Third Of Incubation Research Articles

Embryonic Thermal Manipulation Affects Ventilation, Metabolism, Thermal Control and Central Dopamine in Newly Hatched and Juvenile Chicks.

The first third of incubation is critical for embryonic development, and environmental changes during this phase can affect the physiology and survival of the embryos. We evaluated the effects of low (LT), control (CT), and high (HT) temperatures during the first 5 days of incubation on ventilation (E), body temperature (Tb), oxygen consumption (O2), respiratory equivalent (E/O2), and brain monoamines on 3-days-old (3d) and 14-days-old (14d) male and female chickens. The body mass of LT animals of both ages and sexes was higher compared to HT and CT animals (except for 3d males). The heart mass of 14d HT animals was higher than that of CT animals. Thermal manipulation did not affect E, O2 or E/O2 of 3d animals in normoxia, except for 3d LT males E, which was lower than CT. Regarding 14d animals, the HT females showed a decrease in E and O2 compared to CT and LT groups, while the HT males displayed a lower O2 compared to CT males, but no changes in E/O2. Both sexes of 14d HT chickens presented a greater Tb compared to CT animals. Thermal manipulations increased the dopamine turnover in the brainstem of 3d females. No differences were observed in ventilatory and metabolic parameters in the 3d animals of either sexes, and 14d males under 7% CO2. The hypercapnic hyperventilation was attenuated in the 14d HT females due to changes in O2, without alterations in E. The 14d LT males showed a lower E, during hypercapnia, compared to CT, without changes in O2, resulting in an attenuation in E/O2. During hypoxia, 3d LT females showed an attenuated hyperventilation, modulated by a higher O2. In 14d LT and HT females, the increase in E was greater and the hypometabolic response was attenuated, compared to CT females, which resulted in no change in the E/O2. In conclusion, thermal manipulations affect hypercapnia-induced hyperventilation more so than hypoxic challenge, and at both ages, females are more affected by thermal manipulation than males.

A Systematic Review of Metabolic Heat in Sea Turtle Nests and Methods to Model Its Impact on Hatching Success

JJust as organisms do not passively exist in their environment, developing sea turtle embryos affect their own incubation microclimate by producing metabolic heat and other waste products. This metabolic heat ultimately contributes to successful development, but it is unclear how it influences embryonic traits such as hatchling sex, and whether trends exist in the magnitude of metabolic heat produced by different species. In this systematic review, we document all empirical measurements of metabolic heat in sea turtle species, its impact on their development, and explore the methods used to predict nest temperature and how these methods account for metabolic heat. Overall we found metabolic heat increases throughout incubation in all seven species. Typically, the temperature at the center of an egg clutch peaked during the final third of incubation, and exceeded the adjacent sand temperature by 2.5°C. Metabolic heat was not influenced by species or clutch size (n = 16 studies), but this finding was likely influenced by inconsistency in the methods used to measure metabolic heat, and by localised differences in sand properties, such as moisture, albedo and thermal conductivity. The influence of metabolic heat on embryo sex determination and survival was dependent on the sand temperature surrounding the nest chamber, and had an appreciable affect only when it caused nest temperatures to exceed key thresholds for sex determination and survival. Correlative models describe relationships between empirical data to predict sand temperature, while mechanistic models are based on physical laws and do not require extrapolation when predicting novel situations, such as climate change. Methods for modelling nest temperature were either correlative (70% of publications) or mechanistic (30% of publications). Most correlative models (74%) accounted for metabolic heat when predicting nest temperatures, but no mechanistic models did – largely because they were developed for predicting primary sex ratios, which are widely believed to be unaffected by metabolic heat. Consequently, developing a generalisable mechanistic model that incorporates metabolic heat will be critical for predicting incubation success as the sand temperatures at sea turtle beaches increase due to anthropogenic climate change.

