HERPETOLOGICAL JOURNAL, Vol. I, pp. 280-284 (1988) 280
STUDIES ON THE GROWTH OF THE DESERT TORTOISE (TESTUDO SULCATA) IN SUDAN: CHANGES IN MORPHOMETRICS AND BODY WEIGHT FROM HATCHING TO ONE YEAR (O+)
z. N. MAHMOUD AND D. A. EL NAIEM
Deparrmenr of Zoology, Fa cu/ry ofScience, Universil)' of Kharroum. Kharroum. Sudan.
(Accepred //. 11.87)
ABSTRACT
Changes in morphometrics and body weight during growth was deduced from observations of individual Testudo sulcata of known age. A strong positive correlation was found to exist between plastron width (r = 0.97), carapace length (r = 0.94), carapace width (r = 0.94), body weight (r = 0.99) and plastron length. Changes in morphometrics and body weight during growth in their first year of life has been investigated. The tortoises increased in size at a rate of 1.3764 x 10-3mm day-1 (plastron length), 1.0992 x J0-3mm day-1 (plastron width), 1.5273 x J0-3mm day-1 (carapace length), 1.4206 x J0-3mm day-I (carapace width) and 5.45 19 x J0-3g day-I (body weight). The values of the intercept (a), regression coefficient (b) and instantaneous growth rate (K) were calculated for T. sulcata and from similar growth data in the literature. Their relation to morphological changes in tortoises and turtles have been discussed.
INTRODUCTION ·top and back with a shut of glass for viewing on the front. The enclosure contained a shallow concrete pool Current ideas on reptiles life histories suggest that (0.3 x 0.3m). Food was offered every other day and individuals exhibit a series of growth rates during their readily accepted. It consisted of Medicago saliva and lives as a function of the source of energy and costs of Vicus bengalensis. During February, 1987 the tortoises growth, activity and reproduction (Gibbons, 1968; were unable to feed. This was probably due to a Wilbur, 1975; Andrews, 1982). This discontinuity in bacterial infection of the mouth. Treatment consisted the rate of growth and the endangered status of many of a daily dose of I ml of Rivocllin (Rivopharm, reptilian species make identification of growth rates an Switzerland) administered orally for one week. The important area of research, especially in the early mouth condition responded well, and the animals then stages of the life history. began to gain weight rapidly once more. Although growth, morphometrics and the relative MEASUREMENTS growth of a part in relation to that of the entire organism in many chelonian species have been studied Each individual was marked in a coded pattern by in detail (see Cagle, 1950; Gibbons and Semlitsch, filling the marginal scute to produce slight notches in 1982; Meek, 1982; Long, 1984; Mahmoud, El Naeem the bones. To aid recognition, dark marker paint was and Hamad, 1986), early growth has received Jess placed on the notched marginal scute and renewed attention and none of the published work (King, 1964 mostly at the time of measurement. Records for each on Testudo gracea, Blackwell, 1968 on Kinixys homeana, individual were kept. These consisted of age, weight in . Cloudsley-Thompson, 1970 on T. sulcata, Tryon and g, (measured with a Mettler balance sensitive to 0. I g), Hulsey, 1977 on Clemmys muhlenebergi, Bienefield, and four linear measurements: plastron length (PL) 1979 on Hy dromedusa tectife ra, Davis, 1979 on (greatest length measured at the midline), plastron Geochelene carbonaria, Peters and Finne, 1979 on width (PW) (maximum width along the midline) Geochelone gigantica, Brown, Marvey and Wilkins, carapace length (CL) (greatest length measured along 1982 on Erelmohelys imbricata and Inskeep, 1984 on the midline) and carapace width (CW) (maximum Cuora ambainensis) has rigorously been quantified. width along the midline). These measurements were From