Metabolic response to cooling temperatures in chicken embryos and hatchlings after cold incubation

We asked to what extent cold exposure during embryonic growth, and the accompanying hypometabolism, may interfere with the normal development of thermogenesis. White Leghorn chicken eggs were incubated in control conditions (38 degrees C) or at 36 or 35 degrees C. Embryos incubated at a lower temperature (34 degrees C) failed to hatch. The cold-incubated embryos had lower oxygen consumption (VO2) and body weight (W) throughout incubation, and hatching was delayed by about, respectively, 1 and 2 days. The W-VO2 relationship of the cold-incubated embryos was as in controls, indicating that cold-induced hypometabolism was at the expense of the growth, not the maintenance, component of VO2. At embryonic day E11, the metabolic response to changes in ambient temperature (T) over the 30-39 degrees C range was typically poikilothermic, with Q10 = 1.8-1.9, and similar among all sets of embryos. Toward the end of incubation (E20), the thermogenic responses of the cold-incubated embryos were significantly lower than in controls. This difference occurred also in the few-hour old hatchlings (H1), even though, at this time, W was similar among groups. Exposure to cold during only the last 3 days of incubation (from E18 to H1), i.e. during the developmental onset of the endothermic mechanisms, did not lower the thermogenic capacity of the hatchlings. In conclusion, sustained cold-induced hypometabolism throughout incubation blunted the rate of embryonic growth and the development of thermogenesis. This latter phenomenon could be an example of epigenetic regulation, i.e. of environmental factors exerting a long-term effect on gene expression.     

Ontogeny of heart rate responses to exogenous melatonin in Muscovy duck and chicken embryos

One of the major physiological effects of melatonin is coupling the internal clock with different organ functions. Despite the long list of functional responses to melatonin discovered in the past, it has been unclear when responsiveness to melatonin develops during ontogeny. The aim of the present study was therefore to investigate in Muscovy duck and chicken embryos, when they start to exhibit heart rate (HR) changes to exogenous melatonin. HR was recorded continuously in Muscovy duck embryos from day 24 of incubation (D24) and in chicken embryos from D17 until hatching. Every day four doses of 10 microg melatonin were injected into each egg at 30 min intervals. In Muscovy duck embryos HR responses to melatonin were first observed on D25; from D27 all embryos responded. In all cases HR decreased immediately after the injection. HR deviation from baseline values and duration of decreased HR period increased during the experimental period. Chicken embryos showed similar responses as Muscovy ducks from D17 onwards; from D18 the response rate was 100%. On D19 dose-response data revealed a partial responsiveness to exogenous melatonin at doses of 0.1 to 1 ng and full responsiveness from 10 ng to 10 microg. The time of the first occurrence of HR responses to melatonin coincides with published results on the start of periodic pineal melatonin secretion. These data suggest that the output signal of the avian internal clock, periodic plasma melatonin fluctuations, could result in periodic cardiac function already prenatally in these two avian species.     

Metabolic responses of chicken embryos to graded, prolonged alterations in ambient temperature

1. Chicken embryos aged 12, 16, 18 and 20 (externally pipped) days of incubation were exposed to graded reductions (2 degrees C) in ambient temperature from 38 to 28 degrees C, exposure to each temperature lasting up to 9 hr. 2. Oxygen uptake was measured first at 38 degrees C and then in the quasi-equilibrium state at lowered temperatures. The temperature coefficient (Q10) was calculated for each egg. 3. For mild cooling (32 degrees C), the Q10 in 18-day-old embryos was about 1.5, while 12- and 16-day-old embryos had a Q10 value of about 2, indicating that a feeble homeothermic metabolic response to cooling appears in late prenatal embryos. It became more marked in externally pipped embryos and further augmented in hatchlings.     

