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     

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.     

Heart rate during development in the turtle embryo: effect of temperature

 Growth and development can occur over a wide range of physical conditions in reptiles. Cardiovascular function must be critical to this ability. However, information on cardiovascular function in developing reptiles is lacking. Previous work indicated that in reptiles the effects of temperature on growth and metabolism are largely restricted to early development. This study examined whether the previously observed effects of temperature and different perinatal patterns of metabolism observed in amniotic vertebrates are correlated with cardiovascular function. Embryonic and hatchling carcass mass, heart mass and heart rate (HR) were compared for snapping turtle eggs (Chelydra serpentina) incubated at 24 ° and 29 °C. Incubation time was shorter at 29 °C (56.2 days) than at 24 °C (71.1 days). Carcass and heart growth showed a sigmoidal pattern at both temperatures. However, cardiac growth showed a relative decrease as incubation proceeded. Incubation temperature significantly affected the HR pattern during development. The HR of embryos incubated at 24 °C was constant for most of incubation (51.8±4.8 min^-1). A small decrease was observed just prior to and a large decrease immediately following hatching (posthatch, 22.3±4.1 min^-1). At 29 °C embryonic HR was greater than at 24 °C early in development (72.3±3 min^-1). The HR steadily decreased to values equivalent to those at 24 °C. The HRs of 24 °C and 29 °C hatchlings were not different. Cardiac output (estimated as the product of heart mass and HR) increased rapidly during early development and then slowed dramatically at both temperatures. These data are consistent with the suggestion that temperature exerts its effects primarily early in development. Furthermore, the changes in cardiovascular function are correlated with metabolic changes in hatching vertebrates. Accepted:12 June 1996     

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.     

温度、湿度对黄喉拟水龟胚胎发育的影响

在9种不同温湿度组合条件（25 ℃和-12 kPa、29 ℃和-12 kPa、33 ℃和-12 kPa、25 ℃和-150 kPa、29 ℃和-150 kPa、33 ℃和-150 kPa、25 ℃和-300 kPa、29 ℃和-300 kPa、33 ℃和-300 kPa）下孵化了黄喉拟水龟卵,研究了温度对黄喉拟水龟卵孵出幼体特征的影响及其与湿度的相互作用对孵化期、孵化成功率和孵出幼体特征的影响.结果表明：黄喉拟水龟卵的初始质量、孵化温度、湿度及温湿度相互作用均显著影响孵化过程中卵质量的增加;同一温度下,孵化湿度越高,卵的终末质量越大;而孵化卵的终末质量与孵化温度并不呈线性相关;孵化温度显著影响黄喉拟水龟卵的孵化期,温度越高、孵化期越短,孵化湿度及温湿度相互作用对孵化期的影响不显著;孵化温度和湿度显著影响孵化成功率和卵壳龟裂率;25 ℃和33 ℃处理组孵出幼体中发现畸形个体,而29 ℃处理组中未发现;孵化温度显著影响孵出幼体的质量、背甲长和宽、腹甲长和宽、体高和尾长;孵化湿度只对孵出幼体的背甲长有影响,对其他被检测的幼体特征无显著影响;温湿度的相互作用对所有被检测的孵出幼体特征无叠加或减弱的显著影响.     

Incubation temperature affects hatching success,embryonic expenditure of energy and hatchling phenotypes of a prolonged egg-retaining snake,Deinagkistrodon acutus (Viperidae)

We used eggs of Deinagkistrodon acutus to study the effects of incubation temperature on hatching success, embryonic expenditure of energy and hatchling phenotypes. One egg from each of the 15 fertile clutches was dissected for determination of egg composition, and a total of 164 eggs were incubated at five constant temperatures. Embryonic mortality increased dramatically at 30 °C, and none of eggs incubated at 32 °C hatched. Within the range from 24 to 30 °C, temperature affected incubation length and most hatchling traits examined. The mean incubation length at 24, 26, 28 and 30 °C was 36.4, 28.7, 21.8 and 15.7 days, respectively. Embryos developing at higher temperatures (28 and 30 °C) consumed more energy but produced less developed (and hence smaller) hatchlings, which characteristically had larger residual yolks but smaller carcasses. A principal component analysis resolved two components (with eigenvalues ⩾1) from ten size (initial egg mass)-free hatchling variables, accounting for 79.3% of variation in the original data. The first component (43.8% variance explained) had high positive loading for size-free values of dry mass, lipid mass, energy contents and ash mass of hatchlings, and the second component (35.5% variance explained) had high positive loading for size-free values of SVL, carcass dry mass and fatbody dry mass. Hatchlings from different incubation temperatures did not differ in scores on the first axis of the principal component analysis, whereas hatchlings from higher incubation temperatures (28 and 30 °C) had significantly lower scores on the second axis than did those from lower incubation temperatures (24 and 26 °C). As the second axis mainly represents traits relating to the developmental condition at hatching, the analysis therefore provided further evidence that eggs incubated at higher temperatures produced less developed hatchlings. Taken together, our data show that the optimal temperatures for embryonic development are relatively low in D. acutus largely due to its use of relatively cool habitats.     

