Plastron Length Research Articles

Comparative Life History of Painted Turtles (Chrysemys picta) in Two Habitats in the Inland Pacific Northwest

I conducted a comparative analysis of life-history attributes of two populations of painted turtles (Chrysemys picta) in the inland Pacific Northwest. A population inhabiting three wastewater lagoons contained proportionately more juveniles than one inhabiting a lake on a wildlife refuge. Average fecundity was significantly higher in the wastewater lagoon population (15.8 vs 13.4 eggs/clutch). Minimum size at the onset of sexual maturity was similar in the two populations for males and females (approximately 90 mm and 160 mm plastron length, respectively). However, turtles grew more rapidly and reached these sizes at younger ages in the wastewater lagoons (two years in males and 6-7 years in females) than in the lake population (three years in males and probably 8-10 years in females). These results contrast with local variation in the timing of maturity described for Trachemys scripta, for which females in populations of fast-growing turtles matured at the same age but at a larger body size with a concomitant increase in clutch size. The difference may be related to a contrast in the two species' clutch size-body size correlation, which is greater for T. scripta than C. picta. Interpopulational differences in fecundity and growth rate may have been related to caloric content and consistent seasonal availability of chironomid larvae and pupae fed upon heavily by the turtles in the waste-water lagoons. Lake turtles fed heavily upon odonate larvae in the early and middle active season, and on amphipods throughout the year. Comparison of the two study populations corroborates earlier reports of enhanced life-history parameters for C. picta in habitats that are nutrient enhanced by anthropogenic activity. Both study populations fit intraspecific patterns of increased clutch size and body size and later maturity for C. picta at more northern latitudes and higher elevations. The highly carnivorous diet of both populations, atypical for this species, may result in the relatively large body sizes and clutch sizes observed.

Organochlorine contaminant concentrations in eggs and their relationship to body size, and clutch characteristics of the female common snapping turtle (Chelydra serpentina serpentina) in lake Ontario, Canada

Statistical analyses were used to determine relationships between body size, clutch size and mass, and relative clutch mass and levels of organochlorine pesticides and seven polychlorinated biphenyl congeners in the eggs of adult female common snapping turtles (Chelydra serpentina serpentina). No significant correlations were found between body size (body mass, carapace length, carapace width, plastron length) and lipid normalized concentrations of p,p′-DDE, mirex, dieldrin, and polychlorinated biphenyl (PCB) congeners (IUPAC): #52, #105, #118, #138, #153, #180, #194, and the sum concentration of those congeners. Small sample size and clumping of data around the mode of the body size values prevented inferences of nonlinear relationships. It was concluded that body size and clutch characteristics are not strong or reliable predictors of the level of contaminants in snapping turtle eggs and that adjustment for those parameters would not reduce variation in contaminant levels among clutches. Other variables such as individual food preferences and/or foraging activities are more likely to cause variation in chemical concentrations among clutches of eggs within a population. In order to reduce interclutch variation in contaminant levels to 38.6–55.9% in snapping turtles, sample sizes of at least 15 clutches per site are recommended.

An Experimental Analysis of Natural Selection on Body Size of Hatchling Turtles

A complete understanding of life history evolution requires an appreciation for the influence of natural selection and genetic variation on intrapopulation phenotypic variation in key life history traits. Experimental manipulation provides particularly useful insight into the biological importance of this variation. Consequently, I undertook a field experiment in which I manipulated body size and evaluated selective predation in order to investigate the ecological and evolutionary significance of phenotypic variation in hatchling turtles. I incubated eggs from 17 clutches of common snapping turtles (Chelydra serpentina) on wet and dry substrates, producing "large" and "small" hatchlings, respectively. Hatchlings were individually marked, measured, and then released simultaneously at a typical nest site in a National Wildlife Refuge area, Whiteside County, Illinois from which the eggs collected originally. Subsequently, hatchlings were recaptured in drift fences erected along the edge of the Mississippi River. Sixty—six of 112 hatchling C. serpentina were recaptured. Survivorship was not related to clutch, incubation conditions, or locomotor performance, but was significantly size dependent. Natural selection favored larger hatchlings. The strength of selection acting directly on three size traits, as measured by standardized selection gradients (°), was 0.327 (PCI [principal component 1] °overall size and mass), 0.282 (PC3 = plastron length), and 0.162 (PC4 = trade—off between hatchling mass and width). The opportunity for selection was moderate (I =0.703), but did not constrain selection. Full—sib heritabilities of body size of hatchling turtles were variable (h2wet = 0.72 ° 0.34 and h2dry = 0.17 @+ 0.28), but were not significantly different between the two moisture treatments. These results provide support for the "bigger is better" hypothesis. Larger hatchling Chelydra serpentina exhibited significantly greater survivorship than smaller individuals during movement from the nest site to water. However, larger body size of hatchling turtles may not evolve rapidly because the strength of selection was moderate in magnitude and the heritability was relatively low. These results emphasize the need for more detailed ecological investigations of the early life history of these organisms. Furthermore, this study highlights the utility of experimental manipulations of phenotypic variation for evaluating the potential impact of natural selection on life history evolution.

