Plastron Length Research Articles

Computed Tomography and 3D Reconstruction of the Respiratory Organs of the Egyptian Tortoise (Testudo kleinmanni)

This study is designed to identify, describe and illustrate the topography of the respiratory organs of the Egyptian tortoise (Testudo kleinmanni) using a digital camera and computed tomography. This may aid in obtaining complete data on dissection procedures, the topography and the initial section outlines and the safety of access during surgical procedures. The core of the present study is a series of photographs showing stages of the dissection. A detailed description of the dissection method and anatomy of the exposed organs are also given. Thirteen wild adult live tortoises, Testudo kleinmanni, (three males and ten females) were collected from Marsa Matroh and Cairo governorates with an age ranging from 15-19 years, weight between 430–450 gm, and carapace, and plastron lengths 10.5-11cm and 9.5-9.8 cm respectively. Computed tomography provides detailed information on the respiratory system, the location of the coelomic structures with respect to the carapace (the upper shell) and the vertebrae, and allows a comparison of cross-sectional anatomic views obtained with the digital camera with images obtained via computed tomography sections of the coelomic structures.

Barnacles on Hawksbill Sea Turtles, Eretmochelys imbricata, in Hormoz Island, Iran

The abundances of the epibiotic barnacles Balanus amphitrite Darwin, 1854 and Chelonibia caretta Spengler, 1790 on female Hawksbill Turtles, Eretmochelys imbricata (Linnaeus, 1766), are described from Hormoz Island, Iran. Barnacles were more frequent on the carapace (average 31 barnacles/turtle) than on the plastron and head. Significant positive correlations were found between the abundance of barnacles and the size of the turtles (straight carapace length and plastron length) but no correlation was found between the number of barnacles and head length. Habitat and individual physical and behavioural differences of Hawksbill Turtles may affect the abundance of attached barnacles.

Population Ecology and Reproduction of the Mexican Mud Turtle (Kinosternon integrum) in Tonatico, Estado de México

ABSTRACT. Ecological data directly from the field are important in understanding the life history strategies of kinosternid species in the tropics. Herein we summarize the basic population ecology and life history of Kinosternon integrum in the municipality of Tonatico (southeastern Estado de Mexico, Mexico). From October 2003 to November 2004, we marked a total of 204 turtles and recaptured 118 of them. Mean population size using the Jolly-Seber model was 197 (95% CI 128–416) individuals, with a sex ratio of 1:1.7, biased to females. Males were larger than females in carapace length and plastron length. The reproductive season starts in late June and finishes in late October. The smallest female with oviductal eggs was 122 mm in carapace length. Mean clutch size was 4 eggs (s = 1.77, range 1–8) and was significantly and positively related to body size. Mean egg length was 30.43 mm (s = 2.24, range 23.92–35.96), mean width was 16.35 mm (s = 1.01, range 12.99–18.30), and mean weight was 5.14 g (s = 0.60, r...

Demographic Parameters of the Neotropical Freshwater Turtle Hydromedusa maximiliani (Chelidae)

Despite the high species richness of the family Chelidae (side-necked turtles) in South America, few demographic studies are available for a neotropical chelid turtle. Here we report data from a long-term (1993–2006) study of Hydromedusa maximiliani. Population size was estimated for two periods (1993–1994 and 2003–2006) by the Jolly-Seber capture-mark-recapture method and the demographic parameters were estimated by Cormack-Jolly-Seber model. The population size estimates showed values that increased over the study period (from 235 to 318 individuals in a 250 ha area), although this result must be viewed with caution despite the large confidence intervals of the estimates. Significantly fewer individuals of intermediate body sizes (80–100 mm plastron length) were present in the 1993–1994 period compared to the 2003–2006 period. The population was female biased with male:female ratio of 1∶2. Survival rate (ϕ) was considerably higher for adult females than for males. The estimated annual population growth rate (λ) was 1.012, and the estimated temporal process variance, the variation in the population growth rate, was practically null. These demographic parameters indicate a healthy population, probably reflecting the protected status of the study area.