Incubation temperature and phenotypic traits of Sceloporus undulatus: implications for the northern limits of distribution

Cold environmental temperature is detrimental to reproduction by oviparous squamate reptiles by prolonging incubation period, negatively affecting embryonic developmental processes, and by killing embryos in eggs directly. Because low soil temperature may prevent successful development of embryos in eggs in nests, the geographic distributions of oviparous species may be influenced by the thermal requirements of embryos. In the present study, we tested the hypothesis that low incubation temperature determines the northern distributional limit of the oviparous lizard Sceloporus undulatus. To compare the effects of incubation temperature on incubation length, egg and hatchling survival, and hatchling phenotypic traits, we incubated eggs of S. undulatus under temperature treatments that simulated the thermal environment that eggs would experience if located in nests within their geographic range at 37°N and north of the species’ present geographic range at latitudes of 44 and 42°N. After hatching, snout–vent length (SVL), mass, tail length, body condition (SVL relative to mass), locomotor performance, and growth rate were measured for each hatchling. Hatchlings were released at a field site to evaluate growth and survival under natural conditions. Incubation at temperatures simulating those of nests at 44°N prolonged incubation and resulted in hatchlings with shorter SVL relative to mass, shorter tails, shorter hind limb span, slower growth, and lower survival than hatchlings from eggs incubated at temperatures simulating those of nests at 37 and 42°N. We also evaluated the association between environmental temperature and the northern distribution of S. undulatus. We predicted that the northernmost distributional limit of S. undulatus would be associated with locations that provide the minimum heat sum (∼495 degree-days) required to complete embryonic development. Based on air and soil temperatures, the predicted northern latitudinal limit of S. undulatus would lie at ∼40.5–41.5°N. Our predicted value closely corresponds to the observed latitudinal limit in the eastern United States of ∼40°N. Our results suggest that soil temperatures at northern latitudes are not warm enough for a sufficient length of time to permit successful incubation of S. undulatus embryos. These results are consistent with the hypothesis that incubation temperature is an important factor limiting the geographic distributions of oviparous reptile species at high latitudes and elevations.     

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。     

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。     

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。     

Embryonic development rate and hatchling phenotypes in the Chinese three-keeled pond turtle (Chinemys reevesii): The influence of fluctuating temperature versus constant temperature

Although the effects of constant temperatures on hatchling traits have been extensively studied in reptiles, the effects of fluctuating temperatures remain poorly understood. Eggs of the Chinese three-keeled pond turtle (Chinemys reevesii) were incubated at a constant temperatures (28 °C) and two fluctuating temperatures (28±3 °C and 28±6 °C) to test for the influence of thermal environment on incubation duration, hatchling traits, and post-hatching growth. Incubation duration was shorter at constant temperature than at fluctuating temperatures. The sex ratio of hatchlings varied among temperature treatments, with more females from 28±6 °C than from 28 °C. The size and mass were greater for hatchlings from a constant temperature than from fluctuating ones, but this difference in body size disappeared when the hatchlings were 3 months old. In addition, the swimming ability, survival, and growth of hatchlings from fluctuating temperatures did not differ from those of hatchlings from constant temperature, when they were kept at an artificial environment without food scarcity or predation. Therefore, the thermal environments with various temperature fluctuations used in this study do not significantly affect fitness-related hatchling traits in this species.     

EXPERIMENTAL EVIDENCE FOR THE EVOLUTIONARY SIGNIFICANCE OF TEMPERATURE-DEPENDENT SEX DETERMINATION

The evolutionary significance of sex-determining mechanisms, particularly temperature-dependent sex determination (TSD) in reptiles, has remained unresolved despite extensive theoretical work. To investigate the evolutionary significance of this unusual sex-determining mechanism, I incubated eggs of the common snapping turtle (Chelydra serpentina) at a male-producing temperature (26°C), a female-producing temperature (30°C), and an intermediate temperature that produced both sexes about equally (28°C). Laboratory experiments indicated that two performance variables, but no morphological measurements, were significantly influenced by incubation temperature (P ≤ 0.05): hatchlings from cooler incubation treatments swam faster than turtles from warmer incubation treatments, and hatchlings from 28°C exhibited a greater propensity to run than did individuals from 26°C and 30°C. In the field, hatchlings from the all-male and all-female producing temperatures had significantly higher first-year survivorship than did consexuals from the incubation temperature that produced both sexes (G = 6.622, P = 0.03). Significant directional selection was detected on propensity of hatchlings to run (β′ = –0.758, P = 0.05): turtles that tended to remain immobile had a higher probability of first-year survivorship than did individuals that moved readily. Thus, the effects of the gender × incubation temperature interaction on survivorship of hatchling turtles observed in the field experiment may have been mediated by temperature-dependent antipredator behavior. These results provide a possible functional explanation for the evolutionary significance of TSD in turtles that is consistent with predictions of theoretical models.     

