Gas Exchange of the Avian Egg Time, Structure, and Function

Data are presented for oxygen consumption water loss duringincubation water vapor conductance of the shell and pore numberof avian eggs and the way in which these values relate not onlyto egg mass but also to incubation time. It is proposed thatall these functions are proportional to the product of egg massand rate of development where the latter is defined as the inverseof incubation time. These interrelationships account at theend of incubation for similar O₂ and CO₂ tensions in the airspace of eggs utilization of calories (0.5 kcal g^–1) andwater loss (15 g g^–1)     

Der embryonale Sauerstoffverbrauch des Buntspechts (Dendrocopos major): Einflu? von Entwicklungsmodus und Bebrütungszeit

Zusammenfassung Der Sauerstoffverbauch von zwei Eiern des Buntspechtes (Dendrocopos major) wurde während der letzten sechs Tage der Embryogenese mit Hilfe eines Durchflußrespirometers gemessen. Der zeitliche Verlauf des embryonalen Stoffwechsels folgt annähernd einer Exponentialfunktion mit Ausnahme einer siebenstündigen Plateauphase am 9. Bebrütungstag. Während der gesamten Embryogenese setzt der Buntspecht 0.9 kJ × g^–1 Frischeimasse um. Dies entspricht nur etwa dem halben Umsatz durchschnittlicher Vogelembryonen (rund 2 kJ × g^–1). Als Ursache dafür wird die kurze Bebrütungszeit des Buntspechts (10 Tage) diskutiert.

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Embryonic oxygen consumption in the Great Spotted Woodpecker (Dendrocopos major) — influence of developmental mode and incubation period

Oxygen consumption of two eggs of the Great Spotted Woodpecker was measured with a two-channel oxygen analyzer using an open flow system. The embryogeny of oxygen consumption nearly follows an exponential equation with the exception of a 7-hour plateau phase on day 9 of incubation. During this period the embryos consume ca. 4 ml O₂ × min^–1. For a given fresh egg mass the eggs of woodpeckers have unusually short incubation periods (10 days measured vs. 17 days expected). Thus a comparison of the embryonic metabolism with that of species having long incubation periods but similar egg sizes shows the influence of a fast embryonic development on avian enbryonic energetics. The total embryonic metabolism of the Great Spotted Woodpecker amounts to 0.9 kJx g^–1 fresh egg mass which is half as much as the value for most other birds (ca. 2 kJ × g^–1).

     

Gas exchange and energy metabolism of the ostrich (Struthio camelus) embryo

We measured oxygen consumption ( ) and carbon dioxide emission ( ) rates, air-cell gas partial pressures of oxygen (P_AO₂) and CO₂ (P_ACO₂), eggshell water vapour conductance and energy content of the ostrich (Struthio camelus) egg, ‘true hatchling’ and residual yolk, and calculated RQ and total oxygen consumption ( ) for ostrich eggs incubated at 36.5°C and 25% relative humidity. The pattern showed a drop of approximately 5% before internal pipping. just prior to internal pipping agrees with allometric calculations. Despite the higher incubation temperature compared to other studies, and the resultant shorter incubation duration (42 days), (91.7 l kg⁻¹) was similar to a previously reported value. RQ values during the second half of incubation (approx. 0.68) were lower than expected for lipid catabolism. Prior to internal pipping, P_AO₂ and P_ACO₂ were 98 and 48.3 torr (13.1 and 6.4 kPa), respectively. The growth pattern of the ostrich embryo is different from the typical precocial pattern, showing a time delay in the rapid growth phase. As a result, the lowered overall energy expenditure for tissue maintenance, as compared to other species, is reflected in the low yolk utilization and high residual yolk fraction of the whole hatchling dry mass. These could also result from the relatively short incubation period of the ostrich egg, thereby evading desiccation by excess water loss.     

