Changes in mass of eggs of softshell turtless (Trionyx spiniferus) incubated under hydric conditions simulating those of natural nests

Rigid-shelled eggs of softshell turtles ( Trionyx spiniferus ) incubated at 29C under hydric conditions simulating those at the interior of natural nests (i.e. eggs not contacting the substrate) declined in mass during incubation owing to the continuous escape of water vapour to air trapped inside the chambers, with eggs incubated in relatively dry chambers declining more in mass than eggs held in relatively wet chambers. Eggs held under hydric conditions approximating those at the periphery of natural nests (i.e. eggs partly buried in the substrate) also declined in mass during incubation, but at lower rates than characterized eggs not contacting the substrate, indicating that absorption of liquid water from the substrate compensated for part of the water vapour escaping to the air inside the chambers. There was no relationship between hatching success and either the position of eggs in the chambers or the wetness of substrates, nor was there any variation among experimental groups in the size of hatchlings. Thus, development of embryos of Trionyx spiniferus seems not to be closely coupled with the hydric environment of the nest, a situation contrasting with that of embryos of those species of turtles producing pliable-shelled eggs.     

The effects of thermal and hydric environments on hatching success, embryonic use of energy and hatchling traits in a colubrid snake, Elaphe carinata.

We examined the effects of thermal and hydric environments on hatching success, the embryonic use of energy and hatchling traits in a colubrid snake, Elaphe carinata. The eggs were incubated at four temperatures ranging from 24 to 32 degrees C on substrates with water potentials of 0 and -220 kPa using a 4x2 factorial design. Both thermal and hydric environments affected the water exchange between eggs and their surroundings. Eggs incubated in wetter substrates gained mass throughout the course of incubation, whereas eggs in drier substrates gained mass during the first half of incubation and lost mass thereafter. Hatching success was noticeably higher at 26 and 30 degrees C than at 24 and 32 degrees C, but among treatments, differences in hatching success were not significant. Temperature significantly affected the duration of incubation and most hatchling traits examined. Deformed hatchlings were found in all temperature treatments, with more deformities observed at 32 degrees C. Hatchlings from eggs incubated at different temperatures differed in wet body mass, but the differences stemmed mainly from variation in water contents. Embryos at different temperatures completed development at nearly the same expenditure of energy and catabolized nearly the same amount of lipids, but hatchlings from different temperatures differed in the development condition of carcass at hatching. Hatchlings from eggs incubated at 26 degrees C were larger in SVL than those from other higher or lower incubation temperatures, characteristically having larger carcasses; hatchlings from 32 degrees C eggs were smaller in SVL and had smaller carcasses but larger residual yolks than those from lower incubation temperatures. Hatchlings from eggs incubated at 24 degrees C were shorter in tail length but greater in size (SVL)-specific body wet mass than those from higher incubation temperatures. Within the range from -220 to 0 kPa, the substrate water potential did not affect hatching success, the embryonic use of energy and all hatchling traits examined, and the effects of temperature were independent of the effects of substrate water potential. Therefore, our data add evidence showing that embryonic development in reptiles with pliable-shelled eggs is relatively insensitive to variation in hydric environments during incubation.     

Water exchange of flexible-shelled eggs and its effect on hatchling traits in the Chinese skink,<Emphasis Type="Italic"> Eumeces chinensis</Emphasis>

Flexible-shelled eggs of the Chinese skink (Eumeces chinensis) were used to determine the routes of water exchange with the environment and the effects of water exchange on hatchling traits. Eggs were incubated under three different hydric conditions at 28 °C. One group (ground eggs) was half-buried in incubation substrate. The second group (upper eggs) rested on the ground eggs but did not contact the substrate directly, and the third group was placed on a plastic platform above the substrate. Ground and upper eggs increased in mass and hatched successfully, while all eggs resting on the plastic platform lost mass and died within a week. Hence, E. chinensis eggs cannot sustain water balance through exchange of water vapor in air alone, but can absorb water from the substrate and other eggs and develop well. Water gained by upper eggs was only 20% of that absorbed by ground eggs, but hatchlings from the two treatments did not differ in morphology or locomotor performance. Therefore, the degree of water exchange of E. chinesis eggs has little effect on embryonic development and hatchling traits. The insensitivity of the eggs to variations in water exchange may be an adaptation against extreme hydric conditions in a species that deposits its eggs close to the soil surface.Communicated by I.D. Hume     

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。     

Influence of water availability during incubation on hatchling size, body composition, desiccation tolerance, and terrestrial locomotor performance in the snapping turtle Chelydra serpentina

The effects of water availability during incubation on the water contents of neonatal snapping turtles at hatching were examined, along with the influence of hatchling water content on desiccation tolerance and terrestrial locomotor performance. The water contents of hatchlings from eggs incubated on wet substrates were both absolutely and proportionally greater than were those of hatchlings from eggs incubated on dry substrates. Hatchlings with greater water contents at hatching were able to survive longer and to lose more water before physiological performance was adversely affected by desiccation. Increased water contents in hatchlings with greater water availability during incubation may enhance survival by increasing the amount of water the animal can afford to lose before dehydration begins to adversely affect whole animal performance.     