Effectiveness of shading to mitigate the impact of high temperature on sea turtle clutches considering the effect on primary sex ratios

Developmental success of sea turtle clutches depends on incubation temperature, which also determines sex ratio of hatchlings. As global temperatures are rising, several studies have proposed mitigation strategies such as irrigation and shading to increase hatching success. Our study expands upon this research and measures the effects of using boxes with different degrees of shade coverage (50%, 80%, and 90%) on sand temperature and water content. Boxes were fully covered with fabric in 2017/2018 (top and sides) but were side open in 2018/2019. We took measurements at olive ridley (Lepidochelys olivacea) and leatherback (Dermochelys coriacea) turtle nest depths (45 and 75 cm) at Playa Grande, Costa Rica. Shading reduced temperature by up to 0.8 °C and up to 0.4 °C at 45 cm and 75 cm, respectively. There were statistically significant differences between shading and control treatments at both depths, but differences between shade treatments were only significant when using side open boxes, possibly due to air flow. Shading had no effect on water content. While the impact of using shaded boxes on temperature was low, the potential impact on primary sex ratios was large. If shading were applied to leatherback clutches, the percentage of female hatchlings could vary by up to 50%, with a maximum difference around the pivotal temperature (temperature with 1:1 sex ratio). Shading can be useful to increase hatching success, but we recommend avoiding it at temperatures within the transitional range (temperatures that produce both sexes), or using it only during the last third of incubation, when sex is already determined. As global warming will likely continue, understanding potential impact and effectiveness of mitigation strategies may be critical for the survival of threatened sea turtle populations.

Relationship between Metabolic Heating and Nest Parameters in Green Turtles (Chelonia mydas, L. 1758) on Samandağ Beach, Turkey.

Acquiring information about metabolic heating is necessary for the improved understanding of nesting beaches. However, there are limited studies on metabolic heating of green turtle (Chelonia mydas, L. 1758) on Mediterranean beaches. The present study sought to determine the metabolic heating, and its effect on the feminization of green turtle hatchlings during 2016 and 2017 nesting season on Samandağ Beach, Hatay, Turkey. Moreover, the relations between metabolic heating and nest parameters, and spatio-temporal differences of metabolic heating were evaluated. Nest temperatures were recorded by using data loggers placed at the center of nests (n = 18), and the same depth was used to determine the sand temperature that was 50 cm back of the egg chamber. The mean incubation duration was calculated as 51.1 days, and the mean distance of nests from sea and the mean nest depth were measured as 32.4 meters and 67.70 cm, respectively. The mean numbers of embryo that is early, middle and late embryonic stages were found as 110.8, 93.2 and 93.05, respectively. The mean clutch size was found as 110.8. Mean metabolic heating was 0.37°C in the middle third of incubation for both years. The metabolic heating in both years was close to the as reported in the other green turtles nesting beaches in the Mediterranean. The feminization effect of metabolic heating was calculated as 6.8% in the green turtle nests on Samandağ Beach. Metabolic heating did not vary spatially, and the clutch size was the most important factor in metabolic heating and explained a large proportion of the variation in metabolic heating.

Sex ratio estimates for species with temperature-dependent sex determination differ according to the proxy used

Knowledge of the sex ratio of a population is crucial to understand their structure and dynamics. For species, such as marine turtles, with temperature-dependent sex determination, this knowledge provides a baseline in advance of climate change. Determining the primary sex ratio for marine turtle populations is challenging since offspring lack sexually dimorphic external characteristics. Therefore several proxies have been used to estimate the primary sex ratio of marine turtle populations. However, no study to date has compared estimations of sex ratio when using different proxies to determine the most accurate and to detect potential bias. To address this, we estimated the sex ratio of natural loggerhead, Caretta caretta, nests using 8 different proxies: two based on constant temperature equivalent (average of temperature or average temperature weighted by the growth of embryos during each time step) both for three developmental periods (the whole incubation, the middle third of incubation and the middle third of development) as well as two proxies based on incubation duration (duration of the whole incubation and of the middle third of development). Sex ratio estimates differed greatly depending on the proxy being used. Here we discuss the differences among proxies based on the biological relevance of underlying hypotheses and highlight the need for studies to accurately determine the thermosensitive period and to obtain appropriate estimates of embryo growth rate to estimate marine turtle sex ratio.

