Search

Life-histories evolve in response to constraints on the time available for growth and development. Nesting date and its plasticity in response to spring temperature may therefore be important components of fitness in oviparous ectotherms near their northern range limit, as reproducing early provides more time for embryos to complete development before winter. We used data collected over several decades to compare air temperature – nest date plasticity in populations of painted turtles and snapping turtles from a relatively warm environment (southeastern Michigan) near the southern extent of the last glacial maximum, to a relatively cool environment (central Ontario) near the northern extent of post-glacial recolonization. For painted turtles, population-level differences in reaction norm elevation for two phenological traits were consistent with adaptation to time constraints, but no differences in reaction norm slopes were observed. For snapping turtle populations, the difference in reaction norm elevation for a single phenological trait was in the opposite direction of what was expected under adaptation to time constraints, and no difference in reaction norm slope was observed. Finally, among-individual variation in individual plasticity for nesting date was detected only in the northern population of snapping turtles, suggesting that reaction norms are less canalized in this northern population. Overall, we observed evidence of phenological adaptation, and possibly maladaptation, to time constraints in long-lived reptiles. Where present, (mal)adaptation occurred by virtue of differences in reaction norm elevation, not reaction norm slope. Glacial history, generation time, and genetic constraint may all play an important role in the evolution of phenological timing and its plasticity in long-lived reptiles. This article is protected by copyright. All rights reserved.

Conditions experienced early in life can influence phenotypes in ecologically important ways, as exemplified by organisms with environmental sex determination. For organisms with temperature-dependent sex determination (TSD), variation in nest temperatures induces phenotypic variation that could impact population growth rates. In environments that vary over space and time, how does this variation influence key demographic parameters (cohort sex ratio and hatchling recruitment) in early life stages of populations exhibiting TSD? We leverage a 17-year data set on a population of painted turtles, Chrysemys picta, to investigate how spatial variation in nest vegetation cover and temporal variation in climate influence early life-history demography. We found that spatial variation in nest cover strongly influenced nest temperature and sex ratio, but was not correlated with clutch size, nest predation, total nest failure, or hatching success. Temporal variation in climate influenced percentage of total nest failure and cohort sex ratio, but not depredation rate, mean clutch size, or mean hatching success. Total hatchling recruitment in a year was influenced primarily by temporal variation in climate-independent factors, number of nests constructed, and depredation rate. Recruitment of female hatchlings was determined by stochastic variation in nest depredation and annual climate and also by the total nest production. Overall population demography depends more strongly on annual variation in climate and predation than it does on the intricacies of nest-specific biology. Finally, we demonstrate that recruitment of female hatchlings translates into recruitment of breeding females into the population, thus linking climate (and other) effects on early life stages to adult demographics.

Hatchling painted turtles (Chrysemys picta) commonly overwinter within their natal nests and survive exposure to temperatures as low as −12°C by supercooling. We report that the supercooling capacity of hatchling C. picta is reduced by direct contact with nest soil which, in samples from northwestern and north-central Nebraska, Indiana, and Ontario, contained potent ice nuclei active in the range of −3.5° to −5°C. These nuclei were sensitive to autoclaving and extractable in water. The supercooling capacity of C. picta hatched in native nest soil, or hatched in sterilized vermiculite (which lacks water-extractable nuclei), and subsequently exposed to nest soil, was reduced by ∼10°C relative to control turtles that were hatched and reared in sterilized vermiculite. The effect of these nuclei was potentiated by the presence of environmental moisture, although even transient exposure to dry nest soil markedly reduced supercooling capacity in ∼50% of the turtles. Unlike turtle species that hibernate underwater (Sternotherus odoratus, Chelydra serpentina, Apalone spinifera), hatchlings of C. picta exhibited an extraordinary capacity for supercooling (temperature of crystallization, −16° to −20°C) when cooled in isolation from external ice nuclei. However, hatchlings of these four species were equally susceptible to inoculation by suspensions of the ice-nucleating bacterium, Pseudomonas syringae. Indirect evidence suggests that the soil nuclei are associated with such microbes. Nucleating activity was higher in soil collected within nests than in soil collected at the same depth, adjacent to these nests. Differences in the activities of ice nuclei in nesting soils may account for geographic and local variation in winter survival of hatchling C. picta. Our finding that similar agents occur in various other terrestrial habitats in central North America suggests that such nuclei may pose a formidable challenge to the overwintering survival of ectothermic animals that rely on supercooling to withstand frost exposure.

Identifying the relative contributions of genetic, maternal, and environmental factors to phenotypic variation is critical for evaluating the evolutionary potential of fitness-related traits. We employed a novel two-step cross-fostering experiment to quantify the relative contributions of clutch (i.e., maternal identity) and maternally chosen nest sites to phenotypic variation during three early life stages (incubation, hibernation, dispersal) of the painted turtle (Chrysemys picta). By translocating eggs between nests in the field, we demonstrated that both clutch and nest site contribute to phenotypic variation at hatching. Because hatchling C. picta hibernate inside nests, we performed a second cross-foster to decouple the effects of the incubation nest with that of the hibernation nest. Incubation nest explained little variation in phenotypes at spring emergence, but winter nest site was important. We found no evidence that mothers select nest sites specific to reaction norms of their own offspring, suggesting that females may select nest sites with microhabitats that broadly meet similar requirements across the population. After hibernation, we released hatchlings to assess performance and phenotypic selection during dispersal. Hibernation nest site influenced physiological performance during dispersal, and we detected nonlinear selection on hatchling carapace length. Our experiment demonstrates that nest-site choice has substantial effects on phenotypic variation and fitness across multiple early life stages.

