morphological study on the olfactory systems of the snapping turtle, chelydra serpentina. | in this study, the olfactory system of a semi-aquatic turtle, the snapping turtle, has been morphologically investigated by electron microscopy, immunohistochemistry, and lectin histochemistry. the nasal cavity of snapping turtle was divided into the upper and lower chambers, lined by the sensory epithelium containing ciliated and non-ciliated olfactory receptor neurons, respectively. each neuron expressed both gαolf, the α-subunit of g-proteins coupling to the odorant receptors, and gαo, the α- ... | 2016 | 27059760 |
phenotypic plasticity in the common snapping turtle (chelydra serpentina): long-term physiological effects of chronic hypoxia during embryonic development. | studies of embryonic and hatchling reptiles have revealed marked plasticity in morphology, metabolism, and cardiovascular function following chronic hypoxic incubation. however, the long-term effects of chronic hypoxia have not yet been investigated in these animals. the aim of this study was to determine growth and postprandial o2 consumption (v̇o2), heart rate (fh), and mean arterial pressure (pm, in kpa) of common snapping turtles (chelydra serpentina) that were incubated as embryos in chroni ... | 2016 | 26608655 |
accumulation and maternal transfer of polychlorinated biphenyls in snapping turtles of the upper hudson river, new york, usa. | we conducted field studies over three years to assess body burdens and maternal transfer of polychlorinated biphenyls (pcbs) as well as indices of sexual dimorphism in snapping turtles (chelydra serpentina) of the upper hudson river (ny, usa.) we collected adult turtles in areas known to be contaminated with pcbs and in nearby reference areas for measurement of body size, precloacal length, and penis size. we analyzed pcb concentrations in eggs collected over three years and in whole blood from ... | 2008 | 18699700 |
snapping turtles (chelydra serpentina) from canadian areas of concern across the southern laurentian great lakes: chlorinated and brominated hydrocarbon contaminants and metabolites in relation to circulating concentrations of thyroxine and vitamin a. | the metabolites of polychlorinated biphenyls (pcbs) and polybrominated diphenyl ethers (pbdes), as well as other halogenated phenolic contaminants (hpcs) have been shown to have endocrine-disrupting properties, and have been reported with increasing frequency in the blood of wildlife, and mainly in mammals and birds. however, little is known about the persistence, accumulation and distribution of these contaminants in long-lived freshwater reptiles. in the present study, in addition to a large s ... | 2015 | 26519832 |
atrazine and glyphosate dynamics in a lotic ecosystem: the common snapping turtle as a sentinel species. | atrazine and glyphosate are two of the most common pesticides used in the us midwest that impact water quality via runoff, and the common snapping turtle (chelydra serpentina) is an excellent indicator species to monitor these pesticides especially in lotic systems. the goals of this study were to (1) quantify atrazine, the atrazine metabolite diaminochlorotriazine (dact), and glyphosate burdens in common snapping turtle tissue from individuals collected within the embarras river in illinois; (2 ... | 2015 | 25678354 |
snapping turtles (chelydra serpentina) as bioindicators in canadian areas of concern in the great lakes basin. 1. polybrominated diphenyl ethers, polychlorinated biphenyls, and organochlorine pesticides in eggs. | we examined the concentrations and spatial patterns of congeners of pbdes, pcbs, and organochlorine pesticides in snapping turtle (chelydra serpentina) eggs from areas of concern (aocs) on the canadian shores of lake ontario, st. lawrence river, and connecting channels. eggs from lyons creek (niagara river aoc) reflected a local pcb source over a range of 7.5 km (3.2-10.8) from the welland canal. pcb contamination in eggs declined with increasing distance from the welland canal, whereas the rela ... | 2007 | 18044496 |
molecular and morphological differentiation of testes and ovaries in relation to the thermosensitive period of gonad development in the snapping turtle, chelydra serpentina. | ambient temperatures during embryonic development determine gonadal sex in many reptiles. the temperature sensitive period for sex determination has been defined by shifting eggs between female- and male-producing temperatures in a few species. this phase spans 20-35% of embryogenesis in most species, which makes it difficult to define the mechanisms that transduce temperature into a signal for ovarian versus testicular development. we present an extensive set of studies that define a brief peri ... | 2015 | 25662229 |
a mycoplasma species of emydidae turtles in the northeastern usa. | mycoplasma infections can cause significant morbidity and mortality in captive and wild chelonians. as part of a health assessment of endangered bog turtles (glyptemys muhlenbergii) in the northeastern us, choanal and cloacal swabs from these and other sympatric species, including spotted turtles (clemmys guttata), eastern box turtles (terrapene carolina carolina), wood turtles (glyptemys insculpta), and common snapping turtles (chelydra serpentina) from 10 sampling sites in the states (us) of d ... | 2015 | 25574806 |
influence of feeding ecology on blood mercury concentrations in four species of turtles. | mercury is a relatively well-studied pollutant because of its global distribution, toxicity, and ability to bioaccumulate and biomagnify in food webs: however, little is known about bioaccumulation and toxicity of hg in turtles. total hg (thg) concentrations in blood were determined for 552 turtles representing four different species (chelydra serpentina, sternotherus odoratus, chrysemys picta, and pseudemys rubriventris) from a hg-contaminated site on the south river (va, usa) and upstream refe ... | 2007 | 17702349 |
can natural phenotypic variances be estimated reliably under homogeneous laboratory conditions? | the phenotypic variance is assumed to be greater in a more heterogeneous environment. the validity of this assumption is important for microevolutionists to extrapolate results from the laboratory to field environments. we subjected clutches of eggs from common snapping turtles (chelydra serpentina) to a split-family design to evaluate the variability in incubation time and four size traits of neonates from eggs incubated in the laboratory and those left in situ. mean size measurements were simi ... | 2007 | 17584235 |
comparative shell buffering properties correlate with anoxia tolerance in freshwater turtles. | freshwater turtles as a group are more resistant to anoxia than other vertebrates, but some species, such as painted turtles, for reasons not fully understood, can remain anoxic at winter temperatures far longer than others. because buffering of lactic acid by the shell of the painted turtle is crucial to its long-term anoxic survival, we have tested the hypothesis that previously described differences in anoxia tolerance of five species of north american freshwater turtles may be explained at l ... | 2007 | 17008457 |