鸡胚原始生殖细胞的分离和鸡鸭嵌和体的制备

探索了鸡胚12～17期血液中的原始生殖细胞(PGCs)迁移数量变化规律,将其在液氮中冷冻保存.并以Ficoll密度梯度离心、MiniMACS磁气分离、滤膜三种方法对PGCs进行分离,结果发现12～17期血液中均有PGCs存在,13期达到高峰约47.1±10.5个/μl,在血液中比例为0.0126%.冷冻保存3个月后解冻成活率达80%以上.三种分离方法所得的分离效果分别为95.7%、39.2%、63.0%,纯度为27.5%、8.4%、3.1%.将分离的原始生殖细胞以微注射法转移至14～15期麻鸭胚胎中制备了鸡鸭种间嵌和体,获得8只雏鸭(8/110).以鸡W染色体探针原位杂交法在早期鸭胚性腺中检测到鸡原始生殖细胞,嵌和率达84.2%(16/19).表明鸡原始生殖细胞能够迁移定居到鸭胚性腺中,并有可能增殖分化成有功能的配子.     

Sex ratios in mule duck embryos at various stages of incubation

Mule duck hatcheries have long reported varying degrees of unbalance in the sex ratio, with a preponderance of male mules at hatching. The aim of the present study was to assess the distributions of sex ratios at various stages of development in embryos originating from intra- and intergeneric crosses between parental lineages (Muscovy male x Muscovy female, Pekin male x Pekin female, Muscovy male x Pekin female or Mule, and Pekin male x Muscovy female or Hinny). In Experiment I, embryo sexing was performed on Days 1 and 5 of incubation (by multiplex PCR) and at hatching (by vent observation). The sex ratio was not significantly modified during the early stages of embryo development whatever the genetic origin (P>0.05, Days 1 and Day 5) but our results in mule and hinny ducklings confirmed the preponderance of males among normally hatched ducklings originating from the intergeneric lineage (58.9 and 55.4% males in mules and hinnies, respectively; P<0.05 in both cases). Sex ratio (vent sexing) in second grade (cull) ducklings revealed that 68% of these ducklings were females (P<0.05). In Experiment II, the distribution of sex ratio was also performed in mule duck eggs from 6 batches (400,000 eggs/batch) first examined for fertility (candling) on Day 18 of incubation. These results indicate that the percentage of males present in the population of normally hatched ducklings increases when fertility decreases. In addition, this experiment also revealed that 83.7-90.5% of viable male mule embryos develop up to hatching, compared to only 43.0-51.0% of female mule embryos. Given that a deviation in sex ratio during the first stages of incubation is unlikely (Experiment I), it is concluded that the skewed sex ratio of mule ducks at hatching is primarily due to increased late mortality in female mule embryos occurring between egg transfer and hatching. This mortality originated, at least in part, from the intergeneric origin of female mules, and was marked to a greater or lesser extent depending on the initial success of fertilization in a given batch, a possible indication that the initial quality of gametes may selectively exert its influence at the later stages of embryo development.     

Metabolic responses of fresh-water sunfish to seasonal photoperiods and temperatures

