Ontogeny of heart rate in embryonic and nestling crows (Corvus corone and Corvus macrorhynchos)

The developmental patterns of mean heart rate (MHR) and instantaneous heart rate (IHR) were investigated in embryos and chicks of altricial Corvuscorone and Corvus macrorhynchos. The MHR of embryos increased linearly with time from 250 beats · min⁻¹ at mid-incubation to 290 beats · min⁻¹ in hatchlings. MHR during the pipping period was maximal, but only marginally higher than in hatchlings. MHR was stable at about 290–300 beats · min⁻¹ during the 1st week after hatching. Spontaneous heart rate (HR) decelerations and accelerations were found in embryos and chicks, disturbing the baseline HR with increasing frequency during development. However, the IHR accelerations developed later and were less frequent than in precocial species. IHR and body temperature decreased during mild cold exposure (23–25 °C) and IHR accelerations were reduced in nestlings during the 1st week. We suggest that the development of parasympathetic control of HR in crows occurs at 60% of incubation, similar to precocial embryos, but sympathetic control may be delayed and suppressed in contrast to precocial embryos. Accepted: 3 March 1999     

Development of cardiac rhythms in birds

Heart rate (HR) in avian embryos developing inside an eggshell has been measured by various means while maintaining adequate gas exchange through the eggshell. This is an important requirement in order to avoid adverse effects of impeding gas exchange on the cardiac rhythms of developing embryos. The present report is a review of our ontogenetic study on embryonic HR, which was measured with fulfillment of the above requirement and also hatchling HR measured non-invasively. Firstly, we reviewed measurements of daily changes (developmental patterns) in embryonic mean heart rate (MHR), which were determined from a short-term measurement of HR once a day, in 34 species of altricial and precocial birds. The allometric relationship between the MHR during pipping in altricial birds and their fresh egg masses was the same as that between the MHR at 80% of incubation duration and fresh egg masses in pre-cocial birds. Secondly, we presented the developmental patterns of MHR in chick embryos and hatchlings, which were determined from long-term, continuous measurement of HR before, during and after hatching. The ultradian and circadian rhythms of HR were clearly shown in embryos and hatchlings, respectively. Thirdly, we summarized instantaneous HR fluctuations: HR variability and HR irregularities, in chick embryos and hatchlings. The distinctive patterns were shown in pre-pipped and pipped embryos and newly hatched chicks, individually, which were partly related to autonomic nervous functions and physiological functions.     

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

We measured oxygen consumption (V(O(2))) and carbon dioxide emission (V(CO(2))) rates, air-cell gas partial pressures of oxygen (P(A)O(2)) and CO(2) (P(A)CO(2)), 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 (V(O(2)tot)) for ostrich eggs incubated at 36.5 degrees C and 25% relative humidity. The V(O(2)) pattern showed a drop of approximately 5% before internal pipping. V(O(2)) 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), V(O(2)tot) (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(A)O(2) and P(A)CO(2) 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.     

Water in the Avian Egg Overall Budget of Incubation

The loss of mass in eggs during incubation was examined andevidence is presented to show that this is essentially due toloss of water. The mean fraction of water lost by diffusionthroughout incubation is 0.150 ± 0.025 S D per gram ofegg and 0.162 ± 0.026 S D per gram of egg content for81 species. The water fraction of fresh eggs and of hatchingeggs was examined in 32 species divided according to maturityat hatching, and found to be very similar within each category(83% in altricial 83% in semi-altricial 78% in semi-precocial72% in precocial eggs). The 11% difference between the altricialand precocial categories is statistically significant. Duringincubation, dry matter is metabolized increasing the water fractionwhich is further increased by metabolic water production. Hence,water loss during incubation is mandatory if the relative watercontent of an egg at the end of incubation is to remain essentiallythe same as at the beginning. Equations are developed whichallow one to estimate the difference between diffusive waterloss and the total water loss in altricial and piecocial eggscaused by additional water loss during pipping and hatching.     

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.     

