Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Turtles”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
PubMedDate not supplied

Tetrachromatic input to turtle horizontal cells.

Recent physiological experiments support behavioral and morphological evidence for a fourth type of cone in the turtle retina, maximally sensitive in the ultraviolet (UV). This cone type has not yet been included in the models proposed for connectivity between cones and horizontal cells. In this study, we examined the inputs of UV, S, M, and L cones to horizontal cells. We used the high-resolution Dynamic Constant Response Method to measure the spectral sensitivity of horizontal cells without background light and after adaptation to UV, blue (B), green (G), and red (R) light. We concluded the following: (1) Tetrachromatic input to a Y/B horizontal cell was identified. The spectral-sensitivity curves of the cell in three of the adaptation conditions were well represented by L-, M-, and S-cone functions. Adaptation to blue light revealed a peak at 372 nm, the same wavelength location as that determined behaviorally in the turtle. A porphyropsin template could be closely fitted to the sensitivity band in that region, strong evidence for input from a UV cone. (2) The spectral-sensitivity functions of R/G horizontal cells were well represented by the L- and M-cone functions. There was no indication of UV- or S-cone inputs into these cells. (3) The spectral sensitivities of the monophasic horizontal cells were dominated by the L cone. However, the shape of the spectral-sensitivity function depended on the background wavelength, indicating secondary M-cone input. Connectivity models of the outer retina that predict input from all cone types are supported by the finding of tetrachromatic input into Y/B horizontal cells. In contrast, we did not find tetrachromatic input to R/G and monophasic horizontal cells. Chromatic adaptation revealed the spectral-sensitivity function of the turtle UV cone peaking at 372 nm.

Adaptation, Ocular↗
PubMedDate not supplied

Spatial-chromatic interactions in C-type horizontal cells of the turtle (Mauremys caspica) retina.

Horizontal cells are second-order retinal neurons that play a key role in spatial information processing. In some cold-blooded vertebrates such as turtles, a subtype of these cells, the chromaticity horizontal cells exhibit color-opponent responses and therefore are considered to be important also for color information processing. To reveal spatial and color interactions, the receptive-field properties of Red/Green and Yellow/Blue chromaticity horizontal cells in the retina of the turtle Mauremys caspica were studied by intracellular recordings from the everted eyecup preparation. We found that the polarity of the photoresponses depended not only upon the wavelength and intensity of the stimulus, but also upon its spatial configuration. Thus, a hyperpolarizing photoresponse that was elicited by full-field stimulation with bright light of wavelength close to the "neutral" one was reversed in polarity to a pure depolarizing one when a small spot or a thin annular pattern were used for stimulation. This finding could not be explained either by different balances between depolarizing and hyperpolarizing inputs to different cells or by stray light that effectively reduced the light intensity in the center of the small spot. Rather, it was found that the depolarizing and hyperpolarizing components were characterized by different receptive-field size and that these differences could account for the dependency of response polarity upon the spatial pattern of the stimulus. These findings indicate that color information processing in turtle C-type horizontal cells is a complex process that depends upon the wavelength and intensity of the light stimulus as well as upon its spatial properties.

Animals↗
PubMedDate not supplied

Neural interactions between cone photoreceptors and horizontal cells in the turtle (Mauremys caspica) retina.

Horizontal cells and cone photoreceptors in the vertebrate retina are interconnected by a complex network of synapses leading to the generation of color-coded responses in chromaticity horizontal cells. A simple cascade model of excitatory feedforward and inhibitory feedback synapses had been suggested to underlie these observations. In this study, the photoresponses of cones and horizontal cells were recorded intracellularly from the turtle eyecup. Three different approaches were adopted in order to test quantitatively the cascade model. Comparing linearity functions between these neurons indicated multiple excitatory inputs to each type of horizontal cells. The depolarizing photoresponses of R/G C-type horizontal cells were considerably faster than those of L-type horizontal cells but slower than those recorded from L-cones. This observation disagrees with the basic assumption of the cascade model that assign the depolarizing photoresponses of R/G C-type horizontal cells to a negative feedback pathway from L-type horizontal cells onto M-cones. Finally, the action spectra of each of the three types of horizontal cells could not be solely accounted for by input from one spectral type of cones. Only by assuming excitatory and inhibitory inputs from all spectral types of cones, the action spectra of all types of horizontal cells could be reconstructed. These findings suggest that the negative feedback pathways from horizontal cells onto cones in the turtle retina cannot solely account for the chromatic properties of the horizontal cells and support a direct inhibitory inputs from cones to turtle horizontal cells.