Summary 1. Metabolic compensations by pumpkinseed sunfish,Lepomis gibbosus, to photoperiods of 9 and 15 hours and to acclimation temperatures ranging between 5° and 25° C have been examined. Respiration rates of whole fish, their brain, gill and muscle tissues, and opercular frequencies were used as indices of adaptation. Techniques for the determination of respiration rates and opercular frequencies have been outlined and discussed.2. A range in thermal homeostasis has been found forL. gibbosus over which thermal acclimation of respiration is nearly perfect (Q ₁₀ about 1), but which is modifiable by alterations in day length above 10° C. Although less obvious, a relative thermal homeostasis has been detected for opercular frequency as well. Perfection of acclimation appears to be best with both indices in the groups of sunfish which have been adapted to the 15-hour photoperiod.3. Significant differences in rates of respiration, but not in opercular frequencies, have been observed between the long and short-day groups of fall and winter sunfish above 10° C. During spring and with sunfish in breeding condition, these differences were not detected. Both short and long-day fish showed the same higher level of respiration found to be related to short photoperiod adaptation (9 hrs.). It is suggested that the photoperiodic effect of inducing changes in metabolic rates, most directly relates to some process of conditioning the fish for their primary biological function, reproduction.4. Because the characteristics and photoperiod sensitivity of metabolic compensations for temperature byL. gibbosus are not apparent below 10° C, this temperature is considered to be critical ecologically for the species in western Massachusetts. The existence of a lower critical temperature for thermal homeostasis of metabolic functions (capacity adaptation) in sunfish is stressed because of its potential as a sensitive indicator of physiological variations for climate and latitude.5. No indications of compensation for photoperiod (9 and 15 hrs.) and temperatures (7.5° and 20° C) have been detected in the respiration of brain and gill tissues ofL. gibbosus at 25° C except after uncoupling with dinitrophenol. The response of brain respiration with the drug appears to be greatest in sunfish adapted to a 9-hour day and 20° C. In contrast, the dinitrophenol effect upon respiratory change of gill filaments appears to be reversed with respect to the thermal history of the donor fish (highest with acclimation to 7.5° C), but unrelated to the length of the adaptation photoperiod. It is apparent that metabolic systems in different tissues of the same animal or the same tissues in different species, contrast greatly in compensatory responses to temperature and photoperiod. Therefore, the suggestion is offered that the resultant of systemic integration often may be more significantly reflected in responses of whole fishes to changing environmental factors than the possible direct effects of temperature sometimes seen in isolated tissues.

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Stoffwechselreaktionen süßwasserlebender Sonnenbarsche auf jahreszeitliche Photoperioden und Temperaturen

Kurzfassung Beim Gemeinen SonnenbarschLepomis gibbosus wurden nach Adaptation an 9- und 15stündige Photoperioden und an Temperaturen zwischen 5° und 25° C (Anstiegsintervalle 2,5° C) im Herbst und Winter die Respirationsraten bestimmt. Es zeigte sich, daß die Temperaturadaptation der Atmung in einem bestimmten Temperaturbereich nahezu perfekt ist (Q ₁₀ etwa 1); dieser Bereich wird aber durch eine Veränderung der Tageslänge oberhalb einer kritischen Temperatur von ungefähr 10° C modifiziert. Innerhalb dieser Spanne thermischer Homöostasis war die Atmungsintensität von Langtag-Fischen merkbar niedriger und das Ausmaß der Perfektion der Anpassung etwas größer als bei den Kurztag-Fischen. Derartige tageslängenabhängige Unterschiede wurden an Frühjahrsfischen in Brutkondition nicht gefunden. Die stoffwechselphysiologische Akklimatisation vonL. gibbosus läßt sich auch an Hand der Operculumbewegungen nachweisen; sie ist hier allerdings weniger perfekt (Q ₁₀ etwa 1,3) als im Falle der Atmung und offenbar auch weniger von der Tageslänge abhängig. Unterschiede in der Atmungsintensität von Gehirn- und Kiemengewebe bei verschiedenen Tageslängen und Temperaturen scheinen nur als Folge einer Entkoppelung durch Dinitrophenol aufzutreten. Dieser Sachverhalt deutet auf Aktivitätsveränderungen einiger Komponenten der zellulären Systeme dieser Gewebe hin, welche bei der Adaptation an verschiedene Tageslängen und Temperaturen auftreten und erst nach partieller oder vollständiger Entkoppelung der oxydativen Phosphorylierung limitierend für die Stoffwechselintensität werden.

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This investigation was supported in whole by Public Health Service Research Grant GM 06377 from the Division of General Medical Sciences.     

