Effects of seasonally varying hydric conditions on hatchling phenotypes of keelback snakes (Tropidonophis mairii, Colubridae) from the Australian wet-dry tropics

Does water availability during incubation significantly affect the phenotypes of hatchling reptiles in natural nests? Two obstacles to obtaining any general answer to this question are the scarcity of studies on tropical species, and the difficulty of comparing experimental treatments to actual hydric conditions in nature. We used a split‐clutch design to incubate 102 eggs (eight clutches) of a colubrid snake species (the keelback, Tropidonophis mairii), from a floodplain in the Australian wet‐dry tropics. This species breeds over most of the year, and highly seasonal rainfall regimes generate strong shifts in water content of the soil over this period. We measured soil water content in a natural nest, and incubated eggs in both soil and vermiculite (the usual medium for experimental studies) at a range of water contents. These calibration trials let us compare our experimental ‘wet’ and ‘dry’ incubation treatments to conditions in natural nests, in terms of actual water uptake by eggs. Hatchlings from dry incubation were unable to resorb their desiccated yolk and thus were smaller (17% in mass, 12% in body length) than their siblings from moist substrates. Incubation conditions also affected the hatchlings’ muscular strength and locomotor speed: even at the same body length, dry‐incubated hatchlings were weaker and slower than their wet‐incubated siblings. Incubation moisture affected strength differently in males and females. We conclude that seasonal variation in water content of the soil in natural nests can generate strong phenotypic variation in hatchling snakes. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76 , 339–347.     

Egg environments have large effects on embryonic development,but have minimal consequences for hatchling phenotypes in an invasive lizard

Plastic responses of embryos to developmental environments can shape phenotypes in ways that impact fitness. The mechanisms by which developmental conditions affect offspring phenotypes vary substantially among taxa and are poorly understood in most systems. In this study, we evaluate the effects of thermal and hydric conditions on patterns of egg water uptake, embryonic development and yolk metabolism in embryos of the lizard Anolis sagrei to gain insights into how these factors shape morphological variation in hatchlings. Our 3 × 2 experimental design (3 thermal and 2 hydric conditions) revealed that developmental temperature has strong effects on rates of development and yolk metabolism, but the impacts of moisture were minimal. Increased water uptake by eggs under relatively wet conditions resulted in larger hatchlings with less internalized residual yolk than hatchlings from dry‐incubated eggs. However, the relatively small phenotypic differences among treatments may have small fitness consequences. These results demonstrate that embryos of A. sagrei can tolerate a broad range of environmental conditions without substantial impacts on critical morphological traits. Such embryonic tolerances may facilitate colonization and establishment in novel environments. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 25–41.     

Fluctuations in the incubation moisture environment affect growth but not survival of hatchling lizards

Few studies have collected longitudinal data that follow the complete microevolutionary path of an organism linking sources of variation (e.g. environmental versus genetic) to a trait and its subsequent relationship with fitness. Identifying the links within this pathway is imperative for understanding the ecological relevance of effects found at the phenotypic level. Furthermore, experimental studies that examine parts of the pathway in ectothermic organisms often fail to mimic the complexities of the natural developmental environment. Temperature and moisture conditions in reptile nests, for example, can fluctuate greatly on a seasonal and daily basis. Despite the potential effects of fluctuating environments, the vast majority of studies have held environmental treatments constant during the developmental period. We investigated the effects of fluctuating moisture regimes during incubation on eggs, hatchling phenotypes, and subsequent survival in the eastern fence lizard Sceloporus undulatus. Moisture fluctuations during embryonic development caused water absorption by eggs to follow the environmental availability of moisture. Initial hatchling tail length was affected by the pattern of moisture fluctuations, and hatchling growth rates in fluctuating treatments were significantly faster than those in a constant treatment, resulting in larger hatchlings after 4 weeks. A release–recapture experiment conducted in the field did not detect a treatment effect on survival despite the larger body sizes. In summary, although fluctuations affected water absorption by eggs and some hatchling traits, these effects did not have subsequent fitness consequences. The results obtained suggest that egg and hatchling survival are buffered against natural soil moisture fluctuations during incubation, even when egg and hatchling traits are significantly affected. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 89–102.     