Roles of Diet Protein and Temperature in the Growth and Nutritional Energetics of Juvenile Slider Turtles,Trachemys scripta

We determined the effects of dietary protein and Ta on growth rates, food consumption rates, digestion rates, and digestive efficiencies of juvenile slider turtles (Trachemys scripta). Results from this study provide a clearer understanding of how these environmental factors interact in influencing body sizes and growth rates of individuals in wild slider turtle populations. Changes in plastron length, carapace length, and body mass were significantly greater for T. scripta eating 25% and 40% crude protein diets than for those eating 10% crude protein. Those consuming 10% crude protein showed significant decreases in body mass and plastron length over a 13-wk period. Individuals at Ta's of 15°, 22°, 28°, or 34° C had food ingestion rates (kJ wk⁻¹) that increased markedly with an increase in Ta. Increasing dietary crude protein concentration increased turtle ingestion rates and influenced the positive effect of Ta. Increasing dietary crude protein concentration alone did not significantly affect turtle consumption rates but did significantly influence the positive effect of Ta. Digestive efficiencies were very high (because of the pelleted diet). Those turtles that ate at 15° C had a digestive efciency of 99.5%, as compared with 98.3% at 22° C, 94.8% at 28° C, and 95.8% at 34° C. Dietary protein concentration did not influence the digestive efficiencies of T. scripta. These data suggest that dietary protein is an important nutritional component to the growth of juvenile slider turtles and that elevated thermal conditions, combined with a high dietary protein availability, may explain the very high growth rates of slider turtles in some wild populations.

The hawksbill turtle, Eretmochelys imbricata, in Queensland: population structure within a southern Great Barrier Reef feeding ground.

Hawksbill turtles, Eretmochelys imbricata, live at low density on coral reefs in the southern Great Barrier Reef. The biomass of the species on Heron Reef was estimated at 0.82 kg ha-1. This is equivalent to 3.34 turtles km-1. The nesting beaches used by these E. imbricata are unknown. However, within the Great Barrier Reef and Coral Sea region, no regular nesting by the species occurs within 1200 km of these reefal feeding grounds. E. imbricata take up long-term residence in these feeding grounds at a minimum curved carapace length of 35.0cm. The E. imbricata feeding over these reefs ranged in size from these small immatures up to adults with curved carapace length of 87.5cm, but the maturity ratio was very strongly biased toward immatures (maturity ratio=0.01 adults). The sex ratio of all size classes was significantly skewed in favour of females (2.57 : 1 females : male overall) while 2% of the turtles were identified as intersex. Growth data from these turtles indicate that they will be decades old at first breeding. A key for sexing and assessing reproductive maturity of E. imbricata is provided. Regression equations for converting between curved carapace length and other standard measures including straight carapace measures, weight, head length and width and plastron length are described.