Development of heart rate responses to acoustic stimuli in Muscovy duck embryos

Heart rate (HR) of Muscovy duck embryos (Cairina moschata f. domestica) was continuously recorded from the 21st day of incubation (E21) until hatching (E35). During that period, embryos were exposed to different acoustic stimuli (species-specific maternal and duckling calls, music, rectangular and sine waves, white noise). Sudden HR changes occurred at the onset of acoustic stimulation (on-response), as well as spontaneously. From E27 onwards, the response rate was significantly higher than the rate of spontaneous HR changes. The on-response rate increased further until E30. Most responses were elicited by maternal calls and music, but rarely by duckling calls. On-responses could be classified into: HR increase (36.4%), HR decrease (37.9%) and an increase in instantaneous HR variability (23.2%). The increase in HR variability occurred only in response to sounds, but not spontaneously. HR increases were mainly observed when the baseline HR was lower than the long-term HR trend. On-response duration was no longer than 3 min in 90% of all observations. The hourly mean HR and standard deviation did not change, even during phonoperiods composed of several sound patterns and lasting several hours. We conclude that Muscovy duck embryos are able to perceive exogenous acoustic stimuli, and that the acousto-sensory-->cardiac axis is functional from E27.     

Hypoxic incubation blunts the development of thermogenesis in chicken embryos and hatchlings

We asked to what extent sustained hypoxia during embryonic growth might interfere with the normal development of thermogenesis. White Leghorn chicken eggs were incubated at 38 degrees C either in normoxia (Nx, 21% O2) or in hypoxia [Hx, 15% O2, from embryonic day 5 (E5) until hatching]. The Hx embryos had lower body weight (W) throughout incubation, and hatching was delayed by about 10 h. For both groups, all measurements were conducted in normoxia. At embryonic day E11, the static temperature-oxygen consumption (ambient T-Vo2) curve was typically ectothermic (Q10 = 1.92-1.94) and similar between Nx and Hx. Toward the end of incubation (E20), the Q10 averaged 1.41 +/- 0.06 in Nx and 1.79 +/- 0.08 in Hx (P < 0.005), indicating that the onset of the thermogenic response in Hx lagged behind Nx. In the 1-day-old hatchlings (H1), body weight did not significantly differ between Nx and Hx. At H1, the T-Vo2 curves were endothermic-type, and more so in the older (>8 h old) than in the newly hatched (<8 h old) chicks, whether examined statically or dynamically as a function of time. In either case, the thermogenic responses of Hx were lower than those of Nx. In a 43-31 degrees C thermocline, the preferred T of the Hx hatchlings was around 37.3 degrees C, and similar to Nx, suggesting a similar setpoint for thermoregulation. We conclude that hypoxic incubation blunted the development of thermogenesis. This could be interpreted as an example of epigenetic regulation, in which an environmental perturbation during early development alters the phenotypic expression of a regulatory system.     

Molecular mechanisms governing plant responses to high temperatures

The increased prevalence of high temperatures(HTs) around the world is a major global concern, as they dramatically affect agronomic productivity. Upon HT exposure, plants sense the temperature change and initiate cellular and metabolic responses that enable them to adapt to their new environmental conditions.Decoding the mechanisms by which plants cope with HT will facilitate the development of molecular markers to enable the production of plants with improved thermotolerance. In recent decades, genetic, physiological, molecular, and biochemical studies have revealed a number of vital cellular components and processes involved in thermoresponsive growth and the acquisition of thermotolerance in plants. This review summarizes the major mechanisms involved in plant HT responses, with a special focus on recent discoveries related to plant thermosensing, heat stress signaling, and HT-regulated gene expression networks that promote plant adaptation to elevated environmental temperatures.     

Metabolic and organ mass responses to selection for high growth rates in the domestic chicken (Gallus domesticus)

Evolutionary hypotheses suggest that higher rates of postembryonic development in birds should either lower the resting metabolic rate (RMR) in a trade-off between the costs of growth and maintenance or increase RMR because of a buildup of metabolic machinery. Furthermore, some suggest that higher rates of postembryonic development in birds should reduce peak metabolic rate (PMR) through delayed tissue maturation and/or an increased energy allocation to organ growth. We studied this by comparing metabolic rates and organ sizes of fast-growing meat-type chickens (broilers) with those of birds from a laying strain, which grow much slower. During the first week of life, despite growing six times faster, the RMR of the broiler chickens was lower than that of birds of the laying strain. The difference between strains in RMR disappeared thereafter, even though broilers continued to grow twice as fast as layers. The differences between strains in growth rate during the first week after hatching were not reflected in similar differences in the relative masses of the heart, liver, and small intestine. However, broilers had heavier intestines once they reached a body mass of 80 g. In contrast, broilers had relatively smaller brains than did layers. There was a positive correlation, over both strains, between RMR and the masses of leg muscles, intestine, and liver. Furthermore, despite delayed maturation of muscle tissue, broilers exhibited significantly higher PMR. We hypothesize that a balance between the larger relative muscle mass but lower muscle maturation level explains this high PMR. Another correlation, between leg muscle mass and PMR, partly explained the positive correlation between RMR and PMR.     