Animals↗
PubMedDate not supplied

Functional localization of soluble guanylate cyclase in turtle retina: modulation of cGMP by nitric oxide donors.

The second messenger cyclic guanosine monophosphate (cGMP) plays a role in many aspects of retinal processing. cGMP-gated channels function in photoreceptors, Müller, bipolar, and ganglion cells; and cGMP can modulate gap-junction conductivity. In the inner retina, both particulate and soluble guanylate cyclases can elevate levels of cGMP. The soluble isoform of guanylate cyclase is activated by nitric oxide (NO). In turtle retina, nitric oxide synthase, the enzyme that synthesizes NO, has been previously localized in discrete amacrine cells, somata in the ganglion cell layer, and in many processes in the inner plexiform layer. However, there have been no studies localizing soluble guanylate cyclase in the turtle retina. To functionally localize soluble guanylate cyclase, we stimulated retinas with the NO donors (+/-)-S-nitroso-N-acetylpenicillamine or spermine (nitric oxide) adduct, and then used immunocytochemistry to localize increases in cGMP-like immunoreactivity (cGMP-LI). The cells containing soluble guanylate cyclase should show cell autonomous increases in cGMP-LI in response to stimulation with NO. NO-stimulated increases in cGMP-LI occurred in many distinct amacrine cell types, select bipolar cells, some somata in the ganglion cell layer, and in discrete bands of processes in the inner plexiform layer. The pattern of cGMP-LI demonstrated qualitative dose response differences to the NO donors. This is the first localization of soluble guanylate cyclase in specific retinal neurons in the turtle; and the first functional activation of soluble guanylate cyclase in the amacrine cells of any species. The broad neuronal distribution of NO-stimulated cGMP-LI suggests that the NO/soluble guanylate cyclase/cGMP cascade is involved at several levels of visual processing in the inner retina.

Animals↗
PubMed2005

Monitoring mercury in the loggerhead sea turtle, Caretta caretta.

The validity of using blood samples and keratinized scutes for nonlethal routine monitoring of mercury (Hg) in loggerhead sea turtles, Caretta caretta, is evaluated in the context of how effectively these matrixes predict internal tissue Hg burdens and the different temporal scales of exposure they represent. Total Hg (THg) was measured in blood and scutes collected from live captures (n = 34) and liver, kidney, muscle, spinal cord, blood, and scutes collected from freshly stranded loggerhead turtles (n = 6) along the coast of the southeastern United States. Linear regressions between monitoring compartments and internal tissues from stranded animals were all statistically significant (r2 > 0.805, p < 0.015) but varied in their utility as a predictive tool depending on which tissues were paired. Blood was an effective predictor of THg in muscle (r2 = 0.988, p < 0.0001) and spinal cord (r2 = 0.988, p < 0.0001), while scute was the most accurate predictor of THg in liver (r2 = 0.948, p = 0.0010). The strength of the relationship between tissues types is believed to reflect the similarity in the temporal scales they represent and the variability in the fraction of methylmercury present. The stability of Hg in the scute matrix makes this tissue preferable for approximating long-term exposure, while blood Hg levels can be affected by recent changes in Hg intake. THg levels in blood and scutes from live captures were highly correlated (linear regression r2 = 0.926, p < 0.0001) and increased significantly with body mass (r2 = 0.173, p = 0.016 and r2 = 0.187, p = 0.012 respectively), further supporting thatthere is a component reflecting long-term accumulation of Hg in these matrixes. We also present a novel technique using the residuals from the blood-scute regression as an index of recent exposure (IRE). The interpretation of this value is derived from the comparison between the most recent Hg intake (which contributes to the Hg measured in the blood) relative to the average past intake (which is recorded in the scute). A stepwise multiple regression revealed a significant positive relationship between the IRE and the proximity of the capture site to the nearest major industrial river mouth (p = 0.0102). This suggests that there is an elevation of bioavailable Hg in nearshore habitats where terrestrial influences and anthropogenic impacts are high. Seasonal foraging site fidelity and the variability in environmental Hg may explain the high intraspecific variability and occasional highly contaminated turtle seen in this and previous studies.