Growth, Survivorship and Longevity of Painted Turtles Chrysemys picta in a Southwestern Michigan Marsh

-This paper reports results of a mark-recapture study of painted turtles inhabiting a marsh in Kalamazoo County, Michigan, first begun in 1964-1966 and continued intermittently from 1980-1989. The relationship between plastron length (PL) and age (t) was described by von Bertalanffy growth equations for males PL = 111.8(1 0.792e-0?184t) and females PL = 152.2(1 0.852e-01281). Annual survivorship of males and females (26 yr old) was estimated as 0.64-0.83 and 0.29-0.50, respectively. Annual survivorship of juveniles (<6 yr old) was 0.21-0.51. Based on estimated minimum ages of individuals first captured as adults in the 1960s and recaptured in the 1980s, the four oldest males were 31 and the oldest female was 34 yr old. The oldest known-age male and female were 21 yr and 15 yr old, respectively. A comparison of data from the 1960s with that gathered in the 1980s revealed that the growth rates of juveniles and the density of turtles in the marsh have increased, while survival rates have apparently decreased. We speculate that the enhanced growth rates and population density are the result of warmer and drier weather during the 1980s.

Ecological Notes on the Turtle Clemmys insculpta in Northwestern New Jersey

An intensive ecological study of the wood turtle, Clemmys insculpta, was conducted in northwestern New Jersey from 1978-1981. Population density averaged 10.7 turtles/ha over all years. Nearly half (45.5%) of the population consisted of adults >140 mm in plastron length. The adult female-to-male ratio was not significantly different from 1:1. Secondary sexual differences became apparent in the ninth year, but maturity was not attained until the 14th year. While there was little difference in plastron length of adult males and females, males had longer carapaces than females of the same age. Plastral growth decreased from 84% in the first year to 2.3% in the sixth year, but showed an increase to 9.2 and 10.3% in years eight and nine. Since the ratio of abdominal scute to plastron length varied between captures, the use of abdominal scute length to estimate plastron length in Clemmys insculpta seems inappropriate. Courtship and mating occurred in the spring and fall. Females nested in June on elevated, well-drained, fully exposed sites near the stream. Clutch size averaged 8.5 and emergence of hatchlings occurred 70-71 days after nesting. Wood turtles were primarily diurnal throughout the year, but some courtship and nesting activity continued after dark. Estivation did not occur in the field; aquatic hibernation lasted from late November through early March. From May to October wood turtles assumed a solitary, terrestrial life style. Cloacal temperature was more closely correlated with substrate and water temperature than with air temperature. Comparison of temperatures among all activities showed that cloacal temperatures of turtles basking or moving on land were significantly higher than those of turtles found in water. Basking turtles accounted for 45.8% of all captures. Over the four year study period 16.8% of all turtles were found with injuries attributed primarily to raccoons (Procyon lotor). Almost 90% of all animals captured in early

Aspects of ecology of the threatened ringed sawback turtle, Graptemys oculifera

AbstractThe ringed sawback turtle, Graptemys oculifem, is endemic to the Pearl River system of Louisiana and Mississippi in southern USA. In 1986 the species was placed on the U.S. Federal List of Endangered and Threatened Species with status designation of 'threatened'. Existing museum specimens were examined to determine geographic distribution, food, growth and reproduction. Caddisflies, dipteran flies, mayflies, beetles and plant material were the most important food. Many stomachs contained small pieces of wood, suggesting that fallen tree trunks were a "grazing" substrate. Males ranged from 3.2-8.6 cm plastron length, and attained sexual maturity during the third or fourth year at lengths of about 6.0-7.0 cm. Adult males experienced recrudescence of testes, with maximum testis lengths during August and September indicating the probable time of spermatogenesis. Females ranged from 3.3-18.9 cm plastron length, and appeared to attain sexual maturity during the seventh or eighth year at lengths greater than 10.0 cm. The data suggested that ovulation occurs from May through July, nesting during June and ,July, and hatching at least during August. Clutch size appeared to be just two or three eggs.

Growth and body size in Blanding's turtles (Emydoidea blandingi): relationships to reproduction

Growth and reproduction in Blanding's turtles (Emydoidea blandingi) were studied in southeastern Michigan from 1975 through 1988. Average body sizes of both sexes of adults were similar; however, shapes of males were different from those of females. The average size of a group of females with a mean minimum age of 47 years was not significantly different from a younger group with a mean age of 21 years. Clutch size ranged from 3 to 19 ([Formula: see text], N = 280) eggs over 11 years. Clutch wet mass ranged from 60.4 to 183.4 g ([Formula: see text], N = 17), and relative clutch mass of nine females averaged 0.12. Clutch size, and to a lesser degree egg size, showed a significant positive relationship with body size, but not with age of females. Hatchlings averaged 31.0 mm in plastron length, 35.3 mm in carapace length, and 9.2 g in body wet mass. Differences in juvenile growth rates and age at sexual maturity appear to be the major cause of variation in body size of adult Blanding's turtles and the related reproductive output per clutch.