The seasonal timing of oviposition in sand lizards (Lacerta agilis): why early clutches are better

We studied a population of sand lizards (Lacerta agilis) near the northern edge of the species' range in coastal Sweden. We captured, marked, released and recaptured 98 adult female lizards over 5 years. Hatchlings from 146 laboratory-incubated clutches (1279 eggs) from field-caught gravid females were measured, weighed, marked and released at the study site. Female sand lizards usually laid only a single clutch of 4 to 15 eggs each year, but varied considerably in the time of year at which they laid their eggs. Oviposition dates shifted between years depending on weather (basking opportunities), but the relative timing of oviposition was consistent within a given female from year-to-year. The first females to oviposit each year were large animals in good physical condition, that had grown rapidly in previous years. “Early” clutches were larger than “later” clutches, had higher hatching success, and tended to have higher post-hatching survival rates. Offspring from early clutches were larger than “later” hatchlings, and differed in body proportions (probably because seasonal changes in maternal temperatures directly modified offspring phenotypes). Overall, our study documents several strong correlates of the timing of oviposition, and suggests that variation in this trait among females has strong fitness consequences, perhaps related to maternal “quality”. The correlations we observed between oviposition date and other traits that have been invoked as determinants of hatchling survival in reptiles (e.g., hatchling size, body shape, opportunities for multiple mating by the mother) suggest that hypotheses advocating simple causal connections between these traits and hatchling success should be viewed with caution.     

Maternal influences on offspring phenotypes and sex ratios in a multi‐clutching lizard with environmental sex determination

Maternal and environmental factors are important sources of phenotypic variation because both factors influence offspring traits in ways that impact offspring and maternal fitness. The present study explored the effects of maternal factors (maternal body size, egg size, yolk‐steroid allocation, and oviposition‐site choice) and seasonally‐variable environmental factors on offspring phenotypes and sex ratios in a multi‐clutching lizard with environmental sex determination (Amphibolurus muricatus). Maternal identity had strong effects on offspring morphology, but the nature of maternal effects differed among successive clutches produced by females throughout the reproductive season (i.e. maternal identity by environment interactions). The among‐female and among‐clutch variation in offspring traits (including sex ratios) was not mediated through maternal body size, egg size, or variation in yolk steroid hormones. This lack of nongenetic maternal effects suggests that phenotypic variation may be generated by gene by environment interactions. These results demonstrate a significant genetic component to variation in offspring phenotypes, including sex ratios, even in species with environmental sex determination. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 256–266.     

Clutch size manipulation, hatching success and offspring phenotype in the ball python (Python regius)

In a diverse array of avian and mammalian species, experimental manipulations of clutch size have tested the hypothesis that natural selection should adjust numbers of neonates produced so as to maximize the number of viable offspring at the end of the period of parental care. Reptiles have not been studied in this respect, probably because they rarely display parental care. However, females of all python species brood their eggs until hatching, but they do not care for their neonates. This feature provides a straightforward way to experimentally increase or reduce clutch size to see whether the mean clutch size observed in nature does indeed maximize hatching success and/or optimize offspring phenotypes. Eggs were removed or added to newly laid clutches of Ball Pythons ( Python regius ) in tropical Africa (nine control clutches, eight with 50% more eggs added, six with 42% of eggs removed). All clutches were brooded by females throughout the 2-month incubation period. Experimental manipulation of clutch-size did not significantly affect the phenotypes (morphology, locomotor ability) of hatchlings, but eggs in 'enlarged' clutches hatched later, and embryos were more likely to die before hatching. This mortality was due to desiccation of the eggs, with females being unable to cover 'enlarged' clutches sufficiently to retard water loss. Our results support the notion of an optimal clutch size, driven by limitations on parental ability to care for the offspring. However, the proximate mechanisms that generate this optimum value differ from those previously described in other kinds of animals. © 2003 The Linnean Society of London . Biological Journal of the Linnean Society 2003, 78 , 263–272.     