Sources and Significance of Among-Individual Reproductive Variation in a Northern Population of Painted Turtles (Chrysemys picta)

Painted Turtles (Chrysemys picta) are often used to test life-history theory. However, within populations, the factors that contribute to among-individual variation in egg size and clutch size are poorly understood, and an understanding of the biotic and abiotic parameters that contribute to this variation is important when framing patterns of maternal investment in a life-history context. We examined proximate sources of reproductive variation in a northern population of Painted Turtles, we attempted to frame these sources of variation in a life-history context, and we evaluate which optimality model most adequately explains patterns of reproductive allocation in populations of small-bodied turtles. We used multiple linear regression on data from 168 first clutches of marked females that nested at a long-term study site in Algonquin Park, Ontario, Canada, in 2004. We found that mean egg mass was positively related to maximum plastron length (MPL) and female age, and negatively related to clutch size and water temperature prior to oviposition. Clutch size was positively related to MPL and carapace height, and negatively related to mean egg mass, and the number of clutches laid in the season. Body size (MPL) was the most important predictor of each reproductive parameter, and residual analysis indicated that egg mass was more conserved than clutch size across the range of female body sizes sampled in this study. Thus, egg size may be optimized as a body size-specific function, and in light of this, we suggest that ‘phenotype-habitat matching’ may occur in C. picta. If a female's phenotype (e.g., body size) influences the selective environment of her eggs and hatchlings (e.g., if larger females generally nest farther away from water), then the optimal strategy of maternal investment should vary among maternal phenotypes. The positive correlation between egg mass and body size that was observed in the present study can be explained in adaptive terms under hypotheses based on the concept of phenotype–habitat matching.

A Quantitative Method for Sex Identification in Emydid Turtles Using Secondary Sexual Characters

Accurate classification of sex is essential for life history studies. Benchmark sizes that can represent the size of either the smallest, average, or upper size limit of males in a population exhibiting secondary sexual characters (SSCs) are often used to assign sex in emydid turtles. This method may be problematic, however, as it ignores variation in SSC development and is unable to identify the sex of smaller individuals. To address these two issues, we present a method using Slider Turtle (Trachemys scripta) standardized residual scores of third foreclaw length and preanal tail length versus plastron length. The use of benchmark sizes that reflected the smallest or average size of male maturity for our population did not compromise accurate sex identification. Additionally, our method was able to accurately sex turtles that were smaller than the benchmark size. Our method has the potential to enhance demographic studies on turtles by allowing researchers to identify juvenile sex ratios.

Skeletochronology: A Method For Determining The Individual Age and Growth of Modern and Fossil Tortoises (Reptilia: Testudines)

Skeletochronology is a method used to estimate the individual ages of animals by counting lines of arrested growth (LAGs) within skeletal tissues. This method was applied to evaluate the ages of modern gopher tortoises, Gopherus polyphemus, from north central Florida and fossil tortoise species, Gopherus laticuneus and Stylemys nebrascensis, from the White River Group in northwestern Nebraska. Different skeletal elements were tested for growth lines and the humerus was determined to be the most useful bone for analysis. LAGS in Gopherus polyphemus were correlated with alternative age estimations based on scute annuli counts, carapace lengths, and plastron lengths. While age estimates were similar in younger individuals, the alternative aging techniques did not accurately reflect the ages of older individuals. Scute wear, sexual dimorphism, and decreased growth with age are factors contributing to this discrepancy. Similarly, LAGS were found in the humeri of Gopherus laticuneus and Stylemys nebrascensis. Fossil specimens range in age from 0 years (hatchling) to over 40 years old. Fossil samples provide insight into changing ecological conditions during the Eocene-Oligocene Transition. This critical period appears to show a shift from a Stylemys nebrascensis to Gopherus laticuneus dominant ecosystem.

Use of Posthatching Yolk and External Forage to Maximize Early Growth in Apalone Mutica Hatchlings

Posthatching yolk in oviparous vertebrates is thought to supply the hatchling with energy for a period of time after hatching in habitats that might require fasting. To examine strategies of posthatching energy use in Apalone mutica, hatchlings were fed or not fed over periods of nine weeks in 2003 and six weeks in 2004. Mass, plastron length, carapace width, and body condition changed during the course of the experiment; all trajectories of change, except carapace width in 2004, differed between fed and unfed hatchlings. Trajectories of fed hatchlings were significantly higher than unfed hatchlings. Fed and unfed hatchlings used internalized yolk at similar rates: 50% of the yolk was depleted by day eight after hatching and 90% by day 27. Metabolic rate (approximately 0.236 ml CO2 h−1) did not differ between fed and unfed hatchlings. Yolk reserves are insufficient to sustain hatchlings to the first overwintering season, but with access to external forage, hatchlings appear to use yolk reserves to meet maintenance demands to support maximal growth.

