Graptemys Geographica Research Articles

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 least in part by differences in their shell composition and buffering capacity. All species tested have large mineralized shells. Shell comparisons included 1) total shell CO2 concentration, 2) volume of titrated acid required to hold incubating shell powder at pH 7.0 for 3 h (an indication of buffer release from shell), and 3) lactate concentration of shell samples incubated to equilibrium in a standard lactate solution. For each measurement, the more anoxia-tolerant species (painted turtle, Chrysemys picta; snapping turtle, Chelydra serpentina) had higher values than the less anoxia-tolerant species (musk turtle, Sternotherus odoratus; map turtle, Graptemys geographica; red-eared slider, Trachemys scripta). We suggest that greater concentrations of accessible CO2 (as carbonate or bicarbonate) in the more tolerant species enable these species, when acidotic, to release more buffer into the extracellular fluid and to take up more lactic acid into their shells. We conclude that the interspecific differences in shell composition and buffering can contribute to, but cannot explain fully, the variations observed in anoxia tolerance among freshwater turtles.

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 degrees C for 72 h ranged from 0 to 100%. Tolerance to freezing was poor in Sternotherus odoratus, Graptemys geographica and Trachemys scripta, intermediate in Chelydra serpentina, and high in Emydoidea blandingii, Chrysemys picta bellii, C. p. marginata, Malaclemys terrapin, and Terrapene ornata, and generally reflected the winter thermal ecology of each taxon. Plasma activity of lactate dehydrogenase (LDH), a novel in vivo index of freeze/thaw damage, corroborated viability assessments and demonstrated that cryoinjury occurred even in surviving turtles. Irrespective of taxon, cryoinjury tended to be higher in smaller individuals and in those having relatively low water contents; however, bases for these associations were not apparent. Screening for certain organic osmolytes that might promote freezing survival by colligatively reducing ice content and limiting cell dehydration showed that the plasma of unfrozen (control) turtles contained small quantities of glucose (1.3-5.8 mmol l(-1)) and lactate (0.6-3.2 mmol l(-1)) and modest amounts of urea (range of mean values for all taxa 8.2-52.3 mmol l(-1)). Frozen/thawed turtles of all taxa accumulated modest amounts of glucose and lactate that jointly raised the plasma solute concentration by 30-100 mmol l(-1). We conclude that organic osmolytes accumulated both before and during freezing may promote survival in species that have evolved a tolerance to freezing, but are not necessarily accumulated for that purpose.

Changes in a Turtle Community from a Northern Indiana Lake: A Long-Term Study1

Abstract Knowledge of the long-term dynamics of freshwater turtle communities is important if we are to understand fully the impacts of human-induced changes in their aquatic and terrestrial habitats. We present data on a turtle community that has been monitored intermittently for more than 20 years and regularly for more than 10 years (1992–2003). The composition of the community has shifted with a decrease in the dominance of Painted Turtles (Chrysemys picta). This shift reflects a decline in the number of C. picta over the past decade, whereas numbers of other species have remained relatively constant. Adult survivorship of C. picta has declined in the past decade. The proportion of C. picta with watercraft propeller damage has increased, whereas propeller damage has remained constant for the two other species for which we have data, the Northern Map Turtle (Graptemys geographica) and the Red-Eared Slider (Trachemys scripta). Our study suggests that the turtle community in Dewart Lake has shifted from ...

Zebra and Quagga Mussels (Dreissena spp.) and Other Prey of a Lake Erie Population of Common Map Turtles (Emydidae: Graptemys Geographica)

The diet of the Common Map Turtle (Graptemys geographica) was studied in Lake Erie habitats associated with a Pennsylvania sandspit peninsula. Three taxa predominated in fecal samples: trichopteran larvae (principally leptocerids), gastropods, and Zebra and Quagga Mussels (Dreissena spp.). Pronounced sexual and size-related differences occurred for these taxa, as adult males fed primarily on trichopterans and snails, while the larger females fed almost exclusively on Dreissena spp., with prevalence of Dreissena spp. increasing with body size. Dietary data from habitats lacking invasive mollusks suggest that the overall reliance on mollusks in the diet may have increased since the invasion of Lake Erie by Dreissena spp. Results are similar to earlier reports concerning the effect of invasive Asian Clams (Corbicula spp.) on decreasing dietary diversity in females of many populations of the four species of Graptemys that have mollusk-adapted mesocephalic females.

