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PubMedDate not supplied

Metabolic heating and the prediction of sex ratios for green turtles (Chelonia mydas).

We compared incubation temperatures in nests (n=32) of the green turtle (Chelonia mydas) on Ascension Island in relation to sand temperatures of control sites at nest depth. Intrabeach thermal variation was low, whereas interbeach thermal variation was high in both control and nest sites. A marked rise in temperature was recorded in nests from 30% to 40% of the way through the incubation period and attributed to metabolic heating. Over the entire incubation period, metabolic heating accounted for a mean rise in temperature of between 0.07 degrees and 2.86 degrees C within nests. During the middle third of incubation, when sex is thought to be determined, this rise in temperature ranged between 0.07 degrees and 2.61 degrees C. Metabolic heating was related to both the number of eggs laid and the total number of hatchlings/embryos produced in a clutch. For 32 clutches in which temperature was recorded, we estimate that metabolic heating accounted for a rise of up to 30% in the proportion of females produced within different clutches. Previous studies have dismissed any effect of metabolic heating on the sex ratio of marine turtle hatchlings. Our results imply that metabolic heating needs to be considered when estimating green turtle hatchling sex ratios.

Animals↗
PubMedDate not supplied

Effect of anoxia and pharmacological anoxia on whole-cell NMDA receptor currents in cortical neurons from the western painted turtle.

The mammalian brain undergoes rapid cell death during anoxia that is characterized by uncontrolled Ca(2+) entry via N-methyl-D-aspartate receptors (NMDARs). In contrast, the western painted turtle is extremely anoxia tolerant and maintains close-to-normal [Ca(2+)](i) during periods of anoxia lasting from days to months. A plausible mechanism of anoxic survival in turtle neurons is the regulation of NMDARs to prevent excitotoxic Ca(2+) injury. However, studies using metabolic inhibitors such as cyanide (NaCN) as a convenient method to induce anoxia may not represent a true anoxic stress. This study was undertaken to determine whether turtle cortical neuron whole-cell NMDAR currents respond similarly to true anoxia with N(2) and to NaCN-induced anoxia. Whole-cell NMDAR currents were measured during a control N(2)-induced anoxic transition and a control NaCN-induced transition. During anoxia with N(2) normalized, NMDAR currents decreased to 35.3%+/-10.8% of control values. Two different NMDAR current responses were observed during NaCN-induced anoxia: one resulted in a 172%+/-51% increase in NMDAR currents, and the other was a decrease to 48%+/-14% of control. When responses were correlated to the two major neuronal subtypes under study, we found that stellate neurons responded to NaCN treatment with a decrease in NMDAR current, while pyramidal neurons exhibited both increases and decreases. Our results show that whole-cell NMDAR currents respond differently to NaCN-induced anoxia than to the more physiologically relevant anoxia with N(2).

Animals↗
PubMed2004

Assessing concordance of fossil calibration points in molecular clock studies: an example using turtles.

Although still controversial, estimation of divergence times using molecular data has emerged as a powerful tool to examine the tempo and mode of evolutionary change. Two primary obstacles in improving the accuracy of molecular dating are heterogeneity in DNA substitution rates and accuracy of the fossil record as calibration points. Recent methodological advances have provided powerful methods that estimate relative divergence times in the face of heterogeneity of nucleotide substitution rates among lineages. However, relatively little attention has focused on the accuracy of fossil calibration points that allow one to translate relative divergence times into absolute time. We present a new cross-validation method that identifies inconsistent fossils when multiple fossil calibrations are available for a clade and apply our method to a molecular phylogeny of living turtles with fossil calibration times for 17 of the 22 internal nodes in the tree. Our cross-validation procedure identified seven inconsistent fossils. Using the consistent fossils as calibration points, we found that despite their overall antiquity as a lineage, the most species-rich clades of turtles diversified well within the Cenozoic. Many of the truly ancient lineages of turtles are currently represented by a few, often endangered species that deserve high priority as conservation targets.

Animals↗
PubMed2005

Extracellular determinants of cardiac contractility in the cold anoxic turtle.