Does the hydric environment affect the incubation of small rigid-shelled turtle eggs?

Hydric environments are hypothesized to have minor effects on the embryonic development of rigid-shelled turtle eggs due to the low water permeability of the eggshell. However, the water reserve in the eggs may still influence their resistance to environmentally induced dehydration. We incubated rigid-shelled turtle eggs (Pelodiscus sinensis) on different moist substrates (from ? 12 to ? 750 kPa) to test the hypothesis that small rigid-shelled eggs would be sensitive to hydric environments. The hydric treatment significantly affected the incubation period, with eggs incubated in the moistest and driest substrates taking longer to hatch than those on the medium-moisture substrates. Hatching success was slightly lower for eggs incubated in dry conditions than those in wet conditions, but the difference was not statistically significant. The heart rates of early embryos were lower on moist substrates than those on dry substrates, but this difference disappeared in late embryos. Hatchlings from the moistest substrate were larger (in carapace length and width) and heavier than those from drier substrates. However, the dry body mass of the hatchlings did not differ among the hydric treatments. The functional performance (righting response) of the hatchlings was affected by the hydric environment. The time to right was shorter for the hatchlings from the substrate of ? 12 kPa than those from ? 220 kPa. These results are consistent with the hypothesis that the hydric environment may significantly affect developing embryos and the resulting hatchlings in turtle species, such as P. sinensis, with small rigid-shelled eggs.     

Environmentally induced variation in body size of turtles hatching in natural nests

Eggs from three snapping turtles (Chelydra serpentina) were divided between two natural nests in a factorial experiment assessing the role of the nest environment as a cause for variation in body size and energy reserves of hatchlings at our study site in northcentral Nebraska. Nest # 1 was located in an unshaded area on the south side of a high sandhill, whereas nest #2 was located in an unshaded area on level ground. Eggs in nest #1 increased in mass over the course of incubation, with eggs at the bottom of the nest gaining more mass than eggs nearer to the surface. In constrast, eggs in nest #2 lost mass during incubation, with eggs at the bottom declining less in mass than eggs at the top of the cavity. Hatchlings from nest #1 were much larger (but contained smaller masses of unused yolk) than hatchlings from nest #2. Additionally, eggs from the lower layers in both nests tended to produce larger hatchings (but with smaller masses of unused yolk) than eggs from the upper layers. Thus, ecologically important variation in body size and nutrient reserves of hatchling snapping turtles results from variation in the environment among and within nests.     

Swimming performance of hatchling green turtles is affected by incubation temperature

In an experiment repeated for two separate years, incubation temperature was found to affect the body size and swimming performance of hatchling green turtles (Chelonia mydas). In the first year, hatchlings from eggs incubated at 26°C were larger in size than hatchlings from 28 and 30°C, whilst in the second year hatchlings from 25.5°C were similar in size to hatchings from 30°C. Clutch of origin influenced the size of hatchlings at all incubation temperatures even when differences in egg size were taken into account. In laboratory measurements of swimming performance, in seawater at 28°C, hatchlings from eggs incubated at 25.5 and 26°C had a lower stroke rate frequency and lower force output than hatchlings from 28 and 30°C. These differences appeared to be caused by the muscles of hatchlings from cooler temperatures fatiguing at a faster rate. Clutch of origin did not influence swimming performance. This finding that hatchling males incubated at lower temperature had reduced swimming ability may affect their survival whilst running the gauntlet of predators in shallow near-shore waters, prior to reaching the relative safety of the open sea.     