Artificial incubation of trumpeter swan eggs: Selected factors affecting hatchability

Eggs collected from captive trumpeter swans (Cygnus buccinator) in 1993 (n = 33) and 1994 (n = 42) were artificially incubated with careful monitoring to identify factors contributing to the low hatch success reported by the Ontario Trumpeter Swan Restoration Program. Fertility was > 80% in both years, whereas hatch success of fertile eggs was 14.3% (n = 4) of 28 eggs in 1993 and 37.1% (n = 13) of 35 eggs in 1994. Necropsy of non‐viable eggs indicated a high incidence of embryonic mortality during early and late incubation. Early embryonic mortality was associated with egg storage times exceeding 7 days (P < 0.05) and bacterial contamination of eggs (P < 0.01). Late mortality was associated with (P < 0.001) increased weight loss during incubation period and may have resulted from incubator temperature and humidity fluctuations. We established patterns of weight loss for eggs and determined that hatched eggs lost 11–15% of initial mass and that weight loss >15% resulted in embryo mortality. Results from this study indicate that collection and handling of eggs before incubation and precise control of the incubator environment are critical to hatchability of eggs. Zoo Biol 18:403–414, 1999. © 1999 Wiley‐Liss, Inc.     

Effects of oxygen concentration during incubation and broiler breeder age on embryonic heat production,chicken development,and 7-day performance

Older breeder flocks produce eggs with a relatively larger yolk and thereby a higher nutrient availability than young breeder flocks. To optimise nutrient utilisation and embryonic development throughout incubation and posthatch period, embryos originating from older breeder flocks may require a higher oxygen availability. The current study investigated effects of broiler breeder flock age and incubational oxygen concentration on embryonic metabolism and chicken development until 7-day posthatch. Similar sized eggs of a young (28–32 week) or old (55–59 week) Cobb 500 breeder flock were incubated at one of three oxygen concentrations (17%, 21% or 25%) from day 7 of incubation until 6 h after emergence from the eggshell. Posthatch, chickens were reared until 7 days of age. Egg composition at the start of incubation, heat production during incubation, and embryo or chicken development at embryonic day (ED)14 and ED18 of incubation, 6 h after hatch and day 7 posthatch were evaluated. An interaction was found between breeder age and oxygen concentration for yolk-free body mass (YFBM) at ED18. A higher oxygen concentration increased YFBM in the old breeder flock, whereas no difference was found between 21 and 25% oxygen in the young breeder flock. Yolk size was larger in the old compared to the young flock from ED0 until 6 h after hatch. Breeder flock age did not affect YFBM at ED14 and 6 h after hatch nor daily embryonic heat production, but there were some effects on relative organ weights. Chickens of the old compared to the young breeder flock showed a higher weight gain at day 7, but at a similar feed conversion ratio (FCR). A higher oxygen concentration during incubation stimulated embryonic development, especially between 17% and 21% of oxygen, in both flock ages_. Although this growth advantage disappeared at 7 days posthatch, a low oxygen concentration during incubation resulted in a higher FCR at 7 days posthatch. Results indicated that breeder flock age seemed to influence body development, with an advantage for the older breeder flock during the posthatch period. Oxygen concentrations during incubation affected body development during incubation and FCR in the first 7 days posthatch. Although an interaction was found between breeder flock age and oxygen concentration at ED18 of incubation, there was no strong evidence that nutrient availability at the start of incubation (represented by breeder flock ages) affected embryo and chicken development at a higher oxygen concentration.     

How incubation temperature influences the physiology and growth of embryonic lizards

Eggs of two small Australian lizards, Lampropholis guichenoti and Bassiana duperreyi, were incubated to hatching at 25 °C and 30 °C. Incubation periods were significantly longer at 25 °C in both species, and temperature had a greater effect on the incubation period of B. duperreyi (41.0 days at 25 °C; 23.1 days at 30 °C) than L. guichenoti (40.1 days at 25 °C; 27.7 days at 30 °C). Patterns of oxygen consumption were similar in both species at both temperatures, being sigmoidal in shape with a fall in the rate of oxygen consumption just prior to hatching. The higher incubation temperature resulted in higher peak and higher pre-hatch rates of oxygen consumption in both species. Total amount of oxygen consumed during incubation was independent of temperature in B. duperreyi, in which approximately 50 ml oxygen was consumed at both temperatures, but eggs of L. guichenoti incubated at 30 °C consumed significantly more (32.6 ml) than eggs incubated at 25 °C (28.5 ml). Hatchling mass was unaffected by either incubation temperature or the amount of water absorbed by eggs during incubation in both species. The energetic production cost of hatchling B. duperreyi (3.52 kJ · g⁻¹) was independent of incubation temperature, whereas in L. guichenoti the production cost was greater at 30 °C (4.00 kJ · g⁻¹) than at 25 °C (3.47 kJ · g⁻¹). Snout-vent lengths and mass of hatchlings were unaffected by incubation temperature in both species, but hatchling B. duperreyi incubated at 30 °C had longer tails (29.3 mm) than those from eggs incubated at 25 °C (26.2 mm). These results indicate that incubation temperature can affect the quality of hatchling lizards in terms of embryonic energy consumption and hatchling morphology. Accepted: 27 January 2000     

