C. John Parmenter

Influence of Incubation Environment on the Development of the Flatback Turtle (Natator depressus)

Abstract During the Australian summers of 1996/1997 and 1997/1998, the embryonic development of Natator depressus was investigated in the laboratory. Eggs were incubated under different thermal and hydric conditions on vermiculite substrates. The thermal environment between 26 and 32 C significantly influenced the water exchange of eggs, incubation duration, nutrient mobilization of embryos, and the size, tissue hydration, and energy reserves of hatchlings. Hatchlings produced at 26 C and 29 C were larger but had lower energy reserves than those produced at 32 C. The influence of the hydric environment depended greatly on the range of substrate water potentials used in experiments. Nutrient mobilization of embryos and the size and energy reserves of hatchlings were dependent on total egg water exchange over the range of 2% gain to 29% loss (at approximately −180 to −3500 kPa incubation substrates) of initial egg mass but independent within the narrower range of 6% gain to 19% loss (at approximately −200 to −650 kPa substrates). Hatching was affected only when eggs lost more than 21% of their initial egg mass (at approximately −1300 kPa). A significant effect of clutch on the morphological and physiological aspects of developing embryos indicated that genetic/maternal factors influenced these traits. Natator depressus eggs seem to be laid with sufficient water reserves for successful embryonic growth and development. In most natural circumstances, this would make them independent of supplementary water from the environment.

The distribution of failed eggs and the appearance of fungi in artificial nests of green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtles

Fungi are often found on the exterior of unhatched eggs in sea turtle nests in eastern Australia. Artificial incubation of green (Chelonia mydas) and loggerhead (Caretta caretta) turtle eggs allowed the radiation of fungi to be monitored. Fortuitous egg mortality provided a nutrient source for common soil mycobiota (Fusarium solani and Pseudallescheria boydii) and served as a focus for the progressive spread of fungal hyphae to adjacent viable eggs. In extreme cases the entire egg mass was enveloped and resulted in nil hatch success.

Incubation Environment and Nest Success of the Flatback Turtle (Natator depressus) from a Natural Nesting Beach

Abstract The thermal and hydric environment during incubation of turtle eggs influences hatchling size, sex, energy reserves, and thus their quality. Information on the natural nest environment of flatback turtles (Natator depressus) is lacking. Therefore, the current study investigated the thermal and hydric environment of their nest chambers and nesting beach (at Peak Island, east coastal Queensland during the 1996/1997 and 1997/1998 nesting seasons). The temperature of nest chambers and the nesting beach showed temporal and spatial variation. Beach temperature increased through the nesting season as summer progressed and showed significant vertical and lateral variation. The temperature in the core of nest chambers increased as incubation progressed (on average 7 C) apparently because of both metabolic heating and the natural seasonal increase in sand temperature. The temperature range of nests was 25.5–36.5 C, with many nests exposed to temperatures above 35 C for extended periods. Water content of sand surrounding nest chambers at the beginning of incubation ranged from 2.6–7.8% (w/w), varying with date of laying and location on the beach. Natator depressus eggs may be more tolerant of high incubation temperatures and severe moisture stress than those of most other sea turtle species. Nest success was not influenced by the position of the nest on the beach but was positively related to clutch size. Neither nest success nor clutch size varied significantly between subsequent clutches of an individual female. Hatchling sex ratio at this beach possibly depends on the date of egg laying. Because high density nesting occurs when beach temperature appears to produce almost all female hatchlings, the hatchling sex ratio at Peak Island is likely to be biased toward females. Data gathered in the current study will assist in the development of management strategies to protect this endemic species.

Egg Components and Utilization of Yolk Lipids during Development of the Flatback Turtle Natator depressus

Abstract The materials and energy invested in each egg by most oviparous reptiles represent the majority of total parental investment in offspring. For Natator depressus from eastern Queensland, Australia, the shell contributed approximately 5%, the albumin 45%, and the yolk 50% to the total egg mass (74 g). Water averaged 79% of the total egg mass. Lipids averaged 29% of the total dry mass of the egg and 35% of the yolk dry mass. Eggs of N. depressus contained a high proportion of yolk lipids and water, with greater “parental investment” than those of nonmarine turtles. Approximately 26–27% of lipids in the egg was used for embryogenesis, whereas 73–74% was transferred to the entire hatchling. Initial yolk lipid in the residual yolk was approximately 30–37% but varied with incubation environment. Residual yolk lipids are likely to be used as the immediate energy source for the hatchlings.