Effects of temperature and moisture during incubation on carcass composition of hatchling snapping turtles (Chelydra serpentina)

Summary Flexible-shelled eggs of common snapping turtles (Chelydra serpentina) were incubated on each of two substrates (vermiculite, sand) at each of three temperatures (26.0°C, 28.5°C, 31.0°C) and three moisture regimes (wet, intermediate, dry). Embryos developing in cool, wet environments mobilized the largest amounts of protein from their yolk and attained the largest size before hatching, whereas turtles developing in warm, dry environments mobilized the smallest quantities of protein and were the smallest in body size at hatching. Embryos on wet substrates mobilized more lipid from their yolk than did embryos on dry media, but ambient temperature had no demonstrable influence on patterns of lipid mobilization. The total reserve of neutral lipid available in residual yolk plus carcass to sustain neonates in the interval prior to the beginning of feeding was largest in hatchlings from dry environments and smallest in animals from wet environments, but was unaffected by temperature during incubation. Hydration of tissues in hatchlings was higher when incubation was in cool, moist conditions than when incubation was in warm, dry settings, thereby indicating that some of the effects of moisture and temperature on mobilization of nutrients by embryos may be mediated by differences in intracellular water. Patterns of response to temperature and moisture recorded for turtles emerging from eggs on sand were similar to those recorded for hatchlings on vermiculite, so no important conclusion would have been affected by incubating eggs on one medium instead of the other.     

An assessment of initial body size in loggerhead sea turtle (Caretta caretta) hatchlings in Turkey

Eggs, hatchlings, and adult loggerhead turtles, and incubation durations of clutches, were measured on three Turkish beaches (Dalyan, Fethiye and G?ksu Delta), and some physical features of nests were compared. These features were not statistically different among the beaches, except for nest depth and distance to the high water mark. There was a positive relationship between hatchling mass and egg size. The carapace length of hatchlings was correlated with both egg diameter and incubation duration. The duration of asynchronous emergence of hatchlings on Fethiye beach was slightly longer than on the other two beaches, and the size of hatchlings decreased as asynchronous emergence proceeded. Of the hatchlings that emerged first, those that died were significantly smaller in SCL and mass than those that lived. These results suggest that smaller hatchlings may not be vigorous enough to emerge earlier from nests, and that they may be less fit.     

The influence of hydric environments during egg incubation on embryonic heart rates and offspring phenotypes in a scincid lizard (Lampropholis guichenoti)

Extensive evidence shows that incubation conditions can affect phenotypic traits of hatchling reptiles, but the relative importance of thermal versus hydric factors, and the proximate mechanisms by which such factors influence hatchling phenotypes, remain unclear for most species. We incubated eggs of an Australian scincid lizard, Lampropholis guichenoti, at four different moisture contents ranging from -500 to 0 kPa. Drier substrates reduced water uptake of eggs and resulted in smaller hatchlings, but other phenotypic traits (incubation periods, hatchling sex, body proportions, running speeds, growth rates post-hatching) were not affected by the hydric environment during incubation. Contrary to our prediction, lower water uptake during incubation (and hence, presumably, more viscous blood) did not affect embryonic heart rates. Thus, as in many other squamate species, hatchling phenotypes and embryonic developmental rates of L. guichenoti are less sensitive to hydric conditions in the nest than to thermal regimes.     

Do changing moisture levels during incubation influence phenotypic traits of hatchling snakes (Tropidonophis mairii, Colubridae)?

Phenotypic traits (e.g., size, strength, speed) of hatchlings in many reptile species are influenced by hydric conditions in the nest. Previous experiments have focused on comparisons between eggs maintained under constant (but different) conditions, but eggs in natural nests frequently experience strong temporal shifts in soil water content during incubation. Keelback snakes (Tropidonophis mairii) in the Australian wet-dry tropics nest over most of the year, so early nests experience decreasing water availability during development, late nests experience increases, and others (midyear) remain stable in this respect. We mimicked these three conditions and incubated 54 eggs (nine from each of six clutches) in a split-clutch design to maintain the same average water content but with differing trajectories through incubation. The experimental treatments significantly affected the total amount of water taken up by the eggs (and thus final egg mass), but incubation periods were unaffected. Hatchling size but not strength showed minor but statistically significant effects of incubation regimes. The ability of keelback eggs to take up excess water whenever it becomes available (either early or late in development) and to retain it even when conditions change buffers embryogenesis effectively (but not completely) against fluctuations in soil water conditions.     