A note on eggshell porosity,nest humidity and the effects of DDE in the grey heron (Ardea cinerea)

• 1.1. Water vapour conductance (G_H2O) was determined for 25 grey heron Ardea cinerea eggs in the laboratory, and in nests during natural incubation at two Scottish colonies.
• 2.2. The mean G_H2O of eggs measured in the nest which successfully hatched was 9.0 mgH;O/mmHg/day and the mean water vapour pressure gradient between egg and nest (ΔP_H2O), measured using “calibrated” duck eggs, averaged at 31 mmHg (4.13 kPa).
• 3.3. Based on eggshell porosity results, from the eggs which hatched, such a gradient would result in a loss of water from the eggs during incubation equivalent to 11% of their fresh weight.
• 4.4. Shell thickness, the number of pores/cm² of eggshell and DDE content were also determined for the 25 eggs measured in the laboratory.
• 5.5. Eggs containing high levels of DDE had thinner shells, more pores in the eggshell and a higher overall eggshell porosity.
• 6.6. The main problem posed by a high level of DDE would appear, however, not to be an excessive water loss from the egg during incubation, but rather eggshell thinning leading to a loss of the egg due to breakage in the nest.

     

Effects of incubation temperature on the energetics of embryonic development and hatchling morphology in the Brisbane river turtle Emydura signata

Incubation temperature and the amount of water taken up by eggs from the substrate during incubation affects hatchling size and morphology in many oviparous reptiles. The Brisbane river turtle Emydura signata lays hard-shelled eggs and hatchling mass was unaffected by the amount of water gained or lost during incubation. Constant temperature incubation of eggs at 24 °C, 26 °C, 28 °C and 31 °C had no effect on hatchling mass, yolk-free hatchling mass, residual yolk mass, carapace length, carapace width, plastron length or plastron width. However, hatchlings incubated at 26 °C and 28 °C had wider heads than hatchlings incubated at 24 °C and 31 °C. Incubation period varied inversely with incubation temperature, while the rate of increase in oxygen consumption during the first part of incubation and the peak rate of oxygen consumption varied directly with incubation temperature. The total amount of oxygen consumed during development and hatchling production cost was significantly greater at 24 °C than at 26 °C, 28 °C and 31 °C. Hatchling mass and dimensions and total embryonic energy expenditure was directly proportional to initial egg mass. Accepted: 18 March 1998     

Effect of Temperature on the Rate of Oxygen Consumption during the Second Half of Embryonic and Early Postembryonic Development of European Pond Turtle <Emphasis Type="Italic">Emys orbicularis</Emphasis> (Reptilia: Emydidae)

Oxygen consumption by eggs of European pond turtle was determined at two constant incubation temperatures of 25 and 28°C during the second half of embryogenesis. During development at both temperatures, the rate of oxygen consumption initially increased to remain constant during the last quarter of embryogenesis. The difference between the rates of oxygen consumption at these temperatures decreased during the studied period. The coefficient Q₁₀ for the rate of oxygen consumption decreased from 9 to 1.7. At an incubation temperature of 28°C, the changes in the rate of oxygen consumption in response to a short-term temperature decrease to 25°C or increase to 30°C depended on the developmental stage and were most pronounced at the beginning of the studied period. During late embryonic and first 2.5 months of postembryonic development, the rate of oxygen consumption did not significantly differ after such temperature changes. The regulatory mechanisms formed during embryonic development are proposed to maintain the level of oxygen consumption during temperature changes.     

