First records of oceanic dive profiles for leatherback turtles, Dermochelys coriacea, indicate behavioural plasticity associated with long-distance migration

We used Satellite Relay Data Loggers to obtain the first dive profiles for critically endangered leatherback turtles outside the nesting season. As individuals moved from the Caribbean out into the Atlantic, key aspects of their diving behaviour changed markedly, in line with theoretical predictions for how dive duration should vary with foraging success. In particular, in the Atlantic, where foraging success is expected to be higher, dives became much longer than in the Caribbean. The deepest-ever dive profile recorded for a reptile was obtained in the oceanic Atlantic, with a 54-min dive to 626 m on 26 August 2002. However, dives were typically much shallower (generally <200 m) and shorter (<40 min). These results highlight the suitability of this species for testing models of dive performance.     

Growth of captive leatherback turtles, Dermochelys coriacea, with inferences on growth in the wild: Implications for population decline and recovery

Leatherback turtles (Dermochelys coriacea) are endangered, and declining population trends suggest that they are vulnerable to becoming extinct in the Pacific Ocean. Population recovery depends on strong conservation measures (e.g., nest protection, reduction of bycatch, and foraging habitat preservation) and on how fast leatherbacks grow and reach maturity, making the latter of grave concern. The research reported here marks the first time that several leatherback turtles have been maintained in captivity for nearly 2 years, from hatchlings (6.31 ± 0.13 cm straight carapace length (SCL) and 46.0 ± 1 g) to juveniles (largest, 72.0 cm SCL and 42.65 kg). Leatherbacks maintained an average growth rate of 31.9 ± 2.8 cm year^− 1 in SCL throughout the study period. A length-mass relationship of the form, mass (kg) = 0.000214 ? SCL (cm) 2.86, fitted our data and data from four other captive studies, 11 wild juveniles, and five studies of adult leatherbacks. Von Bertalanffy, Gompertz and logistic growth functions predicted age-at-maturity for leatherbacks of 16.1, 8.7 and 6.8 years, respectively. The accuracy of these age-at-maturity estimates is discussed in the light of skeletochronological studies as well as estimates obtained from conservation and genetic studies. Our data, in combination with data from sightings, suggest that leatherbacks spend their early years (0 to 5 years of age) growing in the warmer waters of the tropical and subtropical seas before entering cooler temperate waters. Information obtained from turtles incidentally captured in fisheries, supplemented with growth curve data, indicates that leatherbacks are vulnerable to entanglement or hooking in various pelagic gear types, such as drift gill nets and longline within 3 years from nest emergence. Consequently, leatherbacks are exposed to threats from marine fisheries for > 80% of their early life before carapace length characteristic of reproductive maturity is attained.     

Diving behaviour of dugongs, Dugong dugon

The diving behaviour of 15 dugongs (Dugong dugon) was documented using time-depth recorders (TDRs), which logged a total of 39,507 dives. The TDRs were deployed on dugongs caught at three study sites in northern Australia: Shark Bay, the Gulf of Carpentaria and Shoalwater Bay. The average time for which the dive data were collected per dugong was 10.4±1.1 (S.E.) days. Overall, these dugongs spent 47% of their daily activities within 1.5 m of the sea surface and 72% less than 3 m from the sea surface. Their mean maximum dive depth was 4.8±0.4 m (S.E.), mean dive duration was 2.7±0.17 min and the number of dives per hour averaged 11.8±1.2. The maximum dive depth recorded was 20.5 m; the maximum dive time in water >1.5 m deep was 12.3 min. The effects of dugong sex, location (study site), time of day and tidal cycle on diving rates (dives per hour), mean maximum dive depths, durations of dives, and time spent ≤1.5 m from the surface were investigated using weighted split-plot analysis of variance. The dugongs exhibited substantial interindividual variation in all dive parameters. The interaction between location and time of day was significant for diving rates, mean maximum dive depths and time spent within 1.5 m of the surface. In all these cases, there was substantial variation among individuals within locations among times of day. Thus, it was the variation among individuals that dominated all other effects. Dives were categorised into five types based on the shape of the time-depth profile. Of these, 67% of dives were interpreted as feeding dives (square and U-shaped), 8% as exploratory dives (V-shaped), 22% as travelling dives (shallow-erratic) and 3% as shallow resting dives. There was systematic variation in the distribution of dive types among the factors examined. Most of this variation was among individuals, but this differed across both time of day and tidal state. Not surprisingly, there was a positive relationship between dive duration and depth and a negative relationship between the number of dives per hour and the time spent within 1.5 m of the surface after a dive.     