孵化水热环境对渔异色蛇孵化卵和孵出幼体的影响

渔异色蛇卵孵化时能从环境中吸收水分导致质量增加,卵质量的增加与初始卵质量和孵化基质湿度有关。较大幅度的孵化基质湿度变化对孵化期、孵化成功率、胚胎动用孵内物质和能量、孵出幼体的性比、大小和质量无显著影响。孵化期随温度升高而缩短,并显示极强的窝间差异。温度对孵出幼体的性别无影响,但显著影响孵化成功率、胚胎对卵内物质和能量的动用、幼体的大小和质量、躯干和剩余卵黄的质量。孵出幼体总长的两性差异不显著,但雌体体长大于雄体而尾长小于雄体。３２℃不适于孵化渔异色蛇卵,该温度下孵出的幼体躯干发育不良,剩余孵黄较多,尾部均呈畸形,孵化过程中能量转化率较低。２４℃和２６℃中孵出的幼体躯干发育良好,孵化过程中能量转化率较高,各项被测定的幼体特征指标均极相似。     

Comparisons of egg incubation and hatchling traits among captive cohorts of the Chinese three-keeled pond turtle, Chinemys reevesii

Freshly-laid eggs of the Chinese three-keeled pond turtle (Chinemys reevesii) from captive cohorts in Hunan, Shanghai and Jiangxi were incubated at four constant temperatures of 24, 26, 28 and 30 °C to assess the effects of incubation temperature and cohort origin on incubation duration and hatchling phenotypes. Eggs from the three cohorts differed in size and shape. Egg mass and width were greatest in the Hunan cohort, smallest in the Jiangxi cohort, with the Shanghai cohort in between. Incubation duration decreased with increasing temperature and differed among the cohorts, with longer incubation duration for eggs from the Jiangxi cohort than those from the Hunan or Shanghai cohorts. Incubation temperatures significantly affected hatchling size and hatchlings from 30 °C were smaller than those from the lower temperatures in terms of carapace size and body mass. When incubated at a common temperature, hatchlings from the Hunan and Shanghai cohorts were larger than those from the Jiangxi cohort. The swimming capacity of hatchlings was affected by incubation temperature, but did not differ among the cohorts. The characteristics of eggs and hatchlings were similar among the Hunan and Shanghai cohorts, but they differed significantly from the Jiangxi cohort.     

Comparisons of egg incubation and hatchling traits among captive cohorts of the Chinese three-keeled pond turtle, Chinemys reevesii

Freshly-laid eggs of the Chinese three-keeled pond turtle (Chinemys reevesii) from captive cohorts in Hunan, Shanghai and Jiangxi were incubated at four constant temperatures of 24, 26, 28 and 30 °C to assess the effects of incubation temperature and cohort origin on incubation duration and hatchling phenotypes. Eggs from the three cohorts differed in size and shape. Egg mass and width were greatest in the Hunan cohort, smallest in the Jiangxi cohort, with the Shanghai cohort in between. Incubation duration decreased with increasing temperature and differed among the cohorts, with longer incubation duration for eggs from the Jiangxi cohort than those from the Hunan or Shanghai cohorts. Incubation temperatures significantly affected hatchling size and hatchlings from 30 °C were smaller than those from the lower temperatures in terms of carapace size and body mass. When incubated at a common temperature, hatchlings from the Hunan and Shanghai cohorts were larger than those from the Jiangxi cohort. The swimming capacity of hatchlings was affected by incubation temperature, but did not differ among the cohorts. The characteristics of eggs and hatchlings were similar among the Hunan and Shanghai cohorts, but they differed significantly from the Jiangxi cohort.     

Wetness of the nest environment influences cardiac development in pre- and post-natal snapping turtles (Chelydra serpentina)

We dissected hearts from near-term embryos and hatchlings of common snapping turtles (Chelydridae: Chelydra serpentina) whose eggs had incubated on wet or dry substrates, and then dried and individually weighed the heart and yolk-free carcass from each animal. Hearts and carcasses of prenatal and neonatal animals grew at different rates, and the patterns of growth by both heart and carcass differed between wet and dry environments. Hearts grew faster, both in actual mass and in mass adjusted for variation in body size, in embryos and hatchlings whose eggs were incubated on dry substrates than in animals whose eggs were held on wet media. This finding is consistent with a hypothesis that embryos incubating in dry settings experience hypovolemia secondary to dehydration and that enlargement of the heart compensates, in part, for the associated increase in viscosity of the blood. Embryonic turtles seemingly exhibit the same plasticity and response that would be expected from other vertebrate ectotherms subjected to the physiological challenges associated with desiccation and an associated reduction in blood volume.     

