Growth of the turtle Chrysemys scripta under constant controlled laboratory conditions.код для вставкиСкачать
THE ANATOMICAL RECORD 199433-439 (1981) Growth of the Turtle Chrysernys scripta Under Constant Control led Lab0 ratory Conditions BERNARD G. SARNAT, ELIZABETH MCNABB, AND MICHAEL GLASS Section of Oral Biology, School of Dentistry; Division of Plastic Surgery, Department of Surgery, School of Medicine; and Dental Research Institute; Uniuersity of California at Los Angeles, L o s Angeles, California 90024 ABSTRACT The purpose of this study was to determine 1) growth of the turtle shell and change in weight under constant controlled laboratory conditions and 2) whether under these constant conditions there were seasonal changes. Fifty unfed refrigerated eight-week-old hatchling turtles Chrysemys scripta were received in October and maintained in aquaria with 16 hours of artificial light and eight hours of darkness, at 24-27°C and a humidity of 30% and fed twice weekly. Gross linear measurements of the width and length of the plastron and carapace, and total body weights, were taken a t eight weeks and thereafter a t about six-week intervals. During the two-year period the mean increase of the plastron length was from 30.79 t 0.19 mm to 68.32 t 1.58 mm, plastron width from 24.23 t 0.20 mm to 50.43 % 1.03 mm; carapace length from 32.47 t 0.24 mm t o 75.21 t 1.82 mm, carapace width from 31.81 t 0.28 mm to 67.12 1.29 mm, and body weight from 6.94 0.15 gm to 80.63 % 5.02 gm.Calculated daily percent changes revealed that as the turtles aged, the rates decreased. At 56 days of age, weight was the most strongly correlated with its value at 786 days of age. No seasonal differences in growth were noted between the summer and winter periods when turtles would enter winter dormancy in certain natural environments. Environmental factors are reflected in the growth of the turtle * Although there are many references about growth of turtles in varied natural environments, there are few references about growth of the turtle in captivity or under constant controlled conditions in the laboratory (Cagle, '46, '50; Allen and Littleford, '55; Jackson, '70; Ernst and Barbour, '72; Wilbur, '75; Christiansen and Burken, '79). The purposes of this study were to determine under constant controlled laboratory conditions during a two-year period beginning a t the hatchling stage the growth rate of Chrysemys scripta by measuring weight, width, and length of the shell (plastron and carapace); whether under these constant conditions there were seasonal changes as in certain natural environments; and which measurements were most reliable as growth indicators. No similar report was noted in the literature. MATERIALS AND METHODS Fifty unfed refrigerated eight-week-old hatchling red-eared turtles Chrysemys scripta were received from a commercial turtle dealer in October. Within the first week each turtle 0003-276X/81/19930433$02.50 0 1981 ALAN R. LISS, INC. * was topically numbered on selected scutes of the carapace with an indelible felt-tip black marker. They were housed according to size and in groups of four to five, in 11 glass aquaria (40-80 liters each). The turtles were exposed to 16 hours of artificial light and eight hours of darkness for each 24-hour period. Ambient laboratory temperature was 2 6 2 7 ° C with a humidity factor of 300/00.The water was aerated, filtered, and had 0.005% sodium hypochlorite added each week to inhibit bacterial and algal growth. Also included in the aquaria were floating platforms to enable the turtles to get out of the water. The turtles were maintained on a mixed fortified diet of fish, bone meal and multiple vitamins. They were fed ad libitum twice weekly; once on Monday (when the aquaria were cleaned) and again on Thursday. One medium-sized leaf of romaine lettuce was added to each aquarium a t the conclusion of feeding sessions as a food supplement, and mealworms (3-4 per turtle) were given on an Received May 7, 1979 accepted July 11, 1980. BERNARD G. SARNAT, ELIZABETH MCNABB, AND MICHAEL GLASS 434 95% confidence interval and the mean at each time period is given in Figures g 7 for weight, carapace length and width, and plastron length and width. The general trend in all five figures is for the daily percent change to decrease as the animals aged. The very high daily percent change in weight for the first interval (5G70 days) might possibly represent hydration of the turtles (Fig. 3). The two measures of carapace (Figs. 4, 5 ) and pastron length (Fig. 6) might indicate a spurt during the first summer but not in the second. The correlation between weight values a t 56 and 786 days of age is highly significant (r = 0.540, P < 0.001, N = 37), whereas that between carapace width values at 56 and 786 days of age is not statistically significant (r = 0.293, P > 0.05). At 148 days, however, the correlation