Metabolic responses to gradual cooling in chicken eggs treated with thiourea and oxygen

1. Late prenatal chicken embryos in eggs injected with saline showed a feeble homeothermic metabolic response to gradual cooling. This response was absent in thiourea-treated eggs. This suggests that the incipient homeothermic metabolic response before paranatal life may be attributed to thyroid development. 2. The compensatory metabolic response disappeared in embryos exposed to a hypoxic environment, while it was augmented in eggs in pure O2, decreasing as ambient temperature fell. 3. These results may indicate that the homeothermic metabolic response in late embryos is O2-conductance-limited and power-limited as previously suggested.     

Respiratory and cardiovascular responses to acute hypoxia and hyperoxia in internally pipped chicken embryos

During the first day of hatching, the developing chicken embryo internally pips the air cell and relies on both the lungs and chorioallantoic membrane (CAM) for gas exchange. Our objective in this study was to examine respiratory and cardiovascular responses to acute changes in oxygen at the air cell or the rest of the egg during internal pipping. We measured lung (V·_O2lung) and CAM (V·_O2CAM) oxygen consumption independently before and after 60 min exposure to combinations of hypoxia, hyperoxia, and normoxia to the air cell and the remaining egg. Significant changes in V·_O2total were only observed with combined egg and air cell hypoxia (decreased V·_O2total) or egg hyperoxia and air cell hypoxia (increased V·_O2total). In response to the different O₂ treatments, a change in V·_O2lung was compensated by an inverse change in V·_O2CAM of similar magnitude. To test for the underlying mechanism, we focused on ventilation and cardiovascular responses during hypoxic and hyperoxic air cell exposure. Ventilation frequency and minute ventilation (V_E) were unaffected by changes in air cell O₂, but tidal volume (V_T) increased during hypoxia. Both V_T and V_E decreased significantly in response to decreased P_CO2. The right-to-left shunt of blood away from the lungs increased significantly during hypoxic air cell exposure and decreased significantly during hyperoxic exposure. These results demonstrate the internally pipped embryo's ability to control the site of gas exchange by means of altering blood flow between the lungs and CAM.     

Eggs in autumn: responses to declining incubation temperatures by the eggs of montane lizards

Facultative hatching in response to environmental cues may increase the viability of offspring, if the cue that stimulates hatching also predicts the negative consequences of delayed emergence. Declining incubation temperatures might provide such a cue for montane lizards, because eggs that fail to hatch before winter will perish in the nest. I tested this idea by incubating eggs of an alpine scincid lizard ( Bassiana duperreyi ) in the laboratory. For the first half of the incubation period the eggs were kept at nest temperatures typical of those experienced in summer in the field (daily cycle of 18 ± 7.5°C). I then transferred eggs at weekly intervals into cooler regimes (either 15 ± 7.5°C; or with daytime temperatures unchanged but dropping to 0°C overnight). Contrary to prediction, the eggs did not hatch early. However, transfer to lower temperatures caused only a relatively short delay in hatching, because of a virtual temperature-independence of developmental rates late (but not early) in incubation. Decreasing incubation temperatures also modified hatchling running speeds and post-hatching growth rates, even if the thermal decrease occurred only shortly before the usual time of hatching. These processes plausibly affect hatchling fitness in cold-climate reptiles, and might be adaptations to montane habitats. Alternatively, they may prove to be widespread in other (warmer-climate) reptile taxa, in which case no adaptive hypothesis need be proposed. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 76 , 71–77.     