these data, relative growth rates were calculated made with a calibrated tape, accurate to I mm. and correlations were estimated by Linear regression. This paper describe some aspects of the early growth STASTISTICAL ANALYSIS (O+) in Testudo sulcata fromhatching to one year after Regression analysis of plastron length as well as hatching. other morphometric measurements, and body weight were carried out in accordance with the following equation. MATERIAL AND METHODS X =a+bY where: MAINTENANCE Y is the plastron length in mm; a=th e intercept and Newly hatched T. sulcata (I6 from the same clutch) b the regression coefficient of the morphometric were kept in an enclosure ( 1.3 x 1.3 x 2m) wired on the measurement in mm or body weight in g. GROWTH OF TESTUD O SULCATA 28 1
Relative growth rates, measured as rate of increase growth in T. sulcata was tested by plotting the two per day, were calculated from the formula (Brody, parameters against each other. The linearity of the 1945). points (Fig. 1) suggest either parameter can be used to K assess growth. = LnXi - LnX0 ti - to Growth in plastron width and carapace width was where: investigated in relation to plastron length. The K, is the instantaneous relative growth rate linearity of the points and the regression analysis show X and Xi are the morphometric measurements a high correlation between PW, CL, CW and the 0 lengthening of the plastron (Fig. 1; Table 1) where 88, or body weight at the beginning and end of the age 88 and 94 per cent of the points respectively, were interval t to t Ln, is the base of the natural logarithm. 0 ; accounted for. RESULTS
F'og .2 RELATIVE GROWTH The reliability of using either plastron length or 4. 2
carapace length as criteria for the measurement of 4.0 30
3.8 F'll 1 140 200 16 - 27 190 3.4 � 130 180 3.2 24
170 3.0
120 160 2.8 21
150 2.6
110 140 2.4 18
130 2.2
100 120 2.0 15
110 1.8
90 100 1.6 12
"' E 90 � 1.4 E
80 80 1.2 9
70 1.Q
70 60 0.8 .� 6 0.6 50
0.4 60 40
03 30 o .___.___._.....__.___..__.___.__.___.___._.....__�'-.__J o so 20 0 1 4 .5 6 7 8 9 10 11 ·�c 10 1 MorthS> t ,_...,.AAy19e6 Apri/May1987
��___.__ _.___ _.___ ,______.._ _ __, 0 � � ro � � � m Fig. 2 Instantaneous relative growth rate of plastron length Plastron l�h( mm) ( +--+ ), plastron width ( •--• ) , carapace length ( o--o) , Fig. Relationship between, plastron width (•--•), carapace width (@--@), and body weight (•------•) carapace length ( Parameter Intercept Regression Correlation (a) coefficient coefficient (b) (r) r2 Carapace length -8.8351 1.4757 0.94 88 Carapace width -3.3556 1.5284 0.94 88 Plastron width 14.8838 0.8121 0.97 94 Body weight -201.64338 4.5262 0.99 98 TABLE 1: Results of the regression analysis of some morphoqietric measurements (mm) and of body weight (g) on plastron length (mm) of T. su/cata. 282 Z. N. MAHMOUD AND D. A. EL NAIEM The regression between plastron length and body F1-;i 4 weight (Fig. I) expressed by the equation: 2.4 W = 201 .6438 + 4.5262 x PL indicates that body weight increased relatively faster 2 .3 than plastron length, because the regression coefficient 2 2 (b) is greater than (Table I). The correlation is very I 2.1 highly significant and 98 per cent of the points are accounted for. 2.0 The plot of the monthly instantaneous relative 1.9 growth rates (Fig. 2) shows that carapace length and � 18 width had a greater overall relative rate of growth than plastron length and width. However, the inconsistency t 17 � in this trend throughout the year is probably due to the aJ 1.6 °' formation of a carapace of the same shape. 3 1.5 Fig.3 14 190 13 90 ISO 1.2 170 80 160 150 2.0 70 140 .c. g. 19 130 .!< 6 18 60 120 � � 1.7 110 °' 3 I 6 50 100 1.5 E 90 -;;, 5 '0 80 � :6. 0 I c 5 6 s 9 10 11 12 .!