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At least 451 records · Page 25Linked to original sources
PubMed2006

Individual variation in feeding habitat use by adult female green sea turtles (Chelonia mydas): are they obligately neritic herbivores?

Satellite telemetry and stable isotope analysis were used to confirm that oceanic areas (where water depths are >200 m) are alternative feeding habitats for adult female green sea turtles (Chelonia mydas), which have been thought to be obligate herbivores in neritic areas (where depths are <200 m). Four females were tagged with satellite transmitters and tracked during post-nesting periods from Ogasawara Islands, Japan. Three females migrated to neritic habitats, while transmissions from another female ceased in an oceanic habitat. The overall mean nighttime dive depths during oceanic swimming periods in two females were <20 m, implying that the main function of their nighttime dives were resting with neutral buoyancy, whereas the means in two other females were >20 m, implying that they not only rested, but also foraged on macroplankton that exhibit diel vertical migration. Comparisons of stable carbon and nitrogen isotope ratios between 89 females and the prey items in a three-source mixing model estimated that 69% of the females nesting on Ogasawara Islands mainly used neritic habitats and 31% mainly used oceanic habitats. Out of four females tracked by satellite, two females were inferred from isotope ratios to be neritic herbivores and the two others oceanic planktivores. Although post-nesting movements for four females were not completely consistent with the inferences from isotope ratios, possibly due to short tracking periods (28-42 days), their diving behaviors were consistent with the inferences. There were no relationships between body size and the two isotope ratios, indicating a lack of size-related differences in feeding habitat use by adult female green turtles, which was in contrast with loggerhead sea turtles (Caretta caretta). These results and previous findings suggest that ontogenetic habitat shifts by sea turtles are facultative, and consequently, their life histories are polymorphic.

Animal Migration↗
PubMed2006

Dugong grazing and turtle cropping: grazing optimization in tropical seagrass systems?

Grazing by dugongs and cropping by green turtles have the capacity to alter the subsequent nutritional quality of seagrass regrowth. We examined the effects of simulated light and intensive grazing by dugongs and cropping by turtles on eight nutritionally relevant measures of seagrass chemical composition over two regrowth periods (short-term, 1-4 months; long-term, 11-13 months) at two seagrass communities (a mixed species community with Zostera capricorni, Halophila ovalis, Halodule uninervis, Cymodocea rotundata and C. serrulate; and a monospecific bed of Halodule uninervis) in tropical Queensland, Australia. The concentrations of organic matter, total nitrogen, total water-soluble carbohydrates, total starch, neutral detergent fiber, acid detergent fiber, acid lignin, as well as the in vitro dry matter digestibility (IVDMD) were measured in the leaves and below-ground parts of each species using near-infrared reflectance spectroscopy (NIRS). Regrowth of preferred species such as H. ovalis and H. uninervis from simulated intensive dugong grazing after a year exhibited increased (by 35 and 25%, respectively, relative to controls) whole-plant N concentrations. Similarly, regrowth of H. ovalis from simulated turtle cropping showed an increase in the leaf N concentration of 30% after a year. However, these gains are tempered by reductions in starch concentrations and increases in fiber. In the short-term, the N concentrations increased while the fiber concentrations decreased. These data provide experimental support for a grazing optimization view of herbivory in the tropical seagrass system, but with feedback in a different manner. Furthermore, we suggest that in areas where grazing is the only major source of natural disturbance, it is likely that there are potential ecosystem level effects if and when numbers of dugongs and turtles are reduced.

Animals↗
PubMed2006

An XX/XY sex microchromosome system in a freshwater turtle, Chelodina longicollis (Testudines: Chelidae) with genetic sex determination.

Heteromorphic sex chromosomes are rare in turtles, having been described in only four species. Like many turtle species, the Australian freshwater turtle Chelodina longicollis has genetic sex determination, but no distinguishable (heteromorphic) sex chromosomes were identified in a previous karyotyping study. We used comparative genomic hybridization (CGH) to show that C. longicollis has an XX/XY system of chromosomal sex determination, involving a pair of microchromosomes. C-banding and reverse fluorescent staining also distinguished microchromosomes with different banding patterns in males and females in approximately 70% cells examined. GTG-banding did not reveal any heteromorphic chromosomes, and no replication asynchrony on the X or Y microchromosomes was observed using replication banding. We conclude that there is a very small sequence difference between X and Y chromosomes in this species, a difference that is consistently detectable only by high-resolution molecular cytogenetic techniques, such as CGH. This is the first time a pair of microchromosomes has been identified as the sex chromosomes in a turtle species.