Metabolic and cardiorespiratory responses of summer flounder Paralichthys dentatus to hypoxia at two temperatures

To quantify the tolerance of summer flounder Paralichthys dentatus to episodic hypoxia, resting metabolic rate, oxygen extraction, gill ventilation and heart rate were measured during acute progressive hypoxia at the fish's acclimation temperature (22° C) and after an acute temperature increase (to 30° C). Mean ±s.e. critical oxygen levels (i.e. the oxygen levels below which fish could not maintain aerobic metabolism) increased significantly from 27 ± 2% saturation (2·0 ± 0·1 mg O(2) l(-1) ) at 22° C to 39 ± 2% saturation (2·4 ± 0·1 mg O(2) l(-1) ) at 30° C. Gill ventilation and oxygen extraction changed immediately with the onset of hypoxia at both temperatures. The fractional increase in gill ventilation (from normoxia to the lowest oxygen level tested) was much larger at 22° C (6·4-fold) than at 30° C (2·7-fold). In contrast, the fractional decrease in oxygen extraction (from normoxia to the lowest oxygen levels tested) was similar at 22° C (1·7-fold) and 30° C (1·5-fold), and clearly smaller than the fractional changes in gill ventilation. In contrast to the almost immediate effects of hypoxia on respiration, bradycardia was not observed until 20 and 30% oxygen saturation at 22 and 30° C, respectively. Bradycardia was, therefore, not observed until below critical oxygen levels. The critical oxygen levels at both temperatures were near or immediately below the accepted 2·3 mg O(2) l(-1) hypoxia threshold for survival, but the increase in the critical oxygen level at 30° C suggests a lower tolerance to hypoxia after an acute increase in temperature.     

Metabolic responses of hibernating golden-mantled ground squirrels Citellus lateralis to lowered environmental temperatures

1. Hibernating C. lateralis were exposed to lowered ambient temperatures in order to investigate the relationship between hibernation stress and the thermoregulatory responses of the animals. 2. The least hibernation-stress squirrels exhibited a passive decline in metabolic rate until their body temperatures stabilized close to microenvironmental temperature. 3. The most stressed individuals aroused from hibernation in response to the declining ambient temperatures. 4. Intermediately stressed animals demonstrated an initial passive decline in temperature; however, at various temperatures (0.3-6.8 degrees C), this group increased their metabolic rate but did not arouse from hibernation.     

Respiratory and cardiovascular responses to acute hypoxia and hyperoxia in internally pipped chicken embryos.

During the first day of hatching, the developing chicken embryo internally pips the air cell and relies on both the lungs and chorioallantoic membrane (CAM) for gas exchange. Our objective in this study was to examine respiratory and cardiovascular responses to acute changes in oxygen at the air cell or the rest of the egg during internal pipping. We measured lung (VO2(lung)) and CAM (VO2(CAM)) oxygen consumption independently before and after 60 min exposure to combinations of hypoxia, hyperoxia, and normoxia to the air cell and the remaining egg. Significant changes in VO2(total) were only observed with combined egg and air cell hypoxia (decreased VO2(total)) or egg hyperoxia and air cell hypoxia (increased VO2(total)). In response to the different O2 treatments, a change in VO2(lung) was compensated by an inverse change in VO2(CAM) of similar magnitude. To test for the underlying mechanism, we focused on ventilation and cardiovascular responses during hypoxic and hyperoxic air cell exposure. Ventilation frequency and minute ventilation (V(E)) were unaffected by changes in air cell O2, but tidal volume (V(T)) increased during hypoxia. Both V(T) and V(E) decreased significantly in response to decreased P(CO2). The right-to-left shunt of blood away from the lungs increased significantly during hypoxic air cell exposure and decreased significantly during hyperoxic exposure. These results demonstrate the internally pipped embryo's ability to control the site of gas exchange by means of altering blood flow between the lungs and CAM.