Maternal investment in reproduction and its consequences in leatherback turtles

Maternal investment in reproduction by oviparous non-avian reptiles is usually limited to pre-ovipositional allocations to the number and size of eggs and clutches, thus making these species good subjects for testing hypotheses of reproductive optimality models. Because leatherback turtles (Dermochelys coriacea) stand out among oviparous amniotes by having the highest clutch frequency and producing the largest mass of eggs per reproductive season, we quantified maternal investment of 146 female leatherbacks over four nesting seasons (2001–2004) and found high inter- and intra-female variation in several reproductive characteristics. Estimated clutch frequency [coefficient of variation (CV) = 31%] and clutch size (CV = 26%) varied more among females than did egg mass (CV = 9%) and hatchling mass (CV = 7%). Moreover, clutch size had an approximately threefold higher effect on clutch mass than did egg mass. These results generally support predictions of reproductive optimality models in which species that lay several, large clutches per reproductive season should exhibit low variation in egg size and instead maximize egg number (clutch frequency and/or size). The number of hatchlings emerging per nest was positively correlated with clutch size, but fraction of eggs in a clutch yielding hatchlings (emergence success) was not correlated with clutch size and varied highly among females. In addition, seasonal fecundity and seasonal hatchling production increased with the frequency and the size of clutches (in order of effect size). Our results demonstrate that female leatherbacks exhibit high phenotypic variation in reproductive traits, possibly in response to environmental variability and/or resulting from genotypic variability within the population. Furthermore, high seasonal and lifetime fecundity of leatherbacks probably reflect compensation for high and unpredictable mortality during early life history stages in this species.     

Hatching success, delay of emergence and hatchling biometry of the spur-thighed tortoise, Testudo graeca, in south-western Spain

Hatching success, egg incubation, emergence and hatchling characteristics were assessed for 44 naturally incubating nests of Testudo graeca in south-western Spain. Nest predation rate was 4.5% and overall hatching success was 82.4%. Incubation periods ranged from 78 to 114 days, and hatchlings delayed emergence from the nest from one to 23 days. Emergences occurred from mid August to late September, and were not correlated with nesting dates, but earlier laid nests had longer incubation times, which was probably owing to lower temperatures experienced by clutches laid at the beginning of the nesting season. Variance of hatchling body size and mass was high and was mainly influenced by the gravid female. Mean straight carapace length was 34.14mm, and mean body mass 10.8g. Hatchlings from clutches laid last in the nesting season had significantly better physical condition. Hatchling mass was positively correlated with egg mass, and both variables were positively correlated with emergence date. Both better physical condition and relatively late emergence may confer advantages to hatchlings in the face of unfavourable environmental conditions in autumn.     

The influence of maternal thermal environments on reproductive traits and hatchling traits in a Lacertid lizard,Takydromus septentrionalis

The thermal environment can induce substantial variation in important life-history traits. Experimental manipulation of the thermal environment can help researchers determine the contribution of this factor to phenotypic variation in life-history traits. During the reproductive season, we kept female northern grass lizards, Takydromus septentrionalis (Lacertidae), in three temperature-controlled rooms (25, 28 and 32 °C) to measure the effect of the maternal thermal environment on reproductive traits. Maternal thermal environment remarkably affected reproductive frequency and thereby seasonal reproductive output, but had little effect on reproductive traits per clutch or hatchling traits. Females kept at 32 °C produced more clutches and thus had shorter clutch intervals than females from 28 to 25 °C. Clutch size, clutch mass, relative clutch mass, egg size and hatchling traits did not vary among the three treatments. The eggs produced by the females were incubated at 27 °C and the traits of hatchlings were measured. The result that egg (offspring) size was independent of maternal thermal environments is consistent with the prediction of the optimal egg size (offspring) theory. The eggs produced by low temperature females (28 and 25 °C) took longer time to complete their post-oviposition development than did eggs produced by high temperature females (32 °C). This suggests that the eggs from low temperatures might have been laid when the embryos were at relatively early stages. Therefore, maternal thermal environment prior to oviposition could affect post-oviposition development in T. septentrionalis.     