Animals↗
PubMed1985

Effects of gonadectomy and steroid treatment on plasma gonadotropins and the response of superfused pituitaries to gonadotropin-releasing hormone in the turtle Sternotherus odoratus.

Gonadectomized (gonadex) turtles, Sternotherus odoratus, had significantly elevated plasma FSH, but LH was less consistently affected. Estradiol (E2)-implants suppressed plasma FSH in gonadex females but not in males: testosterone (T) partially suppressed FSH in males. In contrast, E2-treatment markedly suppressed pituitary LH content and in vitro LH secretion in gonadex and intact turtles (inhibitory effects of E2 were less in intact than ovariectomized females). These steroid effects were relatively specific for gonadotropin; pituitary TSH content was not altered. In vitro, pituitary LH secretion responded to doses of GnRH greater than or equal to 1 ng/ml and LH output remained elevated for at least 3 hr of continuous superfusion with gonadotropin-releasing hormone (GnRH). In general, gonadectomy elevated pituitary responsiveness to GnRH while E2 and T suppressed this responsiveness; the effects of E2 are greater in gonadectomized than intact turtles. Thus, negative gonadal feedback appears to be involved in the secretion of gonadotropins in turtles, and steroidal actions may be partly due to suppression of pituitary hormone content and responsiveness to GnRH.

Animals↗
PubMed1986

Steroid hormones reverse sex in turtles.

Injection of estradiol benzoate into eggs of snapping turtles and painted turtles caused all embryos to develop as females. A similar but less consistent female-determining effect was associated with injection of testosterone proprionate. Both species of turtles have temperature-dependent sex determination in nature, whereby embryos incubated at cool temperatures (25 degrees) develop as males and embryos incubated at warm temperatures (31 degrees) develop as females. Exogenous estrogens have been shown to feminize embryos in a wide variety of reptiles, although feminization by estrogens as well as testosterone has been demonstrated previously in only one turtle (Pieau, 1974).

Animals↗
PubMed1988

High-affinity binding of [3H]estradiol-17 beta by an estrogen receptor in the liver of the turtle.

Specific [3H]estradiol-17 beta ([3H]E2) binding activity (EBA) with characteristics of an estrogen receptor (ER) was demonstrated in cytosols and nuclear extracts of the female turtle, Chrysemys picta. Three different receptor assays (dextran-coated charcoal assay, hydroxylapatite batch procedure, and DNA-cellulose chromatography) were evaluated in terms of their applicability in analyzing large numbers of samples. For the measurement of cytosolic EBA, the hydroxylapatite batch procedure was found to be the most reliable assay. On the other hand, the dextran-coated charcoal assay was found to be the most appropriate method for the measurement of nuclear EBA. Turtle hepatic EBA binds [3H]E2 with high affinity (cytosolic, 17.4 +/- 2.8 X 10(9) M-1; nuclear, 17.7 +/- 1.9 X 10(9) M-1), limited capacity (cytosolic, 133.7 +/- 4.6 fmol/g tissue; nuclear, 81.1 +/- 9.0 fmol/g tissue), and strict steroid specificity. The EBA bound natural estrogens (E2, estrone, estriol) as well as the nonsteroidal estrogen, diethylstilbestrol, but exhibited little affinity for androgens, progesterone, or corticosterone. The turtle hepatic EBA resembled mammalian and avian ERs in terms of binding characteristics; however, unlike mammalian and avian ERs it was shown to be heat-labile. Incubation at 30 degrees caused rapid loss of [3H]E2 binding activity in both cytosolic and nuclear fractions. The exchange between [3H]E2 and the endogenously bound estrogen was slow at 4 and 15 degrees, but the exchange process was facilitated in the presence of the chaotropic salt, NaSCN. Establishment of quantitation methods for both cytosolic and nuclear forms of EBA will enable future investigation of the mechanism and regulation of estrogen action in the liver of this turtle species.

Animals↗
PubMed1989

Effect of ambient temperature on serotonin, norepinephrine, and epinephrine contents in the pineal-paraphyseal complex of the soft-shelled turtle (Lissemys punctata punctata).