physiological responses to freezing in hatchlings of freeze-tolerant and -intolerant turtles. | freeze tolerance is a complex cold-hardiness adaptation that has independently evolved in a diverse group of organisms, including several ectothermic vertebrates. because little is known about the mechanistic basis for freeze tolerance in reptiles, we compared responses to experimental freezing in winter-acclimatized hatchlings representing nine taxa of temperate north american turtles, including ones that tolerated freezing and others that did not. viability rates of hatchlings frozen to -3 deg ... | 2006 | 16758216 |
dietary exposure of bde-47 and bde-99 and effects on behavior, bioenergetics, and thyroid function in juvenile red-eared sliders (trachemys scripta elegans) and common snapping turtles (chelydra serpentina). | juvenile red-eared sliders (trachemys scripta elegans) and snapping turtles (chelydra serpentina) were fed food dosed with brominated diphenyl ether-47 (bde-47) or bde-99 for 6 mo beginning approximately 9 mo posthatch. during the exposure period, measurements of growth, bioenergetics, and behavior were made; thyroid function and accumulation were quantified postexposure. whole-body concentrations of both congeners were lower in red-eared sliders compared with snapping turtles after 6 mo of expo ... | 2014 | 25210006 |
toxicity of pesticides associated with potato production, including soil fumigants, to snapping turtle eggs (chelydra serpentina). | turtles frequently oviposit in soils associated with agriculture and, thus, may be exposed to pesticides or fertilizers. the toxicity of a pesticide regime that is used for potato production in ontario on the survivorship of snapping turtle (chelydra serpentina) eggs was evaluated. the following treatments were applied to clean soil: 1) a mixture of the pesticides chlorothalonil, s-metolachlor, metribuzin, and chlorpyrifos, and 2) the soil fumigant metam sodium. turtle eggs were incubated in soi ... | 2014 | 24105794 |
an egg injection technique to evaluate the effect of polychlorinated biphenyls on the hatching success of the snapping turtle (chelydra serpentina serpentina). | embryos of oviparous organisms are exposed to contaminants by two pathways: contaminant uptake from the surrounding environment, and the transfer from female to offspring (maternal transfer). the initial source of contaminant exposure for most embryos is likely to be maternal transfer; therefore, maternal transfer studies are critical in determining the effects of contaminants on future populations. injection of contaminants directly into eggs is one route of experimental contaminant exposure th ... | 2011 | 21191884 |
high incidence of deformity in aquatic turtles in the john heinz national wildlife refuge. | the john heinz national wildlife refuge is subject to pollution from multiple sources. we studied development of snapping turtle (chelydra serpentina) and painted turtle (chrysemys picta) embryos from the refuge from 2000 through 2003. mean annual deformity rate of pooled painted turtle clutches over four years ranged from 45 to 71%, while that of snapping turtle clutches ranged from 13 to 19%. lethal deformities were more common than minor or moderate deformities in embryos of both species. adu ... | 2006 | 16360253 |
polycyclic aromatic hydrocarbons affect survival and development of common snapping turtle (chelydra serpentina) embryos and hatchlings. | polycyclic aromatic hydrocarbons (pahs) are toxic compounds found in the john heinz national wildlife refuge in philadelphia, pennsylvania. we assessed the impact of pahs and crude oil on snapping turtle development and behavior by exposing snapping turtle eggs from the refuge and from three clean reference sites to individual pahs or a crude oil mixture at stage 9 of embryonic development. exposure to pahs had a significant effect on survival rates in embryos from one clean reference site, but ... | 2006 | 16360251 |
anoxia tolerance and freeze tolerance in hatchling turtles. | freezing survival in hatchling turtles may be limited by ischemic anoxia in frozen tissues and the associated accumulation of lactate and reactive oxygen species (ros). to determine whether mechanisms for coping with anoxia are also important in freeze tolerance, we examined the association between capacities for freezing survival and anoxia tolerance in hatchlings of seven species of turtles. tolerance to freezing (-2.5 degrees c) was high in emydoidea blandingii, chrysemys picta, terrapene orn ... | 2005 | 15739066 |
secretory proteins in the reproductive tract of the snapping turtle, chelhydra serpentina. | sds-polyacrylamide gel electrophoresis was used to separate the secretory proteins produced by the epithelial and endometrial glands of the uterine tube and uterus in the snapping turtle chelydra serpentina. the proteins were analyzed throughout the phases of the reproductive cycle from may to august, including preovulatory, ovulatory, postovulatory or luteal, and vitellogenic phases. the pattern of secretory proteins is quite uniform along the length of the uterine tube, and the same is true of ... | 2004 | 15596394 |
observations on the leech placobdella ornata feeding from bony tissues of turtles. | the leech placobdella ornata was observed feeding from the blood sinuses of the plastron and carapace bones of chelydra serpentina and chrysemys picta. evidence of successful feeding included blood upwelling from the point of attachment and gastric ceca of the leeches freshly filled with blood after removal. there was an apparent preference for the sulci between scales of the shell. | 2004 | 15562628 |
skeletal development of macrochelys temminckii (reptilia: testudines: chelydridae). | few descriptions of the development and sequence of chondrification and ossification of the entire skeleton of turtles exist, particularly compared to other groups of reptiles. in this study, the embryonic skeleton and its ontogenesis are described for the alligator snapping turtle, macrochelys temminckii (chelydridae). morphological descriptions utilize cleared and double-stained embryonic specimens and form the basis of comparison of the ontogenesis of the skeleton between this species and its ... | 2005 | 15536645 |
diagnosis of skeletal injuries in chelonians using computed tomography. | computed tomography (ct) was used to diagnose the cause of lameness in a radiated tortoise (geochelone radiata) and to determine the extent of shell and skeletal trauma in two snapping turtles (chelydra serpentina). the radiated tortoise's lameness was ultimately attributed to luxation of the right-shoulder joint that was not detected during plain film radiography. axial and appendicular fractures were identified in one of the snapping turtles that were not detected during plain film radiography ... | 2004 | 15305520 |