Development and regulation of heart rate in embryos and hatchlings of gulls (Larus schistisagus and Larus crassirostris) in relation to growth

We compared the developmental patterns of mean heart rate in Larus crassirostris and L. schistisagus embryos and chicks with other avian species of different hatchling developmental modes. We proposed that, since mean heart rate is inversely related to fresh egg mass in all birds, larger species reached a higher fraction of their hatchling mean heart rate by the end of the early phase of incubation and that heart rate contributions to supplying the increasing metabolic demands during mid and late incubation phases were less important than in smaller avian species. Mean heart rate was essentially independent of age throughout the mid-incubation phase (33% of normalised incubation until pipping), but increased with time during early (L. schistisagus only investigated) and late-incubation phases in both species. The O₂ pulse of L. schistisagus embryos and chicks increased linearly with yolk-free body mass (log-log) after the early-phase of incubation until shortly before pipping, but was independent of body mass in the periods before and after. We conclude that a high heart rate in this first period is probably more important for increasing the circulation of nutrients to the embryo at a stage when extra-embryonic circulation to the yolk sac is limited by the size of the growing area vaculosa. Furthermore, large increases in mean heart rate during the late-incubation phase are probably important for increasing the cardiac output to hatching levels with onset of endothermy. However, mean heart rate is stable over the mid-incubation while O₂ pulse increases, suggesting that increases in stroke volume and other circulatory adjustments may be entirely responsible for the largest increases in O₂ transport during incubation of large avian species. Accepted: 18 May 2000     

Development of the pulmonary surfactant system in two oviparous vertebrates

In birds and oviparous reptiles, hatching is often a lengthy and exhausting process, which commences with pipping followed by lung clearance and pulmonary ventilation. We examined the composition of pulmonary surfactant in the developing lungs of the chicken, Gallus gallus, and of the bearded dragon, Pogona vitticeps. Lung tissue was collected from chicken embryos at days 14, 16, 18 (prepipped), and 20 (postpipped) of incubation and from 1 day and 3 wk posthatch and adult animals. In chickens, surfactant protein A mRNA was detected using Northern blot analysis in lung tissue at all stages sampled, appearing relatively earlier in development compared with placental mammals. Chickens were lavaged at days 16, 18, and 20 of incubation and 1 day posthatch, whereas bearded dragons were lavaged at day 55, days 57-60 (postpipped), and days 58-61 (posthatched). In both species, total phospholipid (PL) from the lavage increased throughout incubation. Disaturated PL (DSP) was not measurable before 16 days of incubation in the chick embryo nor before 55 days in bearded dragons. However, the percentage of DSP/PL increased markedly throughout late development in both species. Because cholesterol (Chol) remained unchanged, the Chol/PL and Chol/DSP ratios decreased in both species. Thus the Chol and PL components are differentially regulated. The lizard surfactant system develops and matures over a relatively shorter time than that of birds and mammals. This probably reflects the highly precocial nature of hatchling reptiles.     

Development of cardiac rhythms in altricial avian embryos

Mean heart rate (MHR) was determined during incubation and in hatchlings of 14 altricial avian species to investigate (1) if there is a common developmental pattern of heart rate in altricial embryos and (2) if heart rate changes during incubation are correlated with changes in embryonic growth rate. On the basis of normalized incubation MHR increased approximately linearly in 12 of 14 species from as early as 30-40% of incubation to that of pipped embryos. The MHR of hatchlings was equal to or higher than that of pipped embryos in seven species. Passerine embryos and hatchlings maintained higher MHR in comparison to parrots of similar egg mass, which may reflect phylogenetic differences in development. Embryonic MHR increased at a higher rate while embryonic growth rates were highest during the first 40% of incubation in tit, budgerigar and crow embryos than during subsequent development when relative growth rates decreased. MHR became independent of yolk-free wet mass at a smaller fraction of hatchling mass in budgerigar and crow than in the tit, suggesting that MHR is more likely to increase continuously after 40% of incubation in small altricial species than larger species.     

Intraclutch Hatch Synchronization in Pheasants and Mallard Ducks

Synchronization of hatching within clutches of precocial bird species can be achieved either by acceleration or retardation, i.e. by shortening or prolonging the incubation period. The ability of mallard ( Anas platyrhynchos ) and ring-necked pheasant ( Phasianus colchicus ) embryos to accelerate or retard hatching was tested by incubating separate clutches, of which three eggs had 2 d longer or shorter incubation time than the others, and observing their individual time of pipping (breaking of the shell). Mallard embryos were able to delay hatching by on average 0.6 d (43% of the eggs delayed at least 1 d), but were better at acceleration (on average 1.3 d; 91% of the eggs accelerated more than 1 d). Conversely, pheasant embryos were only able to accelerate by 0.4 d (50% accelerated more than 1 d), but were better at delaying the hatching (1.2 days; 77% delayed more than 1 d). This difference between the species may depend on different degrees of relatedness within clutches in pheasants and mallards. It may also be an effect of the more developed sensory and neuromuscular systems in galliforms; a reduction of the incubation period would mean that the development of, for example, locomotion would be insufficient at hatching.     