Animals↗
PubMed2001

Snapping turtles (Chelydra serpentina) as monitors for mercury contamination of aquatic environments.

We assessed the distribution of mercury in snapping turtles (Chelydra serpentina) by analyzing front shoulder muscle, back leg muscle, tail muscle, blood, liver, and marginal carapacial scute (shell) of 26 adult turtles from five small lakes. Total mercury concentration in muscle ranged from 50 to 500 ng g(-1) wet weight and was highly correlated among the three tissue locations. There was no relationship between muscle mercury concentration and body size. Mercury concentration in blood was similar to muscle; the correlation with muscle mercury concentration was significant but there was some variability. Mercury concentration in shell was much higher than in muscle or blood, ranging from 500 to 3300 ng g(-1), and was highly correlated with muscle mercury concentration. Liver mercury concentration was similar to shell, but was highly variable and uncorrelated with any other tissue. We conclude that snapping turtles accumulate mercury from their environment and may be useful monitors of mercury contamination.

Animals↗
PubMedDate not supplied

Global phylogeography of the ridley sea turtles (Lepidochelys spp.) as inferred from mitochondrial DNA sequences.

The Kemp's ridley sea turtle (Lepidochelys kempi) is restricted to the warm temperate zone of the North Atlantic Ocean, whereas the olive ridley turtle (L. olivacea) is globally distributed in warm-temperate and tropical seas, including nesting colonies in the North Atlantic that nearly overlap the range of L. kempi. To explain this lopsided distribution, Pritchard (1969) proposed a scenario in which an ancestral taxon was divided into Atlantic and Pacific forms (L. kempi and L. olivacea, respectively) by the Central American land bridge. According to this model, the olive ridley subsequently occupied the Pacific and Indian Oceans and recently colonized the Atlantic Ocean via southern Africa. To assess this biogeographic model, a 470 bp sequence of the mtDNA control region was compared among 89 ridley turtles, including the sole L. kempi nesting population and 7 nesting locations across the range of L. olivacea. These data confirm a fundamental partition between L. olivacea and L. kempi (p = 0.052-0.069), shallow separations within L. olivacea (p = 0.002-0.031), and strong geographic partitioning of mtDNA lineages. The most divergent L. olivacea haplotype is observed in the Indo-West Pacific region, as are the central haplotypes in a parsimony network, implicating this region as the source of the most recent radiation of olive ridley lineage. The most common olive ridley haplotype in Atlantic samples is distinguished from an Indo-West Pacific haplotype by a single nucleotide substitution, and East Pacific samples are distinguished from the same haplotype by two nucleotide substitutions. These shallow separations are consistent with the recent invasion of the Atlantic postulated by Pritchard (1969), and indicate that the East Pacific nesting colonies were also recently colonized from the Indo-West Pacific region. Molecular clock estimates place these invasions within the last 300,000 years.

Animals↗
PubMed2004

Endangered species: where leatherback turtles meet fisheries.

The dramatic worldwide decline in populations of the leatherback turtle (Dermochelys coriacea) is largely due to the high mortality associated with their interaction with fisheries, so a reduction of this overlap is critical to their survival. The discovery of narrow migration corridors used by the leatherbacks in the Pacific Ocean raised the possibility of protecting the turtles by restricting fishing in these key areas. Here we use satellite tracking to show that there is no equivalent of these corridors in the North Atlantic Ocean, because the turtles disperse actively over the whole area. But we are able to identify a few 'hot spots' where leatherbacks meet fisheries and where conservation efforts should be focused.

Animal Migration↗
PubMed2004

Endangered species: Pan-Atlantic leatherback turtle movements.