Incubation of eggs of tuatara, Sphenodon punctatus

Eggs of the tuatara, Sphenodon punctatus , were incubated either buried or half buried in vermiculite at constant temperatures of 15, 18, 20, 22 and 25 °C and constant water potentials between —90 and —400 kPa. Many clutches failed completely, possibly because they had been taken from females prior to proper shell development. Failed eggs were significantly smaller than successful eggs. Incubation is unsuccessful at 15 °C. Hatching success is high between 18 and 22 °C but low at 25 °C, but equally successful between 18 and 22°C. Incubation is strongly influenced by temperature, with mean incubation periods of 328 days at 18 °C, 259 days at 20 °C, 169 days at 22 °C and 150 days at 25 °C. Water potential generally has little influence on incubation time at a given temperature. Buried eggs hatch sooner than partially buried eggs at 20 °C but the large range makes significance dubious.
Eggs on the driest substrata at 18 and 20 °C lose water initially but then gain water through the rest of incubation. Eggs in all other conditions gain water throughout incubation, with the rate of i water absorption being maintained or increasing late in incubation. The suggestion that increasing rate of water absorption late in incubation facilitates explosive hatching is not supported. Egg mass at the time of hatching varies from 132 to 398% of initial values, depending on incubation conditions. Final egg mass is not affected significantly by incubation temperature. Hence, rates of absorption increase with temperature.
Water potential has no influence on hatchling size. However, hatchlings from buried eggs generally are significantly larger than those from partially buried eggs.     

孵化温度对王锦蛇胚胎代谢和幼体适合度的影响

孵化温度所驱动的爬行动物的表型变异是生理生态学研究的热点。本研究以王锦蛇(Elaphe carinata)为实验动物,检验了24℃和28℃孵化温度对王锦蛇胚胎代谢速率、孵化过程中的卵重量、孵出幼体代谢和行为的影响。研究结果显示:卵重和胚胎的呼吸代谢均与孵化时间呈正相关;28℃下胚胎代谢速率大于24℃;幼蛇孵出15 d内体重随着生长时间的延长而减小,24℃孵出幼体的代谢速率大于28℃孵出幼体,两温度下孵出幼体的呼吸代谢速率和生长时间无显著关系;28℃孵出幼体的疾游速和吐信频次均大于24℃;两孵化温度孵出幼体的选择体温无显著差异,但在消耗完体内的剩余卵黄后28℃孵出幼体有60%的个体摄食,而24℃孵出幼体无摄食个体。总体而言,王锦蛇28℃孵出幼体适合度优于24℃孵出幼体。     

Influence of the nest environment on bone mineral content in hatchling painted turtles (Chrysemys picta)

We performed an experiment at a field site in north-central Nebraska to assess the role of the nest environment in inducing variation in bone mineral content in hatchling painted turtles Chrysemys picta (Schneider 1783). The contents of several newly constructed nests were manipulated by reciprocal transplant, after which the eggs were allowed to incubate for 8 wk under natural conditions. The nests were then excavated, and the eggs were brought into the laboratory to complete incubation and hatch under standard conditions of temperature and moisture. The hatchlings were killed, and their carcasses and residual yolks were analyzed separately for calcium and phosphorus. More of the random variation in carcass calcium and phosphorus was related to the nest in which eggs incubated (37% and 42%, respectively) than was associated with the clutch of origin (21% and 37%). Moreover, hatchlings from some nests contained substantially more calcium and phosphorus than did hatchlings from other nests, both in terms of the absolute amounts of the elements in their carcasses (pointing to variation in body size) and in terms of the concentrations of those elements (pointing to variation in bone density). The amounts of calcium and phosphorus in carcasses of hatchlings were positively correlated with changes in mass of their eggs during the 8 wk that the eggs incubated in nests in the field, thereby indicating that the influence of the nest environment on developing embryos probably was mediated by water exchanges experienced by the eggs. These findings indicate that developmental plasticity underlies a major fraction of the variation in mineral content of hatchling painted turtles emerging from nests in the field. Phenotypic variation attributable to plasticity consequently needs to be addressed in models for life-history evolution of painted turtles and other chelonians producing eggs with soft, flexible shells.     

Incubation of rigid-shelled turtle eggs: do hydric conditions matter?

Rigid-shelled eggs of the broad-shelled river turtle Chelodina expansa were incubated at 28 degrees C in wet (-100 kPa), intermediate (-350 kPa) and dry (-750 kPa) conditions. Incubation period was influenced by clutch of origin, but was independent of incubation water potential. Rates of water gained from the environment and pre-pipping egg mass were influenced by incubation water potential -- eggs incubating at higher (less negative) water potentials absorbing more water from their environment. Hatchlings from wet conditions had greater mass but a smaller amount of residual yolk than hatchlings from dry conditions and it is suggested that the amount of yolk converted to tissue is influenced by the amount of water absorbed by the egg during incubation. Water content of yolk-free hatchlings from the -100-kPa treatment was greater than those from the -350-kPa and -750-kPa treatments, but the water content of residual yolks was similar across all hydric conditions.