Interaction between eggshell temperature and carbon dioxide concentration after day 8 of incubation on broiler chicken embryo development

Carbon dioxide (CO₂) is considered to be an important factor during incubation of eggs. Effects attributed to higher CO₂ concentrations during experiment might be due to confounding effects of other environmental conditions, such as incubation temperature. To disentangle effects of eggshell temperature (EST) and CO₂ concentration, an experiment was conducted. A total of 630 Cobb 500 hatching eggs from 37 to 45 wk commercial breeder flocks were collected and incubated according to treatments. The experiment was setup as a complete randomized 2 × 3 factorial design, resulting in 6 treatments. From day 8 of incubation onward, broiler eggs were exposed to one of two EST (37.8 or 38.9 °C) and one of three CO₂ concentrations (0.1, 0.4 or 0.8%). Eggs were incubated in climate-respiration chambers and metabolic heat production was determined continuously. At day 18 of incubation and at 6 h after hatching, embryo and chicken quality were determined by evaluation of organ weights, navel condition, blood metabolites and hepatic glycogen. Hatching time and chicken length at 6 h after hatching showed an interaction between EST and CO₂ concentration (both P = 0.001). Furthermore, no effect of CO₂ concentration was found on embryo development or chicken quality. Metabolic heat production between day 8 and 18 of incubation was not affected by either EST or CO₂. At day 18 of incubation, an EST of 38.9 °C resulted in a higher egg weight loss, longer embryos, higher yolk free body mass (YFBM) and lower heart weight than an EST of 37.8 °C (all P < 0.008). At 6 h after hatching, an EST of 38.9 °C resulted in a higher residual yolk weight and lower YFBM, liver weight and heart weight than an EST of 37.8 °C (all P < 0.003). Lactate, uric acid and hepatic glycogen were not affected by EST at either day 18 of incubation or at hatch. Glucose was not affected by EST at day 18 of incubation, but at hatch, it was higher at an EST of 37.8 °C than at an EST of 38.9 °C (P = 0.02). It can be concluded that effects of CO₂ concentration (at concentrations ≤0.8%) on embryonic development and chicken quality appear to be limited when EST is maintained at a constant level. Moreover, a higher EST from day 8 of incubation onward appears to negatively affect chicken quality at hatch.     

The cooling time of fertile chicken eggs at different stages of incubation

We asked whether or not the thermal characteristics of fertile avian eggs changed throughout incubation. The cooling and warming times, expressed by the time constant τ of the egg temperature response to a rapid change in ambient temperature, were measured in fertile chicken eggs at early (E7), intermediate (E11) and late (E20) stages of embryonic development. Same measurements were conducted on eggs emptied of their content and refilled with water by various amounts. The results indicated that (1) the τ of a freshly laid egg was ~50 min; (2) τ decreased linearly with the drop in egg water volume; (3) the dry eggshell had almost no thermal resistance but its wet inner membrane contributed about one-third to the stability of egg temperature; (4) the egg constituents (yolk, albumen and embryonic tissues) and the chorioallantoic circulation had no measurable effect on τ; (5) the presence of an air pocket equivalent in volume to the air cell of fertile eggs reduced τ by about 3 min (E7), 5 min (E11) and 11 min (E20). Hence, in response to warming the egg τ at E20 was slightly shorter than at E7. In response to cooling, the egg τ at E20 was similar to, or longer than, E7 because embryonic thermogenesis (evaluated by measurements of oxygen consumption during cold) offset the reduction in τ introduced by the air cell. In conclusion, until the onset of thermogenesis the thermal behavior of a fertile egg is closely approximated by that of a water-filled egg with an air volume equivalent to the air cell. It is possible to estimate the cooling τ of avian eggs of different species from their weight and incubation time.     

Metabolism,temperature relations,maternal behavior,and reproductive energetics in the ball python (Python regius)

Summary Thermogenic incubation has been documented in two large species of pythons, but the phenomenon has not been studied in small species with concomitantly large heat transfer coefficients. We describe behavior, metabolic rates, mass changes, and temperature relations for adult ball pythons (Python regius), the smallest member of the genus, during the reproductive cycle. Egg and hatchling metabolism and hatchling growth rates were also examined.Rates of oxygen consumption ( ) of both gravid and non-gravid snakes showed typical ectothermic responses to changing ambient temperature (T _a). TheQ ₁₀ forT _a's of 20–35°C was 2.2–2.3. The of gravid females was significantly greater than that of non-gravid snakes at allT _a. Maximum oxygen consumption ( max) during forced exercise was about 12 times resting atT _a=30°C.Eggs (5–6 per female) were laid in April. Total clutch mass was approximately 32% of the females' pre-oviposition mass. After oviposition, mother snakes coiled tightly around their clutches and remained in close attendance until the eggs hatched in June. Sudden decreases inT _a elicited abrupt but transient 2- to 4-fold increases in the of incubating females. Similar responses were not observed in non-incubating snakes. The steady-state of incubating females was independent ofT _a. In no case was body temperature (T _b) elevated more than a few tenths of a degree aboveT _a in steady-state conditions.The of developing eggs increased sigmoidally through the 58–70 day incubation period. Total oxygen consumption during incubation atT _a=29.2°C was about 3.61 per egg. Young snakes quadrupled their mass during their first year of growth.Compared to larger python species which are endothermic during incubation, ball pythons have similar aerobic scopes and higher mass-specific max. However, effective endothermy in ball pythons is precluded by high thermal conductance and limited energy stores.     