The overall extent of habitat use by leatherback turtles in the North Atlantic, and hence their possible interactions with longline fisheries, is unknown. Here we use long-term satellite telemetry to reveal that leatherbacks range throughout the North Atlantic, indicating that closing limited areas to longline fisheries will probably have only partial success in reducing turtle bycatch. Although turtles dive very deeply on occasion (one descended to a maximum depth of 1,230 metres, which represents the deepest dive ever recorded for a reptile), they generally restrict their diving to less than 250 metres, which increases the chance that they will encounter longline hooks.

Animal Migration↗
PubMed1993

Adenosine, a "retaliatory" metabolite, promotes anoxia tolerance in turtle brain.

Contrary to what is found in most vertebrates, the brains of certain turtle species maintain ATP levels and ion homeostasis and survive prolonged anoxia. The hypothesis tested here is that the release of adenosine and its binding to A1 receptors are essential for this anoxic tolerance. Studies were conducted in the isolated turtle cerebellum, which did release adenosine to the extracellular space during anoxia. When adenosine receptor antagonists [theophylline, 8-cyclopentyltheophylline (CPT), or 8-cyclopentyl-1,3-dipropylxanthine (DPCPX)] were added to the superfusate under control conditions, they had no effect on extracellular potassium ion activity ([K+]o). During anoxia, however, these antagonists provoked maximal efflux of K+ (anoxic depolarization). Anoxic depolarization occurred earlier during anoxia with theophylline (a nonspecific adenosine receptor antagonist) than with CPT or DPCPX, which specifically block A1 receptors. Therefore, adenosine release and effects mediated by A1 receptors are essential to anoxia tolerance in turtle brain.

Adenosine↗
PubMed1996

Diving behaviour and haemoglobin function: the primary structure of the alpha- and beta-chains of the sea turtle (Caretta caretta) and its functional implications.

The amino acid sequence of the alpha- and beta-chains of haemoglobin (Hb) from the loggerhead sea turtle (Caretta caretta) has been determined. Comparison with that of human Hb shows differences in several residues involved in both alpha 1 beta 1 and alpha 1 beta 2 packing contacts. On the whole, in spite of the mutations, the essential characteristics of both interfaces seem to be maintained. The functional properties of the sea turtle Hb have been investigated at different temperatures and as a function of proton, chloride and organic phosphate concentrations. In addition to overall similarities shared with most of the vertebrate Hbs previously described, this molecule shows significant differences which could be related to the life behaviour of the turtle. In fact, while the shape of the Bohr-effect curve is well adapted for gas exchange during prolonged dives, the very small enthalpy change for O2 binding ensures that O2 delivery becomes essentially insensitive to the temperature changes of the environment. Moreover, and similarly to the case of emperor penguin Hb, the small alkaline Bohr effect appears to be only choride-linked, since the pH dependence of the O2 affinity is abolished in the absence of this ion. These functional characteristics are discussed on the basis of the primary structure of alpha- and beta-chains.

Adaptation, Physiological↗
PubMed2003

Phylogeography of the coronulid barnacle, Chelonibia testudinaria, from loggerhead sea turtles, Caretta caretta.

The barnacle, Chelonibia testudinaria, is a common inhabitant of the marine turtle epibiont community and plays a key role in the development of this community. Phylogeographic analysis of 79 cytochrome c oxidase I (COX1) sequences for barnacles collected from five populations found contrasting patterns of divergence for populations in the Atlantic vs. the Pacific Ocean. Our analysis indicates that the two Pacific populations, Senri Beach, Japan and Bahia Magdalena, Mexico, were not only highly divergent from the Atlantic populations but are highly divergent from one another. We suggest that barnacles from these populations may represent cryptic species. In contrast, sequence divergence was greatly reduced among barnacles collected from Wassaw Island, GA, USA, Keewaydin, FL, USA, and Kyparissia, Pèloponnésus Island, Greece. A reduction in sequence diversity at the latter site was attributed to a recent range expansion into the Mediterranean Sea. We examined historical patterns of migration among the three Atlantic and Mediterranean populations using the program migrate. This analysis indicates a high rate of migration from Keewaydin to Wassaw Island, contrasted with a much lower rate of migration in the opposite direction. The estimated migration rate from Kyparissia to Keewaydin was also non-negligible. We suggest that the association between C. testudinaria and loggerhead turtles and the patterns of turtle migration have played key roles in the expansion of the range of C. testudinaria into the Mediterranean Sea and the subsequent patterns of barnacle migration. We further propose that the difference between ocean basins, with respect to the impact of host migration on barnacle gene flow, probably stems from the fact that host-mediated dispersal in the Atlantic depends on advanced stage juveniles and adults while any host-mediated dispersal in the Pacific would have to involve early "pelagic" stage juvenile loggerheads.