Reproductive Allometry in the Common Map Turtle, Graptemys geographica

According to optimal offspring size theory, natural selection pressures balance the egg size/clutch size trade-off at a point where increases in maternal body size result in increases in clutch size but not increases in egg size. However, many turtle species show increasing egg size with increasing maternal body size. The anatomical-constraints hypothesis explains this pattern by hypothesizing that smaller females lay smaller-than-optimal eggs because of morphological constraints; larger eggs simply would not pass through the pelvic aperture and caudal gap of the shell. We examined relationships among female body size (measured as plastron length), clutch size and egg size for a population of common map turtles (Graptemys geographica) at Presque Isle State Park in Erie, Pennsylvania. Correlation analyses were conducted using log-transformed data in order to address questions of isometry and allometry. Clutch mass increased isometrically with plastron length. Egg size and clutch size were both significantly negatively allometric in their relationship with plastron length. It appears that larger females split the increased reproductive allocation made possible by increased maternal volume devoted to eggs between increasing both clutch size and egg size, consistent with predictions of the anatomical-constraints hypothesis.

Growing and shrinking in the smallest tortoise, Homopus signatus signatus: the importance of rain

Climate change models predict that the range of the world's smallest tortoise, Homopus signatus signatus, will aridify and contract in the next decades. To evaluate the effects of annual variation in rainfall on the growth of H. s. signatus, we recorded annual growth rates of wild individuals from spring 2000 to spring 2004. Juveniles grew faster than did adults, and females grew faster than did males. Growth correlated strongly with the amount of rain that fell during the time just before and within the growth periods. Growth rates were lowest in 2002-2003, when almost no rain fell between September 2002 and August 2003. In this period, more than 54% of the tortoises had negative growth rates for their straight carapace length (SCL), shell height (SH), and shell volume (SV); maximum shrinking for SCL, SH, and SV was 4, 11, and 12%, respectively. The shell of H. s. signatus has some flexibility dorso-ventrally, so a reduction in internal matter due to starvation or dehydration may have caused SH to shrink. Because the length and width of the shell seem more rigid, reversible bone resorption may have contributed to shrinkage, particularly of the shell width and plastron length. Based on growth rates for all years, female H. s. signatus need 11-12 years to mature, approximately twice as long as would be expected allometrically for such a small species. However, if aridification lowers average growth rates to the level of 2002-2003, females would require 30 years to mature. Additionally, aridification would lower average and maximum female size, resulting in smaller eggs and hatchlings. These projected life history responses to aridification heighten the threat posed by the predicted range contraction of this red-listed species.

Shell characteristics and sexual dimorphism in the Namaqualand speckled padloper, Homopus signatus signatus

There is little quantitative information regarding the two subspecies of the world's smallest tortoise, Homopus signatus. To help characterise the northern subspecies H. s. signatus and evaluate the development of shell size and colour patterns, we measured shell characteristics of wild juvenile, male and female H. s. signatus. When scaling shell dimensions on carapace length, male shell size represented an extension of juvenile shell size for shell height, width and volume, but not plastron length. The slope of plastron length scaled on carapace length was smaller for males than for juveniles or females, suggesting differential growth of the plastron. The smaller male plastron translates to large shell openings, perhaps to improve locomotion and to facilitate tail movement during copulation. Conversely, the slope of female shell height, width and volume (scaled) was larger than for juveniles or males, presumably providing more space to accommodate follicles and the large egg. Serration of the marginal scutes and shell colour changed with body size, and shell colour pattern differed between sexes. The carapace was darker at intermediate body sizes (large juveniles and small adults); the increase in dark appearance resulted primarily from widening of the dark pigment band around scute margins as growth laminae were added. Both the lighter shell colour and reduced serration of large adults may be due to shell wear; large adults may produce less dark pigment, and older laminae disappear due to flaking or peeling. Females had a darker overall colour, more rays and fewer speckles than did males. This dimorphism may relate to thermoregulation, gamete protection or intraspecific communication. Both male and female patterns may confer crypsis if the sexes use microhabitats differently.