with 786 days of age is highly significant (r = 0.513, P < 0.001).The correlationbetween carapace length values at 56 and 786 days of age is significant (r = 0.394, P < 0.05) and becomes highly significant a t 70 and 786 days of age (r = 0.528, P < 0.001).This same pattern is RESULTS observed for plastron width values with the The approximate relative size of the carapace corresponding correlation coefficients equal to and plastron on a centimeter grid and dorso- 0.316 and 0.510. The correlation between the ventral radiographs from 58 to 810 days of age plastron lengthvalues a t 56 and 786 days of age are illustrated in Figure 1. The superposed is significant (r = 0.386, P < 0.05) and is highly tracings of the photographs of the plastrons a t significant a t 148 days of age (r = 0.516, P < 58,443, and 810 days of age illustrate (Fig. 2) 0.001). Each measurement at an early age is the differential in growth. significantly related to its value a t 786 days of The growth patterns of weight, carapace age. These correlations show weight to be correlength and width, and plastron length and lated most strongly at 56 days of age and that width were calculated for each turtle as an av- the carapace and plastron measurements are erage daily percent change. An approximate strongest at 70 and 148 days of age. infrequent, treat basis. For each aquarium there was a separate 8-10-liter stainless steel container used for a g4-hour feeding period. Data were collected and recorded first a t eight weeks of age and thereafter at about sixweek intervals for the first 18 months, and a t about 12-weekintervals for the last six months. Gross direct linear measurements of the maximum width and length of the carapace and plastron were recorded to the nearest 0.1 mm with a sliding Helios dial reading needlepointed caliper. Each measurement was taken twice. An average of the two values was used. Weights were recorded to the nearest 0.1 gm with the use of a two-pan triple beam balance. Radiographs were obtained a t the beginning usually at a targetlfilm distance of 50 cm, with the X-ray machine operated a t 40 kVp, 15 mA, and a n exposure time of 4 seconds and after about 4 months when the turtles were larger and more mineralized at a targetlfilm distance of 70 cm, 65 kVp, 10 mA, and a n exposure time of 2 seconds. TABLE 1. Mean weights, and carapace and plastron widths and lengths and their associated standard errors of turtles at 16 intervals from 56 to 786 days of age Carapace Plastron Dates Age in days Weight (gm) Width (mm) Length (mm) Width (mm) Length (mm) 1015 10119 11/18 115 2116 3/31 5/11 6122 814 9/15 10127 1215 1/19 417 715 1014 56 70 100 148 190 233 274 316 359 40 1 443 482 527 606 695 786 6.94 t 0.15 9.18 t 0.14 10.31 t 0.20 15.59 t 0.50 20.88 t 0.77 27.16 f 1.02 32.01 f 1.31 36.77 t 1.63 41.63 % 1.80 46.10 t 2.35 50.27 t 2.76 54.70 t 2.96 59.05 t 3.35 63.52 c 3.72 73.72 2 4.39 80.63 t 5.02 31.81 t 0.28 31.71 t 0.26 33.06 t 0.29 37.78 ? 0.42 41.80 f 0.54 46.11 t 0.61 49.07 t 0.65 51.91 t 0.74 55.01 t 0.81 56.83 f 0.93 58.23 t 1.01 59.35 t 1.05 60.92 t 1.09 62.82 t 1.18 64.75 t 1.29 67.12 t 1.29 32.47 f 0.24 33.23 +- 0.24 35.16 x 0.29 40.86 % 0.48 44.97 2 0.72 49.86 t 0.71 53.02 t 0.81 55.81 t 0.93 59.16 t 0.97 61.27 2 1.18 62.88 ? 1.32 64.57 ? 1.35 66.69 t 1.43 69.34 c 1.59 72.47 t 1.69 75.21 ? 1.82 24.23 f 0.20 24.23 t 0.19 25.40 t 0.21 29.96 t 0.34 33.29 t 0.44 36.17 t 0.48 38.19 t 0.51 40.21 f 0.70 42.15 t 0.62 43.35 t 0.74 44.25 2 0.78 45.11 0.83 46.72 f 0.90 47.61 f 0.92 49.61 f 1.00 50.43 t 1.03 30.79 t 0.19 30.89 2 0.23 32.22 c 0.24 36.96 c 0.39 41.08 f 0.52 44.79 t 0.59 47.79 t 0.67 50.17 t 0.81 53.69 f 0.94 55.50 t 1.09 56.98 t 1.18 58.33 t 1.17 60.56 e 1.23 63.03 t 1.39 66.37 t 1.47 68.32 t 1.58 * TURTLE GROWTH IN LABORATORY 435 Fig. 1. Photographs of approximate relative size of carapace and plastron on a centimeter grid and dorsoventral radiographs from 58 to 810 days of age. Note change in ocelli on the plastrons (Table 1). BERNARD G. SARNAT, ELIZABETH MCNABB, AND MICHAEL GLASS 436 4 Fig. 2. Superposedtracings of plastron photographs of a turtle. Note the differentialin growth between 58 and 443 days, and 443 and 810 days of age (see Fig. 1 and Table 1). WEIGHT - Mean ..__. '2 Standard Errors 2 : 8 1.0 I \ DBC1 Apr 1 Aug 1 Dec 1 Apr I Age in Days Figs. %7. Daily percent change is defined from the mid-point of each age interval during the two-year period. Fig. 3. Weight. 437 TURTLE GROWTH IN LABORATORY CARAPACE LENGTH - Mean .....f2 Standard Errors Dec 1 Apr 1 Dec I Aug I A ~ 1I Age in Days Fig. 4. Carapace length. CARAPACE WIDTH - Mean ._. ..Standard Errors t2 I D& 1 Apr I Aug 1 Dee1 Age in Days Fig. 5. Carapace width. Apr 5 438 BERNARD G. SARNAT, ELIZABETH MCNABB, AND MICHAEL GLASS PLASTRON LENGTH -- Mean _.. ._ '2 Standard Errors 2;2 Dee I 1 I 1 380 Apr I 1 422 462 I 504 566 Dec I Aug I 650 Apr I I 739 Aug I Age in Days Fig. 6. Plastron length PLASTRON WIDTH - Mean __..f-2 Standard Errors -&p3 Dec 1 Apr I 337 Aug 380 1 422 562 504 Dec 1 Age in Days Fig. 7. Pastron width. 