Growth, maturity, and sexual dimorphism in the wood turtle, Clemmys insculpta

Growth in the wood turtle (Clemmys insculpta) is described using the von Bertalanffy growth model and nonlinear regression. Growth in both sexes is similar until about 160 mm plastron length. Males grew at a faster rate after this size. Males appear to mature at a larger size and later age than females, although age-specific body size is highly variable. Sexual size dimorphism, in carapace length, is pronounced, with males attaining mean body sizes significantly larger (1.07–1.10 times) than those of adult females. Plastron length is an inappropriate measure of sexual size dimorphism because of the development of plastral concavity in males. Females tend to predominate in samples, possibly owing to differential maturity of the sexes. The direction of sexual size dimorphism may be maintained by intrasexual competition among males for access to females. Data for several adults captured at intervals of from 9 to 20 years support the concept of indeterminate growth.

Courtship of the Turtle, Pseudemys nelsoni

With the exception of Jackson and Davis' studies of the courtship of Trachemys scripta elegans (1972a) and Pseudemys concinna suwanniensis (1972b), our knowledge of the courtship patterns of these genera is based on fragmentary and anecdotal accounts (e.g., Davis and Jackson, 1973; Lardie, 1973; Jackson, 1977). Here we describe the courtship behavior of male Pseudemys nelsoni. Our results are based on the courtship behavior of two small adult males kept in the laboratory and 16 observations of courtship in the field at Rock Springs run, Apopka, Florida (Kramer, 1986). Most laboratory observations were made by UF on a male (plastron length = 18 cm) housed in a 100 x 40 x 40 cm aquarium. Water temperature varied from 22 to 30?C in the summer and from 20 to 26?C in the winter. An arti-

Flow cytometric analysis of the effects of low-level radiation exposure on natural populations of slider turtles (Pseudemys scripta).

Aquatic turtles inhabiting seepage basins containing low concentrations of radioactive and non-radioactive contaminants possess significantly greater variation in DNA content in blood cells than turtles from a control population. This variation, measured on a flow cytometer as the coefficient of variation of the cells in Gl of the cell cycle, is positively correlated with plastron length and estimated age of the turtles. Multiple peaks indicative of aneuploid mosaicism also were observed. We conclude that radiation or some unidentified chemical in the seepage basins likely acts as a clastogenic agent that causes chromosomal rearrangements leading to deletions and duplications that have the effect of increasing DNA content variation in blood cells. The proliferation of a mutant cell line leads to aneuploid mosaicism and the observation of multiple peaks in the DNA histograms.

Growth Rates of Immature Green Turtles, Chelonia mydas, on Feeding Grounds in the Southern Bahamas

Growth in carapace length, carapace width, plastron length and body mass was measured in 149 growth increments for 122 green turtles, Chelonia mydas, at Great Inagua, Rahamas. Initial carapace length of the 149 growth increments ranged from 28.3-75.5 cm. Absolute growth rates for all linear parameters decreased with increasing size, but no significant difference in absolute growth rates for body mass was noted over the size range measured. Equations were developed to convert carapace length or plastron length to mass so that growth in mass could be modeled from data for either linear parameter. Three sizespecific growth models-Von Bertalanffy, Gompertz and logistic-were tested for goodness of fit. The Von Bertalanffy model had the best fit for seven body size parameters. With increasing size, there was a significant negative allometric relationship between carapace width and carapace length, but the relationship between plastron length and carapace length was isometric. Growth rates were compared with those of other green turtle populations. In our study area, green turtles grow more slowly than hawksbills, Eretmochelys imbricata, or loggerheads, Caretta caretta, of similar size.