Painted turtles (Chrysemys picta) survive months of anoxic submergence, which is associated with large changes in the extracellular milieu where pH falls by 1, while extracellular K+, Ca++, and adrenaline levels all increase massively. While the effect of each of these changes in the extracellular environment on the heart has been previously characterized in isolation, little is known about their interactions and combined effects. Here we examine the isolated and combined effects of hyperkalemia, acidosis, hypercalcemia, high adrenergic stimulation, and anoxia on twitch force during isometric contractions in isolated ventricular strip preparations from turtles. Experiments were performed on turtles that had been previously acclimated to warm (25 degrees C), cold (5 degrees C), or cold anoxia (submerged in anoxic water at 5 degrees C). The differences between acclimation groups suggest that cold acclimation, but not anoxic acclimation per se, results in a downregulation of processes in the excitation-contraction coupling. Hyperkalemia (10 mmol L(-1) K+) exerted a strong negative inotropic effect and caused irregular contractions; the effect was most pronounced at low temperature (57%-97% reductions in twitch force). Anoxia reduced twitch force at both temperatures (14%-38%), while acidosis reduced force only at 5 degrees C (15%-50%). Adrenergic stimulation (10 micromol L(-1)) increased twitch force by 5%-19%, but increasing extracellular [Ca++] from 2 to 6 mmol L(-1) had only small effects. When all treatments were combined with anoxia, twitch force was higher at 5 degrees C than at 25 degrees C, whereas in normoxia twitch force was higher at 25 degrees C. We propose that hyperkalemia may account for a large part of the depressed cardiac contractility during long-term anoxic submergence.

Acclimatization↗
PubMed2006

Energetics during hatchling dispersal of the olive ridley turtle Lepidochelys olivacea using doubly labeled water.

Studies of metabolism are central to the understanding of the ecology, behavior, and evolution of reptiles. This study focuses on one phase of the sea turtle life cycle, hatchling dispersal, and gives insight into energetic constraints that dispersal imposes on hatchlings. Hatchling dispersal is an energetically expensive phase in the life cycle of the olive ridley turtle Lepidochelys olivacea. Field metabolic rates (FMRs), determined using the doubly labeled water (DLW) method, for L. olivacea hatchlings digging out of their nest chamber, crawling at the sand surface, and swimming were five, four, and seven times, respectively, the resting metabolic rate (RMR). The cost of swimming was 1.5 and 1.8 times the cost of the digging and crawling phases, respectively, and we estimated that if L. olivacea hatchlings swim at frenzy levels, they can rely on yolk reserves to supply energy for only 3-6 d once they reach the ocean. We compared our RMR and FMR values by establishing an interspecific RMR mass-scaling relationship for a wide range of species in the order Testudines and found a scaling exponent of 1.06. This study demonstrates the feasibility of using the DLW method to estimate energetic costs of free-living sea turtle hatchlings and emphasizes the need for metabolic studies in various life-history stages.

Animals↗
PubMed2006

Influence of the nest environment on bone mineral content in hatchling painted turtles (Chrysemys picta).

We performed an experiment at a field site in north-central Nebraska to assess the role of the nest environment in inducing variation in bone mineral content in hatchling painted turtles Chrysemys picta (Schneider 1783). The contents of several newly constructed nests were manipulated by reciprocal transplant, after which the eggs were allowed to incubate for 8 wk under natural conditions. The nests were then excavated, and the eggs were brought into the laboratory to complete incubation and hatch under standard conditions of temperature and moisture. The hatchlings were killed, and their carcasses and residual yolks were analyzed separately for calcium and phosphorus. More of the random variation in carcass calcium and phosphorus was related to the nest in which eggs incubated (37% and 42%, respectively) than was associated with the clutch of origin (21% and 37%). Moreover, hatchlings from some nests contained substantially more calcium and phosphorus than did hatchlings from other nests, both in terms of the absolute amounts of the elements in their carcasses (pointing to variation in body size) and in terms of the concentrations of those elements (pointing to variation in bone density). The amounts of calcium and phosphorus in carcasses of hatchlings were positively correlated with changes in mass of their eggs during the 8 wk that the eggs incubated in nests in the field, thereby indicating that the influence of the nest environment on developing embryos probably was mediated by water exchanges experienced by the eggs. These findings indicate that developmental plasticity underlies a major fraction of the variation in mineral content of hatchling painted turtles emerging from nests in the field. Phenotypic variation attributable to plasticity consequently needs to be addressed in models for life-history evolution of painted turtles and other chelonians producing eggs with soft, flexible shells.