56b 650 Apr I 739 Aug I TURTLE GROWTH IN LABORATORY DISCUSSION In a study of the growth of animals the ideal method is to make repeated observations a t regular intervals on a large population of the same individuals of known age living under the same constant conditions. This we attempted to do in the laboratory rather than repeat a study, of which there are many excellent ones, in the natural environment with its many uncontrolled variables (Cagle, '46, '50; Allen and Littleford, '55; Jackson, '70; Ernst and Barbour, '72). The turtle shell because of its firmness, ready availability, and with only the thin scutes covering the bone, was a n excellent model for accurate study of gross bone growth. The growth peak was reached during the first year and from then on the rate decelerated (Figs. S 7 ) (Cagle, '46, '50; Jackson, '70; Gibbons, '68). In the natural environment when the water temperature was below 10-15"C, turtles became less active and went into dormancy (Cagle, '50; Sexton, '65; Felger et al., '76). In this two-year experiment the temperature was maintained between 24" and 27°C. The turtles did not go into dormancy, and growth continued throughout the year a t a regular rate. This could be compared with another similar experiment except for either changing the lightldark period or lowering the temperature for certain periods. Although we tried to raise the turtles under ideal conditions, there were limiting factors such as aquarium size and absence of a natural growing plant and animal diet. Contrary to the statement that turtles maintained in zoos or laboratories often refuse to feed during the winter (Cagle, '50; Suzuki, '63), our turtles fed well from October through April. They did not become dormant, and they continued to grow. Jackson ('70) studied growth of turtles inhabiting Fannin Spring in Florida with a virtually constant temperature of 2 Z 23°C. A dramatic decrease in growth rate occurred over the winter months despite the turtles' remaining active and feeding. He mentioned that cold air temperatures and a shorter day length might have been factors. Jackson ('70) stated that it was difficult to account for what appeared to be almost a complete cessation of growth, and he raised the question of an inherent growth cycle regulated perhaps by the changing seasonal light/dark ratio. 439 Wilbur ('75) found that weight was the best measure to predict furture growth. We found this to be true a t 56 days of age. Cagle ('46) reported in his study of turtles in the natural environment that plastron length was the best indicator of future growth and we found this to be true at 148 days of age. Cagle ('50) found no significant correlation between egg size and plastron length in predicting future growth. A later study will be to determine, by means of radiopaque implants (in bones of the plastron) and serial radiographs, the contribution of selected sutures to growth of the turtle shell during a Z3-year period. ACKNOWLEDGMENTS This project was supported in part by Biomedical Research Support grant RR05304 from the National Institutes of Health. We are grateful to Alan B. Forsythe, Onelio Clark, and Peter Lestrel for the statistical evaluation; Charles G. Wishowski for Figures 1 and 2; Irene Petravicius for Figures 3 through 7; and the School of Dentistry Word Processing Center for assistance in the preparation of this manuscript. LITERATURE CITED Allen, J.F., and R.A. Littleford (1955)Observations on the feeding habits and growth of immature diamondback terrapins. Herpetologica, I 1 :77-80. Cagle, F.R. (1946)The growth of the slider turtle,Pseudemys scripta elegans. Am. Mid. Nat., 36.685729. Cagle, F.R. (1950) The life history of the slider turtle Pseudemys scripta troostii (Holbrook). Ecol. Monogr., 20:32-54. Christiansen, J.L., and R.R. Burken (1979) Growth and maturity of the snapping turtle (Chelydra serpentinn) i n Iowa. Herpetologica, 35:261-266. Emst, C.H., and R.W. Barbour (1972) Turtles of the United States. The University Press of Kentucky, Lexington, Kentucky. Felger, R.S., K. Clifton, and P.J. Regal (1976) Winter dormancy in sea turtles. Science, 191:283-285. Copeia, 3:314-318. Gibbons, J.W. (1968) Growth rates of the common snapping turtle, Chelydra serpentina, i n a polluted river. Herpetologica, 24:26&267. Jackson, C.G., Jr. (1970) A biometrical study of growth i n Pseudemys concinna suwanniensis. Copeia, 3:52%534. Sexton, O.J. (1965) The annual cycle of growth and shedding i n the midland painted turtle, Chrysemyspicta mrginata. Copeia, 2:31&318. Suzuki, H.K. (1963) Studies on the osseous system of the slider turtle. Ann. NY Acad. Sci., 109:351-410. Wilbur, H.M. (1975) A growth model for the turtle Chrysemys picta. Copeia, 2:337-343.