The effect of incubation temperatures on nest success of flatback sea turtles (Natator depressus)

Oviparous species are threatened in a warming world if their nesting distribution does not change or if they cannot adapt to changing environmental conditions. Consequently, documenting the thermal characteristics of nests and nesting habitats is an important area of research for threatened species, as is the identification of temperatures that embryos are unable to tolerate. Here we used generalised additive mixed models to examine the relationship between nest success (hatching success, emergence success and late-stage mortality) and nest temperature, nest depth and clutch size of flatback sea turtles (Natator depressus) collected over three breeding seasons (2012/2013–2014/2015) at an island rookery (Delambre Island, 20°26′56.38′′S, 117°4′42.29′′E) and on a nearby mainland rookery (Bells Beach, 20°36′51.77′′S, 117° 9′7.55′′E) in north-western Australia. We also examined seasonal and rookery differences in nest success with data collected over six breeding seasons (2009/2010–2014/2015). Mean nest temperature over the entire incubation period was the best predictor of hatching success and emergence success (explaining 37.15 and 39.15 % deviance in results, respectively), with both variables declining beyond about 32.5 °C. Mean temperature in the final third of incubation was the best predictor of late-stage mortality, explaining 73.91 % deviance with mortality increasing when nest temperatures exceeded 34 °C. Our results provide important data for identifying the optimum conditions for embryonic survival in this species, thereby aiding the assessment of the vulnerability of this Data Deficient species to global warming.

Nest temperatures of the Piai and Sayang Islands green turtle (Chelonia mydas) rookeries, Raja Ampat Papua, Indonesia: Implications for hatchling sex ratios

Tapilatu RF, Ballamu F. 2015. Nest temperatures of the Piai and Sayang Islands green turtle (Chelonia mydas) rookeries, Raja Ampat Papua, Indonesia: Implications for hatchling sex ratios. Biodiversitas 16: 102-107. Sex determination and hatching success in sea turtles is temperature dependent. Warmer sand temperatures may skew sea turtle population sex ratios towards predominantly females and high sand temperatures may also decrease hatching success. Therefore, understanding nest temperatures is important for conservation programs, including the evaluation of the potential impact of global climate change. Nest temperatures were monitored during the 2013 nesting season of the green sea turtle, Chelonia mydas, at Piai and Sayang Islands, Raja Ampat, West Papua, Indonesia. Nest temperatures increased from 29oC early in the incubation to 34-36oC in the middle, before decreasing again. Monitored nest temperatures were similar across all beaches. Nest temperatures increased 2-4oC during the middle third of incubation due to metabolic heating. Hatchling sex ratio inferred from nest temperature profiles indicated a strong female bias. This finding is consistent with the relatively warm thermal profiles of the majority of the nesting beaches. This also included some extremely warm nest temperatures that were associated with lower hatching success. Information from this study provides a foundation for developing conservation strategies for enhancing hatchling production with optimal sex ratios at the most important nesting beaches for the western Pacific green sea turtle. This study is the first comprehensive assessment of sex ratios for green sea turtles in Raja Ampat and represents the initiation of a long-term database that can be used at a local level to develop strategies that could potentially offset the impact of long-term climate change on the western Pacific green sea turtle.

Equilíbrio ácido-básico de embriões e pintos de corte em momentos críticos da incubação e submetidos a diferentes períodos de transferência para o nascedouro

Foram analisados os níveis de pCO2, pO2, pH e HCO3 - de embriões e pintos de corte provenientes de matrizes novas e velhas, nos momentos anteriores à bicagem interna e externa da casca e ao nascimento, submetidos a diferentes períodos de transferência para as condições ambientais dos nascedouros. Os tratamentos foram definidos pela idade da matriz (33 e 63 semanas) e pela transferência para o nascedouro (aos 15, 17 e 19 dias). O delineamento experimental foi em parcelas subdivididas, sendo a parcela os três momentos de transferência e a subparcela as duas idades das matrizes. Foram utilizadas seis repetições para cada tratamento, e o embrião ou o pinto foi considerado uma repetição. Os dados normais e homogêneos foram submetidos às análises de variância, e as médias comparadas pelos testes F, de Tukey e SNK. Embriões cujos ovos foram transferidos aos 15 dias para o nascedouro apresentaram melhor equilíbrio ácido-básico durante as fases pré-natal e perinatal. Durante o último terço da incubação, independentemente das diferentes condições ambientais às quais os embriões são submetidos e da idade da matriz, há capacidade de resposta fisiológica que permite uma estabilidade no equilíbrio ácido-básico dos pintos após a eclosão.