Animals↗
PubMed1997

Concentration and membrane fluidity dependence of odor discrimination in the turtle olfactory system.

In the present study, we examined the concentration dependence of odor discrimination in turtle olfactory bulbar responses using the cross-adaptation technique. In the odorant pairs with diverse molecular structures, the degree of discrimination was unchanged or only slightly decreased with an increase in odorant concentrations, suggesting that odorants are well discriminated even at high concentrations. In the odorant pairs with closely related molecular structures, the degree of discrimination was decreased with an increase in odorant concentrations. An increase in the temperature of turtle olfactory epithelium also decreased the ability to discriminate these odorants. There was a good correlation between changes in the odor discriminating ability induced by an increase in odor concentrations and those induced by a temperature increase. The liposomes were made of lipids extracted from the turtle olfactory epithelia and changes of their membrane fluidity induced by adsorption of odorants were monitored with DPH. There was a good correlation between a decrease in odor discriminating ability and the membrane fluidity changes induced by odorants. We suggest that decreases in odor discriminating ability induced either by an increase in odor concentration or by a temperature increase are ultimately caused by changes in the membrane fluidity.

Animals↗
PubMed1995

Conservation and dynamics of microsatellite loci over 300 million years of marine turtle evolution.

Microsatellite loci consisting of (CA)n repetitive arrays were obtained from three species of marine turtle, and primers were designed to test for polymorphism within species and the persistence of microsatellites across species. Homologous loci were found in each test of six marine species within two families (Cheloniidae and Dermochelyidae), as well as in a freshwater species (Emydidae, Trachemys scripta), which indicates a conservation of flanking sequences spanning approximately 300 million years of divergent evolution. The persistence of homologous microsatellites across marine turtles was confirmed by direct sequencing of loci across species and by the discovery of polymorphism in 24 of 30 cross species tests. The conservation of flanking sequences could be due to a slow rate of base substitution in turtle nuclear DNA, as previously reported for mtDNA. In contrast, the presence of up to 25 alleles per locus per species indicates that the replication slippage events responsible for changes in allele length operate as in mammals. Comparisons of alleles among species revealed that alleles of the same length may not be homologous due to mutations within the flanking sequences. Levels of heterozygosity were consistently higher in species from which the primers were designed, which suggests problems with cross-species comparisons of variability. Within species, microsatellite variation between divergent populations was consistent with results from previous mtDNA studies indicating the usefulness of microsatellites for comparing male- versus female-mediated gene flow.

Animals↗
PubMed1992

Hydroxysteroid dehydrogenase activity associated with sexual differentiation in embryos of the turtle Trachemys scripta.

Many turtles exhibit temperature-dependent sex determination. We have examined the hypothesis that incubation temperature causes a differential expression of steroidogenic enzymes in embryonic turtles. The activities of three steroidogenic enzymes were studied histochemically in turtle (Trachemys scripta) embryos at different developmental stages: sexually undifferentiated (Stage 15), differentiating (Stage 17), and differentiated (Stage 26; i.e., hatchling). Steroidogenic enzymes were detected in several tissues prior to, during, and after gonadal differentiation in embryos incubated at both male-producing and female-producing temperatures. In all embryos, ene-5-3 beta-hydroxysteroid dehydrogenase (HSDH) was detected only in adrenal tissue. 3 alpha-HSDH was localized in adrenal tissue, as well as in the mesonephros and liver. 17 beta-HSDH was evident in mesonephric, hepatic, and gut tissues. In hatchlings, ene-5-3 beta-HSDH and 3 alpha-HSDH were evident in the adrenal gland, whereas 3 alpha-HSDH and 17 beta-HSDH were present in the mesonephros and liver. While there was some variation in the activities of these enzymes during development, no temperature-specific pattern was apparent. At no stage were the enzymes observed in genital ridge/gonad. Our results show that T. scripta embryos possess enzymes necessary for steroid hormone synthesis. The segregated distributions of the enzymes suggest that a multi-organ regulatory system may mediate embryonic steroidogenesis. Our results do not indicate the genital ridge/gonad the principle site of steroid synthesis, although it may possess other enzymes that influence steroidogenesis.