< t t 70 >- Age(Months i .l 20 40 growth modes are represented by the regression lines. 30 weight were plotted against age on a linear scale, a 10 20 sigmoid growth pattern was obtained (Fig. 3). The plot 10 of the logarithmic value of the mean plastron length 0 and the mean body weight against age, straighten the 0 4 8 9 10 11 a curve for plastron length (Fig. 4). A body weight (•-- •) of O+ T. sulcata and time in months weight (Fig. 4 and Table 2). The points of intersection during June 1986 and May 1987. of the regression lines were observed to lie between days 84 and 282 after hatching. The three regression ABSOLUTE GROWTH were highly significant (P<0.01) and most of the points When the mean plastron length and mean body were accounted for by the three lines. Parameter Intercept Regression Correlation (a) coefficient coefficient (b) (r) r2 Plastron length I.71 53 0.0154 0.97 94 Body weight First growth mode 1.2346 0.2241 0.94 88 Second growth mode 1.8091 0.0226 0.96 92 Third growth mode 1.2338 0.0856 0.99 98 TABLE 2: Results of regression analysis for the relationship between plastron length (X, log mm) and body weight (X, log g) with age (Y, months) in T. sulcata. The regression following the equation. Y =a + b logX, where a and b are constants. GROWTH OF TE STUDO SULCA TA 283 Species No. of Duration Body Plastron Plastron Carapace Carapace Reference animals t -t weight length width length width o I in days g. day-I mm day-1 mm day-1 mm day-1 mm day-1 10-.1 10-3 10-3 10-3 10-3 Geoche/one carbonaria 15 76 5.69 2.01 Davis, 1979 Geoche/one gigantica 8 96 8.37 3.54 2.72 3.92 Peters and Fine, 1979 Kinixys homeana 3 95 13.25 Blackwell, 1968 Testudo gracea 5 12 5.72 2.43 King, 1964 T. su/cata 18 10.30 2.41 1.31 Cloudsley-Thompson, 1970 T. su/cma 16-9 365 5.45 1.38 1.09 1.53 1.42 Present work C/emmys muhlenbergii 2 367 6.36 2.36 Tryon and Hulsey, 1977 Hy dromedusa tectifera 7 122 7.27 2.36 2.22 Benefi eld, 1977 Eretmochelys imbricata 103 365 8.93 Brown et al. , 1986 Curo amboinenisis 199 5.52 1.86 1.98 Inskeep, 1984 TABLE 3: Calculated Instantaneous growth rate (k-value) for some chelonians (present work and literature) Growth in the weight of hatch ling T. su/cata per unit Ernst and Lovich ( 1986) stated that straight line time was characterised by an initial fast growing period carapace measurement includes much hidden growth at a rate of 11. 46 x 10-Jg day-1 until about August, masked in its curvature. followed by a slow growing rate of 1.50 x 10-Jg day-1 Mathematical models based on plastron length until about February and a fast growing rate of 5.13 x could be misleading if differences in plastron length 10-Jg day-1 by the time when the animals are one year between males and fe males exist. Although plastron old (Table 2 and 3). The growth in plastron length length dimorphism has been demonstrated in several followed the same trend and during these period a rate chelonian species (Berry and Shine, 1980; Branch, of 1.52 x 10-3mm day-1, 0.65 x 10-3mm day-1 and 1984), the clearest sex discrimination fu nctions (tail 1.85 x 10-Jmm day-1 was computed. length and anal region measurements) failed to distinguish the sex of O+ T. sulcata (Mahmoud and DISCUSSION Mustafa, 1987). In the present study all of T. sulcata examined were small in size (under 106mm plastron During the growth of newly hatched T. sulcata a length) and can only safely be classified as juveniles. strong positive correlation was fo und between Therefore, the plastron length is clearly a useful plastron length and other morphometric measurements measurement for describing the growth of O+ (Table I). Similar fi ndings have been reported between T. sulcata. plastron length and carapace length in young hatch ling The present study showed