Animal Migration↗
PubMed1999

Antibody against Testudo herpesvirus is not common in Chinese soft-shelled turtles.

Seventy-six serum samples of Chinese soft-shelled turtles (Trionyx sinensis) were collected at Jiangsu Province, China. The neutralization test (NT) was performed with the sera, Testudo herpesvirus (THV) and turtle heart cells (THC). Neutralizing antibodies were detected in five of 76 samples and the titres were 1:10-1:20. Having optimized the conditions, the dot-enzyme-linked immunosorbent assay (Dot-ELISA) was developed and eight serum samples exhibited positive results. Five samples were positive by both NT and Dot-ELISA. The percentage of positive samples was only 6.6% (NT) and 11% (ELISA). It is suggested that THV infection is not a serious problem for the Chinese soft-shelled turtle culture in this region.

Animals↗
PubMed2003

Odorant specificity of three oscillations and the DC signal in the turtle olfactory bulb.

The odour-induced population response in the in vivo turtle (Terepene sp.) olfactory bulb consists of three oscillatory components (rostral, middle and caudal) that ride on top of a DC signal. In an initial step to determine the functional role of these four signals, we compared the signals elicited by different odorants. Most experiments compared isoamyl acetate and cineole, odorants which have very different maps of input to olfactory bulb glomeruli in the turtle and a different perceptual quality for humans. We found substantial differences in the response to the two odours in the rise-time of the DC signal and in the latency of the middle oscillation. The rate of rise for cineole was twice as fast as that for isoamyl acetate. Similarly, the latency for the middle oscillation was about twice as long for isoamyl acetate as it was for cineole. On the other hand, a number of characteristics of the signals were not substantially different for the two odorants. These included the latency of the rostral and caudal oscillation, the frequency and envelope of all three oscillations and their locations and spatial extents. A smaller number of experiments were carried out with hexanone and hexanal; the oscillations elicited by these odorants did not appear to be different from those elicited by isoamyl acetate and cineole. Qualitative differences between the oscillations in the turtle and those in two invertebrate phyla suggest that different odour processing strategies may be used.

Animals↗
PubMed1970

Chloride and potassium activities in luminal fluid of turtle thyroid follicles as determined by selective ion-exchanger microelectrodes.

Cl(-) and K(+) activities in the follicular lumen and the intraluminal potential of the same lumen were measured simultaneously with specific liquid ion-exchanger and 3 M KCl microelectrodes, respectively, in turtle thyroid glands. The Cl(-) equilibrium potential between the thyroid interstitium and the lumen calculated from the measured Cl(-) activities was higher than the directly measured intraluminal potential. These data indicate that Cl(-) is actively transported out of the follicular lumen in turtle thyroid gland. On the other hand, the calculated K(+) equilibrium potential was not different from the directly measured potential, which indicates that K(+) is probably distributed passively according to the electrochemical gradients between the interstitial and the luminal compartments in turtle thyroid gland. Results obtained from the specific liquid ion-exchanger microelectrode studies correlate well with those obtained from previous radioautographic observations and chemical determinations.

Animals↗
PubMed1997

Philopatry of male marine turtles inferred from mitochondrial DNA markers.