The aim of the present investigation was to ascertain the influence of ambient temperature on serotonin, norepinephrine, and epinephrine contents in the pineal-paraphyseal complex of soft-shelled turtles. Turtles were exposed to low (10 degrees) and high (32 degrees) temperatures for 7 days in an incubator with the same photoperiod (12L:12D). Control animals were also kept in the same incubator at 25 degrees for similar duration with the same photoperiod. The findings revealed that ambient temperatures significantly altered serotonin, norepinephrine, and epinephrine content in the pineal-paraphyseal complex of turtles. The results thus indicate that ambient temperature has some influence on pineal serotonin, norepinephrine, and epinephrine contents in soft-shelled turtles.

Animals↗
PubMed1990

Seasonal changes in serum gonadal steroids associated with migration, mating, and nesting in the loggerhead sea turtle (Caretta caretta).

Adult male loggerhead sea turtles, Caretta caretta, exhibited a "prenuptial" spermatogenic cycle that was coincident with increased concentrations of serum testosterone (T). Serum T was high during the months when migration and mating have been recorded for males. In contrast to females, males appear to be annual breeders. Nine reproductively active female C. caretta (as verified through laparoscopy) were tagged with sonic transmitters and were repeatedly bled prior to migration. Four months prior to the nesting season, the ovaries of reproductively active females had hundreds of vitellogenic follicles of approximately 1.5 cm in diameter (i.e., half the size of ovulatory follicles). Approximately 4-6 weeks prior to migration from feeding grounds to mating and nesting areas, serum estradiol-17 beta (E2) concentrations increased significantly and remained high for approximately 4 weeks, suggesting a period of increased vitellogenesis. During a 1- to 2-week period prior to migration, serum E2 decreased significantly, while serum T concentrations increased (at least) until the time of migration. Serum T, E2, and progesterone (PRO) were elevated during nesting if a turtle was going to nest again during that nesting season. During the last nesting of a season, turtles had low serum concentrations of T, E2, and Pro. The prenuptial pattern of gonadal recrudescence and gonadal steroid production in both male and female C. caretta contrasts with those of many temperate freshwater turtles, and this type of reproductive pattern may have been facilitated by adaptation to a tropical marine environment.

Animals↗
PubMed1977

The respiratory gas exchange of sea turtle nests (Chelonia, Caretta).

Sea turtles lay about 100 leathery-shelled eggs in a 25 cm diameter chamber carefully excavated about 50 cm deep in a nesting beach, where the eggs exchange gases (at approximately 28 degrees C) during their 60-day incubation period. The sand surrounding the spherical nest chamber restricts the diffusion of gases into and out of the nest so that as embryonic development progresses, PO2 decreases and PCO2 increases in the gas inside the nest. PO2 falls to 80-100 torr and PCO2 rises to 40-60 torr inside 100-egg man-made Chelonia and Caretta nests. The change in gas tensions in the nest during development is very similar to that seen in the air cell of the chicken egg. Gas tensions inside the turtle nest and in the sand surrounding the nest can be described by a radial steady-state diffusion model. The rate of diffusion of gases in the sand is 30-50% of the rate found in the nest and 6-12% of the rate found in an equal volume of air. The sand surrounding the turtle nest appears to determine the gas exchange of the eggs in the nest and is functionally analogous to the shell surrounding the chicken embryo. The female sea turtle may construct her nest so as the maximize its gas exchange and minimize gas partial pressure gradients inside the nest.

Animals↗
PubMed1979

Ventilatory response to inspired CO2 in the sea turtle: effects of body size and temperature.

The ventilatory response of green turtles (Chelonia mydas) to inspired CO2 was tested. Both immature (0.9--1.35 kg) and adult (59--130 kg) animals responded with increased ventilation (VE) that was primarily (immature) or exclusively (adult) due to increased respiratory frequency. The VE of the immature turtles while breathing air increased with temperatures between 15 and 35 degrees C with a Q10 of 1.95, but the peak VE of these turtles while breathing 4.5% CO2 in air was not significantly different at 15, 25 or 35 degrees C. VE increased irregularly with time throughout an hour of CO2 breathing in both groups, although several of the adult animals exhibited a first-breath response to CO2 and all animals increased VE within 5 min after the onset of CO2 breathing. The VE of an immature turtle at 35 degrees C increased with graded increases in CO2 up to 6%, but at 15 and 25 degrees C VE increased only up to 4.5% and decreased with 6% CO2. The results are discussed in terms of possible receptor mechanisms involved.

Aging↗
PubMed1984

Anti-immunoglobulin induced histamine release from naturally abundant basophils in the snapping turtle, Chelydra serpentina.