characterization of contaminants in snapping turtles (chelydra serpentina) from canadian lake erie areas of concern: st. clair river, detroit river, and wheatley harbour. | pcbs, organochlorine pesticides and dioxins/furans in snapping turtle eggs and plasma (chelydra serpentina) were evaluated at three areas of concern (aocs) on lake erie and its connecting channels (st. clair river, detroit river, and wheatley harbour), as well as two inland reference sites (algonquin provincial park and tiny marsh) in 2001-2002. eggs from the detroit river and wheatley harbour aocs had the highest levels of p,p'-dde (24.4 and 57.9 ng/g) and sum pcbs (928.6 and 491.0 ng/g) wet we ... | 2004 | 15276278 |
lactate accumulation, glycogen depletion, and shell composition of hatchling turtles during simulated aquatic hibernation. | we submerged hatchling western painted turtles chrysemys picta schneider, snapping turtles chelydra serpentina l. and map turtles graptemys geographica le sueur in normoxic and anoxic water at 3 degrees c. periodically, turtles were removed and whole-body [lactate] and [glycogen] were measured along with relative shell mass, shell water, and shell ash. we analyzed the shell for [na+], [k+], total calcium, total magnesium, pi and total co2. all three species were able to tolerate long-term submer ... | 2004 | 15235017 |
lack of biological effects of water accommodated fractions of chemically- and physically-dispersed oil on molecular, physiological, and behavioral traits of juvenile snapping turtles following embryonic exposure. | snapping turtle (chelydra serpentina) eggs were exposed to two concentrations of chemically- or physically-dispersed water accommodated fractions of weathered arabian light crude oil (low=0.5 and high=10 g oil/l water). solutions were passed through nest substrate to simulate alterations in composition during percolation to egg depth. hatchlings were raised for 13 months during which numerous endpoints were measured. prior to percolation, total pah ("tpah"; the sum of 52 pahs measured) in physic ... | 2009 | 19631965 |
the platelet-derived growth factor signaling system in snapping turtle embryos, chelydra serpentina: potential role in temperature-dependent sex determination and testis development. | the platelet-derived growth factor (pdgf) signaling system is known to play a significant role during embryonic and postnatal development of testes in mammals and birds. in contrast, genes that comprise the pdgf system in reptiles have never been cloned or studied in any tissue, let alone developing gonads. to explore the potential role of pdgf ligands and their receptors during embryogenesis, we cloned cdna fragments of pdgf-a, pdgf-b, and receptors pdgfr-alpha and pdgfr-beta in the snapping tu ... | 2009 | 19523392 |
survival and behavior of freshwater turtles after rehabilitation from an oil spill. | an oil spill in february 2000 at the john heinz national wildlife refuge in southeastern pennsylvania affected four species of freshwater turtles including painted turtles (chrysemys picta), snapping turtles (chelydra serpentina), red-eared slider turtles (trachemys scripta), and red-bellied turtles (pseudemys rubriventris). in the summer and fall of 2000, there were no differences in survival, home range, and temperature preference of 16 oil exposed/rehabilitated (oer) turtles, 18 possibly expo ... | 2003 | 12927492 |
the physiology of overwintering in a turtle that occupies multiple habitats, the common snapping turtle (chelydra serpentina). | common snapping turtles, chelydra serpentina (linnaeus), were submerged in anoxic and normoxic water at 3 degrees c. periodic blood samples were taken, and po(2), pco(2), ph, [na(+)], [k(+)], [cl(-)], total ca, total mg, [lactate], [glucose], hematocrit, and osmolality were measured; weight gain was determined; and plasma [hco(3)(-)] was calculated. submergence in normoxic water caused a decrease in pco(2) from 10.8 to 6.9 mmhg after 125 d, partially compensating a slight increase in lactate and ... | 2016 | 12529844 |
yolk hormone levels in the eggs of snapping turtles and painted turtles. | although yolk steroids appear to play important roles in the development, growth, and behavior of some birds, their effects in oviparous reptiles are largely unknown. these investigations were initiated to determine initial levels of steroid hormones in the yolks of eggs from two turtle species. clutches of snapping turtle (chelydra serpentina) and of painted turtle (chrysemys picta) eggs were collected and individual egg yolks were analyzed for estradiol-17beta (e(2)) and testosterone (t) using ... | 2002 | 12161198 |
wetness of the nest environment influences cardiac development in pre- and post-natal snapping turtles (chelydra serpentina). | we dissected hearts from near-term embryos and hatchlings of common snapping turtles (chelydridae: chelydra serpentina) whose eggs had incubated on wet or dry substrates, and then dried and individually weighed the heart and yolk-free carcass from each animal. hearts and carcasses of prenatal and neonatal animals grew at different rates, and the patterns of growth by both heart and carcass differed between wet and dry environments. hearts grew faster, both in actual mass and in mass adjusted for ... | 2002 | 12095870 |
lipid metabolism during embryonic development of the common snapping turtle, chelydra serpentina. | the metabolism of lipids and fatty acids during embryonic development of chelydra serpentina (common snapping turtle) was investigated. substantial changes in lipid class and fatty acid composition occurred as lipids were transferred from the yolk to the yolk sac membrane (ysm) and then to the brain, eyes, heart, and lungs of the hatchling. lipids were hydrolyzed in the yolk prior to transport to the ysm, shown by a large increase in free fatty acids (ffas) during the second half of development. ... | 2009 | 19416694 |
cross-reactivity of a polyclonal antibody against chinemys reevesii vitellogenin with the vitellogenins of other turtle species: chelydra serpentina , macrochelys temminckii , and pelodiscus sinensis. | vitellogenin (vtg), a yolk-precursor protein in oviparous vertebrates, is a useful biomarker for reproductive physiology and environmental estrogenic pollution. to examine interspecific applicability of an enzyme-linked immunosorbent assay (elisa) for quantifying chinemys reevesii vtg, we observed cross-reactivity between a polyclonal antibody against chinemys reevesii vtg and the vtgs from other turtle species: chelydra serpentina (chelydridae), macrochelys temminckii (chelydridae), and pelodis ... | 2008 | 19267600 |
expression of p450(arom) in malaclemys terrapin and chelydra serpentina: a tale of two sites. | the formation of estrogens from androgens in all vertebrates is catalyzed by the "aromatase" complex, which consists of a membrane bound p(450) enzyme, p(450) aromatase (which binds the androgen substrate and inserts an oxygen into the molecule), and a flavoprotein (nadph-cytochrome p450 reductase). among vertebrates, the two major sites of aromatase expression are the brain and gonads. given the importance of estrogen in reptile sex determination, we set out to examine whether p450arom was invo ... | 2001 | 11748616 |