Animals↗
PubMed1994

Role of aromatization in testosterone-induced inhibition of luteinizing hormone secretion in female turtles, Trachemys scripta.

Both 17 beta-estradiol (E2) and testosterone (T) were shown to inhibit in vitro pituitary LH secretion in the turtle Trachemys scripta. Since T was approximately 500 times less potent than E2, and 5 alpha-dihydrotestosterone was even less active than T, the inhibitory action of T may result from its aromatization to estrogen. We utilized both in vivo and in vitro approaches to elucidate the roles of T and estrogen in the negative feedback of pituitary LH secretion. Gonadectomy of adult (vitellogenic) females significantly elevated plasma LH. Adult females treated with fadrozole (an aromatase inhibitor) with or without daily injections of keoxifene (an antiestrogen) also showed an increase in plasma LH to a level comparable to that observed in gonadectomized females, whereas plasma LH levels of juvenile females treated with fadrozole remained undetectable. In vitro LH secretion in response to GnRH in juvenile females was significantly inhibited by 48-h exposure to 50 ng/ml T or 100 pg/ml E2. Both fadrozole (200 microM) and keoxifene (200 nM) significantly blocked this T-induced inhibition of LH secretion, demonstrating that T lacks intrinsic inhibitory activity. Confirmation of the inhibition of aromatase activity by fadrozole comes from metabolic studies of 1 beta-[3H]androstenedione using turtle brain, ovary, and pituitary. In vitro, fadrozole altered the metabolism of 1 beta-[3H]androstenedione and inhibited aromatase activities in these tissues. These results indicate that the inhibitory effect of T is largely mediated through its aromatization to estrogen, and that estrogen is primarily responsible for the suppressed LH secretion in vitellogenic adult turtles.

Androstenedione↗
PubMed1998

Low extracellular dopamine levels are maintained in the anoxic turtle (Trachemys scripta) striatum.

The uncontrolled increase of extracellular dopamine (DA) has been implicated in the pathogenesis of hypoxic/ischemic damage in the mammalian brain. But unlike the harmful release of excitatory neurotransmitters such as glutamate and aspartate, which occurs on brain depolarization, excessive extracellular DA levels occur even with mild hypoxia in the mammalian brain. The purpose of this study was to determine whether hypoxia/anoxia provokes a similar increase in the anoxic tolerant turtle brain. Extracellular DA was measured in the striatum of the turtle using microdialysis followed by high-performance liquid chromatography analysis. Results show that extracellular DA was held to normoxic levels over 4 hours of anoxia. Treatment with the specific DA transport blocker GBR 12909 during anoxia resulted in a significant increase in DA to 236% over basal levels. The ability to maintain low striatal extracellular DA may be an important adaptation for anoxic survival in the turtle brain; a contributing factor is the continued functioning of DA uptake mechanisms during anoxia.

Animals↗
PubMed2005

Nesting fidelity and molecular evidence for natal homing in the freshwater turtle, Graptemys kohnii.

Numerous studies of sea turtle nesting ecology have revealed that females exhibit natal homing, whereby they imprint on the nesting area from which they hatch and subsequently return there to nest as adults. Because freshwater turtles comprise the majority of reptiles known to display environmental sex determination (ESD), the study of natal homing in this group may shed light on recent evolutionary models of sex allocation that are predicated on natal homing in reptiles with ESD. We examined natal homing in Graptemys kohnii, a freshwater turtle with ESD, using mitochondrial sequencing, microsatellite genotyping and mark and recapture of 290 nesting females. Females showed high fidelity to nesting areas, even after being transplanted several kilometres away. A Mantel test revealed significant genetic isolation by distance with respect to nesting locations (r=0.147; p<0.05), suggesting that related females nest in close proximity to one another. The patterns of fidelity and genotype distributions are consistent with homing at a scale that may affect population sex ratios.