The dose response, temperature sensitivity, time course and calcium dependency of histamine release from snapping turtle basophils treated with rabbit anti-turtle immunoglobulin (RATIg) sera was explored. This investigation indicated that the level of histamine release induced by RATIg was dependent upon the concentration of RATIg with concentrations of 350 mcg/ml inducing optimal release. In addition, release was temperature dependent with release increasing over a temperature range of 10 degrees C to maximal at 27 degrees C. Release was also dependent on the length of exposure to RATIg. Release increased steadily over a time period of 0 to 30 minutes with the higher concentrations of RATIg inducing the most rapid release. Basophil-histamine release was also found to be calcium dependent. This study indicates that the snapping turtle basophil possesses similar characteristics to that of its mammalian counterparts. It is proposed that the very wide temperature range over which turtle basophils release histamine is an important feature in he immune resistance of this ectothermic animal.

Animals↗
PubMed1992

Reduced sensitivity of O2 transport to allosteric effectors and temperature in loggerhead sea turtle hemoglobin: functional and spectroscopic study.

The functional and spectroscopic (EPR and absorbance) properties of the adult loggerhead sea turtle (Caretta caretta) hemoglobin have been studied with special reference to the action of allosteric effectors and temperature. Present results indicate that turtle Hb displays a very low O2 affinity and a very small sensitivity to allosteric effectors and temperature. Furthermore, the amplitude of the Bohr effect for O2 binding is strongly reduced. In parallel, EPR and absorbance spectroscopic properties of the nitrosylated derivative of turtle Hb suggest that the hemoprotein is in a low-affinity conformation, even in the absence of allosteric effectors. These findings suggest the existence of unusual molecular mechanisms modulating the basic reaction of Hb with O2, which may be linked to specific physiological needs related to the diving behavior of the turtle.

Allosteric Regulation↗
PubMedDate not supplied

Isolation and structural characterization of insulin, glucagon and somatostatin from the turtle, Pseudemys scripta.

The chelonians occupy an important position in phylogeny representing a very early branching from the ancestral reptile stock. Hormonal polypeptides in an extract of the pancreas of the red-eared turtle were purified to homogeneity by reversed phase HPLC and their primary structures were determined. Turtle insulin is identical to chicken insulin. Turtle glucagon differs from chicken glucagon by the substitution of a serine by a threonine residue at position 16 and from mammalian glucagon by an additional substitution of an asparagine by a serine residue at position 28. Turtle pancreatic somatostatin is identical to mammalian somatostatin-14. The crocodilians are phylogenetically much closer to the birds than are the chelonians. Alligator insulin, however, contains three amino acid substitutions relative to chicken insulin. Thus, caution is required when inferring phylogenetic relationships based upon a comparison of amino acid sequences of homologous peptides.

Amino Acid Sequence↗
PubMedDate not supplied

Differential N-acetylation of alpha-MSH and beta-endorphin in the intermediate pituitary of the turtle, Pseudemys scripta.

Steady-state analyses of the intermediate pituitary of the turtle, Pseudemys scripta, indicated that alpha-MSH-sized immunoreactive forms and beta-endorphin-sized immunoreactive forms are major end products of melanotropic cells. Three forms of alpha-MSH-related immunoreactivity were detected. The two major forms had the same reversed-phase HPLC properties as synthetic N,O-diacetyl-ACTH(1-13)-NH2 and N-acetyl-ACTH(1-13)-NH2. These forms accounted for 97% of the total alpha-MSH-related immunoreactivity detected. A minor peak of ACTH(1-13)-NH2 was also detected. Multiple forms of beta-endorphin-related immunoreactivity were detected, which varied in net positive charge (+1 to +5), apparent molecular weight (2.4 to 3.5 kDa), and degree of N-terminal acetylation. Although N-acetylated forms of beta-endorphin were detected in the turtle intermediate pituitary, the major forms of turtle beta-endorphin were nonacetylated. These features of the turtle intermediate pituitary POMC-specific N-acetylation mechanism are similar to, yet distinct from, the POMC N-acetylation mechanisms observed for mammals. These data suggest that POMC-specific N-acetylation mechanisms were present in reptiles prior to the divergence of the anapsid and synapsid lines.

Acetylation↗
PubMed1984

Cytoskeletal control of alanine transport across the rat and turtle small intestine.