Descriptive Ecology of a Turtle Assemblage in an Urban Landscape

We studied turtle populations inhabiting a canal and a lake (both man-made) within a heavily disturbed, urban setting. Six aquatic and semi-aquatic turtle species were collected in both habitats: spiny softshell turtle (Apolone spinifera), painted turtle (Chrysemys picta), common snapping turtle (Chelydra serpentina), common map turtle (Graptemys geographica), common musk turtle (Sternotherus odoratus) and red-eared slider (Trachemys scripta). While G. geographica was the most common species in the canal habitat, T. scripta was most common in the lake habitat. We describe patterns of sexual size dimorphism and sex ratios for the three most abundant species (G. geographica, T. scripta and S. odoratus). We discuss our data in light of problems facing turtle assemblages in urban settings.

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 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.

Prevalence and Colonization of Placobdella on Two Species of Freshwater Turtles (Graptemys geographica and Sternotherus odoratus)

It is generally accepted that bottom-dwelling turtles have a higher ectoparasite load than turtles that bask aerially because of effects of desiccation on ectoparasites, especially with regard to leeches. We compared number of leeches (primarily Placobdella parasitica) on field-caught Common Musk Turtles (Sternotherus odoratus) and Common Map Turtles (Graptemys geographica). The bottom-dwelling species S. odoratus had more than 20 times the number of leeches than the aerial-basking species G. geographica. We then exposed cleaned (leech-free) turtles to leeches in mesocosms (cattle tanks) to measure the rate of colonization. In this experiment, S. odoratus had more than four times the number of leeches as G. geographica after 24 h of exposure, even though G. geographica were unable to bask under these experimental conditions. We suggest that desiccation threat alone does not explain the species-specific differences in leech loads on aquatic turtles.

Overwintering in the nest by hatchling map turtles (Graptemys geographica)

We monitored 75 natural nests of Graptemys geographica (Lesueur, 1817) in central Pennsylvania to determine the tactics and patterns of hatchling emergence. Following incubation, all hatchlings in 95% of nests delayed emergence from their natal nest cavities throughout autumn and winter until the following spring. Nests were constructed in a variety of substrates ranging from loose sand or coal to hard-packed clay mixed with gravel. Time from egg deposition to natural hatchling emergence averaged 333 days. During winter, hatchlings tolerated subzero temperatures as low as –8 °C, which are lethal to hatchlings of some sympatric species. Emergence occurred from 10 April to 25 May, and most hatchlings were found during morning following rain. There was an interactive effect of minimum daily air temperature and rainfall level 1 day prior to emergence on the number of hatchlings emerging each day. One half of all hatchlings found dead were contained in nests in which autumn emergence had apparently occurred. We speculate that autumn emergence by hatchlings of some turtle species may be an adaptive response to nest conditions likely to provide poor environments for successful overwintering.

Diel Activity Patterns of the Turtle Assemblage of a Northern Indiana Lake

We investigated the daily activity patterns of seven species of turtles in a northern Indiana lake over 10 y using the numbers of captures in fyke nets as an index of activity. Chrysemys picta and Graptemys geographica were active throughout the daylight hours. Sternotherus odoratus and Chelydra serpentina were crepuscular. Trachemys scripta was diurnal; however, its activity was concentrated in the morning hours. Apalone spinifera was diurnal as well, with most activity in the afternoon and very little in the morning. Emydoidea blandingii was rarely captured, and all captures were made during daytime hours. Activity patterns did not change substantially between two sampling periods from mid-May to mid-June and from late-July to early-August. These activity patterns are consistent with differences in the frequency of basking: baskers are diurnal (e.g., C. picta, G. geographica, T. scripta, E. blandingii and A. spinifera), whereas those that are secretive are crepuscular (e.g., S. odoratus and C. serpentina).

Adaptations to terrestrial overwintering of hatchling northern map turtles, Graptemys geographica.

We conducted a 3-year field and laboratory study of winter biology in hatchlings of the northern map turtle ( Graptemys geographica). At our study area in northern Indiana, hatchlings routinely overwintered in their natal nests, emerging after the weather warmed in spring. Winter survival was excellent despite the fact that hatchlings were exposed frequently to subfreezing temperatures (to -5.4 degrees C). In the laboratory, cold-acclimated hatchlings exhibited low rates of evaporative water loss (mean=2.0 mg g(-1) day(-1)), which would enable them to conserve body water during winter. Laboratory-reared hatchlings were intolerant of freezing at -2.5 degrees C for 24 h, conditions that are readily survived by freeze-tolerant species of turtles. Winter survival of hatchling G. geographica probably depended on their extensive capacity for supercooling (to -14.8 degrees C) and their well-developed resistance to inoculative freezing, which may occur when hatchlings contact ice and ice-nucleating agents present in nesting soil. Supercooled hatchlings survived a brief exposure to -8 degrees C. Others, held at -6 degrees C for 5 days, maintained ATP concentrations at control levels, although they did accumulate lactate and glucose, probably in response to tissue hypoxia. Therefore, anoxia tolerance, as evidenced by the viability of hatchlings exposed to N(2) gas for 8 days, may promote survival during exposure to subfreezing temperatures.