Animals↗
PubMed1982

The morphology of the bipolar cells, amacrine cells and ganglion cells in the retina of the turtle Pseudemys scripta elegans.

The morphology of the neurons that contribute to the inner plexiform layer of the retina of the turtle Pseudemys scripta elegans has been studied by light microscopy of whole-mount material stained by the method of Golgi. Cells have been distinguished on the basis of criteria that include dendritic branching patterns, dendritic morphology, dendritic tree sizes and stratification of processes in the inner plexiform layer. Many of the neurons have dendritic trees oriented parallel to and a few exhibit an orthogonal orientation with the linear visual streak present in the retina of this species. The neurons of the turtle retina have been compared, where possible, with the neurons of the lizard retina as described by Cajal. The findings are discussed in relation to other vertebrate retinas, and correlations are made with recent electrophysiological recordings of the turtle retina. Comments are made with regard to the significance of orientation of neurons relative to the linear visual streak.

Action Potentials↗
PubMed2003

Molecular systematics, phylogeography, and the effects of Pleistocene glaciation in the painted turtle (Chrysemys picta) complex.

The painted turtle, Chrysemys picta, is currently recognized as a continentally distributed polytypic species, ranging across North America from southern Canada to extreme northern Mexico. We analyzed variation in the rapidly evolving mitochondrial control region (CR) in 241 turtles from 117 localities across this range to examine whether the painted turtle represents a continentally distributed species based on molecular analysis. We found strong support for the novel hypothesis that C. p. dorsalis is the sister group to all remaining Chrysemys, with the remaining Chrysemys falling into a single, extremely wide-ranging and genetically undifferentiated species. Given our goal of an evolutionarily accurate taxonomy, we propose that two evolutionary lineages be recognized as species within Chrysemys: C. dorsalis (Agassiz 1857) in the southern Mississippi drainage region, and C. picta (Schneider 1783) from the rest of the range of the genus. Neither molecular nor recent morphological analyses argue for the hybrid origin of C. p. marginata as previously proposed. Within C. picta, we find evidence of at least two independent range expansions into previously glaciated regions of North America, one into New England and the other into the upper Midwest. We further find evidence of a massive extinction/recolonization event across the Great Plains/Rocky Mountain region encompassing over half the continental United States. The timing and extent of this colonization is consistent with a recently proposed regional aridification as the Laurentide ice sheets receded approximately 14,000 years ago, and we tentatively propose this paleoclimatological event as a major factor shaping genetic variation in Chrysemys.

Animals↗
PubMed2006

Robust hierarchical state-space models reveal diel variation in travel rates of migrating leatherback turtles.

1. Biological and statistical complexity are features common to most ecological data that hinder our ability to extract meaningful patterns using conventional tools. Recent work on implementing modern statistical methods for analysis of such ecological data has focused primarily on population dynamics but other types of data, such as animal movement pathways obtained from satellite telemetry, can also benefit from the application of modern statistical tools. 2. We develop a robust hierarchical state-space approach for analysis of multiple satellite telemetry pathways obtained via the Argos system. State-space models are time-series methods that allow unobserved states and biological parameters to be estimated from data observed with error. We show that the approach can reveal important patterns in complex, noisy data where conventional methods cannot. 3. Using the largest Atlantic satellite telemetry data set for critically endangered leatherback turtles, we show that the diel pattern in travel rates of these turtles changes over different phases of their migratory cycle. While foraging in northern waters the turtles show similar travel rates during day and night, but on their southward migration to tropical waters travel rates are markedly faster during the day. These patterns are generally consistent with diving data, and may be related to changes in foraging behaviour. Interestingly, individuals that migrate southward to breed generally show higher daytime travel rates than individuals that migrate southward in a non-breeding year. 4. Our approach is extremely flexible and can be applied to many ecological analyses that use complex, sequential data.

Animal Migration↗
PubMed2006

Microsatellites provide insight into contrasting mating patterns in arribada vs. non-arribada olive ridley sea turtle rookeries.

