LACTATE LIMITS LIFE
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Abstract:
Most North American freshwater turtle neonates typically hatch in late summer or early fall and move from their subterranean nests to nearby lakes and ponds, avoiding winter's subzero temperatures in the water's depths. However, painted turtle (Chrysemys picta) hatchlings remain entombed in their shallow subterranean nest throughout their first winter, frequently experiencing ice and body temperatures as low as -10°C. Nevertheless, the hatchlings emerge unscathed when the ground thaws in the spring.Although two mechanisms could explain the painted turtle hatchling's remarkable cold tolerance (a capacity for supercooling and an ability to tolerate freezing), supercooling is thought to play a significant role in the neonate's ability to overwinter. However, the importance of freeze tolerance in survival continues to be debated. Gary and Mary Packard of Colorado State wondered why hatchling painted turtles can only recover from a few days of freezing under relatively mild conditions (-2 to -2.5°C) and decided to investigate whether lactate accumulation in the hatchling's tissues affects the youngster's freeze tolerance.The Packards explain that when hatchlings freeze, much of the extracellular water forms ice, preventing the circulatory system from functioning and the delivery of oxygen for mitochondrial ATP production. Cells are instead forced to meet their ATP demands through anaerobic glycolysis, which causes an increase in tissue lactic acid levels, known as anoxic lactic acidosis. Normally, unfrozen turtles counteract the dangerous drop in tissue pH that accompanies lactate accumulation by the release of carbonate buffers into the blood from the shell, and lactate is also transported to and sequestered in the shell itself. However, these buffering processes may not be available to frozen hatchlings due to their arrested circulation.Assessing lactate's role in freeze tolerance, the Packards exposed recently hatched painted turtles to freezing conditions at -2°C for periods between zero and eight days. Every second day, the Packards thawed a group of animals and recorded the mortality percentage. They also measured whole-body lactate levels from another group that was not allowed to thaw. The team found that the frozen hatchlings' mortality levels were correlated with the amount of whole-body lactate. They also found that the frozen turtles' whole-body lactate levels were greater than those previously measured from comparable supercooled turtles, which maintain a functional circulatory system. Thus,freezing compromises the hatchling's ability to effectively deal with the anoxic lactic acidosis that accompanies anaerobic metabolism, a phenomenon the Packards suspect is due to the cessation of the circulation that occurs with freezing.The Packards hypothesize that without a functional circulatory system,frozen turtles cannot shuttle lactate from individual tissues to the shell to be sequestered or mobilize the shell's buffers. As a result, individual organs may accumulate lactate to lethal levels sooner than if the circulatory system remained operational. As follows, the Packards suggest that a cold tolerance strategy based on freezing is more stressful than a strategy based on supercooling and argue that the inability to deal with lactic acidosis may be one of the reasons why hatchling painted turtles are unable to tolerate freezing for prolonged time periods.Keywords:
Hatchling
Painted turtle
Supercooling
Hatchling
Sea turtle
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Hatchling
Painted turtle
Overwintering
Cryobiology
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Hatchling
Chelydra
Painted turtle
Animal ecology
Altricial
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We measured temperatures inside seven natural nests of painted turtles (Chrysemys picta) at our study site in north central Nebraska during the winter of 1987–1988. Although the lowest temperature recorded in some nests was only slightly below 0 °C, the minimum temperature measured in other nests was as low as −6.2 °C. Viable hatchlings were present in all of the nests at the end of the winter, however, which indicates that hatchling painted turtles can withstand exposure to low temperatures that would kill hatchlings of other species.
Hatchling
Painted turtle
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We monitored temperatures during the winter of 1995–1996 inside 18 nests containing hatchling painted turtles (Chrysemys picta). The study was performed at the Valentine National Wildlife Refuge in north-central Nebraska to assess survival of neonatal turtles in relation to the thermal environment inside their hibernacula. Minimum temperatures in the nests varied from −3 to −21 °C, and were better predictors of survival of hatchlings than other measures of the thermal environment. All hatchlings survived in nests where the temperature never went below −7 °C, some animals survived in nests where the minimum was between −7 and −13 °C, but no turtle survived in a nest where the minimum was below −14 °C. Hatchlings probably survived the cold by sustaining a state of supercooling, because the duration of exposure to low temperatures was far too long for animals in most nests to have survived in a frozen state.
Hatchling
Painted turtle
Overwintering
Wildlife refuge
Critical thermal maximum
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Hatchling painted turtles, (Chrysemys picta) in north central Nebraska overwinter terrestrially within the nest cavity. Nest temperatures as low as −2.1 °C were recorded during January 1982 within nests from which hatchlings survived. Under laboratory conditions, nine turtles survived a cooling cycle (0 to −8.0 to 0 °C) over a 29-h period. Four of these turtles exhibited the ability to supercool to temperatures as low as −8.9 °C at which point freezing occurred. Partial freeze tolerance was exhibited by one individual. The ability of hatchling painted turtles to supercool and to survive subfreezing temperatures may be an important factor in the northern distribution of this species.
Hatchling
Painted turtle
Supercooling
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To evaluate the effects of organized turtle watches on female sea turtles and their eggs, we quantified nesting behavior and hatchling production of loggerhead turtles ( Caretta caretta ) in south Brevard Country, Florida, U.S.A. We compared the duration of five phases of nesting behavior, the directness of the turtle’s return path, rate of travel during return crawl, hatching success, and hatchling emergence success between experimental and control turtles. Experimental turtles nested while observed by an organized turtle watch group consisting of at least 15 people; control turtles were not observed by a turtle watch group. Experimental turtles spent significantly less time camouflaging nest sites than did control turtles. The duration of the other four phases of nesting behavior were not significantly different between the two groups. Experimental turtles also traveled less‐direct paths during return crawls, although their rates of travel were not significantly different from those of control turtles. Hatching success and hatchling emergence success were not significantly different between experimental and control turtle nests in either year. Although turtle watch groups influenced nesting behavior, they were not found to be detrimental to hatchling production. Florida’s turtle watch program is a means for garnering public support for sea turtle conservation through education, and it should continue.
Hatchling
Sea turtle
Nesting (process)
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Painted turtle
Ecological trap
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We report the season of emergence from the nest of hatchlings of five species of freshwater turtles from a wetlands/stream/lake complex in southcentral New Hampshire from 1988–1994. Only hatchling Chrysemys picta (Painted Turtle) overwintered in the nest and emerged the following spring, although there were some cases of autumn emergence, as well as some nests with hatchlings that emerged in both seasons. In nests monitored over the winter, mortality ranged from 26–100%. Hatchlings of the other four species—Chelydra serpentina (Snapping Turtle), Glyptemys insculpta (Wood Turtle), Clemmys guttata (Spotted Turtle), and Emydoidea blandingii (Blanding's Turtle)—emerged only in autumn.
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Chelydra
Painted turtle
Nesting season
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Sex ratios of hatchling painted turtles (Chrysemys picta) are influenced by the hydric environment when eggs are exposed to fluctuating temperatures similar to those encountered in natural nests. When temperature varies between 18 and 30 °C over the course of a single day, nearly equal numbers of males and females hatch from eggs held on wet substrates, but, primarily, males emerge from eggs on dry substrates. The influence of the hydric environment on sex ratios of painted turtles developing in natural nests has important ecological implications, and may be a factor influencing both selection of nest sites by gravid females and sex ratios of hatchlings.
Painted turtle
Hatchling
Hydric soil
Chelydra
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