[show abstract][hide abstract] ABSTRACT: 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 ornata, and Malaclemys terrapin and low in Graptemys geographica, Chelydra serpentina, and Trachemys scripta. Hatchlings survived in a N(2) atmosphere at 4 degrees C for periods ranging from 17 d (M. terrapin) to 50 d (G. geographica), but survival time was not associated with freeze tolerance. Lactate accumulated during both stresses, but plasma levels in frozen/thawed turtles were well below those found in anoxia-exposed animals. Activity of the antioxidant enzyme catalase in liver increased markedly with anoxia exposure in most species, but increased with freezing/thawing only in species with low freeze tolerance. Our results suggest that whereas oxygen deprivation occurs during somatic freezing, freeze tolerance is not limited by anoxia tolerance in hatchling turtles.
Journal of Comparative Physiology B 05/2005; 175(3):209-17. · 2.02 Impact Factor
[show abstract][hide abstract] ABSTRACT: Overwintering habits of hatchling Blanding's turtles (Emydoidea blandingii) are unknown. To determine whether these turtles are able to survive winter in aquatic habitats, we submerged hatchlings in normoxic (155 mmHg Po2) and hypoxic (6 mmHg Po2) water at 4 degrees C, recording survival times and measuring changes in key physiological variables. For comparison, we simultaneously studied hatchling softshell (Apalone spinifera) and snapping (Chelydra serpentina) turtles, which are known to overwinter in aquatic habitats. In normoxic water, C. serpentina and A. spinifera survived to the termination of the experiment (76 and 77 d, respectively). Approximately one-third of the E. blandingii died during 75 d of normoxic submergence, but the cause of mortality was unclear. In hypoxic water, average survival times were 6 d for A. spinifera, 13 d for E. blandingii, and 19 d for C. serpentina. Mortality during hypoxic submergence was probably caused by metabolic acidosis, which resulted from accumulated lactate. Unlike the case with adult turtles, our hatchlings did not increase plasma calcium and magnesium, nor did they sequester lactate within the shell. Our results suggest that hatchling E. blandingii are not particularly well suited to hibernation in hypoxic aquatic habitats.
Physiological and Biochemical Zoology 01/2005; 78(3):356-63. · 2.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: We integrated field and laboratory studies in an investigation of water balance, energy use, and mechanisms of cold-hardiness in hatchling painted turtles (Chrysemys picta) indigenous to west-central Nebraska (Chrysemys picta bellii) and northern Indiana (Chrysemys picta marginata) during the winters of 1999-2000 and 2000-2001. We examined 184 nests, 80 of which provided the hatchlings (n=580) and/or samples of soil used in laboratory analyses. Whereas winter 1999-2000 was relatively dry and mild, the following winter was wet and cold; serendipitously, the contrast illuminated a marked plasticity in physiological response to environmental stress. Physiological and cold-hardiness responses of turtles also varied between study locales, largely owing to differences in precipitation and edaphics and the lower prevailing and minimum nest temperatures (to -13.2 degrees C) encountered by Nebraska turtles. In Nebraska, winter mortality occurred within 12.5% (1999-2000) and 42.3% (2000-2001) of the sampled nests; no turtles died in the Indiana nests. Laboratory studies of the mechanisms of cold-hardiness used by hatchling C. picta showed that resistance to inoculative freezing and capacity for freeze tolerance increased as winter approached. However, the level of inoculation resistance strongly depended on the physical characteristics of nest soil, as well as its moisture content, which varied seasonally. Risk of inoculative freezing (and mortality) was greatest in midwinter when nest temperatures were lowest and soil moisture and activity of constituent organic ice nuclei were highest. Water balance in overwintering hatchlings was closely linked to dynamics of precipitation and soil moisture, whereas energy use and the size of the energy reserve available to hatchlings in spring depended on the winter thermal regime. Acute chilling resulted in hyperglycemia and hyperlactemia, which persisted throughout winter; this response may be cryoprotective. Some physiological characteristics and cold-hardiness attributes varied between years, between study sites, among nests at the same site, and among siblings sharing nests. Such variation may reflect adaptive phenotypic plasticity, maternal or paternal influence on an individual's response to environmental challenge, or a combination of these factors. Some evidence suggests that life-history traits, such as clutch size and body size, have been shaped by constraints imposed by the harsh winter environment.
Physiological and Biochemical Zoology 01/2004; 77(1):74-99. · 2.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: The overwintering habits of hatchling Blanding's turtles, Emydoidea blandingii (Holbrook, 1838), are not well understood. To ascertain whether these turtles are well suited to hibernation on land, we examined susceptibility to dehydration, supercooling capacity, resistance to inoculative freezing, capacity for freeze tolerance, and physiological responses to somatic freezing in laboratory-reared, hatchling E. blandingii. Rates of evaporative water loss (mean ± SE = 4.1 ± 0.2 mg·g-1·d-1) were intermediate to rates previously reported for the hatchlings of species known to hiber - nate on land and in water. Supercooled hatchlings recovered from a 1-h exposure to -8 °C or a 7-d exposure to -4 °C. Additional turtles supercooled to -14.3 ± 1.2 °C (mean ± SE) before spontaneously freezing. However, when immersed in frozen soil, their capacity to supercool was severely limited by an inability to resist inoculative freezing following contact with external ice and ice nuclei. Therefore, hatchlings likely do not use supercooling as a winter survival strat - egy. Hatchlings tolerated a 72-h period of somatic freezing to -3.5 °C and responded to somatic freezing by increasing plasma concentrations of the putative cryoprotectants lactate and glucose. Our results suggest that hatchling E. blandingii could overwinter in moist, terrestrial hibernacula where risk of dehydration is reduced and freeze toler- ance is promoted.