Incubation water loss,shell conductance,and pore dimensions in Adelie Penguin eggs

Summary In order to understand water loss regulation of bird eggs in very dry climates eggs of the Adelie Penguin were studied at Cape Bird, Ross Island, Antarctica. During incubation 125 g Adelie Penguin eggs lose about 447 mg of water per day, resulting in an overall estimated loss, during 35 days of incubation, of 13% of their initial mass. The eggshell conductance of 13.1 mg H₂O·day^-1·torr^-1 occurs from 9100 pores with an effective radius and pore length of 11 m and 600 m, respectively. In this study the water vapor pressure of the egg was 44 torr, estimated from the egg temperature of 35.9°C. Ambient temperature was-4°C, with an absolute humidity of less than 3 torr, resulting in an overall vapor pressure difference between the egg and the environment of 41 torr. This difference was divided between the egg and nest conductance in a ratio of ca. 1:5.     

Gas exchange and blood gases of Puna teal (Anas versicolor puna) embryos in the Peruvian Andes

Oxygen consumption, air cell gases, hematology, blood gases and pH of Puna teal (Anas versicolor puna) embryos were measured at the altitude at which the eggs were laid (4150 m) in the Peruvian Andes. In contrast to the metabolic depression described by other studies on avian embryos incubated above 3700 m, O₂ consumption of Puna teal embryos was higher than even that of some lowland avian embryos at equivalent body masses. Air cell O₂ tensions dropped from about 80 toor in eggs with small embryos to about 45 toor in eggs containing a 14-g embryo; simultaneously air cell CO₂ tension rose from virtually negligible amounts to around 26 torr. Arterial and venous O₂ tensions (32–38 and 10–12 toor, respectively, in 12- to 14-g embryos) were lower than described previously in similarly-sized lowland wild avian embryos or chicken embryos incubated in shells with restricted gas exchange. The difference between air cell and arterial O₂ tensions dropped significantly during incubation to a minimum of 11 torr, the lowest value recorded in any avian egg. Blood pH (mean 7.49) did not vary significantly during incubation. Hemoglobin concentration and hematocrits rose steadily throughout incubation to 11.5 g · 100 ml^-1 and 39.9%, respectively, in 14-g embryos.Abbreviations PO₂ partial pressure gradient of O₂ - BM body mass - D diffusion coefficient - G gas conductance (cm³·s^-1·torr^-1) - conductance to water vapor - IP internal pipping of embryos - P _ACO₂ partial pressure of carbon dioxide in air cell - P _AO₂ partial pressure of oxygen in air cell - P _aCO₂ partial pressure of carbon dioxide in arterial blood - P _aCO₂ partial pressure of oxygen in arteries - P _H barometric pressure (torr) - PCO₂ partial pressure of carbon dioxide - P _IO₂ partial pressure in ambiant air - PO₂ partial pressure of oxygen - P _VCO₂ venous carbon dioxide partial pressure - P _VO₂ mixed venous oxygen partial pressure - SE standard error - VO ₂ oxygen consumption     

High Environmental Temperature Increases Glucose Requirement in the Developing Chicken Embryo