Sex ratios in naturally incubating Macrochelys temminckii nests, a species with type II temperature-dependent sex determination

The alligator snapping turtle, Macrochelys temminckii, exhibits type II temperature-dependent sex determination (TSD), wherein females are produced at high and low incubation temperatures. This TSD pattern is well studied at constant temperatures, but little work has focused on sex ratios in natural nests that experience daily and seasonal temperature fluctuations. We monitored nesting activity of reintroduced Macrochelys temminckii at Tishomingo National Wildlife Refuge in 2010–2011. Nests located prior to predation were excavated to determine clutch size and the eggs were reburied with a temperature data logger to collect nest temperatures. Overall, 24% of nests were protected with wire mesh prior to predation, and the average clutch size in intact nests was 22.4 eggs. Nest predation rates in the study population will likely approach 100% if nest protection efforts do not continue. Temperature profiles were used to compare estimated sex ratios using two methods—mean nest temperature during middle third of incubation and the degree-day model—to actual sex ratios in naturally incubated Macrochelys temminckii nests. The sex ratio in all 2010 recruits was female-biased (91.8% female); 2011 nests did not produce any hatchlings, likely the result of severe drought. The predicted sex ratios based on mean nest temperature and the degree-day model matched actual sex ratios in the warmer nests (0% male), but the degree-day model estimate proved more accurate in the cooler nest. A strongly skewed population sex ratio could become a threat to this reintroduced population if the strongly female-biased sex ratio in 2010 reflects a long-term trend.

Females first? Past, present and future variability in offspring sex ratio at a temperate sea turtle breeding area

AbstractThe long‐term survival of species with temperature‐dependant sex determination requires a sufficient range of incubation temperatures to ensure that both males and females are produced. The primary sex ratio of sea turtles is determined by the temperature experienced by eggs during the middle third of incubation. Here, we investigated the variability in the production of male and female offspring by loggerhead sea turtles Caretta caretta at six nesting beaches in the temperate breeding area of Zakynthos, Greece. Hatchling sex ratios were estimated using incubation durations and sand temperatures for 2007–2009, while the empirical relationship between air and sand temperature was used to infer historical (1875–2010) and future (2011–2100) hatchling sex ratios. First, all six beaches produced males; 55% of production was across five beaches, while 45% was focused on one beach (primarily in July). Second, male production varied across the season in different years; there was an initial peak in June, with production (rising, declining or plateauing) later in the season being regulated by August air temperatures. Interestingly, the annual male production rate estimated from the 3‐year dataset (23%) was half that estimated from the 135‐year reconstruction (50%), with the latter showing broad interannual variation. Finally, modelled predictions of future sex ratios ranged from a conservative 7.6% decline in male production by 2100 versus no production by 2038. This study provides a baseline from which predicted trends in hatchling sex ratio, in parallel to regular field assessments, could be used to provide guidelines for the selection of appropriate nest protection management protocols, to maintain required sex ratios that safeguard the future of this population.