Procaine inhibited significantly (P less than 0.01) alanine accumulation in the rat intestinal strips in a concentration-dependent pattern, whereas it showed no effect on alanine uptake by the turtle intestinal cells. Colchicine and Vinca alkaloids at 5 X 10(-4) and 1.5 X 10(-6) M respectively caused a significant inhibition (P less than 0.01) of intracellular alanine concentration in the rat with no effect noticed in the turtle. Unidirectional influx of alanine across the brush border membrane of the rat was significantly (P less than 0.01) reduced in the presence of procaine, colchicine and vincristine in the preincubation medium. The same drugs did not show any effect on alanine influx into the turtle small intestine. Electron microscopy showed major structural alterations in the cytoskeletal organization of the turtle intestine in response to procaine, colchicine or vincristine treatment. It is proposed that microtubular system may participate in the overall transport mechanism of alanine across the small intestine.

Alanine↗
PubMed1987

Characterization of angiotensin I-converting enzyme activity in the freshwater turtle, Amyda japonica.

1. Angiotensin I-Converting Enzyme (ACE) activity has been characterized in the freshwater turtle, Amyda japonica. 2. Peak activity of ACE in plasma from the freshwater turtle was shown at pH 9.0, which was more alkaline compared to that of mammals. 3. Chloride requirements for the optimal ACE activity were different from species. 4. ACE inhibitors, EDTA, teprotide (SQ 20,881), Captopril (SQ 14,225) showed dose-dependent inhibitions of ACE activity in plasma from the freshwater turtle as well as mammals. 5. ACE activity was found in several different tissues with a different activity showing the highest activity in kidney homogenate from the freshwater turtle, Amyda japonica.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1983

Somatostatin-like immunoreactivity in the forebrain of Pseudemys turtles.

Previous investigations of cortical organization in the brain of the turtle have revealed many features typical of mammalian neocortex. Recent evidence suggests that many neocortical neurons contain neuroactive peptides. The possibility that one such peptide, somatostatin, is found in the turtle brain was tested using immunocytochemical techniques. Intense somatostatin-like immunoreactivity was observed in many neurons and fibers in turtle cortex, as well as in several forebrain nuclei. Cortical neurons with several different dendritic configurations showed immunoreactive labelling, including bipolar, stellate and pyramidal cell types. In addition, stained cells and processes were observed in close association with the ependyma of the lateral ventricle. Other forebrain regions containing immunoreactive neurons included the dorsal ventricular ridge, the basal telencephalic nuclei and the hypothalamus. These data support the idea that peptidergic neurons existed in the pallium of an ancestor common to modern mammals and reptiles. We speculate that somatostatin plays a similar role in the normal function of all types of cortex and suggest that turtle cortex may provide a useful model for the study of this cortical neuropeptide.

Animals↗
PubMed1995

Enzymatic control of glycogenolysis during anoxic submergence in the freshwater turtle Trachemys scripta.

Freshwater turtles Trachemys scripta elegans endure prolonged severe hypoxia, and even complete anoxia, while diving or hibernating underwater. Metabolic adaptations supporting survival include the activation of glycogenolysis and glucose output from liver, as well as strong metabolic rate depression. The present study analyzes the enzymes of both the phosphorolytic (glycogen phosphorylase, phosphorylase b kinase, cAMP-dependent protein kinase) and glucosidic (alpha-glucosidase) pathways of glycogenolysis in turtle organs. Turtles were subjected to 5 hr of submergence in N2-bubbled water at 7 degrees C and then activities of phosphorolytic and glucosidic enzymes were assayed in liver, heart, brain, and red and white skeletal muscle, and compared with aerobic controls. In vitro incubations also assessed protein kinase A control of phosphorolytic enzymes. A functional enzyme cascade system for the activation of glycogen phosphorylase was found in all organs, and both phosphorylase and phosphorylase kinase were stimulated by in vitro incubation with the catalytic subunit of cAMP-dependent protein kinase. Anoxic submergence led to significant increases in phosphorylase activities in liver and heart (phosphorylase a rose 2- and 2.5-fold, respectively) but phosphorylase kinase and protein kinase A activities in liver were reduced after 5 hr exposure. Both acidic (pH 4) and neutral (pH 7) forms of alpha-glucosidase were detected in all five organs with highest activities in liver. Activity of acid alpha-glucosidase, which degrades lysosomal glycogen, increased by 2-fold in liver during anoxic submergence. The data show that glycogen breakdown in turtle liver during anoxic submergence may result from coordinated activations of both the cytoplasmic phosphorolytic and the lysosomal glucosidic pathways of glycogenolysis.

Adaptation, Physiological↗