孵化温度对赤链蛇胚胎代谢和幼体行为的影响

研究了赤链蛇(Dinodon rufozonatum)在孵化过程中卵的生长、孵化期、胚胎代谢和孵出幼体行为表现的热依赖性。结果显示:孵化温度对孵化期、卵增重、孵化过程中消耗的总能量和孵出幼体的运动表现有显著影响,但不影响胚胎代谢率、孵化成功率和幼体吐信频次。孵化期随着孵化温度的升高而缩短,孵化过程中,24℃终末卵重和胚胎代谢率显著大于30℃,而27℃与其他两个温度没有差异;27℃孵出幼体游速较24℃快,30℃孵出幼体与其他两个温度孵出幼体的游速无显著差异。上述结果显示:24—30℃是赤链蛇适合的孵化温度范围,与赤链蛇所处的生境温度相近。     

Embryonic heart rate and oxygen pulse in two procellariiform seabirds,Diomedea immutabilis and Puffinus pacificus

Developmental patterns of embryonic heart rate were measured non-invasively in two procellariiform seabirds, the Laysan albatross (Diomedea immutabilis) and wedge-tailed shearwater (Puffinus pacificus), during prepipping and after pipping. The O₂ pulse, defined as the O₂ consumption per single heart beat, was calculated using the previously reported O₂ consumption for these species. The embryonic heart rate of the albatross was not changed by internal pipping (initial pipping event in this species), remained unchanged during the prolonged internal pipping period and tended to increase, although insignificantly, with the initiation of external pipping (second pipping event). Heart rate in the shearwater remained unchanged during the late prepipping stages, did not change with external pipping (initial pipping event), but increased during the prolonged internal pipping period (second pipping event) and reached a maximum on the last day of incubation. The developmental pattern of heart rate in the shearwater was very similar to that reported previously for the brown noddy, a member of the order Charadriiformes but with the same pipping sequence. Developmental patterns of embryonic O₂ pulse were also different between the two procellariiform seabirds. However, those of the shearwater and the noddy were similar. The sequence of access to atmospheric O₂ during development and hatching may be an important factor determining the developmental patterns of embryonic heart rate and O₂ pulse.Abbreviations A-VO₂ difference, arteriovenous oxygen difference - BCG ballistocardiogram of egg - CV coefficient of variation - EP external pipping - HR heart rate - IP internal pipping - mass mass of freshly laid egg - SD standard deviation     

Mechanism and cost of synchronous hatching

1. Synchrony in the timing of births is thought to have evolved as a general predator avoidance strategy. In turtles, synchronous hatching may facilitate group emergence from the nest, which in turn, may limit predation by diluting an individual's risk of predation or by simply swamping predators upon emergence. However, synchronizing hatching should not be easily achieved in natural nests because of thermal gradients affecting developmental rates.
2. We evaluated pipping synchrony in the painted turtle ( Chrysemys picta ), where the drive to hatch synchronously may be reduced, because in many populations, hatching and emergence are dissociated through hatchlings overwintering within a nest.
3. We also assessed developmental mechanisms through which synchrony occurs and explored potential trade-offs between pipping synchrony and individual fitness by determining potential short and long-term neuromuscular developmental costs to hatching prematurely. These data were also used to develop a theoretical model to determine how differential embryonic maturation rates affect hatching synchrony.
4. Underdeveloped embryos pipped much earlier than expected and at similar times to their more advanced sibs. In addition, a trade-off between hatching synchronously and neuromuscular development (motility) was evident several days after hatching and up to 9 months later, after the overwintering period.
5. Synchronous hatching is an ancestral trait in turtles, but its relevance today is not solely for predator avoidance in all species.
6. Abiotic factors during incubation (e.g. temperature regime and moisture) have long-term effects on reptiles during ontogeny but it is also clear that incubation behaviour is major factor for the persistence of these developmental costs.     