that in T. sulcata the body Platemys platycephala (r = 0.99) by Ernst and Lovich weight increases relatively faster than plastron length ( 1986) and in adult of Gopherus agassizi ( r = 0.99) by (b >I, Table !). The calculated regression coefficient Medica, Bury and Turner (1975). They have also been values (b) showed that the o+ old tortoises tend to calculated from the data of Peters and Finne ( 1979) in increase more in weight than in length when compared one year old G. gigantica (r = 0.93). Plastron length can with O+ old turtles (Table 4). This might be due to therefore be used as the independant variable in relatively faster growth of tortoises as that they relative and absolute growth studies, due to its become dome-shaped with increase in size, while relatively constant rate of growth. Ernst ( 1977) and turtles tends to remain fl at. Similar observations have Species Intercept Regression Correlation Reference (a) coefficient coefficient (b) (r) Tortoises: Geoche/one carbonaria -125.7299 2.9536 0.98 Davis, 1979 Geoche/one gigantica -150.3738 3.7163 0.91 Peters and Finne, 1979 T. sulcata -224.0133 4.8143 0.97 Present work Turtles: Hy dromadusa tectifera -23. 1891 0.8578 0.99 Benefield, 1977 C/emmys muhlenbergii -25.3801 1.0118 0.98 Tryon and Hulsey, 1977 Cure ambo/mensis -37.3781 1.2047 0.93 Inskeep, 1984 TABLE 4: Regression analysis of carapace length (mm) and body weight (g) describing the early growth in some chelonians. 284 Z. N. MAHMOUD AND D. A. EL NAIEM been reported in E. imbricata by Brown et al. ( 1982). Brown, R. A., Harvey, G. C. M. and Wilkins, L. A. (1982). Mosiman ( 1958) and Long ( 1984) reported that the Growth of Jamaican Hawksbill turtles (Eretmochelys length of the flat soft-shell turtles had greater intercept imbricata) reared in capativity. British Journal of Her values as opposed to other, more domed species. The petology 6, 233-236. same opinion hold true when the intercept value of Cagle, F. R. (l950). The life history of the slider turtle, T. sulcata (present study) and calculated values for Pseudemys scrip/a (Molbrook). Ecological Monographs tortoises and turtles (literature) are compared 20, 32-54. (Table 4). Cloudsley-Thompson, · J. L. ( 1970). On the biology of desert tortoise Tes1udo sulca1n in Sudan .Journal of In T. sulcata late summer and early winter account . Zoology London, 160, 17-33. for the lower K-values during mid-August to mid Davis, S. ( 1979). Husbandry and breeding of the red-footed et al. G. agasszi J anuary. Medica (1975) fo und that tortoise Geochelone carbonaria at the National Zoo grew most rapidly during the spring (mid-April) and logical Park, Washington, ln1erna1ional Zoo Yearbook early summer (first week of July). However, the 19, 50-53. discrepancy of the K-value (present work and Ernst, C. M. (1977). Biological notes on the bog turtles, literature) is due to difference in the species, their Clemmys muhlenbergic HerpelOlogica 33, 24 1-246. zoogeography, the duration of the study and number Ernst, C. H. and Lovich, .I . E. ( 1986). Morphometry in the of animals involved (Table 3). chelid turtle, Platemys platycephala. The Herpetological Additional long term growth data are required to Journal I, 66-70. verify whether the fl uctuation in K-value is due to Gibbons, J. W. (1976). Aging phemomena in reptiles. seasonality and/or some physiological factors that Experimental Aging Research Ed. by M. F. Ebas, B. E. need to be investigated. To cast light on these Eleftheriou and P. K. Klias pp. 454-475. EAR Inc. Bar problems, records for the 1986 hatchling will continue Harbor, Maine. and the 1987 hatchling are now studied in terms of the Gibbons, .I. W. and Semlitsch. R. D. ( 1982). 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