water economy, this bird has apparently taken these adaptations to an extreme. The constraints that preclude hypothermia, which could increase the capacity for fasting even more, remain unknown.Abbreviations BM
body mass
- BMR
basal metabolic rate
- EWL
vaporative water loss
- MR
metabolic rate
- T3
triiodothyronine
-
Ta
ambient temperature
-
Tb
body temperature
-
VO2
oxygen consumption 相似文献
This study investigated the effects of 12 weeks of aerobic exercise plus voluntary food restriction on the body composition, resting metabolic rate (RMR) and aerobic fitness of mildly obese middle-aged women. The subjects were randomly assigned to exercise/diet (n = 17) or control (n = 15) groups. The exercise/diet group participated in an aerobic training programme, 45–60 min · day –1 at 50%–60% of maximal oxygen uptake (VO2max), 3–4 days · week–1, and also adopted a self-regulated energy deficit relative to predicted energy requirements (–1.05 MJ · day –1 to –1.14 MJ · day –1 ). After the regimen had been followed for 12 weeks, the body mass of the subjects had decreased by an average of 4.5 kg, due mainly to fat loss, with little change of fat free mass (mff). The absolute RMR did not change, but the experimental group showed significant increases in the RMR per unit of body mass (10%) and the RMR per unit of mff (4%). The increase in RMR/mff was not correlated with any increase in VO2max/mff. The resting heat production per unit of essential body mass increased by an average of 21%, but the resting heat production rate per unit of fat tissue mass remained unchanged. We concluded that aerobic exercise enhances the effect of moderate dietary restriction by augmenting the metabolic activity of lean tissue. 相似文献
Two experiments were undertaken to investigate the effects of warming the body upon the responses during a subsequent cold water immersion (CWI). In both experiments the subjects, wearing swimming costumes, undertook two 45-min CWIs in water at 15° C. In experiment 1, 12 subjects exercised on a cycle ergometer until their rectal temperatures (Tre) rose by an average of 0.73°C. They were then immediately immersed in the cold water. Before their other CWI they rested seated on a cycle ergometer (control condition). In experiment 2, 16 different subjects were immersed in a hot bath (40° C) until their Tre rose by an average of 0.9° C; they were then immediately immersed in the cold water. Before their other CWI they were immersed in thermoneutral water (35° C; control condition). Heart rate in both experiments and respiratory frequency in experiment 1 were significantly (P < 0.05) higher during the first 30 s of CWI following active warming. In experiment 1, the rate of fall of Tre during the final 15 min of CWI was significantly (P < 0.01) faster when CWI followed active warming (2.46° C · h–1) compared with the control condition (1.68°C · h–1). However, this rate was observed when absolute Tre was still above that seen in the control CWIs. It is possible, therefore, that if longer CWIs had been undertaken, the two temperature curves may have converged and thereafter fallen at similar rates; this was the case with the aural temperature (Tau) seen in experiment 1 and the Tau and Tre in experiment 2. It is concluded that pre-warming is neither beneficial nor detrimental to survival prospects during a subsequent CWI. 相似文献
Thermal requirements for development and life table statistics ofAphis gossypii Glover (Homoptera, Aphididae) were determined over a range of constant temperatures from 10 to 30°C. The lower development
threshold and the sum of effective temperatures were 6.9°C and 90.1°C, respectively, for preimaginal development, and 5.8°C
and 113.6°C from birth to the onset of reproduction. Mean total fecundity ranged from 36 larvae per female at 10°C to 76 larvae
at 30°C. On a time scale of days, net reproductive rate (Ro) increased with increasing temperature while generation time (T) decreased causing the intrinsic rate of increase (rm) to increase linearly from 0.115 to 0.465. On a day-degree scalerm only varied from 0.019 to 0.028 because the growth ofRo was compensated by an increase inT with increase in temperature. The nearly constantrm in terms of day-degrees, over a wide range of temperatures, greatly simplifies the prediction of future population numbers
ofA. gossypii. 相似文献
Recently the gut fluorescence technique has been critisized because of the possible degradation of chlorophyll into nonfluorescent derivatives during passage through copepod guts and changes of the gut passage time with food concentration. Here pigment budgets have been calculated in 6 experiments with Calanus finmarchicus CIV caught 2 km offshore of the Murmansk Marine Biological Institute (the Barents Sea, Dalnije Zelentsi) in September 1992. Copepods were fed with culture of Platymonas viridis at different concentrations. Gut pigment and ingestion rate increased with food concentration in a similar way. On average between 78% and 89% of ingested chlorophyll was recovered in the guts and faecal pellets. No trend for a greater loss of fluorescence at low food concentration than at high was observed. Pigment content of faecal pellets incubated in filtered seawater decreased by 20–30% in the first 7–12 h and by up to 60% in 48 h. The decline of pigment content was accompanied by a rapid bacterial growth (by a factor of 3 in 48 h). Gut passage time increased with decreasing food concentration (from 40 min at 9 µg pigm l–1 to 64 min at 0.9 µg pigm l–1). These results together with some data by other authors suggest that the gut fluorescence method can be used to estimate in situ grazing rate providing gut passage time is measured properly and there are no losses of faecal material. However, careful consideration should be given to the previous feeding history of copepods. 相似文献
Pueruli of the Western Rock Lobster Panulirus cygnus (George, 1962) are thought to be nonfeeding. Consequently, the metabolic rate is expected to be low during this stage in order to conserve energy reserves. Furthermore, since water temperature potentially has a substantial impact on energetic needs, the puerulus possibly exhibits mechanisms to reduce the effect of temperature on energy consumption. To test these propositions the metabolic rate was measured in post-settlement pueruli and in juveniles at two water temperatures. A respirometer of variable volume (10–50 ml) was designed for this purpose, incorporating a dark-type oxygen sensor. Results were compared with data available from the literature.
Oxygen consumption in pre-molt pueruli and in intermolt juveniles (1.48 to 5.65 μmol O2· individual−1·h−1 on average) was substantially higher than in post-settlement pueruli (1.06–1.41μmol O2·ind.−1h−1). These significant changes could only partly be explained through changes in biomass. Furthermore, no significant effect of an increased water temperature (from 18 to 23 ° C) could be detected on the metabolic rate in post-settlement pueruli, and the effect is moderate in pre-molt pueruli (Q10 = 1.95). The water temperature has, however, a substantially greater impact on first and second molt juveniles (Q10 = 2.46 to 4.80).
The energetic demand was calculated from oxygen consumption and indicate that energetic needs of post-settlement pueruli is low compared with both pre-molt pueruli and juveniles. A low energetic demand and a reduced effect of temperature on energy consumption is of considerable benefit to a non-feeding larva, and may provide the puerulus with a means of extending the duration of the non-feeding stage and increasing the chance for survival beyond metamorphosis to the first feeding stage. Results indicate that the energetic demand during metamorphosis may be considerable. It is postulated that energetic requirements of the planktonic (actively swimming) puerulus larvae are considerably higher and are likely to be more temperature dependent. 相似文献