Metabolic fates of yolk lipid and individual fatty acids during embryonic development of the coot and moorhen

There is currently little information regarding the metabolic fates of yolk lipid and individual fatty acids during embryonic development of free-living avian species. Here we report the pattern of lipid utilization during embryonic development of the coot (Fulica atra) and the moorhen (Gallinula chloropus), two related species producing precocial offspring from eggs with a distinctive fatty acid composition and with an incubation period similar to that of the chicken. By the time of hatching, the proportions of the initial yolk lipid that had been transferred to the embryo were 88.2% and 79.8% for the coot and moorhen respectively. During the whole incubation period, 42.9% and 40.0% of the initial yolk lipid of the coot and moorhen respectively were lost from the system due to oxidation for energy, equating to 47.8% and 50.0% respectively of the actual amount of lipid transferred over this time. Thus, the lipid received by the embryos of both species is partitioned almost equally between the alternative fates of energy metabolism and incorporation into tissue lipids. In the coot, this 50:50 split between oxidation and tissue formation was maintained during the hatching process. The proportions of arachidonic (20:4n-6) and docosahexaenoic (22:6n-3) in the yolk lipids of these species were 2.5-3.5 times higher than in eggs of domestic poultry. In contrast to the situation in the chicken, there was no preferential uptake of 22:6n-3 from the yolk during coot and moorhen development. The fatty acid compositions of the whole body lipids of the coot and moorhen hatchlings were almost identical to those of the initial yolks indicating that, unlike the chicken, these species display relatively little overall biomagnification of 20:4n-6 and 22:6n-6 during development. It is suggested that the yolk fatty acid profiles of the coot and moorhen are particularly well matched to the requirements of the embryo, reducing the need for selective uptake of 22:6n-3 and for the overall biomagnification of 22:6n-3 and 20:4n-6.     

Patterns of Metabolism and Growth in Avian Embryos

Metabolic rates of embryos of precocial birds increase rapidlyuntil about 80% through incubation, then increase slowly remainconstant or even decline. In altricial species, embryo metabolicrates increase continuously and at an accelerating rate throughout incubation. Total energy cost of development is higher inprecocial than in altricial species. Growth patterns of altricialand precocial embryos differ in the same way as does metabolicrate. Embryo growth rates decline late in incubation in precocialspecies, but increase continuously in altricial species. Embryometabolic rate in cal/hr (P) is related to embryo mass in grams(M) and growth rate in grams/day (GR) by the equation P = 12.17GR+ 1.66M + 1.81. The energy cost of growth in avian embryos is292 cal/g. The energy cost of maintenance is 1.66 cal/g hr andappeals to be independent of embryo mass. Differences in growthpatterns account for the observed differences in metabolic ratesand total energy costs of development. High energy costs ofmaintenance account for high total developmental costs in piecocialspecies and in species that have unusually long incubation periods.     

When to be born? Prolonged pregnancy or incubation enhances locomotor performance in neonatal lizards (Scincidae)

The degree of offspring development at hatching (or birth) varies among species within most major vertebrate lineages; altricial vs. precocial birds offer the clearest example of a trade-off between early hatching and the degree of locomotor development of the hatchling. No such diversity has been reported for reptiles, but we suggest that natural selection may fine-tune the time of hatching (in oviparous species) or birth (in viviparous species) to optimize offspring phenotypes and hence, maximize fitness. This hypothesis predicts enhanced neonatal performance after more prolonged incubation or gestation, within as well as among populations. Both published and original data on Australian scincid lizards support this prediction. In a field study, viviparous alpine skinks (Niveoscincus microlepidotus) that gave birth later in the season had faster-running offspring, that had a higher probability of surviving through the first year of life. The enhanced performance and survival were not secondary results of larger offspring size. After controlling for effects of mean incubation temperature, prolonged development also correlated with enhanced locomotor performance in hatchlings from eggs of an oviparous skink (Bassiana duperreyi) incubated at warm temperatures (> 20 degrees C) but not at cooler temperatures (< 20 degrees C). We suggest that embryonic reptiles control their date of hatching or birth and thus, their stage of development at this critical life-history transition.     

Hatching of cladoceran resting eggs: temperature and photoperiod

Summary 1. We identified temperature and photoperiod conditions under which the hatching of 45 cladoceran species could be elicited. Identification of appropriate hatching cues is of primary importance for the exploration of the ties between active and diapausing stages.
2. Incubation temperature affected the hatching success of resting eggs isolated from Danish, Belgian/Dutch and Spanish sediments. In general, most hatchlings and species were retrieved at 15 °C. Danish and Belgian/Dutch resting eggs hatched more successfully under a long day photoperiod than in continuous illumination.
3. Most species could be retrieved after incubation of resting eggs isolated from a limited amount of sediment (0.4 kg) under a single, well chosen combination of temperature and photoperiod. Processing additional sediment samples under seven more incubation regimes only allowed detection of 21% (Spain) to 34% (Denmark) more species.
4. The incubation period for resting eggs to hatch was strongly influenced by incubation temperature. Our results show that hatching experiments aimed at assessing cladoceran species richness and conducted at 15 °C should be continued for a period of at least 2 weeks, after which a random subset of hatchlings (e.g. n  = 100) can be selected from the total hatchling assemblage.     

