Metabolic scaling in turtles

Bennett and Dawson (1976) presented an analysis of the relationship of metabolic rate (MR) and body mass among turtles, based on 10 studies, but unlike most of other groups of ectotherms, there has been no update to include the many later reports on turtles. Here I present a review of the data on turtle metabolic rates at 20, 25, and 30 °C, along with regression equations and graphical analyses from a large number of studies. Two generalities emerge: (1) reported metabolic rates for sea turtles are higher than for other chelonians, although it is not certain whether this is an intrinsic characteristic of sea turtles or an artifact related to experimental conditions (such as greater activity of sea turtles in metabolic chambers and the fact that a number of studies were done with the turtles out of water), and (2) the slopes of the log–log plots of metabolic rate (MR) vs. body mass [b in the allometric equation MR = a(mass)^b] are mostly lower than previously reported in smaller studies.     

Tegmento-thalamic relations in turtles

A focus of evoked potentials and the largest number of spike responses of single units to tegmental stimulation were found in immobilized turtles (Emys orbicularis), lightly anesthetized with chloralose, in the ventral region of the thalamus, which is a heterosensory zone of predominantly somatosensory modality. Incomplete separation of lateral- and medial-tegmental projections between the dorsal and ventral portions of the ventral thalamic region respectively was discovered. Tegmental stimulation, coinciding with or preceding electrodermal or photic stimulation, causes predominant depression of somatic single unit responses, but has less effect on visual responses. The possibility of comparison of tegmento-thalamic systems in reptiles and mammals is discussed.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 2, pp. 165–174, March–April, 1980.     

Tegmento-telencephalic relations in turtles

Electrophysiological characteristics of tegmental projections in the forebrain were studied in immobilized turtles (Emys orbicularis), anesthetized with chloralose. The main zone of representation of the tegmentum is located in the striatum, where evoked responses with shorter latencies were recorded and a larger number of units responding distinctly to tegmental stimulation was concentrated than in the dorsal ventricular ridge and general cortex. At the striatal level predominance of lateral tegmental projections was found in the lateral zone and of medial tegmental projections in the medial zone of the striatum. An inhibitory action of conditioning stimulation of the tegmentum on somatic evoked potentials and single unit responses was established. An attempt was made to compare the tegmento-telencephalic system in reptiles and mammals.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 255–263, May–June, 1980.     

Hatching behavior in turtles

Incubation temperature plays a prominent role in shaping the phenotypes and fitness of embryos, including affecting developmental rates. In many taxa, including turtles, eggs are deposited in layers such that thermal gradients alter developmental rates within a nest. Despite this thermal effect, a nascent body of experimental work on environmentally cued hatching in turtles has revealed unexpected synchronicity in hatching behavior. This review discusses environmental cues for hatching, physiological mechanisms behind synchronous hatching, proximate and ultimate causes for this behavior, and future directions for research. Four freshwater turtle species have been investigated experimentally, with hatching in each species elicited by different environmental cues and responding via various physiological mechanisms. Hatching of groups of eggs in turtles apparently involves some level of embryo-embryo communication and thus is not a purely passive activity. Although turtles are not icons of complex social behavior, life-history theory predicts that the group environment of the nest can drive the evolution of environmentally cued hatching.     

Respiration in neonate sea turtles

The pattern and control of respiration is virtually unknown in hatchling sea turtles. Using incubator-raised turtles, we measured oxygen consumption, frequency, tidal volume, and minute volume for leatherback (Dermochelys coriacea) and olive ridley (Lepidochelys olivacea) turtle hatchlings for the first six days after pipping. In addition, we tested the hatchlings' response to hypercapnic, hyperoxic, and hypoxic challenges over this time period. Hatchling sea turtles generally showed resting ventilation characteristics that are similar to those of adults: a single breath followed by a long respiratory pause, slow frequency, and high metabolic rate. With hypercapnic challenge, both species responded primarily by elevating respiratory frequency via a decrease in the non-ventilatory period. Leatherback resting tidal volume increased with age but otherwise, neither species' resting respiratory pattern nor response to gas challenge changed significantly over the first few days after hatching. At the time of nest emergence, sea turtles have achieved a respiratory pattern that is similar to that of actively diving adults.     