Recent studies of mitochondrial DNA (mtDNA) variation among marine turtle populations are consistent with the hypothesis that females return to beaches in their natal region to nest as adults. In contrast, less is known about breeding migrations of male marine turtles and whether they too are philopatric to natal regions. Studies of geographic structuring of restriction fragment and microsatellite polymorphisms at anonymous nuclear loci in green turtle (Chelonia mydas) populations indicate that nuclear gene flow is higher than estimates from mtDNA analyses. Regional populations from the northern and southern Great Barrier Reef were distinct for mtDNA but indistinguishable at nuclear loci, whereas the Gulf of Carpentaria (northern Australia) population was distinct for both types of marker. To assess whether this result was due to reduced philopatry of males across the Great Barrier Reef, we determined the mtDNA haplotypes of breeding males at courtship areas for comparison with breeding females from the same three locations. We used a PCR-restriction fragment length polymorphism approach to determine control region haplotypes and designed mismatch primers for the identification of specific haplotypes. The mtDNA haplotype frequencies were not significantly different between males and females at any of the three areas and estimates of Fst among the regions were similar for males and females (Fst = 0.78 and 0.73, respectively). We conclude that breeding males, like females, are philopatric to courtship areas within their natal region. Nuclear gene flow between populations is most likely occurring through matings during migrations of both males and females through nonnatal courtship areas.

Animals↗
PubMed2000

Direct evidence for local oscillatory current sources and intracortical phase gradients in turtle visual cortex.

Visual stimuli induce oscillations in the membrane potential of neurons in cortices of several species. In turtle, these oscillations take the form of linear and circular traveling waves. Such waves may be a consequence of a pacemaker that emits periodic pulses of excitation that propagate across a network of excitable neuronal tissue or may result from continuous and possibly reconfigurable phase shifts along a network with multiple weakly coupled neuronal oscillators. As a means to resolve the origin of wave propagation in turtle visual cortex, we performed simultaneous measurements of the local field potential at a series of depths throughout this cortex. Measurements along a single radial penetration revealed the presence of broadband current sources, with a center frequency near 20 Hz (gamma band), that were activated by visual stimulation. The spectral coherence between sources at two well-separated loci along a rostral-caudal axis revealed the presence of systematic timing differences between localized cortical oscillators. These multiple oscillating current sources and their timing differences in a tangential plane are interpreted as the neuronal activity that underlies the wave motion revealed in previous imaging studies. The present data provide direct evidence for the inference from imaging of bidirectional wave motion that the stimulus-induced electrical waves in turtle visual cortex correspond to phase shifts in a network of coupled neuronal oscillators.

Animals↗
PubMedDate not supplied

Lactic acid buffering by bone and shell in anoxic softshell and painted turtles.

We tested two hypotheses: first, that the inferior anoxia tolerance of the softshell turtle, Apalone spinifera, compared to the western painted turtle, Chrysemys picta bellii, is related to its less mineralized shell, and second, that turtle bone, like its shell, stores lactate during prolonged anoxia. Lactate concentrations of blood, hindlimb bone, and shell were measured on normoxic Apalone and Chrysemys and after anoxic submergence at 10 degrees C for 2 and 9 d, respectively. Blood and shell concentrations of Ca(2+), Mg(2+), Na(+), K(+), and inorganic phosphate (P(i); for shell only) were also measured. Because a preliminary study indicated lactate distribution in Chrysemys throughout its skeleton during anoxia at 20 degrees C, we used hindlimb bones as representative skeletal samples. Apalone shell, though a similar percentage of body mass as Chrysemys shell, had higher water content (76.9% vs. 27.9%) and only 20%-25% as much Ca(2+), Mg(2+), CO(2), and P(i). When incubated at constant pH of 6.0 or 6.5, Apalone shell powder released only 25% as much buffer per gram wet weight as Chrysemys shell. In addition, plasma [Ca(2+)] and [Mg(2+)] increased less in Apalone during anoxia at an equivalent plasma lactate concentration. Lactate concentrations increased in the shell and skeletal bone in both species. Despite less mineralization, Apalone shell took up lactate comparably to Chrysemys. In conclusion, a weaker compensatory response to lactic acidosis in Apalone correlates with lower shell mineralization and buffer release and may partially account for the poorer anoxia tolerance of this species.

Acidosis, Lactic↗