Temperature-dependent sex determination of Ascension Island green turtles

We examined the role played by temperature in the duration of incubation and sex ratio of green turtle hatchlings at Ascension Island, one of the most important green turtle rookeries in the Atlantic. Temperature at control sites at nest depth and in 39 green turtle nests was measured using small temperature recording devices. The sex ratio of hatchlings was ascertained in a sub-sample of monitored nests allowing the description of the relationship between intranest temperature and hatchling sex ratio, demonstrating a pivotal incubation temperature of 28.8°C. The seasonal profile in sex ratio of hatchlings produced on all nesting beaches at Ascension Island was estimated, showing that a female-biased sex ratio would be expected with a female:male ratio of the order of 3:1. The use of nest temperature, air temperature, sand temperature at control sites, and incubation duration as proxies to estimate hatchling sex ratio are discussed.

Breeding periodicity for male sea turtles, operational sex ratios, and implications in the face of climate change

Species that have temperature-dependent sex determination (TSD) often produce highly skewed offspring sex ratios contrary to long-standing theoretical predictions. This ecological enigma has provoked concern that climate change may induce the production of single-sex generations and hence lead to population extirpation. All species of sea turtles exhibit TSD, many are already endangered, and most already produce sex ratios skewed to the sex produced at warmer temperatures (females). We tracked male loggerhead turtles (Caretta caretta) from Zakynthos, Greece, throughout the entire interval between successive breeding seasons and identified individuals on their breeding grounds, using photoidentification, to determine breeding periodicity and operational sex ratios. Males returned to breed at least twice as frequently as females. We estimated that the hatchling sex ratio of 70:30 female to male for this rookery will translate into an overall operational sex ratio (OSR) (i.e., ratio of total number of males vs females breeding each year) of close to 50:50 female to male. We followed three male turtles for between 10 and 12 months during which time they all traveled back to the breeding grounds. Flipper tagging revealed the proportion of females returning to nest after intervals of 1, 2, 3, and 4 years were 0.21, 0.38, 0.29, and 0.12, respectively (mean interval 2.3 years). A further nine male turtles were tracked for short periods to determine their departure date from the breeding grounds. These departure dates were combined with a photoidentification data set of 165 individuals identified on in-water transect surveys at the start of the breeding season to develop a statistical model of the population dynamics. This model produced a maximum likelihood estimate that males visit the breeding site 2.6 times more often than females (95%CI 2.1, 3.1), which was consistent with the data from satellite tracking and flipper tagging. Increased frequency of male breeding will help ameliorate female-biased hatchling sex ratios. Combined with the ability of males to fertilize the eggs of many females and for females to store sperm to fertilize many clutches, our results imply that effects of climate change on the viability of sea turtle populations are likely to be less acute than previously suspected.

Effects of rising temperature on the viability of an important sea turtle rookery

A warming world poses challenges for species with temperature-dependent sex determination, including sea turtles, for which warmer incubation temperatures produce female hatchlings. We combined in situ sand temperature measurements with air temperature records since 1850 and predicted warming scenarios from the Intergovernmental Panel on Climate Change to derive 250-year time series of incubation temperatures, hatchling sex ratios, and operational sex ratios for one of the largest sea turtles rookeries globally (Cape Verde Islands, Atlantic). We estimate that light-coloured beaches currently produce 70.10% females whereas dark-coloured beaches produce 93.46% females. Despite increasingly female skewed sex ratios, entire feminization of this population is not imminent. Rising temperatures increase the number of breeding females and hence the natural rate of population growth. Predicting climate warming impacts across hatchlings, male-female breeding ratios and nesting numbers provides a holistic approach to assessing the conservation concerns for sea turtles in a warming world. © 2014 Macmillan Publishers Limited.

Different male vs. female breeding periodicity helps mitigate offspring sex ratio skews in sea turtles

 The implications of climate change for global biodiversity may be profound with those species with little capacity for adaptation being thought to be particularly vulnerable to warming. A classic case of groups for concern are those animals exhibiting temperature-dependent sex-determination (TSD), such as sea turtles, where climate warming may produce single sex populations and hence extinction. We show that, globally, female biased hatchling sex ratios dominate sea turtle populations (exceeding 3:1 in >50% records), which, at-a-glance, reiterates concerns for extinction. However, we also demonstrate that more frequent breeding by males, empirically shown by satellite tracking 23 individuals and supported by a generalized bio-energetic life history model, generates more balanced operational sex ratios (OSRs). Hence, concerns of increasingly skewed hatchling sex ratios and reduced population viability are less acute than previously thought for sea turtles. In fact, in some scenarios skewed hatchling sex ratios in groups with TSD may be adaptive to ensure optimum OSRs.