transmission of haemogregarina balli from painted turtles to snapping turtles through the leech placobdella ornata. | six leeches (placobdella ornata) were allowed to feed on a painted turtle (chrysemys picta marginata) infected with haemogregarina balli and subjected to a period of diapause before being allowed to feed on 2 laboratory-reared snapping turtles (chelydra serpentina). weekly examination of thin blood films revealed infections of the turtles at 130 days postfeeding. these observations provide support for broad host specificity of hemogregarine parasites of chelonians. | 2001 | 11695407 |
experimental exposure of eggs to polybrominated diphenyl ethers bde-47 and bde-99 in red-eared sliders (trachemys scripta elegans) and snapping turtles (chelydra serpentina) and possible species-specific differences in debromination. | polybrominated diphenyl ethers (pbdes) are a bioaccumulative, persistent, and toxic class of flame retardants that can potentially impact turtles in natural habitats via exposure through maternal transfer. to simulate maternal transfer in the present study, pbde congeners bde-47 and bde-99 were topically applied to the eggshell and were allowed to diffuse into the egg contents of the red-eared slider (trachemys scripta elegans) and snapping turtle (chelydra serpentina). eggs were topically dosed ... | 2013 | 23147837 |
carbon dioxide (co2) laser treatment of cutaneous papillomas in a common snapping turtle, chelydra serpentina. | carbon dioxide (co2) laser was used to treat multiple cutaneous papillomas on an adult female common snapping turtle, chelydra serpentina serpentina. a combination of excisional and ablative techniques provided excellent intraoperative visibility and postoperative results due to the laser's unique ability to incise and vaporize soft tissue. | 2008 | 18634218 |
cold-hardiness and evaporative water loss in hatchling turtles. | north american turtles hatch in late summer and spend their first winter either on land or underwater. adaptations for terrestrial overwintering of hatchlings in northern regions, where winter thermal and hydric regimes are harsh, have not been systematically investigated in many species. we measured intrinsic supercooling capacity, resistance to inoculative freezing, and desiccation resistance in hatchlings of terrestrial and aquatic turtles collected from northern (terrapene ornata, chrysemys ... | 2008 | 11436135 |
morphogenesis of the turtle shell: the development of a novel structure in tetrapod evolution. | the turtle shell is an evolutionary novelty that is synapomorphic for chelonians. the carapace is initiated by the entrapment of the ribs by the carapacial ridge (cr), a lateral bulge of the dorsal ectoderm and dermal mesoderm. the mechanisms by which the cr is initiated, the ribs entrapped and the dorsal dermis ossified, remains unknown. similarly, the formation of the plastron remains unexplained. here, we present a series of anatomical investigations into plastron and carapace formation in th ... | 2007 | 11341674 |
seasonal changes in physiology and development of cold hardiness in the hatchling painted turtle chrysemys picta. | hatchling painted turtles (chrysemys picta) commonly hibernate in shallow, natal nests where winter temperatures may fall below -10 degrees c. although hatchlings are moderately freeze-tolerant, they apparently rely on supercooling to survive exposure to severe cold. we investigated seasonal changes in physiology and in the development of supercooling capacity and resistance to inoculative freezing in hatchling chrysemys picta exposed in the laboratory to temperatures that decreased from 22 to 4 ... | 2000 | 11044384 |
temperature-dependent sex determination modulates cardiovascular maturation in embryonic snapping turtles chelydra serpentina. | we investigated sex differences in cardiovascular maturation in embryos of the snapping turtle chelydra serpentina, a species with temperature-dependent sex determination. one group of eggs was incubated at 26.5°c to produce males. another group of eggs was incubated at 26.5°c until embryos reached stage 17; eggs were then shifted to 31°c for 6 days to produce females, and returned to 26.5°c for the rest of embryogenesis. thus, males and females were at the same temperature when autonomic tone w ... | 2013 | 23125337 |
expression of putative sex-determining genes during the thermosensitive period of gonad development in the snapping turtle, chelydra serpentina. | modes of sex determination are quite variable in vertebrates. the developmental decision to form a testis or an ovary can be influenced by one gene, several genes, environmental variables, or a combination of these factors. nevertheless, certain morphogenetic aspects of sex determination appear to be conserved in amniotes. here we clone fragments of nine candidate sex-determining genes from the snapping turtle chelydra serpentina, a species with temperature-dependent sex determination (tsd). we ... | 2007 | 18391536 |
an appraisal of the use of an infrared digital monitoring system for long-term measurement of heart rate in reptilian embryos. | measurement of heart rate (fh) in embryonic reptiles has previously imposed some degree of invasive treatment on the developing embryo. recently a non-invasive technique of fh detection from intact eggs was developed for commercial avian breeders and has since been used in biological research. this device uses infrared light, enabling it to detect heartbeats in very early embryos. however, infrared light is a source of heat and extended enclosure of an egg in the device is likely to affect tempe ... | 2015 | 26086361 |
critical windows of cardiovascular susceptibility to developmental hypoxia in common snapping turtle (chelydra serpentina) embryos. | environmental conditions fluctuate dramatically in some reptilian nests. however, critical windows of environmental sensitivity for cardiovascular development have not been identified. continuous developmental hypoxia has been shown to alter cardiovascular form and function in embryonic snapping turtles (chelydra serpentina), and we used this species to identify critical periods during which hypoxia modifies the cardiovascular phenotype. we hypothesized that incubation in 10% o2 during specific ... | 2015 | 25730266 |
snapping turtles (chelydra serpentina) as bioindicators in canadian areas of concern in the great lakes basin. ii. changes in hatching success and hatchling deformities in relation to persistent organic pollutants. | hatching success and deformities in snapping turtle hatchlings (chelydra serpentina) were evaluated using eggs collected from 14 sites in the canadian lower great lakes, including areas of concern (aoc), between 2001 and 2004. eggs were analyzed for pcbs, pbdes, and pesticides. between 2002 and 2004, hatchling deformity rates were highest in two aocs (18.3-28.3%) compared to the reference sites (5.3-11.3%). hatching success was poorest in three aocs (71.3-73.1%) compared to the reference sites ( ... | 2008 | 18039552 |
toxicity of nitrogenous fertilizers to eggs of snapping turtles (chelydra serpentina) in field and laboratory exposures. | many reptiles oviposit in soil of agricultural landscapes. we evaluated the toxicity of two commonly used nitrogenous fertilizers, urea and ammonium nitrate, on the survivorship of exposed snapping turtle (chelydra serpentina) eggs. eggs were incubated in a community garden plot in which urea was applied to the soil at realistic rates of up to 200 kg/ha in 2004, and ammonium nitrate was applied at rates of up to 2,000 kg/ha in 2005. otherwise, the eggs were unmanipulated and were subject to ambi ... | 2007 | 17702542 |