Turtle Habitat Use in a Reach of the Upper Mississippi River

Turtle community composition was determined in three habitats—open river, slough, and backwater—of the Mississippi River near Hamilton, Illinois. While seven species of turtles were collected during the study, distinct communities were found in each of the habitats. The open river site was dominated by female smooth softshell turtles, Apalone muticas, which made up approximately 80% of the community in this habitat. While turtles were abundant in the backwater habitat, only three species, red-eared slider (Trachemys scripta), common snapping turtle (Chelydra serpentina), and painted turtle (Chrysemys picta), were collected. Though all three species were common in the backwater, the red-eared slider was the most abundant. The habitat with the most abundant and diverse turtle community was the slough. In addition to red-eared sliders, the most abundant species collected, common snapping turtles, painted turtles, smooth softshell turtles, spiny softshell turtles (Apalone spinifera), common map turtles (Graptemys geographica), and false map turtles (G. pseudogeographica), were also collected in this habitat. The slough habitat had permanent water with low current velocities and abundant basking and refuge sites, which provide the best conditions for most of the turtle species collected.

The physiology of hibernation in common map turtles ( Graptemys geographica)

Map turtles from Wisconsin were submerged at 3°C in normoxic and anoxic water to simulate extremes of potential respiratory microenvironments while hibernating under ice. In predive turtles, and in turtles submerged for up to 150 days, plasma P o 2, P co 2, pH, [Cl −], [Na +], [K +], total Mg, total Ca, lactate, glucose, and osmolality were measured; hematocrit and body mass were determined, and plasma [HCO 3 −] was calculated. Turtles in anoxic water developed a severe metabolic acidosis, accumulating lactate from a predive value of 1.7 to 116 mmol/l at 50 days, associated with a fall in pH from 8.010 to 7.128. To buffer lactate increase, total calcium and magnesium rose from 3.5 and 2.0 to 25.7 and 7.6 mmol/l, respectively. Plasma [HCO 3 −] was titrated from 44.7 to 4.3 mmol/l in turtles in anoxic water. Turtles in normoxic water had only minor disturbances of their acid–base status and ionic statuses; there was a marked increase in hematocrit from 31.1 to 51.9%. This study and field studies suggest that map turtles have an obligatory requirement for a hibernaculum that provides well-oxygenated water (e.g. rivers and large lakes rather than small ponds and swamps) and that this requirement is a major factor in determining their microdistribution.

An aggregation of overwintering Leopard Frog, Rana pipiens, and Common Map Turtles, Graptemys geographica, in northern Vermont

An aggregation of overwintering Leopard Frog, Rana pipiens, and Common Map Turtles, Graptemys geographica, in northern Vermont

Dispersal from and fidelity to a hibernaculum in a northern Vermont population of Common Map Turtles, Graptemys geographica

Dispersal from and fidelity to a hibernaculum in a northern Vermont population of Common Map Turtles, Graptemys geographica

Physiology of common map turtles (Graptemys geographica) hibernating in the Lamoille river, Vermont.

Common map turtles (Graptemys geographica) were collected from a natural underwater hibernaculum in Vermont at monthly intervals during the winter of 1997-1998. Blood was sampled by cardiac puncture and analyzed for pH, PCO(2), PO(2), and hematocrit; separated plasma was tested for Na(+), K(+), Cl(-), total [Ca], total [Mg], [lactate], and osmolality (mOsm kg(-1) H(2)O). Control (eupneic; 1 degrees C) values for pH, PO(2), PCO(2), [HCO(3)(-)], and [lactate] were 7.98 +/- 0.03, 47.4 +/- 18.7, 10.1 +/- 0.7 (mm Hg), 36.1 +/- 0.2 (mmol liter(-1)), and 2.1 +/- 0.1 (mmol liter(-1)), respectively. Between November 1997 and March 1998, ice covered the river and the turtles rested on the substratum, fully exposed to the water, and were apneic. Blood PO(2) was maintained at less than 3 mm Hg (range 0.9 +/- 0.2 to 2.1 +/- 0.7 mm Hg), PCO(2) decreased slightly, plasma [lactate] was <5 mmol liter(-1), and plasma [HCO(3)(-)] decreased significantly. In March [lactate] rose to 7.5 +/- 1.5 mmol liter(-l), but there was no acidemia. Map turtles meet most of their metabolic demand for O(2) via aquatic respiration and tolerate prolonged submergence at 1 degrees C with little change in acid-base or ionic status. The adaptive significance of remaining essentially aerobic during winter is to avoid the life-threatening progressive acidosis that results from anaerobic metabolism. J. Exp. Zool. 286:143-148, 2000.