Sexual Dimorphism and Allometry in the Stripe-Necked Terrapin, Mauremys leprosa, in Spain

ABSTRACT We measured 140 stripe-necked terrapins (Mauremys leprosa) from the center of the Iberian Peninsula, Spain. Female body size exceeded that of males, and female shells were wider and more domed than those of males in relation to carapace length. Plastron length was also greater in females, but preanal tail length was greater in males. Tail length showed similar values in both sexes. Morphological aspects related to sexual selection processes and those related to the fecundity of females are discussed as possible explanations of the sexually dimorphic traits in this species.

Population Structure of Florida Box Turtles (Terrapene carolina bauri) at the Southernmost Limit of their Range

We studied a population of Florida Box Turtles, Terrapene carolina bauri, from September 2002 to December 2003, in the Florida Keys at the southernmost limit of its range. Population structure was estimated to be 7.5% juvenile, 58.75% female, and 33.75% male, resulting in a female biased sex ratio (1 male:1.74 females). Population size was estimated at 39.9–114.4 turtles/6 ha in a pine rockland forest, with an estimated density of 4.8–10.2 turtles/ha. Males had significantly longer carapace and plastron lengths than did females. Comparison of data with other populations of T. c. bauri revealed similar morphological characteristics among populations although this southern population had higher mean body mass than did populations in the central parts of its range.

The effects of atrazine and temperature on turtle hatchling size and sex ratios

Temperature influences some hormone-governed developmental processes, as do environmental contaminants known as endocrine-disrupting compounds. Although many vertebrates exhibit developmental sensitivity to temperature or contaminants, little research has focused on the potential interaction of these two external influences during development. Here, embryos of the red-eared slider turtle (Trachemys scripta elegans) are used to model the potential interaction of increased temperature and the herbicide atrazine. The atrazine level selected (0.5 parts per billion) was based on common environmental concentrations and is within the range of federally approved drinking-water levels. Sex ratio was the endpoint of population effect in this study, with an increase in females construed as an effect of either temperature, atrazine, or the two together. Mass, carapace length and width, and plastron length were also assessed as endpoints of individual effects of exposure. Results show that increased temperature or atrazine alone do not affect sex ratio, but that the two interact to significantly increase the female fraction. Plastron length, carapace length and width, and mass were higher in atrazine-exposed turtles kept at the lower temperature, a result with fitness implications.

The Effects of Atrazine and Temperature on Turtle Hatchling Size and Sex Ratios

Temperature influences some hormone-governed developmental processes, as do environmental contaminants known as endocrine-disrupting compounds. Although many vertebrates exhibit developmental sensitivity to temperature or contaminants, little research has focused on the potential interaction of these two external influences during development. Here, embryos of the red-eared slider turtle (Trachemys scripta elegans) are used to model the potential interaction of increased temperature and the herbicide atrazine. The atrazine level selected (0.5 parts per billion) was based on common environmental concentrations and is within the range of federally approved drinking-water levels. Sex ratio was the endpoint of population effect in this study, with an increase in females construed as an effect of either temperature, atrazine, or the two together. Mass, carapace length and width, and plastron length were also assessed as endpoints of individual effects of exposure. Results show that increased temperature or atrazine alone do not affect sex ratio, but that the two interact to significantly increase the female fraction. Plastron length, carapace length and width, and mass were higher in atrazine-exposed turtles kept at the lower temperature, a result with fitness implications.

Gross morphometry of young Geochelone sulcata (Testudines: Testudinidae) in Costa Rica

The African Spur tortoise, Geochelone sulcata, has been introduced to Costa Rica. A total of 31 tortoises were measured for 26 gross morphometry parameters. All individuals measured were inmature, aged from 5 to 34 months, and were born in captivity in La Garita de Alajuela, Costa Rica. Mean straight carapace length was 83.1 mm, mean straight plastron length was 68.3 mm and mean maximum height was 46.2 mm. All the measurements were correlated, except tail length and cloacal distance. Weight had the highest positive allometry coefficient. All the variables were joined in two Principal Components; tail length and cloacal distance in Factor 2 and the rest of them in Factor 1. Lack of correlation among tail measures and the other variables as well as their inclusion in a different Factor could be related with an incipient development of sexual dimorphism characters.