nondestructive indices of mercury exposure in three species of turtles occupying different trophic niches downstream from a former chloralkali facility. | turtles are useful for studying bioaccumulative pollutants such as mercury (hg) because they have long life spans and feed at trophic levels that result in high exposure to anthropogenic chemicals. we compared total hg concentrations in blood and toenails of three species of turtles (chelydra serpentina, sternotherus odoratus, and graptemys geographica) with different feeding ecologies from locations up- and downstream of a superfund site in virginia, usa. mercury concentrations in turtle tissue ... | 2013 | 23010870 |
polychlorinated biphenyl concentrations, congener profiles, and ratios in the fat tissue, eggs, and plasma of snapping turtles (chelydra s. serpentina) from the ohio basin of lake erie, usa. | concentrations and profiles of polychlorinated biphenyls (pcbs) were determined in three tissues of adult snapping turtles (chelydra serpentina serpentina) from six locations in the ohio basin of lake erie to characterize tissue variation and geographic trends. the locations included the ohio areas of concern, i.e., the ashtabula, black, and maumee rivers; the ottawa river near toledo; and two reference sites. mean total pcbs were greatest in turtles from the ottawa river followed by the maumee, ... | 2006 | 16583258 |
adjustments in cholinergic, adrenergic and purinergic control of cardiovascular function in snapping turtle embryos (chelydra serpentina) incubated in chronic hypoxia. | adenosine is an endogenous nucleoside that acts via g-protein coupled receptors. in vertebrates, arterial or venous adenosine injection causes a rapid and large bradycardia through atrioventricular node block, a response mediated by adenosine receptors that inhibit adenylate cyclase and decrease cyclic amp concentration. chronic developmental hypoxia has been shown to alter cardioregulatory mechanisms in reptile embryos, but adenosine's role in mediating these responses is not known. we incubate ... | 2014 | 25106687 |
comparative effects of in ovo exposure to sodium perchlorate on development, growth, metabolism, and thyroid function in the common snapping turtle (chelydra serpentina) and red-eared slider (trachemys scripta elegans). | perchlorate is a surface and groundwater contaminant found in areas associated with munitions and rocket manufacturing and use. it is a thyroid-inhibiting compound, preventing uptake of iodide by the thyroid gland, ultimately reducing thyroid hormone production. as thyroid hormones influence metabolism, growth, and development, perchlorate exposure during the embryonic period may impact embryonic traits that ultimately influence hatchling performance. we topically exposed eggs of red-eared slide ... | 2012 | 22871607 |
substrate color-induced melanization in eight turtle species from four chelonian groups. | background color convergence of prey occurring through local adaptation or phenotypically plastic responses can reduce predation rates by visual predators. we assessed the capacity for substrate color-induced melanization in eight turtle species within the groups chelydridae, emydidae, kinosternidae, and trionychidae by rearing individuals on black or white substrates for 160 days. in all aquatic turtle species, integuments of the head and carapace of the individuals that were reared on a black ... | 2014 | 24993507 |
highly elevated levels of perfluorooctane sulfonate and other perfluorinated acids found in biota and surface water downstream of an international airport, hamilton, ontario, canada. | per- and poly-fluorinated compounds (pfcs), which include perfluorinated carboxylates (pfcas) and sulfonates (pfsas) and various precursors, are used in a wide variety of industrial, commercial and domestic products. this includes aqueous film forming foam (afff), which is used by military and commercial airports as fire suppressants. in a preliminary assessment prior to this study, very high concentrations (>1 ppm wet weight) of the pfsa, perfluorooctane sulfonate (pfos), were discovered in the ... | 2012 | 22208739 |
absorption of current use pesticides by snapping turtle (chelydra serpentina) eggs in treated soil. | reptiles often breed within agricultural and urban environments that receive frequent pesticide use. consequently, their eggs and thus developing embryos may be exposed to pesticides. our objectives were to determine (i) if turtle eggs are capable of absorbing pesticides from treated soil, and (ii) if pesticide absorption rates can be predicted by their chemical and physical properties. snapping turtle (chelydra serpentina) eggs were incubated in soil that was treated with 10 pesticides (atrazin ... | 2011 | 21862099 |
toxicity of pesticide and fertilizer mixtures simulating corn production to eggs of snapping turtles (chelydra serpentina). | many reptiles oviposit in soils associated with agricultural landscapes. we evaluated the toxicity of a pesticide and fertilizer regime similar to those used in corn production in ontario on the survivorship of exposed snapping turtle (chelydra serpentina) eggs. the herbicides atrazine, dimethenamid, and glyphosate, the pyrethroid insecticide tefluthrin, and the fertilizer ammonia, were applied to clean soil, both as partial mixtures within chemical classes, as well as complete mixtures. eggs we ... | 2011 | 21831407 |
embryonic temperature influences juvenile temperature choice and growth rate in snapping turtles chelydra serpentina. | snapping turtles (chelydra serpentina) demonstrate temperature-dependent sex determination (tsd): intermediate egg incubation temperatures (23-27 degreesc) produce males, while extreme temperatures produce females. snapping turtles are also sexually dimorphic: adult males are typically larger than females. previous researchers hypothesized that male-producing egg temperatures enhanced the growth rate of juvenile turtles, resulting in the adult dimorphism and potentially providing an adaptive ben ... | 1998 | 9427676 |
multi-scale hierarchy of chelydra serpentina: microstructure and mechanical properties of turtle shell. | carapace, the protective shell of a freshwater snapping turtle, chelydra serpentina, shields them from ferocious attacks of their predators while maintaining light-weight and agility for a swim. the microstructure and mechanical properties of the turtle shell are very appealing to materials scientists and engineers for bio-mimicking, to obtain a multi-functional surface. in this study, we have elucidated the complex microstructure of a dry chelydra serpentina's shell which is very similar to a m ... | 2011 | 21783154 |