Diving behaviour, dive cycles and aerobic dive limit in the platypus Ornithorhynchus anatinus

We investigated the diving behaviour, the time allocation of the dive cycle and the behavioural aerobic dive limit (ADL) of platypuses (Ornithorhynchus anatinus) living at a sub-alpine Tasmanian lake. Individual platypuses were equipped with combined data logger-transmitter packages measuring dive depth. Mean dive duration was 31.3 s with 72% of all dives lasting between 18 and 40 s. Mean surface duration was 10.1 s. Mean dive depth was 1.28 m with a maximum of 8.77 m. Platypuses performed up to 1600 dives per foraging trip with a mean of 75 dives per hour. ADL was estimated by consideration of post-dive surface intervals vs. dive durations. Only 15% of all dives were found to exceed the estimated ADL of 40 s, indicating mainly aerobic diving in the species. Foraging platypuses followed a model of optimised recovery time, the optimal breathing theory. Total bottom duration or total foraging duration per day is proposed as a useful indicator of foraging efficiency and hence habitat quality in the species.     

Stable carbon and nitrogen isotope discrimination in soft tissues of the leatherback turtle (Dermochelys coriacea): Insights for trophic studies of marine turtles

The trophic ecology of marine vertebrates has been increasingly studied via stable isotope analysis of body tissues. However, the theoretical basis for using stable isotopes to elucidate consumer–prey relationships remains poorly validated for most taxa despite numerous studies using this technique in natural systems. In this study, we measured stable carbon and stable nitrogen diet-tissue discrimination (Δ_dt) in whole blood, red blood cells, blood plasma solutes, and skin of leatherback sea turtles (Dermochelys coriacea; N = 7) maintained in captivity for up to 424 days and fed an isotopically consistent control diet with a mean C:N ratio of 2.94:1.00 and an energetic content of 20.16 ± 0.39 kJ g^− 1 Dry Mass. We used a random-effect repeated measure model to evaluate isotopic consistency among tissue samples collected on days 276, 348, and 424. Both δ¹³C and δ¹⁵N remained consistent among sampling events in all tissues (all 95% posterior intervals for the slopes of a linear model included zero), indicating that all tissues had fully integrated diet-derived stable isotope compositions. Mean tissue-specific δ¹³C ranged from − 18.30 ± 0.16‰ (plasma solutes) to − 15.54 ± 0.14‰ (skin), whereas mean δ¹⁵N was from 10.06 ± 0.22‰ (whole blood) to 11.46 ± 0.10‰ (plasma solutes). The computed Δ_dt factors for carbon ranged from − 0.58‰ (plasma solutes) to + 2.25‰ (skin), whereas Δ_dt for nitrogen was from + 1.49 (red blood cells) to + 2.85 (plasma solutes). As the only discrimination factors available for leatherback turtles, our data will be useful for future interpretations of field-derived stable isotope data for this species. The inherent variability in Δ_dt values among individuals was low, which supports the value of these data for dietary reconstructions. However, it is important to note that tissue-specific discrimination factors for leatherbacks contrast with the widely accepted values for endothermic species (0–1‰ for C, 3–5‰ for N), and are also different from values established for hard-shelled turtles. This underscores the need for species- and tissue-specific discrimination factors before interpreting trophic studies of wild animals, including marine turtles.     