Development of thermoregulation in Hawaiian brown noddies (Anous stolidus pileatus)

1. 1.|Oxygen consumption ( ) and body temperture (T_b) of Hawaiian brown noddies (Anous stolidus pileatus [Aves: Laridae]) during late incubation and in the first 24 h after hatching were measured at ambient temperatures (T_a) between 28 and 38°C and between 15 and 43°C, respectively. Evaporative cooling by hatchings at T_a of 36–43°C was also measured.

2. 2.|Throughout the late incubation stages studied, and T_b both varied directly with T_a in an ectothermic pattern.

3. 3.|The hatchlings successfully regulated T_b at T_a between ca. 29 and 43°C.

4. 4.|The functional basis of the abrupt increase in thermoregulatory capacity with hatching is discussed.

Enumeration of Enterococcus sp. using a modified mE method

A modified mE medium (mEI) containing the chromogenic substrate indoxyl-β- D -glucoside to detect β- D -glucosidase activity was evaluated with respect to specificity and recovery of enterococci from environmental waters. Extending incubation from 24 to 48 h improved enterococci recovery but 77% of the colonies classified as non-target were confirmed as enterococci. Randomly chosen enterococcal isolates from sewage, exposed in microcosms containing 0·22 μm membrane filtered fresh or estuarine water, exhibited differences in persistence as a function of exposure treatment. Decreasing the concentration of or eliminating indoxyl-β- D -glucoside from mE did not significantly affect recovery of purified isolates.     

Do temperature fluctuations during incubation always play an important role in shaping the phenotype of hatchling reptiles?

Fluctuating temperatures (FTs) influence hatchling phenotypes differently from constant temperatures (CTs) in some reptiles, but not in others. This inconsistency raises a question of whether thermal fluctuations during incubation always play an important role in shaping the phenotype of hatchlings. To answer this question, we incubated eggs of Naja atra under one CT (28 °C, CT), two temperature-shift [cold first (CF) and hot first (HF) in which eggs were first incubated at 24 or 32 °C and then at the other, each for 20 days, and finally at 28 °C until hatching], and one FT thermal regimes. Female hatchlings were larger in snout–vent length but smaller in tail length, head size than male hatchlings from the same-sized egg; female hatchlings had more ventral scales than did male hatchlings. The FT and HF treatments resulted in shorter incubation lengths. Tail length was greatest in the CT treatment and smallest in the FT treatment, with the CF and HF treatments in between; head width was greater in the CT treatment than in the other three treatments. Other examined hatchling traits did not differ among treatments. The observed morphological modifications cannot be attributed to the effect of thermal fluctuations but to the effect of temperatures close to the upper and lower viable limits for the species. Our results therefore support the hypothesis that hatchling phenotype is not altered by thermal fluctuation in species with no phenotypic response to incubation temperature within some thresholds.     

Developmental basis for telencephalon expansion in waterfowl: enlargement prior to neurogenesis

Some altricial and some precocial species of birds have evolved enlarged telencephalons compared with other birds. Previous work has shown that finches and parakeets, two species that hatch in an immature (i.e. altricial) state, enlarged their telencephalon by delaying telencephalic neurogenesis. To determine whether species that hatch in a relatively mature (i.e. precocial) state also enlarged their telencephalon by delaying telencephalic neurogenesis, we examined brain development in geese, ducks, turkeys and chickens, which are all precocial. Whereas the telencephalon occupies less than 55 per cent of the brain in chickens and turkeys, it occupies more than 65 per cent in ducks and geese. To determine how these species differences in adult brain region proportions arise during development, we examined brain maturation (i.e. neurogenesis timing) and estimated telencephalon, tectum and medulla volumes from serial Nissl-stained sections in the four species. We found that incubation time predicts the timing of neurogenesis in all major brain regions and that the telencephalon is proportionally larger in ducks and geese before telencephalic neurogenesis begins. These findings demonstrate that the expansion of the telencephalon in ducks and geese is achieved by altering development prior to neurogenesis onset. Thus, precocial and altricial species evolved different developmental strategies to expand their telencephalon.