Responses of turtle assemblage to environmental gradients in the St. Croix River in Minnesota and Wisconsin, U.S.A.

We investigated how environmental gradients measured along the St. Croix River in Minnesota and Wisconsin, U.S.A., influenced the turtle assemblage. Among seven species, the five most common species were generalists and had wide distributions throughout the study area. However, patterns in assemblage structure were related to environmental gradients along the river. Sex ratios were male-dominated for the five most common species, and few or no juveniles were captured during the study. The first two canonical axes of a canonical correspondence analysis accounted for 92.7% of the variation in species-environment gradients. Most of the variation in distribution and abundance was attributed to gradients in channel morphology and physical characteristics along the river channel. Abundances of common snapping (Chelydra serpentina), false map (Graptemys pseudogeographica), and painted (Chrysemys picta bellii) turtles were associated with muck substrates and the number of basking sites (i.e., snags, rocks), which increased farther downstream. Abundance of spiny softshell turtles was closely related to increased water velocity and depth, which were related to hydraulic control points in the river. Abundance of common map turtles was associated with the presence of open sandy areas, uniform channel bottom, and gravel substrates. Geomorphic changes along the St. Croix River clearly influence the turtle assemblage and these specific relations should be considered in efforts to preserve and restore components of the assemblage.

Map Turtle Winter Leech Loads

Adult common map turtles, Graptemys geographica (n = 243), were obtained in November 1995 from a hibernation site in the Lamoille River, Vermont. Of the 208 female turtles examined, 151 (72.6%) had at least 1 leech (Placobdella parasitica) attached and 10 of 35 males (28.6%) were similarly parasitized. Mean abundances were 1.49 (SD = 1.461, n = 208) for female turtles and 0.34 (SD = 0.591, n = 35) for males; the difference was significant (t = 4.558, df = 241, P < 0.001). Leech broods were found on 34 of 208 female turtles (16.3%) and 2 of 35 males (5.7%). One of the leeches was of record size (77.7 mm total length); another specimen measuring 64.4 mm had 153 brood-sized (x = 4.5 mm) young attached to its venter. Because of poor visibility and partial ice cover, only 7 turtles were recovered in March 1996. All of these turtles had attached leeches, and 4 turtles had broods of 9-52 young ranging in length from 4.58 to 5.78 mm. One Placobdella ornata was found in the March sample. Our results suggest that leeches of various size classes remain attached to hibernating adult map turtles throughout the winter.

Predation on zebra mussels (Dreissena polymorpha) by captive-reared map turtles (Graptemys geographica)

The suitability of the Eurasian zebra mussel, Dreissena polymorpha, as prey for the common map turtle, Graptemys geographica, was tested under laboratory conditions. The turtles, which were reared in captivity without contact with molluscs, readily consumed zebra mussels in every feeding trial. Mussels were ingested whole. Repeated exposure to zebra mussels in successive trials did not increase consumption rates (ca. 11 mussels/turtle per day), suggesting that the turtles required little time to recognize and efficiently utilize zebra mussels as prey. The turtles were offered zebra mussels ranging from 4 to 34 mm in length and consumed mussels as large as 32 mm, but mussels larger than 25 mm were consumed at lower rates. Turtles consumed lower numbers of zebra mussels in the presence of an alternative prey, the prosobranch snail Bithynia tentaculata, which is common in map turtle habitats in the Great Lakes – St. Lawrence River system. Populations of map turtles and zebra mussels are sympatric in the upper St. Lawrence River, Lake Champlain, the lower Great Lakes, and the upper Mississippi River basin. Our results suggest that map turtles may forage on zebra mussels in nature, but zebra mussels will be important prey only when preferred or more profitable prey are scarce.

Distribution and abundance of Common Map Turtles, Graptemys geographica, in the Ottawa River, Quebec

Distribution and abundance of Common Map Turtles, Graptemys geographica, in the Ottawa River, Quebec

Preferred body temperatures in five nearctic freshwater turtles: A preliminary study

1. 1. The preferred body temperature of five freshwater turtle species was determined in a thermal gradient. 2. 2. There was no significant difference between the mean preferred temperatures (MPTs) of Pseudemys rubriventris, Clemmys insculpta, and Graptemys geographica. 3. 3. The MPT of Trachemys scripta elegans was significantly higher ( P < 0.05) than the MPT of Emydoidea blandingi and both were significantly lower ( P < 0.05) than the MPTs of the other three species. 4. 4. No intraspecific or interspecific correlation between body wt and MPT was found.