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.     

Effects of incubation temperature on hatchling phenotypes in an oviparous lizard with prolonged egg retention: are the two main hypotheses on the evolution of viviparity compatible?

Females of several lizard species modify their body temperature during pregnancy, probably in connection with the optimisation of hatchling phenotypes. We studied variations in the temperature selected by gravid females compared with those selected by males and non-gravid females in an oviparous population of Zootoca vivipara (Jacquin, 1797) (Squamata: Lacertidae) of Northern Spain and examined the effects of incubation temperature on the phenotypic variation of hatchlings. Cloacal temperatures of gravid females active in the field were lower than those of males and non-gravid females, as well as the temperatures selected in a thermal gradient created in the laboratory (mean±s.d.: 32.33±1.27 °C for gravid females; 34.05±1.07 °C for males and non-gravid females). Effects of temperature were assessed by incubating eggs at five constant temperatures (21, 25, 29, 32 and 34 °C). Incubation time decreased as temperature increased, following a negative exponential function. Incubation temperatures also affected the hatchlings’ morphology: hatchlings incubated at 34 °C had shorter heads than those from other temperatures. Survival at 34 °C (58%) was significantly lower than at the other temperatures (mean 93%). Pregnant females select lower body temperature, approaching the temperatures that optimise hatchling phenotypes, according to predictions of the maternal manipulation hypothesis on the evolution of viviparity. The shift in preferred temperature by pregnant females would result in only a very short delay, if any, of hatching time and, because the temperature selected by pregnant females is much higher than average temperatures recorded in natural nests of Z. vivipara, egg retention considerably shortens incubation time, according to predictions of the cold-climate hypothesis. Our experimental results indicate that the two main hypotheses on the evolution of viviparity are compatible in our study model.     

Direct effects of incubation temperature on morphology,thermoregulatory behaviour and locomotor performance in jacky dragons (Amphibolurus muricatus)

Incubation temperature is one of the most studied factors driving phenotypic plasticity in oviparous reptiles. We examined how incubation temperature influenced hatchling morphology, thermal preference and temperature-dependent running speed in the small Australian agamid lizard Amphibolurus muricatus. Hatchlings incubated at 32 °C grew more slowly than those incubated at 25 and 28 °C during their first month after hatching, and tended to be smaller at one month. These differences were no longer significant by three months of age due to selective mortality of the smallest hatchlings. The cooler incubation treatments (25 °C and 28 °C) produced lizards that had deeper and wider heads. Hatchlings from 28 °C had cooler and more stable temperature preferences, and also had lower body temperatures during a 2-h thermoregulatory behaviour trial. Locomotor performance was enhanced at higher body temperatures, but incubation temperature had no measurable effect either independently or in interaction with body temperature. Our study demonstrates that incubation temperature has direct effects on morphology and thermoregulatory behaviour that appears to be independent of any size-dependent effects. We postulate a mechanistic link between these two effects.     

Effects of constant and fluctuating incubation temperatures on hatching success and hatchling traits in the diamondback terrapin (Malaclemys terrapin) in the context of the warming climate

As global temperatures continue to rise, so too will the nest temperatures of many species of turtles. Yet for most turtle species, including the estuarine diamondback terrapin (Malaclemys terrapin), there is limited information on embryonic sensitivity to elevated temperature. We incubated eggs of M. terrapin at three, mean temperatures (31, 34, 37 °C) under two thermal exposure regimes (constant or semi-naturally fluctuating temperature) and measured hatching success, developmental rate, and hatchling size. Hatching success was 100% at 31 °C and 67% at 34 °C, respectively; at 37 °C, all eggs failed early in the incubation period. These values were unaffected by exposure regime. The modeled LT₅₀ (temperature that was lethal to 50% of the test population) was 34.0 °C in the constant and 34.2 °C in the fluctuating thermal regime, reflecting a steep decline in survival between 33 and 35 °C. Hatchlings having been incubated at a constant 34 °C hatched sooner than those incubated at 31 °C under either constant or fluctuating temperature. Hatchlings were smaller in straight carapace length (CL) and width after having been incubated at 34 °C compared to 31 °C. Larger (CL) hatchlings resulted from fluctuating temperature conditions relative to constant temperature conditions, regardless of mean temperature. Based upon recent temperatures in natural nests, the M. terrapin population studied here appears to possess resiliency to several degrees of elevated mean nest temperatures, beyond which, embryonic mortality will likely sharply increase. When considered within the mosaic of challenges that Maryland's M. terrapin face as the climate warms, including ongoing habitat losses due to sea level rise and impending thermal impacts on bioenergetics and offspring sex ratios, a future increase in embryonic mortality could be a critical factor for a population already experiencing ecological and physiological challenges due to climate change.     