EGF-Induced Expansion of Migratory Cells in the Rostral Migratory Stream

The presence of neural stem cells in the adult brain is currently widely accepted and efforts are made to harness the regenerative potential of these cells. The dentate gyrus of the hippocampal formation, and the subventricular zone (SVZ) of the anterior lateral ventricles, are considered the main loci of adult neurogenesis. The rostral migratory stream (RMS) is the structure funneling SVZ progenitor cells through the forebrain to their final destination in the olfactory bulb. Moreover, extensive proliferation occurs in the RMS. Some evidence suggest the presence of stem cells in the RMS, but these cells are few and possibly of limited differentiation potential. We have recently demonstrated the specific expression of the cytoskeleton linker protein radixin in neuroblasts in the RMS and in oligodendrocyte progenitors throughout the brain. These cell populations are greatly altered after intracerebroventricular infusion of epidermal growth factor (EGF). In the current study we investigate the effect of EGF infusion on the rat RMS. We describe a specific increase of radixin⁺/Olig2⁺ cells in the RMS. Negative for NG2 and CNPase, these radixin⁺/Olig2⁺ cells are distinct from typical oligodendrocyte progenitors. The expanded Olig2⁺ population responds rapidly to EGF and proliferates after only 24 hours along the entire RMS, suggesting local activation by EGF throughout the RMS rather than migration from the SVZ. In addition, the radixin⁺/Olig2⁺ progenitors assemble in chains in vivo and migrate in chains in explant cultures, suggesting that they possess migratory properties within the RMS. In summary, these results provide insight into the adaptive capacity of the RMS and point to an additional stem cell source for future brain repair strategies.     

A Rostral Sensory Mechanism in Oikopleura dioica (Appendicularia)

The ventral sense organ, below the mouth, is composed of 30 primary sensory cells situated in a row perpendicular to the long axis of the animal. Each cell carries one long and slender, modified cilium which arises from an apical pocket in the cell. The sensory cells project 15 axons at each side of the pharynx to the brain, which is rostrally paired and terminates in bulb-like swellings. Each of these bulbs contains four cell bodies, which, according to their fine structure, as well as the synaptic connections with receptor and brain fibers, belong to three different types. It is suggested that the sense organ is a chemosensor and that its remarkable similarity to the vertebrate mechanisms for olfaction makes it probable that the appendicularian Oikopleura dioica possesses a ‘protochordate’ counterpart to the craniate olfactory apparatus.     

Vapour-to-liquid nucleation in cone pores

In this work, we perform a systematic study on the vapour-to-liquid nucleation in a cone pore by using comparatively the classical nucleation theory (CNT) and the constrained lattice density functional theory (constrained LDFT). Three different nucleation scenarios are observed depending on the contact angle θ and apex angle α: the spontaneous phase transition, nucleation with a critical nucleus in Cassie state and nucleation with a critical nucleus in Wenzel state. We also found that both the diagram for nucleation mechanisms and the reduced nucleation barriers with respect to the homogeneous nucleation given by the CNT are at least qualitatively consistent with those from the constrained LDFT. For an increasingly small critical nucleus, the difference between nucleation behaviours from two methods becomes significant due to the macroscopic approximations embedded in CNT, which fails to describe the curvature dependence of surface tension, the line tension effect and the space confinement effect.     

Octagonal nuclear pores

Negative staining of isolated nuclear envelopes by phosphotungstate shows that the nuclear pores are octagonal rather than circular. Pores of the same shape and approximately the same width, 663 ± 5 A, were demonstrated in the newt, Triturus, the frog, Rana, and the starfish, Henricia. The outer and inner diameters of the annulus associated with each pore are respectively greater and less than the width of the pore itself. For this reason surface views of the envelope, unless negatively stained, fail to show the true dimensions of the pores.     

Glutamate Transmission in the Rostral Ventrolateral Medullary Sympathetic Premotor Pathway

1. The aim of these studies was to test the hypothesis that glutamate is the principal excitatory neurotransmitter in the sympathetic premotor pathway from the rostral ventrolateral medulla (RVLM) to the sympathetic preganglionic neurons (SPNs) in the thoracic spinal cord.2. Iontophoretic and pressure ejection of glutamate receptor agonists and antagonists was made onto antidromically identified splanchnic and adrenal SPNs before and during electrical stimulation of the RVLM in urethane/chloralose-anesthetized, artificially ventilated rats.3. SPNs were excited by both NMDA and non-NMDA glutamate receptor agonists. Blockade of glutamate receptors in the IML interrupted the ability of electrical activation of sympathetic premotor neurons in the RVLM to excite SPNs. Within the IML, antergradely labeled terminals of RVLM neurons were found to contain glutamate immunoreactivity and to make asymmetric synapses on local dendrites.4. These data support a significant role for glutamate neurotransmission in mediating the tonic and phasic excitation of SPNs by the sympathetic premotor pathway from the RVLM. It seems likely that stimulation of the RVLM produces glutamate release from both C1 and non-PNMT-containing axon terminals in the IML.     