Aggregating behaviour,social interactions and possible spawning in the deep‐water fish Coryphaenoides rupestris

A dense aggregation of the roundnose grenadier Coryphaenoides rupestris was observed with a towed camera at a depth of 1500 m in the Rockall Trough during September. The density of fish was 100 times greater than other sites. Within the aggregation the fish showed directional alignment, rapid swimming actions, mid‐water swimming and social interactions similar to those associated with spawning in other Gadiformes.     

Activity of neck-muscle motoneurones during eye cleaning behaviour in the cricket Gryllus campestris

The activity of neck-muscle motoneurones which control head movements during eye cleaning behaviour was recorded from motor nerves with chronically implanted electrodes in unrestrained crickets. We show that motoneurones of the dorso-ventral muscles displayed strong activity differences between both sides of the neck, with higher discharge frequencies either ipsi- or contralateral to the direction of the head movement. Motoneurones innervating dorsal-longitudinal muscles were equally active on both sides. A single excitatory motoneurone of one dorso-ventral muscle showed a discharge pattern unequivocally related to eye cleaning. Lesions of connectives revealed that this motoneurone is monitored by interneuronal pathways from the suboesophageal ganglion although the primary sensory axons eliciting eye cleaning, project into the prothoracic ganglion.     

The frequency distribution of Hymenolepis diminuta cysticercoids in natural,sympatric populations of Tenebrio molitor and T. obscurus

Rau M. E. 1979. The frequency distribution of Hymenolepis diminuta cysticercoids in natural, sympatric populations of Tenebrio molitor and T. obscurus. International Journal for Parasitology9: 85–87. Natural, sympatric populations of Tenebrio molitor and T. obscurus were examined for cysticercoids of Hymemlepis diminuta. The distribution of cysticeroids in both species and both sexes conformed to the negative binomial. Cysticeroids were more prevalent and the mean intensity of infection was higher in T. obscurus than in T. molitor. No differences in the intensity of infection were detected between the sexes. Larvae of both beetle species were always very lightly infected. The significance of these factors in the transmission of the infection to the rat definitive host is discussed.     

Effects of precocene I and II on flight behaviour in Oncopeltus fasciatus, the migratory milkweed bug

Treatment of newly emerged adult Oncopeltus fasciatus with the corpus allatum inhibitors. 7-methoxy-2,2-dimethyl chromene or 6,7-dimethoxy-2,2-dimethyl chromene (preocene I and II) results in an inhibition of long-term flight (presumed migratory) behaviour in both males and females and inhibition of oögenesis in females. Treatment of reproductive females with precocene briefly stimulates flight behaviour (which ceases in such females as oviposition begins) and then subsequently inhibits it. Oviposition also ceases in such females and oöcyte resorption occurs. Topical application or injections of JH III to precocenetreated animals results in immediate restoration of the tendency to make long tethered flights while corpora cardiaca extract injections, corpora cardiaca implantation, sham implantation, sham injections and sham topical applications were ineffective in restoring prolonged flight behaviour to precocene-treated animals.Restoration of flight by JH III injection was observed within 1 hr after treatment with the hormone. These results indicate that JH is necessary for prolonged flight and presumably migratory behaviour in this species and its stimulatory effect on flight behaviour is immediate. Possible mechanisms of action of the hormone on flight behaviour are discussed.     

Isolation of the abdomen releases oviposition behaviour in females of the cricket, Acheta domesticus

Upon isolation, abdomens of adult female house crickets (Acheta domesticus) produced abdominal and ovipositor movements characteristic of normal oviposition. Oviposition behaviour was thus released even in reproductively mature or immature virgins where under normal conditions it was never observed. Decapitation was not sufficient to release oviposition behaviour but transection of the ventral nerve cord between the thorax and the abdomen of immobilized females evoked the response. These observations indicate that the motor programmes for certain components of the oviposition sequence reside in the abdominal ganglia. Moreover, the prerequisite circuitry for ovipositional posturing of the abdomen and ovipositor appears to be functional prior to sexual maturity and insemination, primed by mating, and subject to inhibition by the thoracic ganglia.