Influence of incubation temperature on morphology, locomotor performance, and early growth of hatchling wall lizards (Podarcis muralis)

Eggs of wall lizards (Podarcis muralis) were incubated at three temperatures approaching the upper limit of viability for embryonic development in this species (26, 29, and 32 degrees C) to assess the influence of temperature on various aspects of hatchling phenotype likely affecting fitness. The thermal environment affected size and several morphometric characteristics of hatchling lizards. Hatchlings from eggs incubated at 32 degrees C were smaller (snout-vent length, SVL) than those from 26 and 29 degrees C and had smaller mass residuals (from the regression on SVL) as well as shorter tail, head, and femur relative to SVL. Variation in the level of fluctuating asymmetry in meristic and morphometric traits associated with incubation temperatures was quite high but not clearly consistent with the prediction that environmental stress associated with the highest incubation temperatures might produce the highest level of asymmetry. When tested for locomotor capacity in trials developed at body temperatures of 32 and 35 degrees C, hatchlings from the 32 degrees C incubation treatment exhibited the worst performance in any aspect considered (burst speed, maximal length, and number of stops in the complete run). Repeated measures ANCOVAs (with initial egg mass as covariate) of snout-vent length and mass of lizards at days 0 and 20 revealed significant effects of incubation temperature only for mass, being again the hatchlings from eggs incubated at 32 degrees C those exhibiting the smallest final size. All together, our results evidenced a pervasive effect of thermal regime during incubation (and hence of nest site selection) on hatchling phenotypes. However, incubation temperature does not affect hatchling phenotypes in a continuous way; for most of the analysed traits a critical threshold seems to exist between 29 and 32 degrees C, so that hatchlings incubated at 32 degrees C exhibited major detrimental effects. J. Exp. Zool. 286:422-433, 2000.     

The variance of incubation temperatures does not affect the phenotype of hatchlings in a colubrid snake, Xenochrophis piscator

It has been documented in some reptiles that fluctuating incubation temperatures influence hatchling traits differently than constant temperatures even when the means are the same between treatments; yet whether the observed effects result from the thermal variance, temperature extremes or both is largely unknown. We incubated eggs of the checkered keelback snake Xenochrophis piscator under one fluctuating (Ft) and three constant (24, 27 and 30 °C) temperatures to examine whether the variance of incubation temperatures plays an important role in influencing the phenotype of hatchlings. The thermal conditions under which eggs were incubated affected a number of hatchling traits (wet mass, SVL, tail length, carcass dry mass, fatbody dry mass and residual yolk dry mass) but not hatching success and the sex ratio of hatchlings. Body sizes were larger in hatchlings from incubation temperatures of 24 and 27 °C compared with the other two treatments. Hatchlings from the four treatments could be divided into two groups: one included hatchlings from the 24 and 27 °C treatments, and the other included hatchlings from the 30 °C and Ft treatments. In the Ft treatment, the thermal variance was not a significant predictor of all examined hatchling traits, and incubation length was not correlated with the thermal variance when holding the thermal mean constant. The results of this study show that the mean rather than the variance of incubation temperatures affects the phenotype of hatchlings.     

Accumulation of lactate by supercooled hatchlings of the painted turtle (Chrysemys picta): implications for overwinter survival

Hatchlings of the North American painted turtle (Chrysemys picta) typically spend their first winter of life inside the shallow, subterranean nest where they completed embryogenesis the preceding summer. Neonates at northern localities consequently may be exposed during winter to subzero temperatures and frozen soil. Hatchlings apparently survive exposure to such conditions by supercooling, but the physiological consequences of this adaptive strategy have not been examined. We measured lactate in hatchling painted turtles after exposure to each of three temperatures (0 °C, −4 °C, and −8 °C) for three time periods (5 days, 15 days, and 25 days) to determine the extent to which overwintering hatchlings might rely on anaerobic metabolism to regenerate ATP. Whole-body lactate increased with increasing duration of exposure and decreasing temperature, and the highest levels were associated with the group that experienced the highest mortality. These results indicate that animals may develop a considerable lactic acidosis during a winter in which temperatures fall below 0 °C for weeks or months and that accumulation of lactate may contribute to mortality of overwintering animals. Accepted: 20 October 1999