Incubation Temperatures and Metabolic Heating of Relocated and In Situ Loggerhead Sea Turtle (Caretta caretta) Nests at a Northern Rookery

Miniature temperature loggers were used to better understand the incubation temperatures, patterns in metabolic heating, and potential implications for sex determination of relocated and in situ loggerhead sea turtle clutches near the northern extent of their nesting range. All sea turtles display temperature-dependent sex determination, with cooler nests producing males and warmer nests producing females. Analysis of the factors that affect incubation temperatures provides insight into variation in hatchling sex ratios over temporal and spatial scales and may help to guide management measures for the imperiled loggerhead sea turtle. Although no temperature difference was detected between relocated and in situ clutches during the thermal sensitive period, relocated nests hatched more quickly and incubated at warmer temperatures than in situ clutches for the entire incubation period. Metabolic heating was apparent in all clutches, beginning during the middle third of incubation, with the greatest gradient between nest temperature and surrounding sand temperatures (x ¯ = 1.5 ± 0.05°C) that occur during the final third of incubation. The magnitude of metabolic heating was not different between relocated and in situ clutches. Diel temperature fluctuations within nests were significantly less pronounced than in adjacent sand, which implies a degree of thermal buffering within the nest chamber. During the thermosensitive period, all nests incubated at a mean temperature above that of the estimated pivotal temperature (29.2°C), which implies a strongly female-biased hatchling sex ratio during the portion of the nesting season monitored. Potential impacts on incubation temperature and resultant sex ratios should be considered and explored on a beach-by-beach basis before adopting nest relocation as a conservation measure.

Impact of Clutch Relocation on Green Turtle Offspring

ABSTRACT For species with temperature‐dependent sex determination, such as marine turtles, global climate change poses numerous threats. At the nesting beach, rising temperatures are predicted to further skew already female‐biased sex ratios and increase embryonic mortality; sea‐level rise and resultant coastal squeeze may leave few alternative breeding habitats in developed regions. As a result, clutch relocation, a commonly used management tool to reduce egg loss, may become necessary for safeguarding populations. Although studies have examined the impact of relocation on clutch success, few have examined the impact of this practice on the sex or phenotypic characteristics of hatchlings produced. We used a randomized block design experiment to examine effects of relocation on green turtle (Chelonia mydas) clutches. We compared hatching success, thermal conditions, and size (length and mass) of hatchlings from in situ control clutches with those subjected to 2 relocation methods, while controlling for maternal and other environmental effects. Relocated clutches did not vary significantly from control clutches in incubation temperature or inferred sex ratios during the critical middle third of incubation when sex is thought to be determined. Hatchling size was also unaffected by relocation. Both relocation methods, however, resulted in a 20% reduction in hatching success in comparison to in situ clutches. Clutch relocation is, however, likely to affect the population primary sex ratio, when clutches are relocated from sites in proximity to the sea where tidal inundation is a threat. Here, cooler conditions are likely to produce more males than are the warmer female‐producing temperatures higher up the beach. For clutches at risk, relocation is a viable process and does not appear to affect hatchling size or predicted sex ratios if relocation sites are selected in areas utilized by other females. We urge caution, however, when moving clutches from potentially male‐producing sites, particularly given predicted impacts of climate change on already female‐biased sex ratios.

Broiler Incubation. 1. Effect of Elevated Temperature During Late Incubation on Body Weight and Organs of Chicks

Three experiments were conducted to investigate the effect of increased egg temperature during the final third of incubation on BW, yolk sac, heart, and digestive organs of broiler chicks at hatching. Egg temperatures were found to be approximately 1.0 to 1.5°C higher than incubator air temperature. Elevated egg temperature (39.5°C) after embryonic day 14 generally accelerated hatching time but decreased the relative weight of the heart in all 3 experiments, whereas BW and relative weights of the gizzard, proventriculus, and small intestines were significantly smaller in 2 of 3 experiments as compared with the control (∼38.2°C). Relative weights of the yolk sac or liver were significantly larger due to elevated egg temperature in single experiments only. A striking feature of the chicks that developed at an elevated egg temperature was their white color as compared with the yellow color of chicks from eggs incubated at more normal temperatures.