mercury concentrations in snapping turtles (chelydra serpentina) correlate with environmental and landscape characteristics. | mercury (hg) deposited onto the landscape can be transformed into methylmercury (mehg), a neurotoxin that bioaccumulates up the aquatic food chain. here, we report on hg concentrations in snapping turtles (chelydra serpentina) across new york state, usa. the objectives of this study were to: (1) test which landscape, water, and biometric characteristics correlate with total hg (thg) concentrations in snapping turtles; and (2) determine whether soft tissue thg concentrations correlate with scute ... | 2011 | 21688194 |
environmental contamination and developmental abnormalities in eggs and hatchlings of the common snapping turtle (chelydra serpentina serpentina) from the great lakes-st lawrence river basin (1989-1991). | during 1989-1991, we assessed developmental abnormalities in embryos and hatchlings from eggs of the common snapping turtle (chelydra serpentina serpentina). eggs were collected and artificially incubated from eight sites in ontario, canada and akwesasne/new york, usa. in eggs from the same clutches we measured 20 organochlorine pesticides, 48 polychlorinated biphenyl (pcbs) congeners including 6 non-ortho pcbs, 8 polychlorinated dibenzodioxins (pcdds), 14 polychlorinated dibenzofurans (pcdfs) a ... | 1998 | 15093107 |
lymphoid aggregates in gonads of embryos, hatchlings, and young of turtles with temperature-dependent sex determination. | cellular infiltrations forming lymphoid-like aggregates were previously observed in gonads of two turtle species exhibiting temperature-dependent sex determination (tsd): at hatching in chelydra serpentina; at and after hatching in emys orbicularis. we show here that such aggregates are also present in gonads of testudo graeca by the end of embryonic development, suggesting that their occurrence is general in turtles. since in c. serpentina, infiltrations were observed mainly in testes exhibitin ... | 2004 | 14743515 |
sexually dimorphic morphology of hatchling snapping turtles (chelydra serpentina) from contaminated and reference sites in the great lakes and st. lawrence river basin, north america. | some organochlorine pesticides and industrial chemicals may alter sexually dimorphic traits through endocrine disruption. therefore, we examined a sexually dimorphic trait, precloacal length, of hatchling snapping turtles (chelydra serpentina) incubated from 31 clutches from a heavily contaminated site (hamilton harbour, on, canada; n = 14), a moderately contaminated site (akwesasne mohawk territory; n = 3), and from a reference site (algonquin provincial park, on, canada; n = 14). the mean sum ... | 2002 | 12013138 |
the pulmonary surfactant system matures upon pipping in the freshwater turtle chelydra serpentina. | pulmonary surfactant (ps), a mixture of phospholipids (pl), neutral lipids and surfactant proteins (sp), lowers surface tension within the lung, which increases lung compliance and improves the removal of fluid at birth. here, we have examined the expression of thyroid transcription factor-1 (ttf-1) and the surfactant protein sp-b, and also the composition of pulmonary surfactant lipids in the developing lung of the turtle chelydra serpentina. lavage and lung tissue were collected from late embr ... | 2002 | 11854378 |
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 simi ... | 2001 | 11683228 |
organochlorine pesticides, pcbs, dibenzodioxin, and furan concentrations in common snapping turtle eggs (chelydra serpentina serpentina) in akwesasne, mohawk territory, ontario, canada. | subsamples of eight clutches of common snapping turtle eggs (chelydra serpentina serpentina) were collected from four sites from the territory of the mohawk nation, akwesasne, on the shore of the st. lawrence river. egg contents were analyzed for organochlorine pesticides, polychlorinated biphenyls (pcbs), dibenzodioxins, and furans. the sites were 2 to 13 km downstream from pcb-contaminated landfill sites. maximum concentrations of total pcbs in snapping turtle clutches were extremely high, and ... | 2001 | 11443374 |
heritable variation for sex ratio under environmental sex determination in the common snapping turtle (chelydra serpentina). | the magnitude of quantitative genetic variation for primary sex ratio was measured in families extracted from a natural population of the common snapping turtle (chelydra serpentina), which possesses temperature-dependent sex determination (tsd). eggs were incubated at three temperatures that produced mixed sex ratios. this experimental design provided estimates of the heritability of sex ratio in multiple environments and a test of the hypothesis that genotype x environment (g x e) interactions ... | 1992 | 1592234 |
chlorinated hydrocarbon concentrations in plasma of the lake erie water snake (nerodia sipedon insularum) and northern water snake (nerodia sipedon sipedon) from the great lakes basin in 1998. | from the great lakes basin, concentrations of 59 congener-specific polychlorinated biphenyls (pcbs) and 14 organochlorine pesticides were measured in blood plasma of northern water snake (nerodia sipedon sipedon) and lake erie water snake (nerodia sipedon insularum), which is endangered in canada. in 1998, four male adult lake erie water snakes were sampled from pelee island, western lake erie; four male northern water snakes were sampled at little lake, about 20 km north of parry sound in centr ... | 2000 | 11031311 |
respiratory responses to short term hypoxia in the snapping turtle, chelydra serpentina. | among vertebrates, turtles are able to tolerate exceptionally low oxygen tensions. we have investigated the compensatory mechanisms that regulate respiration and blood oxygen transport in snapping turtles during short exposure to hypoxia. snapping turtles started to hyperventilate when oxygen levels dropped below 10% o(2). total ventilation increased 1.75-fold, essentially related to an increase in respiration frequency. during normoxia, respiration occurred in bouts of four to five breaths, whe ... | 2000 | 10936762 |
effects of maternal identity and incubation temperature on snapping turtle (chelydra serpentina) metabolism. | individual variation in physiological traits may have important consequences for offspring survivorship and adult fitness. variance in offspring phenotypes is due to interindividual differences in genotype, environment, and/or maternal effects. this study examined the contributions of incubation environment, maternal effects, and clutch identity to individual variation in metabolic rates in the common snapping turtle, chelydra serpentina. we measured standard metabolic rate, as determined by oxy ... | 2006 | 10893169 |
an ontogenetic shift in the response of heart rates to temperature in the developing snapping turtle (chelydra serpentina). | the affect of acute changes in temperature on heart rates was investigated for the first time in a developing reptile. heart rates were determined early and late in incubation in snapping turtle (chelydra serpentina) eggs. late in incubation heart rates at any given temperature were lower than those observed early in incubation. the results of temperature switching experiments late in incubation were consistent with thermal acclimation. | 2000 | 10745125 |