Female Reproductive Cycle and Life History Attributes in a Virginia Population of Painted Turtles, Chrysemys picta

ABSTRAcr. -Female reproductive cycles and life history attributes were studied over a two-year period in a population of Chrysemys picta picta in central Virginia, U.S.A. Ovarian cycles were phenologically similar between years despite differences in temperature and rainfall. Vitellogenesis began in August and continued, except during brumation, into the following May. Clutches averaging 4.2 eggs were laid mid-May to July and did not differ between years. Females matured at six years of age and plastron lengths of >105 mm. Several females each year produced two clutches, and although second clutches were not significantly different from first clutches, they averaged slightly larger. Clutch size and egg width were positively correlated with female body size. A multiple regression model explained over 89% of clutch size variation with the independent variables plastron length, egg mass, and month. Between-year differences in egg measurements were insignificant. Several recent generalizations about aspects of freshwater turtle life histories are supported by results of this study.

Reproduction and Survival of the Desert Tortoise (Scaptochelys agassizii) in Ivanpah Valley, California

Eighty-seven adult desert tortoises (58 females, 29 males) in Ivanpah Valley, California, were fitted with radiotransmitters in 1980 and 1981. All were marked, weighed, and measured and released. Tortoises were then recaptured, weighed and released about every two weeks in 1980 and weekly in 1981. The experiment concluded in the spring of 1982, when 62 tortoises were recovered. Survival of males and females did not differ, but the observed death rate in 1981-82 (18.4%) was significantly greater than that in 1980-81 (4.4%). Females > 200 mm in plastron length exhibited two periods of distinct loss of mass in 1980 (15-28 May, 12-25 June) when masses of males were essentially unchanged. Losses of > 100 g were interpreted as evidence of egg-laying. Eleven of 15 females for which we had season-long records in 1980 laid two clutches, two laid one clutch and two did not lay eggs. The mean number of clutches laid was 1.60. Of 40 females considered in 1981, 20 laid one clutch, 12 laid two clutches and eight did not lay. The mean number of clutches was 1.10. The estimated dry standing crop of forbs in 1980 was about 100 times that in 1981. Estimated biomass of grasses in 1980 was about 25 times that measured in 1981. Analyses of tortoise feces showed that grasses were eaten with equal frequency until mid-May in both years, but that after this time grasses essentially disappeared from 1981 diets. Annuals and seeds were much better represented in early spring diets in 1980 than in 1981. Cacti were more frequent in scats collected in 1981, particularly after mid-May-when about 87% of material in feces was from such plants. Cacti may serve as a reserve supply of energy, but more importantly as a potential source of water. This may partially explain the egg production in 1981-one of the most unfavorable years on record in the Mojave Desert.

Incidental Capture of Diamondback Terrapin by Crab Pots

Two-hundred eighty-one diamondback terrapins (195♂, 86♀) were captured in baited and unbaited crab pots during premolt crab capture studies in South Carolina. Sampling was conducted four consecutive days each week from mid April to mid November, 1979, in the Ashley River estuary, and daily from April to July, 1980 and 1981, in the Wando River estuary. Fifty-five percent of the total were captured in April, and 32% in May. Males outnumbered females 2.3∶1, but this ratio may reflect crab pot entrance bias which restricted entry of large females. Median plastron length of females was 121 mm (range 76–175) and that for males 100 mm. (range 79–128); only two male terrapins equalled or exceeded the minimum legal size limit of 127 mm. Few captured terrapins were drowned when crab pots were checked daily, and it is estimated that capture mortality amounted to 10%. Terrapin catch per baited crab pot averaged 0.16 daily in April and May. Incidental terrapin capture by 743 commercial crabbers (fiscal year 1982 numbers) in South Carolina during April and May was estimated at 2,853 daily, and mortality was estimated at 285. These estimates are exclusive of mortalities resulting from lost pots. The impact of crabbing activities is believed to pose no threat to the terrapin population at current levels of commercial terrapin harvest. Because female terrapins mature at the minimum legal size, no segment of the egg laying population is protected except seasonally. If direct harvest of terrapins ever approaches that of the early twentieth century, then it is recommended that legal size limits be changed to protect a segment of the mature female population.