The importance of sand albedo for the thermal conditions on sea turtle nesting beaches

At Ascension Island and Cyprus, major nesting areas for green turtles (Chelonia mydas) in the Atlantic and Mediterranean, respectively, visual inspection shows some beaches are light in colour while others are darker. We objectively measured the albedo of the sand on different beaches, i.e. the percentage of the incident solar radiation that was reflected from the sand surface. At sites where albedo was recorded, we also measured the temperature of the sand at nest depths. At both rookeries, the sand temperature was markedly higher on darker beaches due to greater absorption of the incident solar radiation over the diurnal cycle. Temperature loggers buried at nest depths revealed seasonal changes in temperature on both islands, but showed that the lowest temperatures found on the darker beaches rarely dropped below the highest temperatures on the lighter beaches. Sea turtles exhibit temperature-dependent sex determination. Since sand albedo is a major avenue for the production of a range of incubation temperatures on both islands, it will also have profound implications for hatchling sex ratios. In comparison with both Ascension Island and Cyprus, for samples collected from sea turtle rookeries around the world there was an even greater range in sand albedo values. This suggests that sand albedo, a factor that has previously received little consideration, will have profound implications for nest temperatures, and hence hatchling sex ratios, for other populations and species.

Climate change and sea turtles : a 150-year reconstruction of incubation temperatures at a major marine turtle rookery

Sea turtles show temperature dependent sex determination. Using an empirical relationship between sand and air temperature, we reconstructed the nest temperatures since 1855 at Ascension Island, a major green turtle (Chelonia mydas) rookery. Our results show that inter-beach thermal variations, previously ascribed to the albedo of the sand, which varies hugely from one beach to another, have persisted for the last century. Reconstructed nest temperatures varied by only 0.5 °C on individual beaches over the course of the nesting season, while the temperature difference between two key nesting beaches was always around 3 °C. Hence inter-beach thermal variations are the main factor causing a large range of incubation temperatures at this rookery. There was a general warming trend for nests, with a mean increase in reconstructed nest temperatures for different months of between 0.36 and 0.49 °C for the last 100 years.

Long-term thermal conditions on the nesting beaches of green turtles on Ascension Island

On 2 of the major nesting beaches used by green turtles Chelonia mydas on Ascension Island, we measured the sand temperature at nest depths throughout the year. For both beaches, the sand temperature was strongly correlated (r2 >= 0.94) with air temperature. We therefore used past records of air temperature to reconstruct sand temperatures on the different beaches throughout the nesting season between 1985 and 1998. This analysis showed that inter-annual differences in sand temperature were small and, while there were consistent thermal changes during the nesting season, over the 14 yr there was little overlap in the temperatures on the 2 beaches, with one being 2.6°C warmer, on average, than the other. This work suggests that inter-beach thermal variation is the major mechanism by which a range of incubation temperatures are realised on Ascension Island and hence is likely to facilitate the production of hatchlings of both sexes.

Heat tolerance, behavioural temperature selection and temperature-dependent respiration in larval Octopus huttoni

This study reports temperature effects on paralarvae from a benthic octopus species, Octopus huttoni, found throughout New Zealand and temperate Australia. We quantified the thermal tolerance, thermal preference and temperature-dependent respiration rates in 1-5 days old paralarvae. Thermal stress (1°C increase h^-1) and thermal selection (~10-24°C vertical gradient) experiments were conducted with paralarvae reared for 4 days at 16°C. In addition, measurement of oxygen consumption at 10, 15, 20 and 25°C was made for paralarvae aged 1, 4 and 5 days using microrespirometry. Onset of spasms, rigour (CT_max) and mortality (upper lethal limit) occurred for 50% of experimental animals at, respectively, 26.0±0.2°C, 27.8±0.2°C and 31.4±0.1°C. The upper, 23.1±0.2°C, and lower, 15.0±1.7°C, temperatures actively avoided by paralarvae correspond with the temperature range over which normal behaviours were observed in the thermal stress experiments. Over the temperature range of 10°C-25°C, respiration rates, standardized for an individual larva, increased with age, from 54.0 to 165.2nmol larvae^-1h^-1 in one-day old larvae to 40.1-99.4nmol h^-1 at five days. Older larvae showed a lesser response to increased temperature: the effect of increasing temperature from 20 to 25°C (Q₁₀) on 5 days old larvae (Q₁₀=1.35) was lower when compared with the 1 day old larvae (Q₁₀=1.68). The lower Q₁₀ in older larvae may reflect age-related changes in metabolic processes or a greater scope of older larvae to respond to thermal stress such as by reducing activity. Collectively, our data indicate that temperatures >25°C may be a critical temperature. Further studies on the population-level variation in thermal tolerance in this species are warranted to predict how continued increases in ocean temperature will limit O. huttoni at early larval stages across the range of this species.