availability of water affects organ growth in prenatal and neonatal snapping turtles (chelydra serpentina). | we manipulated the amount of water that was available to prenatal and neonatal snapping turtles (chelydra serpentina) in order to assess the impact of water on growth by different organs in these animals. three treatments were used: (1) turtles that completed their incubation on a wet substrate, (2) turtles that completed their incubation on a dry substrate, and (3) turtles that spent a few days in water after completing incubation on a dry substrate. turtles hatching on a dry substrate (treatme ... | 2000 | 10707327 |
influence of water availability during incubation on hatchling size, body composition, desiccation tolerance, and terrestrial locomotor performance in the snapping turtle chelydra serpentina. | the effects of water availability during incubation on the water contents of neonatal snapping turtles at hatching were examined, along with the influence of hatchling water content on desiccation tolerance and terrestrial locomotor performance. the water contents of hatchlings from eggs incubated on wet substrates were both absolutely and proportionally greater than were those of hatchlings from eggs incubated on dry substrates. hatchlings with greater water contents at hatching were able to su ... | 2006 | 10603335 |
the relationship of body size to survivorship of hatchling snapping turtles (chelydra serpentina): an evaluation of the "bigger is better" hypothesis. | in many organisms, body size is positively correlated with traits that are presumably related to fitness. if directional selection frequently favors larger offspring (the "bigger is better" hypothesis), the results of such selection should be detectable with field experiments. we tested the "bigger is better" hypothesis in hatchling snapping turtles (chelydra serpentina) by conducting one long-term and three short-term experiments on the university of michigan e.s. george reserve in southeastern ... | 1999 | 28308562 |
embryonic temperature affects metabolic compensation and thyroid hormones in hatchling snapping turtles. | temperature acclimation of adult vertebrates typically induces changes in metabolic physiology. during early development, such metabolic compensation might have profound consequences, yet acclimation of metabolism is little studied in early life stages. we measured the effect of egg incubation temperature on resting metabolic rate (rmr) and blood thyroid hormone levels of hatchling snapping turtles (chelydra serpentina). like many reptiles, snapping turtles have temperature-dependent sex determi ... | 2007 | 10521320 |
effect of dichlorodiphenyltrichloroethane on sex determination of the common snapping turtle (chelydra serpentina serpentina). | recent evidence indicates that 1,1,1-trichloro-2, 2-bis(p-chlorophenyl)ethane (ddt) and some of its metabolites alter reproductive and endocrine function in wildlife. exposure to such endocrine-disrupting compounds during embryonic development can affect sexual differentiation. the authors tested the hypothesis that dichlorodiphenyltrichloroethane (p,p'-dde) causes feminization of the common snapping turtle (chelydra s. serpentina), a species with temperature-dependent sex determination, during ... | 1999 | 10381306 |
effects of environmentally relevant concentrations of atrazine on gonadal development of snapping turtles (chelydra serpentina). | the herbicide atrazine has been suspected of affecting sexual development by inducing aromatase, resulting in the increased conversion of androgens to estrogens. we used snapping turtles (chelydra serpentina), a species in which sex is dependent on the production of estrogen through aromatase activity in a temperature-dependent manner, to investigate if environmentally relevant exposures to atrazine affected gonadal development. eggs were incubated in soil to which atrazine was applied at a typi ... | 2006 | 16519315 |
resistance of the shell membrane and mineral layer to diffusion of oxygen and water in flexible-shelled eggs of the snapping turtle (chelydra serpentina). | at oviposition, flexible eggshells of many turtles have an outer mineral layer and an inner membrane layer of approximately equal thickness. we measured conductances of both layers to h2o and o2 at various levels of eggshell hydration. both the mineral layer of the eggshell and the shell membrane offer significant resistance to diffusion of water vapor and oxygen in eggshells of the snapping turtle, chelydra serpentina. conductance to water vapor increases in both the membrane and mineral layer ... | 1982 | 6890707 |
possible adaptive value of water exchanges in flexible-shelled eggs of turtles. | use of energy reserves by embryos of common snapping turtles (chelydra serpentina) is related to the hydric conditions to which eggs are exposed during incubation and to the net exchanges of water through the eggshells. embryos developing inside eggs with a relatively favorable water balance use more of their energy reserves metabolically and grow larger before hatching than embryos inside eggs with less favorable water exchanges. | 1981 | 17760193 |
endogenous yolk steroid hormones in turtles with different sex-determining mechanisms. | maternal transfer of nutrients, including steroid hormones, to embryos during gestation in viviparous amniotes is well known, but the concordant process in oviparous amniotes is poorly understood. recent evidence suggests that steroid hormones are present in freshly laid eggs of archosaurs and that their concentrations may influence offspring phenotypes. this process might be especially important in reptiles with temperature-dependent sex determination (tsd), because embryonic sex determination ... | 1998 | 9707477 |
photoreceptor coupling in turtle retina. | photoreceptors in the isolated turtle retina of two species of turtle, chelydra serpentina and pseudemus scripta elegans, were penetrated with double-barrel electrodes. physiological responses were recorded through one barrel and neurobiotin tracer was injected from the other. intracellular injection of neurobiotin revealed patterns of tracer-coupled photoreceptors. both the patterns of tracer coupling and the electrophysiology suggest a high degree of specificity of connections. rods seem to be ... | 2015 | 9682876 |
impact of organochlorine contamination on levels of sex hormones and external morphology of common snapping turtles (chelydra serpentina serpentina) in ontario, canada. | recent research has suggested that contaminants in the environment may influence sex differentiation and reproductive endocrine function in wildlife. concentrations of organochlorine contaminants (total polychlorinated biphenyls, pesticides) were higher in the blood plasma of snapping turtles from contaminated sites than in those from reference sites. the ratio of the precloacal length to the posterior lobe of the plastron (ppr) is sexually dimorphic in snapping turtles. there were significant r ... | 1998 | 9518475 |
water relations of pliable-shelled eggs of common snapping turtles (chelydra serpentina). | | 1980 | 7427826 |
the rate of conversion of [14-(14)c]pregnenolone to [4-(14)c]progesterone by corpora lutea of the snapping turtle, chelydra serpentina. | | 1980 | 7419051 |