Environmental conditions during the perinatal period influence metabolic and developmental processes in mammals and avian species, which could impact pre- and postnatal survival and development. The current study investigated the effect of eggshell temperature (EST) on glucose metabolism in broiler chicken embryos. Broiler eggs were incubated at a high (38.9°C) or normal (37.8°C) EST from day 10.5 of incubation onward and were injected with a bolus of [U-¹³C]glucose in the chorio-allantoic fluid at day 17.5 of incubation. After [U-¹³C]glucose administration, ¹³C enrichment was determined in intermediate pools and end-products of glucose metabolism. Oxidation of labeled glucose occurred for approximately 3 days after injection. Glucose oxidation was higher in the high than in the normal EST treatment from day 17.6 until 17.8 of incubation. The overall recovery of ¹³CO₂ tended to be 4.7% higher in the high than in the normal EST treatment. An increase in EST (38.9°C vs 37.8°C) increased ¹³C enrichment in plasma lactate at day 17.8 of incubation and ¹³C in hepatic glycogen at day 18.8 of incubation. Furthermore, high compared to normal EST resulted in a lower yolk-free body mass at day 20.9 (−2.74 g) and 21.7 (−3.81 g) of incubation, a lower hepatic glycogen concentration at day 18.2 (−4.37 mg/g) and 18.8 (−4.59 mg/g) of incubation, and a higher plasma uric acid concentration (+2.8 mg/mL/+43%) at day 21.6 of incubation. These results indicate that the glucose oxidation pattern is relatively slow, but the intensity increased consistently with an increase in developmental stage of the embryo. High environmental temperatures in the perinatal period of chicken embryos increased glucose oxidation and decreased hepatic glycogen prior to the hatching process. This may limit glucose availability for successful hatching and could impact body development, probably by increased gluconeogenesis from glucogenic amino acids to allow anaerobic glycolysis.     

Embryopathic and embryocidal effects of purified fumonisin B1 orFusarium proliferatum culture material extract on chicken embryos

One hundred eight fertile eggs (Columbia × New Hampshire) were assigned to 10 groups of 10 eggs each (2 control groups had 14 eggs each). Five groups of eggs were inoculated on day 1 of incubation, while the other 5 groups were inoculated on day 10. The inoculum of the 4 treatment groups on both day 1 and 10 consisted of 1,10, or 100 µM purified fumonisin B₁ (FB₁) or a culture material extract (CME) ofFusarium proliferatum, having known amounts of FB₁, FB₂ and moniliformin (FB₁ 20 µM; FB₂ 4 µM and moniliformin 7 µM). Inoculum consisted of the respective toxin(s) dissolved in 100 µl double distilled, autoclaved water (diluent). Control eggs were inoculated with diluent only. Mortality was both dose- and time-responsive in all treatments. Eggs inoculated on day 1 with 1 µM FB₁ had 50% mortality; 10 µM FB₁ had 70% mortality; 100 µM FB₁ had 100% mortality; and CME had 100% mortality. Eggs inoculated on day 10 with 1,10 or 100 µM FB₁ or CME had 30, 60, 90 and 80% mortality, respectively. Normal chicks were hatched from all control eggs. The median death times (MDT₅₀) were inversely dose-responsive in all treatments, ranging from 3.0 to 7.4 days in embryos exposed on day 1 and from 3.2 to 9.0 days in those exposed on day 10. Early embryonic changes in exposed embryos included hydrocephalus, enlarged beaks and elongated necks. Pathologic changes were noted in liver, kidneys, heart, lungs, musculoskeletal system, intestines, testes and brain toxin-exposed embryos.     

Respiration rates of subitaneous eggs from a marine calanoid copepod: monitored by nanorespirometry

The oxygen consumption rate during embryogenesis of Acartia tonsa subitaneous eggs were measured at different temperatures (10, 15, 17, 21, 24 and 28°C) with nanorespirometry. The oxygen consumption was constant during the embryogenesis but increased rapidly at hatching time. The mean ± SD oxygen consumption rate increased exponentially with temperature and ranged from 0.09 ± 0.04 (10°C) to 0.54 ± 0.09 nmol O₂ egg⁻¹ h⁻¹ (28°C). The mean ± SD Q₁₀-value was 2.51 ± 0.15. Calculations of energy consumption during embryogenesis ranged from 1.86 to 18.28 mJ depending on temperature and development time. We conclude that the effect of temperature on oxygen consumption rate was far less important than the prolonged development time when calculating the energy consumed during embryogenesis.     