Transient temperature distribution in functionally graded graphite/Polymer nanocomposites based on temperature dependent properties

Transient heat conduction in a functionally graded graphite/polymer nanocomposite (FGN) plate is analyzed using finite element method (FEM). Stepwise gradient structure consisted of four different nanocomposite layers with 0, 5, 10 and 20 wt% of graphite. Thermal conductivity and specific heat capacity of the individual layers were determined using C-Therm TCi Thermal Conductivity Analyzer (Canada) in temperature range of -20 to 100 °C. Temperature history and temperature distribution across the thickness of the plate with two different configurations for two positive and negative temperature gradients are presented.

Temperature-dependent Raman spectra of bamboo-like boron nitride nanotubes

Phonon properties of boron nitride nanotubes (BNNTs) were investigated using Raman spectroscopy at different temperatures and new sp3- bonded BN vibrations were identified. The Raman peak of the E2g mode of BNNTs is found to be downshifted and broadened compared to that of hexagonal BN at the same temperature. By increasing the temperature, the energy of the E2g mode and the sp3-bonding mode are downshifted, with the temperature coefficients being -0.010 and -0.069cm-1/K, respectively. We attribute this downshifting to anharmonic effects as well as the elongation of the B-N bond in BNNT structures with increasing temperature. © 2014 The Japan Society of Applied Physics.

Sand temperatures for nesting sea turtles in the Caribbean: Implications for hatchling sex ratios in the face of climate change

A 200-year time series of incubation temperatures and primary sex ratios for green (Chelonia mydas), hawksbill (Eretmochelys imbricata) and leatherback (Dermochelys coriacea) sea turtles nesting in St. Eustatius (North East Caribbean) was created by combining sand temperature measurements with historical and current environmental data and climate projections. Rainfall and spring tides were important because they cooled the sand and lowered incubation temperatures. Mean annual sand temperatures are currently 31.0. °C (SD. =. 1.6) at the nesting beach but show seasonality, with lower temperatures (29.1-29.6. °C) during January-March and warmer temperatures (31.9-33.3. °C) in June-August. Results suggest that all three species have had female-biased hatchling production for the past decades with less than 15.5%, 36.0%, and 23.7% males produced every year for greens, hawksbills and leatherbacks respectively since the late nineteenth century. Global warming will exacerbate this female-skew. For example, projections indicate that only 2.4% of green turtle hatchlings will be males by 2030, 1.0% by 2060, and 0.4% by 2090. On the other hand, future changes to nesting phenology have the potential to mitigate the extent of feminisation. In the absence of such phenological changes, management strategies to artificially lower incubation temperatures by shading nests or relocating nest clutches to deeper depths may be the only way to prevent the localised extinction of these turtle populations.

NMR determination of ionic structure in plasticized polyether-urethane polymer electrolytes

Solid polymer electrolytes based on amorphous polyether-urethane networks combined with lithium or sodium salts and a low molecular weight cosolvent (plasticizer) have been investigated in our laboratories for several years. Conductivity enhancements of up to two orders of magnitude can be obtained whilst still retaining solid elastomeric properties. In order to understand the effects of the plasticizers and their mechanism of conductivity enhancement, multinuclear NMR has been employed to investigate ionic structure in polymer electrolyte systems containing NaCF₃SO₃, LiCF₃SO₃ and LiClO₃ salts.

With increasing dimethyl formamide (DMF) and propylene carbonate (PC) concentration the increasing cation chemical shift with fixed salt concentration indicates a decreasing anion-cation association consistent with an increased number of charge carriers. ¹³C chemical shift data for the same systems suggests that whilst DMF also decreases cation-polymer interactions, PC does the opposite, presumably by shielding cation-anion interactions. Temperature dependent ⁷Li spin-lattice relaxation times indicate the expected increase in ionic mobility upon plasticization with a shift of the T₁ minimum to lower temperatures. The magnitude of T₁ at the minimum increases upon addition of DMF whereas there is a slight decrease when PC is added. This also supports the suggestion that the DMF preferentially solvates the cation whereas the action of PC is limited to coulomb screening, hence freeing the anion.