aerial and aquatic oxygen uptake by freely-diving snapping turtles (chelydra serpentina). | aerial oxygen consumption of unrestrained, freely-diving warm-and cold-acclimated snapping turtles, chelydra serpentina, was measured at 10, 20, and 30°c. also, simultaneous determinations of aerial and aquatic oxygen uptake by voluntarilydiving animals were made at 4 and 20°c. the standard rates of aerial oxygen consumption are equivalent in cold-and warm-acclimated animals in water and in cold-acclimated ones in air; these rates are all lower than those of warm-acclimated animals in air. thus ... | 1980 | 28309683 |
the effect of malnutrition on immunocompetence and whole body resistance to infection in chelydra serpentina. | | 1979 | 437240 |
seasonal fluctuations in the plasma concentrations of progesterone and oestradiol-17 beta in the female snapping turtle (chelydra serpentina). | plasma concentrations of progesterone and oestradiol-17 beta were determined by radioimmunoassay procedures in the sexually mature female snapping turtle at four different stages of the annual ovarian cycle. the highest level of progesterone in the peripheral plasma was detected during the luteal stage (june), whereas the concentration of oestradiol was highest (280 pg/ml) in may, immediately before ovulation. | 1979 | 429947 |
embryonic temperature influences juvenile temperature choice and growth rate in snapping turtles chelydra serpentina. | snapping turtles (chelydra serpentina) demonstrate temperature-dependent sex determination (tsd): intermediate egg incubation temperatures (23-27 degrees c) produce males, while extreme temperatures produce females. snapping turtles are also sexually dimorphic: adult males are typically larger than females. previous researchers hypothesized that male-producing egg temperatures enhanced the growth rate of juvenile turtles, resulting in the adult dimorphism and potentially providing an adaptive be ... | 1998 | 9503646 |
purification and partial amino acid sequences of two distinct albumins from turtle plasma. | two putative albumins, denoted alb-1 (apparent molecular mass of 67 kda) and alb-2 (68 kda), were purified from plasma of the emydid turtle (trachemys scripta). concentrations in serum or plasma were determined by radioimmunoassay using 125i-labeled alb-1. in juvenile turtles (less than 2 years of age), serum concentrations of alb-1 and alb-2 were 2.72 +/- 0.23 mg/ml and 1.68 +/- 0.22 mg/ml, respectively, while concentrations in plasma pooled from adult turtles were 4.2 mg/ml and 2.6 mg/ml, resp ... | 1997 | 9440230 |
seasonal changes in gonadal activity and the effects of stress on reproductive hormones in the common snapping turtle, chelydra serpentina. | the seasonal gonadal cycle (including gonadal histology, sex steroids, and gonadotropins) was studied in freshly captured common snapping turtles, chelydra serpentina, from wisconsin, and the effects of capture stress were evaluated. the ovarian and testicular cycles are shorter than those reported in other freshwater turtles; the cycles commence in mid-may and terminate in early september, immediately after the completion of gonadal growth and maturation. in the female, testosterone (t), 17beta ... | 1997 | 9268617 |
oviductal morphology in relation to hormonal levels in the snapping turtle, chelydra serpentina. | microscopic and in situ visual observations were used to relate circulating hormone levels to morphological changes in the oviduct of the snapping turtle chelydra serpentina throughout the ovarian cycle. increase in levels of progesterone (p), estradiol (e2) and testosterone (t) levels coincide with an increase in number and growth of endometrial glands, luminal epithelial cells and secretory droplets throughout the oviduct. testosterone and estradiol levels rose significantly (p < 0.05) after t ... | 2006 | 16384588 |
fine structure of the chromophobe in the pars distalis of the common snapping turtle, chelydra serpentina. | chromophobes of the pars distalis in young chelydra serpentina have sparse cytoplasm with no specific granules; however, many cytoplasmic filaments are present. the chromophobes are connected to the other cell types by desmosomes, while different types of junctional specializations occur between adjacent chromophobes. cytoplasmic filaments traverse the cytoplasm in a random manner and terminate on both the junctional complexes and the nuclear envelope. it is proposed that, in addition to providi ... | 1976 | 1248046 |
heart rate during development in the turtle embryo: effect of temperature. | growth and development can occur over a wide range of physical conditions in reptiles. cardiovascular function must be critical to this ability. however, information on cardiovascular function in developing reptiles is lacking. previous work indicated that in reptiles the effects of temperature on growth and metabolism are largely restricted to early development. this study examined whether the previously observed effects of temperature and different perinatal patterns of metabolism observed in ... | 1996 | 8981759 |
temperature-dependent sex determination in the snapping turtle: manipulation of the embryonic sex steroid environment. | in certain reptiles with temperature-dependent sex determination (tsd), estrogens act as a signal for female differentiation. because aromatase produces estrogens from androgens, this enzyme plays a pivotal role in tsd. whether androgens act as the signal for male differentiation in tsd species in not yet clear. we manipulated the hormonal environment in eggs of the common snapping turtle (chelydra serpentina) to determine the effects of an estrogen (estradiol 17-beta), an aromatase inhibitor (f ... | 1994 | 7851724 |
the graft-versus-host reaction in the snapping turtle chelydra serpentina. | | 1973 | 4148147 |
lymphoid tissue in the snapping turtle, chelydra serpentina. | | 1972 | 4638093 |
structure and development of the optic tectum of the snapping turtle (chelydra serpentina l.). | | 1971 | 5132820 |
survival of xenogeneic grafts of embryonic pigment and carapace rudiments in embryos of chelydra serpentina. | | 1970 | 4922223 |
extirpation experiments on embryonic rudiments of the carapace of chelydra serpentina. | | 1970 | 5482414 |
twinning in the common snapping turtle, chelydra serpentina. | | 1970 | 5461766 |
eimeria chelydrae n. sp. (protozoa: eimeriidae) from the snapping turtle, chelydra serpentina. | | 1969 | 5388988 |
the maturation of the capacity to reject skin allografts and xenografts in the snapping turtle, chelydra serpentina. | | 1969 | 4893941 |
a series of stages in the embryonic development of chelydra serpentina. | | 1968 | 5681661 |
motility of the turtle embryo, chelydra serpentina (linné). | periodic motility of turtle embryos was observed during their incubation periods (60 +/- 5 days). cyclic activity was first observed between days 10 to 14; it increased to a peak level of 50 percent of the standard observation period on day 30 +/- 5, then declined to low levels until hatching activities were initiated. during the first third of the incubation period, motility of the turtles closely resembled that previously described for chick embryos at similar stages of development. | 1967 | 5212408 |