Molecular studies of sea turtles have shown that the frequency of multiple paternity (MP) varies between species, and between rookeries of the same species. This study uses nuclear microsatellite markers to compare the incidence of MP in two neighbouring olive ridley rookeries on the Pacific coast of Costa Rica, with contrasting nesting behaviours -- the 'arribada' population nesting at Ostional and the solitary nesters of Playa Hermosa. Using two highly polymorphic microsatellite markers, we tested 13 nests from each location and found a significant difference (P < 0.001) between the level of MP of the arribada rookery (92%- the highest found for marine turtles) and that of the solitary nesting rookery (30%). Additional analyses based on six microsatellite loci revealed no genetic differentiation between nesting females from the two locations, or between nesting females and attendant males from the Ostional breeding area. Sixty-nine per cent of the nests with MP were fathered by a minimum of three different males, and three nests showed evidence of at least four fathers. The results suggest that the differences observed in levels of MP between arribada and solitary rookeries are due to an effect of abundance of individuals on the mating system. This is supported by a regression analysis combining other paternity studies on sea turtles which shows that levels of MP increase with increasing abundance of nesting females.

Alleles↗
PubMed2006

The genetic structure of Australasian green turtles (Chelonia mydas): exploring the geographical scale of genetic exchange.

Ecological and genetic studies of marine turtles generally support the hypothesis of natal homing, but leave open the question of the geographical scale of genetic exchange and the capacity of turtles to shift breeding sites. Here we combine analyses of mitochondrial DNA (mtDNA) variation and recapture data to assess the geographical scale of individual breeding populations and the distribution of such populations through Australasia. We conducted multiscale assessments of mtDNA variation among 714 samples from 27 green turtle rookeries and of adult female dispersal among nesting sites in eastern Australia. Many of these rookeries are on shelves that were flooded by rising sea levels less than 10 000 years (c. 450 generations) ago. Analyses of sequence variation among the mtDNA control region revealed 25 haplotypes, and their frequency distributions indicated 17 genetically distinct breeding stocks (Management Units) consisting either of individual rookeries or groups of rookeries in general that are separated by more than 500 km. The population structure inferred from mtDNA was consistent with the scale of movements observed in long-term mark-recapture studies of east Australian rookeries. Phylogenetic analysis of the haplotypes revealed five clades with significant partitioning of sequence diversity (Phi = 68.4) between Pacific Ocean and Southeast Asian/Indian Ocean rookeries. Isolation by distance was indicated for rookeries separated by up to 2000 km but explained only 12% of the genetic structure. The emerging general picture is one of dynamic population structure influenced by the capacity of females to relocate among proximal breeding sites, although this may be conditional on large population sizes as existed historically across this region.

Animal Migration↗
PubMed2007

Phylogeography of the green turtle, Chelonia mydas, in the Southwest Indian Ocean.

Patterns of mitochondrial DNA (mtDNA) variation were used to analyse the population genetic structure of southwestern Indian Ocean green turtle (Chelonia mydas) populations. Analysis of sequence variation over 396 bp of the mtDNA control region revealed seven haplotypes among 288 individuals from 10 nesting sites in the Southwest Indian Ocean. This is the first time that Atlantic Ocean haplotypes have been recorded among any Indo-Pacific nesting populations. Previous studies indicated that the Cape of Good Hope was a major biogeographical barrier between the Atlantic and Indian Oceans because evidence for gene flow in the last 1.5 million years has yet to emerge. This study, by sampling localities adjacent to this barrier, demonstrates that recent gene flow has occurred from the Atlantic Ocean into the Indian Ocean via the Cape of Good Hope. We also found compelling genetic evidence that green turtles nesting at the rookeries of the South Mozambique Channel (SMC) and those nesting in the North Mozambique Channel (NMC) belong to separate genetic stocks. Furthermore, the SMC could be subdivided in two different genetic stocks, one in Europa and the other one in Juan de Nova. We suggest that this particular genetic pattern along the Mozambique Channel is attributable to a recent colonization from the Atlantic Ocean and is maintained by oceanic conditions in the northern and southern Mozambique Channel that influence early stages in the green turtle life cycle.

Acanthaceae↗