Evolution of bite performance in turtles

Abstract Among vertebrates, there is often a tight correlation between variation in cranial morphology and diet. Yet, the relationships between morphological characteristics and feeding performance are usually only inferred from biomechanical models. Here, we empirically test whether differences in body dimensions are correlated with bite performance and trophic ecology for a large number of turtle species. A comparative phylogenetic analysis indicates that turtles with carnivorous and durophagous diets are capable of biting harder than species with other diets. This pattern is consistent with the hypothesis that an evolutionary increase in bite performance has allowed certain turtles to consume harder or larger prey. Changes in carapace length tend to be associated with proportional changes in linear head dimensions (no shape change). However, maximum bite force tends to change in proportion to length cubed, rather than length squared, implying that changes in body size are associated with changes in the design of the jaw apparatus. After the effect of body size is accounted for in the analysis, only changes in head height are significantly correlated with changes in bite force. Additionally, our data suggest that the ability to bite hard might trade off with the ability to feed on fast agile prey. Rather than being the direct result of conflicting biomechanical or physiological demands for force and speed, this trade‐off may be mediated through the constraints imposed by the need to retract the head into the shell for defensive purposes.     

Rostral migratory stream neuroblasts turn and change directions in stereotypic patterns

Neuroblasts generated in the adult subventricular zone (SVZ) migrate through the rostral migratory stream (RMS) to the olfactory bulb (OB). Previous work uncovered motility ranging from straight to complex, but it was unclear if directional changes were stochastic or exhibited stereotypical patterns. Here, we provide the first in-depth two-photon time-lapse microscopy study of morphological and dynamic features that accompany turning and direction reversals in the RMS. We identified three specific kinds of turning (30–90 degrees): bending of the leading process proximal to the cell body (P-bending 47% of cases), bending of the distal leading process (D-bending 30%) or branching of the leading process or lamellipodium (23%). Bending and branching angles were remarkably constrained and were significantly different from one another. Cells reversed direction (>90 degrees) through D-bendings (54%), branching (11%) or de novo growth of processes from the soma (23%), but not P-bending. Direction reversal was often composed of several iterations of D-bending or branching as opposed to novel modalities. Individual neuroblasts could turn or change direction in multiple patterns suggesting that the patterns are not specific for different lineages. These findings show that neuroblasts in the RMS use a limited number of distinct and constrained modalities to turn or reverse direction.Key words: neurogenesis, subventricular zone, migration, direction, motility     

Biphasal long-distance migration in green turtles

Sea turtles have recently been shown to have the sensory ability to use magnetic information for guidance in the open ocean, although the importance of different potential navigational cues remains unknown. Between May and August 2001, we satellite-tracked green turtles, Cheloniamydas, during their >2000-km postnesting migration from Ascension Island to Brazil, following five individuals both during their transoceanic crossing and while on the Brazilian coast. None of the turtles travelled directly to its final destination but, instead, there were extended (up to 792 km) movements along the coast after the oceanic crossings. The extent of movement along the coast was unrelated to the oceanic crossing route. For example, individuals whose final destination was in the north of Brazil did not follow a more northerly oceanic crossing than those with a more southerly final destination. These observations show that green turtles returning from Ascension Island do not swim directly to their final destination, but instead conduct migration in two distinct phases: a fairly direct open ocean crossing, following which they turn north or south along the coast to reach their final destination. This long-distance migration may therefore be conducted without turtles needing to resort to sophisticated navigational skills. These previously unidentified long coastal movements may heighten the risk of turtles being captured by fishermen. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Hemoprotozoa of freshwater turtles in Queensland

Blood smears from 27 turtles (15 Emydura signata, nine Elseya latisternum, and three Chelodina longicollis) from southeastern Queensland (Australia) were examined for infections by hemoprotozoan parasites between January and June 1999. Infections were found in 26 (96%) of the turtles. Twenty five (93%) were infected with the adeleorin coccidian Haemogregarina clelandi, eight (30%) with the hemosporidian Haemoproteus chelodinae, 11 (41%) with the kinetoplastid flagellate Trypanosoma chelodinae, and eight (30%) with a novel Trypanosoma sp. Despite the high prevalence and intensity of infections, there was no evidence of clinical disease in any of the turtles.