Maternal androgens in the pied flycatcher: timing of breeding and within-female consistency

Maternal hormones can have substantial phenotypic effects in the progeny of many vertebrates. It has been proposed that mothers adaptively adjust hormone levels experienced by particular young to optimize their reproductive output. In birds, systematic variation in egg hormone levels has been related to different female reproductive strategies. Because in many bird species prospects of the offspring change seasonally and with brood number, strategic adjustment of yolk androgen levels would be expected. To test this idea, we induced pied flycatcher (Ficedula hypoleuca) females to nest twice during the same season by removing their first clutches shortly after clutch completion. We collected eggs of first and replacement clutches to measure yolk concentrations of androstenedione (A4) and testosterone (T) and captured the females that laid these clutches for phenotypic measurements. Although average egg androgen levels were remarkably consistent within females, hormone patterns differed considerably between first and replacement clutches. Eggs of replacement clutches were heavier with larger yolks compared to first clutches, but they contained on average lower levels of androgens. Within clutches, androgen concentration increased over the laying sequence in the first clutch, but decreased or remained more constant over the laying sequence in the replacement clutch. Mean yolk T, but not A4 levels, were negatively associated with laying date for both breeding attempts. Moreover, females in good body condition produced eggs containing lower levels of androgens than females in poor condition. Our results are consistent with the idea that differences in yolk androgen levels may be one mechanism underlying seasonal variation in reproductive success and it is possible that changes in egg androgen patterns may reflect a change in female reproductive strategy. High within-female consistency also highlights the possibility that there may be some underlying genetic variation in yolk androgen levels.     

A novel hypothesis for the adaptive maintenance of environmental sex determination in a turtle

Temperature-dependent sex determination (TSD) is widespread in reptiles, yet its adaptive significance and mechanisms for its maintenance remain obscure and controversial. Comparative analyses identify an ancient origin of TSD in turtles, crocodiles and tuatara, suggesting that this trait should be advantageous in order to persist. Based on this assumption, researchers primarily, and with minimal success, have employed a model to examine sex-specific variation in hatchling phenotypes and fitness generated by different incubation conditions. The unwavering focus on different incubation conditions may be misplaced at least in the many turtle species in which hatchlings overwinter in the natal nest. If overwintering temperatures differentially affect fitness of male and female hatchlings, TSD might be maintained adaptively by enabling embryos to develop as the sex best suited to those overwintering conditions. We test this novel hypothesis using the painted turtle (Chrysemys picta), a species with TSD in which eggs hatch in late summer and hatchlings remain within nests until the following spring. We used a split-clutch design to expose field-incubated hatchlings to warm and cool overwintering (autumn–winter–spring) regimes in the laboratory and measured metabolic rates, energy use, body size and mortality of male and female hatchlings. While overall mortality rates were low, males exposed to warmer overwintering regimes had significantly higher metabolic rates and used more residual yolk than females, whereas the reverse occurred in the cool temperature regime. Hatchlings from mixed-sex nests exhibited similar sex-specific trends and, crucially, they were less energy efficient and grew less than same-sex hatchlings that originated from single-sex clutches. Such sex- and incubation-specific physiological adaptation to winter temperatures may enhance fitness and even extend the northern range of many species that overwinter terrestrially.     

Determinants of reproductive success and offspring sex in a turtle with environmental sex determination