Parental Investment in the Chicken Turtle (Deirochelys Reticularia)

Eggs of the chicken turtle (Deirochelys reticularia) were collected in South Carolina from clutches laid in the spring and fall. Clutch size averaged 8.0 eggs (2 SE = 1.6; n = 15) and was weakly correlated with body size of the female. Wet mass of the clutch averaged 72.4 g (2 SE = 11.6, n = 15). There were no significant differences in clutch size or wet mass between spring and fall nesting seasons. Individual eggs laid in the fall (anti x = 10.7 g) were significantly larger than those laid in the spring (anti x = 8.5 g). Fifteen eggs laid in the spring and incubated at 29/sup 0/ +- 2/sup 0/C averaged 152 d to hatching. Hatchling plastron length averaged 24.3 mm, and body wet mass was 6.7 g. Hatchlings (dry mass) contained 27.4% lipid, and the lipids remaining in the neonate at hatching represented 61% of the lipids originally present in the egg. The wet mass of a hatchling is highly correlated with wet mass of the egg. In contrast to clutch size, egg size had a strong positive relationship to body size. A morphological constraint, the width of the pelvic canal, is proposed as having anmore » influence on this relationship. The negative relationship between an optimized egg size and clutch size was not evident, so current optimality models do not appear to be applicable to Deirochelys.« less

Variation in Reproductive Characteristics of Aquatic Turtles

little effect on the correlation between body size and clutch size. A linear model of the relationship between body size (plastron length) and clutch size explained 67% of the variation for Pseudemys floridana, 56% for P. scripta and 25% for Sternotherus odoratus. A linear model was not useful in describing the pattern in the other two species (r2 = .05, Kinosternon subrubrum and .08, Deirochelys reticularia). However, within each of the five species, maximum clutch sizes of the smallest individuals are never as large as the maximum clutch sizes of the largest individuals. Clutch sizes within a species did not vary significantly among years or populations if the effect of body size was removed. Clutch size varied among months in all species, with a trend of decreasing clutch size during the egg-laying season apparent for P. scripta, P. floridana and K. subrubrum. Individuals of four species were recorded laying more than one clutch within a single egg laying season. The proportion of adult females known to have multiple clutches within a year varied for each species. Monthly timing of egg laying was not consistent for an individual female from year to year. No relationship could be identified between clutch frequency and body size in K. subrubrum or P. scripta, the only species for which adequate samples were available for such an analysis.

Studies on the growth, structure and abundance of the Mediterranean spur‐thighed tortoise, Tesudo graeca in field populations

The blackness and physical appearance of Mediterranean spur‐thighed tortoises (Testudo graeca L.) are recorded in field populations. The inter‐relationships between carapace and plastron length, fourth vertebral scute width and other morphometric characters are related to growth. The rear fontanelle is larger in males and the plastron length correspondingly smaller. The relationship between carapace length (y) in mm and body mass (x) in g is strongly allometric and given by y= 16.63 x0–34. The maximum carapace lengths recorded for male and female T. graeca graeca L. in NW. Africa are 151 and 198 mm, and for larger T. graeca ibera Pallas in W. Turkey and NE. Greece 208 and 218 mm, respectively. The growth annuli of epidermal scutes are deposited yearly until external growth ceases. The number is used to assess the age of wild animals. Tortoises can be full‐grown by 19 years but some, especially slower growing ones, deposit further annuli. The biggest mean growth increments occur up to 7 years with the largest in individuals over the 5–12 year period. The proportion of immature tortoises, adult sex ratios, size and body mass structure, age distribution, annual recruitment and survivorship until full‐grown, and abundance (sighting frequency) are compared in northern and southern range populations of NW. African T. g. graeca and S. Anatolian and SE. European (Thrace and Macedonia) ones of T. g. ibera. These are discussed in relation to other tortoise species.

Reproductive parameters and nesting behavior of the Amazon turtle Podocnemis expansa (Testudinata: Pelomedusidae) in Brazil

The Amazon River turtle Podocnemis expansa was studied during the nesting and hatching seasons (October and December of 1978, 1979, and 1980) at a protected site in a Biological Reserve on the Trombetas River, a tributary of the Amazon. Mean carapace length of nesting females was 66 cm and mean carapace width 59 cm. Mean clutch size was 91.5 eggs (with 95% hatching success) and was positively correlated to carapace length, carapace width, plastron length, and plastron width. Carapace width was positively correlated to egg chamber height, and egg chamber diameter was positively correlated with nest depth, clutch size, and plastron width. There is a synchronization between low water and nesting.