Adrenal–kidney–gonad complex measurements may not predict gonad‐specific changes in gene expression patterns during temperature‐dependent sex determination in the red‐eared slider turtle (Trachemys scripta elegans)

Many turtles, including the red-eared slider turtle (Trachemys scripta elegans) have temperature-dependent sex determination in which gonadal sex is determined by temperature during the middle third of incubation. The gonad develops as part of a heterogenous tissue complex that comprises the developing adrenal, kidney, and gonad (AKG complex). Owing to the difficulty in excising the gonad from the adjacent tissues, the AKG complex is often used as tissue source in assays examining gene expression in the developing gonad. However, the gonad is a relatively small component of the AKG, and gene expression in the adrenal-kidney (AK) compartment may interfere with the detection of gonad-specific changes in gene expression, particularly during early key phases of gonadal development and sex determination. In this study, we examine transcript levels as measured by quantitative real-time polymerase chain reaction for five genes important in slider turtle sex determination and differentiation (AR, ERalpha, ERbeta, aromatase, and Sf1) in AKG, AK, and isolated gonad tissues. In all cases, gonad-specific gene expression patterns were attenuated in AKG versus gonad tissue. All five genes were expressed in the AK in addition to the gonad at all stages/temperatures. Inclusion of the AK compartment masked important changes in gonadal gene expression. In addition, AK and gonad expression patterns are not additive, and gonadal gene expression cannot be predicted from intact AKG measurements.

Investigating the potential impacts of climate change on a marine turtle population

AbstractRecent increases in global temperatures have affected the phenology and survival of many species of plants and animals. We investigated a case study of the effects of potential climate change on a thermally sensitive species, the loggerhead sea turtle, at a breeding location at the northerly extent of the range of regular nesting in the United States. In addition to the physical limits imposed by temperature on this ectothermic species, sea turtle primary sex ratio is determined by the temperature experienced by eggs during the middle third of incubation. We recorded sand temperatures and used historical air temperatures (ATs) at Bald Head Island, NC, to examine past and predict future sex ratios under scenarios of warming. There were no significant temporal trends in primary sex ratio evident in recent years and estimated mean annual sex ratio was 58% female. Similarly, there were no temporal trends in phenology but earlier nesting and longer nesting seasons were correlated with warmer sea surface temperature. We modelled the effects of incremental increases in mean AT of up to 7.5°C, the maximum predicted increase under modelled scenarios, which would lead to 100% female hatchling production and lethally high incubation temperatures, causing reduction in hatchling production. Populations of turtles in more southern parts of the United States are currently highly female biased and are likely to become ultra‐biased with as little as 1°C of warming and experience extreme levels of mortality if warming exceeds 3°C. The lack of a demonstrable increase in AT in North Carolina in recent decades coupled with primary sex ratios that are not highly biased means that the male offspring from North Carolina could play an increasingly important role in the future viability of the loggerhead turtle in the Western Atlantic.

The temperature-sensitive period (TSP) during incubation of broad-snouted caiman (Caiman latirostris) eggs

Abstract All crocodiles studied to date exhibit temperature-dependent sex determination. During the many weeks from egg laying to hatch there is a period of 10 to 15 d in the middle third of incubation (in the American alligator) during which the sex of the embryo is irreversibly fixed, referred to as the temperature-sensitive period or TSP. In this work we investigated the TSP in Caiman latirostris eggs incubated at female-inducing and male-inducing temperatures (29° C and 33° C respectively) by switching eggs from 29° C to 33° C and vice versa at timed interval throughout incubation. Compared to Alligator mississippiensis the duration of TSP was longer, and the onset of TSP was at an earlier stage of incubation.

Effects of Nest Depth, Shading, and Metabolic Heating on Nest Temperatures in Sea Turtle Hatcheries

This study investigated the effects of hatchery shading, nest depth, and metabolic heating on the temperature of Chelonia mydas clutches incubated in hatcheries at Ma'Daerah, Terengganu, Malaysia. Metabolic heating was found to be the most influential factor on nest temperature; the number of completely developed eggs explained nearly half of the variation in mean nest temperature. The degree of hatchery shading (70% vs. 100%) and nest depth (50 vs. 75 cm) had little influence on nest temperatures, with mean nest temperatures between 28° and 28.6°C in the first third of incubation (before metabolic heating of the clutch began to have an effect). Nests at a depth of 75 cm had significantly lower daily temperature ranges than nests at a depth of 50 cm, but a maximum mean daily range of 0.5°C (50 cm depth in 70% shade hatchery) resulted in calculated constant temperature equivalents (CTE) being identical to observed mean nest temperatures. The results of this study indicate that, under current climatic conditions in this area, shading between 70% and 100% and nest depths between 50 and 75 cm will incubate green turtle clutches within the optimal temperature range for development. However, this information is site-specific and could vary significantly between locations due to the complex interaction of biological, chemical, and physical factors that influence sea turtle nest temperature.