Despite the importance of maternal effects in evolution, and knowledge of links among nest site choice, timing of nesting, offspring sex, and reproductive success in animals with environmental sex determination, these attributes have not been rigorously studied in a combined and natural context. To address this need we studied the relationships between three maternal traits (nest site choice, lay date, and nest depth) and two fitness‐related attributes of offspring (hatchling sex and embryonic survival) in the riverine turtle Carettochelys insculpta, a species with temperature‐dependent sex determination, for four years. Predation and flooding were the major sources of embryonic mortality in 191 nests. Embryonic survival was influenced by both lay date and nest site choice: in one year when nesting began later than average, nests laid later and at lower elevations were destroyed by early wet season river rises. In other years early nesting precluded flood mortality. However, turtles did not nest at the highest available elevations, and a field experiment confirmed that turtles were constrained to nest at lower elevations where they could construct a nest chamber. The principal determinant of hatchling sex in 140 nests was lay date, which in turn was apparently related to the magnitude of the previous wet season(s). Clutches laid earlier in the season (a female's first clutch) produced mainly males, while later clutches (her second clutch) yielded mostly females, due to seasonal increases in air temperatures. Accordingly, later nesting produced female‐biased hatchling sex ratios in 1996, while earlier nesting resulted in sex ratios near unity in the other years. However, all‐female nests were more likely to be flooded than mixed‐sex or all‐male nests in years when nesting was late. In conclusion, we found evidence that the position of two maternal trait distributions (elevation of the nest site and lay date), associated with the reproductive strategy of C. insculpta, reflect a combination of natural selection, physical constraints, and phenotypic plasticity. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81 , 1–16.     

Fitness of juvenile lizards depends on seasonal timing of hatching,not offspring body size

To understand how selection shapes life-history traits, we need information on the manner in which offspring phenotypes influence fitness. Life-history allocation models typically assume that “bigger offspring are better”, but field data paint a more complex picture: larger offspring size sometimes enhances fitness, and sometimes not. Additionally, higher survival and faster growth of larger offspring might be due to indirect maternal effects (e.g., mothers allocate hormones or nutrients differently to different-sized eggs), and not to offspring size per se. Alternative factors, such as seasonal timing of hatching, may be more important. We examined these issues using 419 eggs from captive jacky dragon lizards (Amphibolurus muricatus). The mothers were maintained under standardized conditions to minimize variance in thermal and nutritional history, and the eggs were incubated under controlled conditions to minimize variance in offspring phenotypes due to incubation temperature and moisture. We reduced the size of half the eggs (and, thus, the size of the resultant hatchlings) from each clutch by yolk extraction. The hatchlings were marked and released at a field site over a 3-month period, with regular recapture surveys to measure growth and survival under natural conditions. Growth rates and survival were strongly enhanced by early-season hatching, but were not affected by hatchling body size.     

The effects of incubation temperature on the morphology and composition of Australian Brush-turkey (<Emphasis Type="Italic">Alectura lathami</Emphasis>) chicks

Environmental heterogeneity during embryonic development generates an important source of variation in offspring phenotypes and can influence the evolution of life histories. The effects of incubation temperature on offspring phenotypes in reptiles has been well documented but remains relatively unexplored in birds as their embryos typically develop over a narrow range of temperatures. Megapode birds (Order Galliformes; Family Megapodiidae) are unique in that their embryos tolerate and develop over a wide range of incubation temperatures, yet little is known of the effect that temperature has on hatchling morphology and composition. Australian Brush-turkey eggs collected on the day of laying were incubated in the laboratory under constant temperatures of 32, 34 and 36°C until hatching in order to determine the influence of temperature on hatchling mass, size and composition. The dry mass of the yolk-free body and residual yolk of hatchlings were temperature dependent, such that higher temperatures produced chicks of lesser yolk-free body mass and greater residual yolk mass than chicks incubated at lower temperatures. However the overall size (linear dimensions) and lipid, protein and ash content of chicks were independent of temperature.     

