Oreochromis aureus exposed during the first 28 days of exogenous feeding to constant 35° C, or fluctuating temperatures (day at 35° C, night at 27° C, and vice versa) showed significantly ( P <0·05) faster growth, least size heterogeneity and better survival rates than siblings under constant 27° C. Constant high temperatures had a strong masculinizing effect (M: F sex ratios of 7·33–19·00: 1·00 v . 0·75–0·82: 1·00 in controls reared at 27° C). Fluctuating temperatures had less masculinizing potential but still produced sex ratios significantly skewed to the detriment of females (M: F sex ratios of 2·33–11·50: 1·00). This suggests that ambient temperature may have represented a sufficient environmental pressure for the selection of thermolabile sex-determinism in this species, and presumably in other Oreochromis spp. The evolutionary advantage of thermosensitivity in Oreochromis spp. is discussed, considering a framework where individual advantages oppose, to some degree, to the population or species interest. 相似文献
Thermoregulatory responses to heat exposure were studied in 12 hand-reared, acclimated pigeons (Columbia livia). Measurements of body temperature (Tcl), brain temperature (Tbr), cutaneous water evaporation (CWE) and respiratory frequency (fr) were carried out in intact conscious heat exposed birds. In a second group of lightly restrained birds, fr and CWE were taken when temperatures of the trunk, brain and air (Ta) were independently changed. Increasing Tbr to 43.5–43.8°C induced a pronounced polypnea (deep and fast, (300 breaths min−1) when Tcl regulated at 42.4°C. Moreover, when hyperthermia (Tcl = 43.0°C) was combined with increased Tbr (43.0–43.8°C) shallow and fast panting (>500 breaths min−1) was evoked. CWE was probably elicited by inputs generated by the skin warm receptors as a result of increased Ta. Moreover it was demonstrated that warming the brain to 42.5°C elicits cutaneous water evaporation in birds exposed to 26°C. When a high Ta (60°C) is accompanied by a high relative humidity (17%), the combined effect generates inputs eliciting intensive panting. The integration of the present and earlier data allows us to generate a model demonstrating the distinguished significance of the trunk, skin and brain thermosensors in the regulation of both respiratory and cutaneous latent heat dissipation. The present model also emphasizes the fact that the highly thermosensitive pigeon brain responds in a similar pattern to that found in mammals 相似文献
Effects of high temperatures on the leaves of Ranunculus glacialis were studied in plants taken from sites located between
2400-2550 m in the Central Alps. Changes in CO2 exchange rates, in vivo chlorophyll fluorescence, and cellular ultrastructure
were investigated during and after an experimental heat exposure. The earliest heat stress effect was inactivation of the
net photosynthetic rate at 38-39 °C. Between 40-42 °C, disorders appeared in the photosynthetic apparatus and in the tonoplast.
Heat shock granules were observed at 42 °C in chloroplasts, and at 44 °C also in mitochondria. In this temperature range,
the dark respiration rate was reversibly enhanced, and an increased number of polyribosomes indicated repair after the primary
injury. Above 44 °C, the degradation progress entered the phase of chronic impairment leading to irreversible damage at 45-46
°C. An unusually wide temperature range from the start of reversible photosynthetic inhibition to incipient necrosis indicated
a pronounced heat sensitivity, particularly in cellular functions, of this arctic-alpine species.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
Hawking F. 1973. The responses to various stimuli of microfilariae of Dirofilaria corynodes, of Dipetalonema marmosetae and of unidentified species of filariae in Saimiri sciureus and Cacajao monkeys. International Journal for Parasitology3: 433–439. A study was made of the responses of the microfilariae of Dirofilaria corynodes, of Dipetalonema marmosetae and of three unknown filariae in Saimiri sciureus and of three other unknown ones in Cacajao rubicundus, to various stimuli applied to the host. These stimuli included exposure of the host to high oxygen or to hypoxia, intravenous injection of acetylcholine or serotonin, and alteration of body temperature. One of the unidentified microfilariae of S. sciureus was thermosensitive and its 24 h cycle is probably controlled by the temperature cycle of its host. The microfilaria of D. corynodes was liberated from the lungs by intravenous injection of acetylcholine and serotonin, thus resembling the microfilariae of D. immitis and D. repens. 相似文献
1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C Thy (F40), local temperature coefficients (Δ/ΔT) and Q10.
2. 2.|Q10 and either F40 or ΔF/ΔT were little or not related.
3. 3.|A positive correlation between F40 and ΔF/ΔT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q10 of <2 and >2.
4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships.
5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.
Author Keywords: Neuronal thermosensitivity; hypothalamic thermosensory function; Temperature and synaptic transmission; avian thermoregulation; mammalian thermoregulation 相似文献
1. 1.|The brain (BR), suboesophageal ganglion (SOG), metathoracic ganglion mass (TG3) or fourth free abdominal ganglion (AG4) were selectively warmed from room temperature (23°C) to 3°C and the effects of elevated ganglion temperature on abdominal ventilatory pumping rate were observed.
2. 2.|Warming the SOG or BR almost always induced a strong increase in ventilatory pumping rate while warming TG3 or AG4 had no consistent effect, inducing about equally often a slight increase, decrease or no change.
3. 3.|It is concluded that the most temperature sensitive elements associated with the ventilatory rhythm generating system are localized within the head ganglia.