Metabolic heating in Mediterranean loggerhead sea turtle clutches

Offspring sex ratio is an important demographic parameter and, given its determination by incubation temperature in sea turtles, might be a key factor for their conservation under climate warming. An appealing approach to estimate hatchling sex ratios is to measure sand temperatures at nest depth and deduce hatchling sex ratios from a beforehand-established relationship of hatchling sex ratio and sand temperature. Such estimates will only be accurate though if metabolic heat produced by the embryos is considered. Judging whether metabolic heating has a potential effect on hatchling sex ratios without actually measuring temperature within clutches would greatly facilitate monitoring protocols. We tested for a relationship between the amount of metabolic heating and the number of developed embryos as well as clutch size in the largest known loggerhead sea turtle ( Caretta caretta) population of the Mediterranean on Zakynthos (Greece). Temperatures were measured within 20 nests as well as at a reference site in the sand at nest depth. Metabolic heating was detected, but only during the last third of the incubation period did nests heat up considerably (1.6 °C on average) above the temperature of the surrounding sand. During the middle third of incubation, when sex is determined, the amount of metabolic heating was negligible. The amount of metabolic heating during the last third of the incubation duration was significantly correlated to the number of offspring developed to at least about 75% of incubation duration. This factor explained nearly 50% of variation in metabolic heating. Metabolic heating was also significantly correlated to clutch size. Given that clutch size within the Mediterranean is largest in Zakynthos loggerheads, we conclude that metabolic heating can be ignored in the estimate of hatchling sex ratios in Mediterranean loggerhead populations. These results thus provide the basis for a feasible monitoring of hatchling sex ratios in the loggerhead sea turtle in the Mediterranean.

Effects of clutch sizes and incubation stage on nest desertion in the female Common Eider Somateria mollissima nesting in the high Arctic

In bird species, one of the trade-offs between reproduction and survival appears in the parental decision to desert the nest. Nest desertion is modulated by several factors including clutch size. However, the incubation stage at which predation occurs is also an important factor. In this study, we examined whether nest desertion was linked to initial clutch size, partial clutch predation (final clutch size) and the incubation stage at which it happened in a capital breeder: the female common eider (Somateria mollissima) nesting in the high Arctic. The study was performed in Kongsfjorden in 2002 on the western coast of the Svalbard Archipelago (78°55′N, 20°07′E). We observed that nest desertion was higher when the initial clutch size was small. Also, females deserted their nests more during the first third of incubation than later. Thus, as incubation proceeded, nest desertion was less likely to occur even after egg reduction. Our results pointed out that this parental decision in female eiders seemed to depend on initial clutch size and on the date into incubation of clutch reduction.

Pivotal range and thermosensitive period of the pig-nosed turtle, Carettochelys insculpta (Testudines: Carettochelydidae), from northern Australia

Understanding temperature-dependent sex determination in nature often depends on knowledge of species-specific attributes that are integrated into the relationship between temperature and sex. We determined two such attributes for the pig-nosed turtle, Carettochelys insculpta Ramsay, 1886, in tropical Australia: the pivotal range in temperature that separates the male-producing domain from the female-producing domain, and the thermosensitive period during which the embryonic sex is influenced by temperature. The pivotal range for C. insculpta was very narrow, spanning only about 1 °C, and was centered on 32 °C, which is high but consistent with temperatures reported for other tropical species. The thermosensitive period spanned developmental stages 17–21 for temperature influence in the direction of maleness and 18–21 for temperature influence in the direction of femaleness. This period is slightly narrower than that for other reptile species but broadly consistent with the middle third of incubation.