ESTABLISHMENT OF WEIGHT HIERARCHIES IN THE BROODS OF HOUSE MARTINS DELICHON URBICA

Nestling birds may differ in size and weight on the first day a clutch is fully hatched, mainly because eggs within clutches hatch over a period of several days. This asynchronous pattern of hatching is usually thought to facilitate brood reduction when the food supply is unpredictably restricted. The purpose of the study reported here was to examine the contribution of egg-weight, clutch-size, hatching spread, food supply and season to weight differences in newly hatched broods of the House Martin. At laying, heavy eggs had a greater moisture and dry weight content than light eggs and immediately before hatching there was a correlation between initial egg-weight and the dry weight of embryo and yolk. Heavier clutches also tended to give rise to heavier hatchlings. There was, however, no correlation of fresh egg-weight with the dry weight of embryos alone and the relative dry weight of embryos in a clutch was dependent on laying sequence. Hatching spread (the number of days between the emergence from the egg of the first and the last hatchling of the clutch) was 0.75 ± 0.46 days for clutches of two and increased with the size of the clutch up to 1.80 ± 0.79 days for clutches of five. When food was scarce during laying, hatching spread was greater. Weight difference in newly hatched broods was correlated with hatching spread and moreover in multivariate analysis was also correlated with periods of food scarcity during laying. It was concluded that all examples of weight hierarchies among hatchlings should not be considered adaptive; in some cases they may be imposed by food scarcity. This can lead to mortality of the runs even if food is plentiful. When the weight hierarchy is not adversely accentuated by food scarcity it may function as previously suggested, to allow brood reduction. Alternatively, particularly among House Martins, it may spread out the peak food needs of individual nestlings thereby spreading the demand on the adults.     

Metabolic heating and the prediction of sex ratios for green turtles (Chelonia mydas)

We compared incubation temperatures in nests (n=32) of the green turtle (Chelonia mydas) on Ascension Island in relation to sand temperatures of control sites at nest depth. Intrabeach thermal variation was low, whereas interbeach thermal variation was high in both control and nest sites. A marked rise in temperature was recorded in nests from 30% to 40% of the way through the incubation period and attributed to metabolic heating. Over the entire incubation period, metabolic heating accounted for a mean rise in temperature of between 0.07 degrees and 2.86 degrees C within nests. During the middle third of incubation, when sex is thought to be determined, this rise in temperature ranged between 0.07 degrees and 2.61 degrees C. Metabolic heating was related to both the number of eggs laid and the total number of hatchlings/embryos produced in a clutch. For 32 clutches in which temperature was recorded, we estimate that metabolic heating accounted for a rise of up to 30% in the proportion of females produced within different clutches. Previous studies have dismissed any effect of metabolic heating on the sex ratio of marine turtle hatchlings. Our results imply that metabolic heating needs to be considered when estimating green turtle hatchling sex ratios.     

Effects of egg size and composition on the size, quality and survival of lapwing Vanellus vanellus chicks

The influence of egg size and composition on the size, quality and survival of lapwing chicks was examined on two farmland study sites in the Midland Valley of Scotland. Eggs comprised 33.1% yolk, 61.3% albumen and 5.6% shell. Whereas the yolk and shell proportions decreased with increasing egg size, the albumen proportion increased. Most variation in egg size was attributable to differences between females but was also influenced by clutch number (eggs in replacement clutches on the rough grazing, but not the arable, site were smaller), clutch size (eggs were smaller in smaller clutches), maternal body condition (females in good condition produced larger eggs) and habitat (since females on the arable site fed more successfully, they were in better condition and laid larger eggs). Chick size, weight and survival were all influenced by egg size. The incubation period varied between 21 and 28 days (mean = 25.2) and was shorter in clutches laid later in the season.     

Offspring size and timing of hatching determine survival and reproductive output in a lizard

Selection on offspring size and timing of birth or hatching could have important consequences for maternal investment strategies. Here we show consistent viability selection on hatchling body length across 2 consecutive years in a lizard that lays several clutches per season. There was no effect of hatching date on survival to maturity. However, both early hatching and large hatchling size increased adult size, which has a positive effect on total reproductive output. Earlier hatching also led to an earlier onset of reproduction. Overall, increased survival probability for large hatchlings and a positive effect of clutch size on recruitment suggest consistent directional selection on both egg size and clutch size within and across years. Because offspring size and timing of hatching are strongly affected by environmental and maternal effects, there should be potential for strong transgenerational effects on reproductive output in this species. We briefly discuss the implications of these results for the evolutionary ecology of maternal investment and population fluctuations in short-lived lizards.     

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.     

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。