Canadian Journal of Zoology-revue Canadienne De Zoologie - CAN J ZOOL. 01/2004; 82(4):594-600.
[show abstract][hide abstract] ABSTRACT: Hatchlings of the painted turtle (Chrysemys picta) commonly hibernate in their shallow, natal nests. Survival at temperatures below the limit of freeze tolerance (approximately -4 degrees C) apparently depends on their ability to remain supercooled, and, whereas previous studies have reported that supercooling capacity improves markedly with cold acclimation, the mechanistic basis for this change is incompletely understood. We report that the crystallization temperature (T(c)) of recently hatched (summer) turtles acclimated to 22 degrees C and reared on a substratum of vermiculite or nesting soil was approximately 5 degrees C higher than the T(c) determined for turtles acclimated to 4 degrees C and tested in winter. This increase in supercooling capacity coincided with elimination of substratum (and, in fewer cases, eggshell) that the hatchlings had ingested; however, this association was not necessarily causal because turtles reared on a paper-covered substratum did not ingest exogenous matter but nevertheless showed a similar increase in supercooling capacity. Our results for turtles reared on paper revealed that seasonal development of supercooling capacity fundamentally requires elimination of ice-nucleating agents (INA) of endogenous origin: summer turtles, but not winter turtles, produced feces (perhaps derived from residual yolk) that expressed ice-nucleating activity. Ingestion of vermiculite or eggshell, which had modest ice-nucleating activity, had no effect on the T(c), whereas ingestion of nesting soil, which contained two classes of potent INA, markedly reduced the supercooling capacity of summer turtles. This effect persisted long after the turtles had purged their guts of soil particles, because the T(c) of winter turtles reared on nesting soil (mean +/- S.E.M.=-11.6+/-1.4 degrees C) was approximately 6 degrees C higher than the T(c) of winter turtles reared on vermiculite or paper. Experiments in which winter turtles were fed INA commonly found in nesting soil showed that water-soluble, organic agents can remain fully active for at least one month. Such INA may account for the limited supercooling capacity (T(c) approximately -7.5 degrees C) we found in turtles overwintering in natural nests and may therefore pose a formidable challenge to the winter survival of hatchling C. picta.
[show abstract][hide abstract] ABSTRACT: These studies address the ability of hatchling Blanding's turtles (Emydoidea blandingii Holbrook, 1838) to overwinter in terrestrial and aquatic environments. Currently, it is not known where these hatchlings overwinter or how they survive different environmental stresses in each habitat. In addition, this is the first on antioxidant responses to freezing and anoxia in hatchling turtles, and survival times during freezing and anoxia among species of turtles. First, cold-hardiness and dehydration resistance were studied to determine if hatchlings could overwinter in a terrestrial environment. Hatchlings were susceptible to dehydration and could not rely on supercooling because of a lack of resistance to inoculation. However, hatchlings had a well developed ability to survive freezing at -3.5°C for 72 h. If hatchlings overwinter in terrestrial environments, they probably overwinter in moist areas that limit dehydration and promote freezing at a high sub-zero temperature. The second study examined whether hatchling Blanding's turtles could overwinter in aquatic habitats. The average survival time was 13 d for hatchlings submerged in anoxic water. Approximately one third of the hatchlings died during 75 d of normoxic submergence, but the cause of mortality was unclear. Mortality during hypoxic submergence was likely caused by metabolic acidosis, which resulted from accumulated lactate. Unlike the case with adult turtles, our hatchlings did not increase plasma calcium and magnesium, nor did they sequester lactate within the shell. Our results suggest that hatchling E. blandingii are not particularly well suited to hibernation in hypoxic aquatic habitats. The third study examined relationships between anoxia tolerance and freeze tolerance among several species of hatchling turtles. Freeze tolerance capacity was not necessarily associated with anoxia tolerance. Although lactate concentrations increased during freezing, they were much lower than the concentrations reached during anoxia. Also, liver catalase activity increased in most species following anoxia and freezing exposure, which suggests that constitutive activities of antioxidants are probably insufficient to metabolize increased reactive oxygen species formation during reoxygenation. In conclusion, although a functional anoxia develops during freezing, the accumulation of lactate does not limit survival. 0.90 MB PDF file Title from second page of PDF document. Thesis (Ph. D.)--Miami University, Dept. of Zoology, 2004. Includes bibliographical references. Mode of access: World Wide Web. System requirements: Adobe Acrobat Reader. Available online via OhioLINK's ETD Center.