Variation in eggshell characteristics and gas exchange of montane and lowland coot eggs

Summary This study determined how structural features of the eggshells of coots (Fulica americana) laid at 4150 m in the Peruvian Andes differed from those at sea level in Peru and California and how these features affected exchange of water vapor, O₂, and CO₂. While barometric pressure at 4150 m was reduced to 60% of that at sea level, the conductance to water vapor, corrected to 760 torr, of montane eggs was 107% of the corresponding lowland value. When the effect of low barometric pressure on the diffusion coefficient of gases was considered, the effective conductance of the montane eggs at altitude was 177% of that at sea level. As a result, daily water loss from the montane eggs was substantially greater than that from lowland ones. The oxygen consumption of montane embryos was lower than that of lowland embryos of all sizes, particularly at larger embryonic masses. Just before pipping, the oxygen consumption of montane embryos was about 60% of the corresponding value for lowland individuals. Air cell oxygen tensions in montane eggs varied between about 65 and 38 torr; these values were about 60–70 torr below those in lowland eggs at equivalent embryonic masses. Just before pipping, the air cell CO₂ tension of montane eggs was about 20 torr below levels in sea level eggs. The eggshell conductance to gases of montane eggs appears to have been selected to promote oxygen delivery at the cost of increased losses of water vapor and CO₂.     

The cost of incubation in relation to clutch-size in the Collared Flycatcher Ficedula albicollis

This study examines the importance of avian incubation costs as determinants of clutch-size variation by performing clutch-size and brood-size manipulations in the same population of Collared Flycatchers Ficedula albicollis during the same breeding season. In 2 5 cases when three or more clutches of the same size were completed on the same day, we moved two eggs on the day after the last egg had been laid from one randomly selected clutch (C) to another (C) and moved two other eggs from this to a third clutch (C⁺). In 20 other cases of simultaneously completed clutches of the same size, we moved two randomly selected young from one brood to a second and from that moved two other young to a third (B, B and B⁺groups). Most females were weighed the day after completion of the clutch and 1–4 days before hatching of the young, and some of them also 10–14 days after hatching of the young. We measured the daily energy expenditure of females incubating manipulated clutches of 4, 6 and 8 eggs by means of the doubly-labelled water (D₂¹⁸O) technique and also recorded their nest attendance. Hatching success of fertilized eggs was reduced in the enlarged clutches compared with control and reduced clutches. Females expired on average 3142.6 ml CO₂ and expended 78.6 kJ per day while incubating, which corresponds to a metabolic intensity of 3.3 times BMR. Daily energy expenditure increased with clutch-size due to higher costs while incubating, and not because of changed activity patterns. There were no significant differences in length of incubation, female mass or mass changes between phases for the C, C and C⁺groups. In both the C and B groups, enlarged broods produced significantly more fledged young than control broods, and those significantly more than reduced broods. Fledgling tarsus-length and mass did not differ significantly between treatments in either the C or B groups. There was no significant difference in breeding success between clutch and brood manipulations. In this season, incubation costs did not entail significant fitness losses, expressed either as fledgling production or female condition. Also, control females could have raised more young to fledging age than they did with no apparent costs.     

Effects of Metabotropic Glutamate Receptor Stimulation on Cerebral O2 Consumption and Blood Flow During Focal Cerebral Ischemia in Rats

This investigation was performed to evaluate the effects of ACPD [(1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid], a metabotropic glutamate receptor agonist, on cerebral O₂ consumption during focal cerebral ischemia. Male Wistar rats were placed in control (n = 7) and ACPD (n = 7) groups under isoflurane anesthesia. Twenty minutes after middle cerebral artery (MCA) occlusion, gauze sponges with 10^–5 M ACPD or normal saline were placed on the ischemic cortex (IC) for a period of 40 min and were changed every 10 min. One hour after MCA occlusion, regional cerebral blood flow (rCBF) was determined using the C¹⁴-iodoantipyrine autoradiographic technique. Regional arterial and venous oxygen saturation were determined using microspectrophotometry. There were no statistical differences in vital signs, blood gases, and hemoglobin between the groups. In the control group, the cerebral blood flow and oxygen consumption of the IC were significantly lower than the contralateral cortex (rCBF: 45 ± 11 vs. 110 ± 11 ml/min/100 g, O₂ consumption: 2.9 ± 0.4 vs. 5.4 ± 1.1 ml O₂/min/100 g). ACPD did not change regional cerebral blood flow of the IC, but did significantly increase the oxygen extraction (7.8 ± 0.2 vs. 6.9 ± 0.3 ml O₂/100 ml) and oxygen consumption of the IC (4.3 ± 1.5 vs. 2.9 ± 0.4) compared to the control IC. Our data demonstrated that topical application of 10^–25 M ACPD to the ischemic area worsened cerebral O₂ balance. These data suggest that metabotropic glutamate receptors are not maximally activated during ischemia in the temporal cortex.