Morphometrics of the pancake tortoise (<i>Malacochersus tornieri</i>) in Tanzania

Observations were made of the morphometrics of captive pancake tortoise ( Malacochersus tornieri ) in June 1995. Carapace length ranges for immature tortoises and adult males and females were 50-115, 123-160 and 129-171 mm respectively. The respective carapace widths were 45-90, 97-130, and 92-129 and 97-130 mm. Carapace height ranges were 15-29, 25-40 and 117-159 mm, respectively, while plastron length ranges were 45-110, 108-150 and 117-159 mm. The relationships between carapace length and width (males: y = 13.763+0.639x; females: y = 17.302+0.639x) and height (males: y=6.851+0.170x, females: y = 17.274+0.170x) were isometric and sexually dimorphic in adults. The relationship between carapace length (x) and plastron length (y) was also isometric (y = 20.438+0.790x) but not sexually dimorphic in adults. The respective mass ranges for immature tortoises, adult males and females were 20-200, 200-500 and 240-580 g. The relationship between mass (x in g) and carapace length (y in mm) were strongly allometric (males: y = 32.026x 0.261 ; females: y = 26.188x 0.261 ) and not sexually dimorphic in adults. That in immature tortoises was y = 16.482x 0.363 . Tanz. J. Sci. Vol. 28(2) 2002: 33-46

Different incubation temperatures result in differences in mass in female red-eared slider turtle hatchlings

The Charnov–Bull model states that environmentally determined sex will prevail in patchy environments where males may fare best in one patch type, whereas females may fare well in a different patch type. To investigate whether or not potential differences manifest early in the life of a turtle with temperature-dependent sex determination, I assessed mass, carapace width and length, and plastron length of hatchlings from three different incubation temperature regimes. Differences in incubation temperature affected mass in turtles of the same sex; the difference appears to support a sex-based rationale for the phenotype. The results bear out an assumption of Charnov–Bull that neonates of the same sex from different temperatures may manifest different attributes (i.e., mass) that could affect their relative fitness.

Aspects of the population and reproductive ecology of sympatric hinge‐back tortoises (Kinixys homeana and K. erosa) in southern Nigeria, on the basis of specimens traded in bush‐meat markets

The ecology and population structure of hinge‐back tortoises (genus Kinixys) was studied in the Niger Delta region of southern Nigeria (West Africa), where these species are actively hunted by local people for subsistence. The work is based not only on capture, mark and recapture study of free‐ranging specimens, but also on dissection of specimens offered for food, already dead, in the bush‐meat markets of the study region. The frequency of observation of the two most common species, i.e. K. homeana and K. erosa, was significantly higher in three areas subjected to ‘tradition conservation’ (because tortoises are worshipped by natives due to animistic taboos) than in three other areas where they are harvested. In particular, the juvenile class was much depleted in the three harvest areas. Analyses of market specimens demonstrated that, in both K. homeana and K. erosa, most of the females with oviductal eggs are found during the peak of the dry season, and that there was a positive relationship between maternal size (plastron length) and number of eggs produced.

DEMOGRAPHY AND DIET OF THE PAINTED TURTLE (CHRYSEMYS PICTA) AT HIGH-ELEVATION SITES IN SOUTHWESTERN COLORADO

We collected data on diet and population ecology of painted turtles (Chrysemys picta) at 2 high-elevation sites in southwestern Colorado during 1996 and 2000. Painted turtles from both sites fit previously reported patterns of delayed maturity and increased body size for C. picta at more northerly latitudes. Minimum body size at sexual maturity was similar at both sites for males (93 to 95 mm plastron length) and females (165 to 177 mm plastron length). Males appeared to reach sexual maturity at 2 to 3 years of age, whereas the onset of sexual maturity in females was delayed until 7 to 8 years of age. Average adult female body size (183 mm) exceeded any previously reported values for this latitude and might reflect an adaptive response to cooler climates and shorter growing seasons. Our analysis of dietary data indicated that painted turtles from these sites did not exhibit the same degree of carnivory (53.8% and 71.7% animal material) compared to more northerly populations of C. picta.