Influence of Diminished Respiratory Surface Area on Survival of Sea Turtle Embryos

It has been suggested that fungal presence on sea turtle eggs may impede gas exchange. To investigate the influence of diminished gas exchange surface upon embryo survivorship, flatback (Natator depressus) and green (Chelonia mydas) eggs were painted with petroleum jelly. Variable proportions of the egg surface were covered, including both respiratory and nonrespiratory domains. Embryo survival varied with site inhibited, proportion of eggshell affected, and species of turtle. If fungi on the exterior of the eggshell are able to impede respiratory gas exchange, their presence on the upper hemisphere (primary gas exchange area in early incubation) will result in the highest embryo mortality. Large eggs are likely to demonstrate a higher survivorship than small eggs, due to their larger available respiratory area and/or to variation in weight or stage-specific embryonic metabolic demands. Interspecific differences in egg size may therefore be a contributory factor to observed mortality rate differences in the natural presence of fungi.

Hydric environment and sex determination in the flatback turtle (Natator depressus Garman) (Chelonia : Cheloniidae)

Eggs of Natator depressus (from eastern Queensland, Australia) were incubated at a constant temperature of 29.5˚C on vermiculite substrate with three different moisture levels: wet (~–180 kPa), intermediate (~–1200 kPa) and dry (~–2000 kPa). The male : female ratios on wet, intermediate and dry substrates were 8 : 7, 5 : 5 and 5 : 8 respectively. Sex determination was not influenced by the hydric environment but was significantly affected by different clutches. A clutch with smaller eggs appeared to produce a higher proportion of females. The pivotal temperature was close to 29.5˚C, with a possibly narrow transitional temperature range of 1˚C. Visual designation of sex was confirmed (100%) by histological examination. Hatching success and the incubation duration were not influenced by the hydric environment.

Calcium Depletion of Eggshell After Fungal Invasion of Sea Turtle Eggs

Abstract The calcium content of flatback (Natator depressus), loggerhead (Caretta caretta), hawksbill (Eretmochelys imbricata), and green (Chelonia mydas) sea turtle eggshells are not significantly different. Green turtle eggs with external fungal invasion by Fusarium solani had significantly reduced calcium content of the outer, inorganic portion of the eggshell.

Thermosensitive period for sexual differentiation of the gonads of the flatback turtle (Natator depressus Garman)

Temperature-dependent sex determination has previously been reported for the flatback turtle (Natator depressus). The present study investigates the thermosensitive embryonic developmental stages for the sexual differentiation of this species. Groups of eggs incubated initially at constant temperatures of 26, 29 and 32°C were shifted once during incubation from either a constant masculinising temperature (26 or 29°C) to a constant feminising temperature (32°C) or vice versa. Findings from this study support the hypothesis that the effect of temperature and the timing of the thermosensitive period are dependent upon the specific temperature utilised during incubation. The thermosensitive developmental stages at masculinising temperatures were different to those of feminising temperatures. For the 26 to 32°C temperature shift, the thermosensitive period was confined to a single developmental stage (Stage 24). Ovarian development was determined at a later developmental stage than testicular development.

Larvae of two signal fly species (Diptera : Platystomatidae), Duomyia foliata McAlpine and Plagiostenopterina enderleini Hendel, are scavengers of sea turtle eggs

Dipteran larvae are known to infest turtle eggs. However, the few studies conducted on this topic have presented conflicting conclusions as to whether the larvae function as scavengers of necrotic nest material or as egg and hatchling predators. These two very different roles in the nest will have equally different effects on the subsequent hatch and emergence success of affected sea turtle nests. The association between dipteran larvae and sea turtle nest invasion was investigated by measuring rates of infestation in excavated green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtle nests at field sites in central Queensland, Australia. Excavations were performed within 24 h of hatchling emergence, and necrotic embryos and dead hatchlings were found to be infested with two larval species of the Platystomatidae: Plagiostenopterina enderleini and Duomyia foliata. This work represents the first description of the association between these dipteran species and sea turtle nests, and a new geographic collection record for D. foliata. High rookery infestation rates versus low prevalence of propagule infestation suggest that the larvae preferentially infest dead embryos. The fact that some pipped hatchlings were devoured in-shell presents the possibility that the larvae may act opportunistically as predators. However, the two dipteran species appear to be primarily scavengers of necrotic material within the nests, which means that the threat to sea turtle populations from these flies is probably minimal.

Deterioration of Green Sea Turtle (Chelonia mydas) Eggs After Known Embryo Mortality

ABSTRACT To determine the time interval between embryonic death and physical alterations in appearance of green turtle (Chelonia mydas) eggs, one each of matched pairs of eggs were inverted after 7–10 days of incubation. Chalkiness of the white spot diminished after 44 hours as maintenance of the chorio-allantoic membrane, contributing to the opaque appearance of viable eggs, ceased after embryo mortality. Results of this study will allow embryo mortality to be attributed to known specific events or conditions within the incubation period.