Field and laboratory studies were conducted during 1989-1994 to investigate the overwintering strategies of hatchling turtles representing four families native to western Nebraska. Whereas hatchling snapping turtles (Chelydra serpentine) and spiny soft-shelled turtles (Apalone spinifera) overwinter in aquatic habitats, yellow mud turtles (Kinosternon flavescens) and ornate box turtles (Terrapene ornata) burrow below the natal nest and hibernate in sandy soil. Painted turtles (Chrysemys picta) overwinter within their shallow natal nests, but this species, and T. ornata, tolerate extensive tissue freezing. Overwintering behaviors of these species are consistent with indices of physiological cold hardiness and patterns of geographic distribution. Frost commonly penetrated and persisted below 10 cm, the soil depth at which hatchling C. picta routinely hibernate. Field and laboratory data suggested that hatchling C. picta survive either by remaining supercooled (unfrozen) or by tolerating tissue freezing, the strategy employed depending on prevailing physiological and microenvironmental conditions. Whereas relatively lower temperatures can be survived in the supercooled state, supercooling capacity may be limited via the inoculation of body fluids by environmental ice. Alternatively, whereas freeze tolerance fortuitously is promoted by ice inoculation, this strategy may be viable only at relatively high subzero temperatures. A cold-hardiness strategy based on both survival mechanisms may promote winter survival in hatchling C. picta by conferring protection under dynamic physiological and microen- vironmental conditions. Physiological cold hardiness and behavior are integrated deter- minants of the northern distributions of temperate region turtles.

The role of early life stages (eggs, neonates, and juveniles) for population persistence in long-lived organisms is thought to be minor. However, few long-term data sets are available to test this assumption. Variation in vital rates over space and time and the potential for the success of early life stages to shape adult reproductive behavior evolutionarily suggest that more thorough consideration of these life stages is necessary. In particular, the impact of climatic variation on early life-stage recruitment is not well understood. Furthermore, predation occupies a significant role in theoretical models of population dynamics, but its impact on populations through variable vital rates of early life stages is unknown. Maternal nest-site choice, an important component of nesting ecology, may influence many offspring traits and respond to selection to optimize offspring success. Overall, we have limited information regarding the long-term patterns of natural fluctuations in the nesting ecology and hatchling recruitment of populations of long-lived organisms. The research site for this ongoing long-term project is on an island in the Mississippi River near Thomson, Illinois, USA. Painted turtles (Chrysemys picta) have been studied extensively at this location since 1989 to examine the ecology and potential demographic consequences of nest-site choice and depredation, with the aim of understanding the evolution of maternal nesting behavior and its effects on offspring phenotype. We monitored the site every day of the nesting season each year to record nesting and depredation events. The data presented here include nesting phenology, nest vegetation cover, total number of nesting events, clutch size, depredation, and hatchling survival. Portions of this data set have been used to address related questions in ecology and evolutionary biology. In particular, climatic variation influences the probability of nest depredation events. Such events are typically nonrandom, primarily occurring adjacent to habitat edges. Because habitat edges may have atypical vegetation composition and vegetation influences nest temperature, such nonrandom depredation could influence offspring recruitment and, hence, population structure. Given the unique scope and accessibility of this data set, researchers and teachers should find it to be a valuable empirical resource for exploring important facets of nesting ecology and hatchling recruitment in a wild population of a long-lived species. The complete data sets corresponding to abstracts published in the Data Papers section of the journal are published electronically in Ecological Archives at 〈http://esapubs.org/archive〉. (The accession number for each Data Paper is given directly beneath the title.)

Nesting ecology and reproduction of painted turtles (Chrysemys picta) in southeast Michigan were intensively studied from 1975 to 1978. The average clutch size of Michigan painted turtles was 7.55, with body size accounting for only 9-13% of the variance. Data on nesting frequency indicate that from 30 to 50% of the females possibly do not reproduce every year and that approx. =6% reproduce twice in a given year. Predation within 48 h of egg-laying is responsible for the failure of 20% of the nests. An additional 12% nest failure is due to various other causes. These data substantially alter the life table previously reported in this population of painted turtles.

The painted turtles, Chrysemys picta, with four subspecies, have the largest range and most northern distribution of any North American freshwater turtle. C. p. bellii in Canada may hibernate for as much as 6 mo, while C. p. dorsalis on the Gulf Coast may not hibernate at all. We subjected both subspecies to simulated hibernation conditions by submerging them in anoxic water at 3°C without access to air to compare physiological responses. Initial acid—base and ionic statuses of animals acclimated to 3° were the same in both subspecies. As anoxia continued, both subspecies showed similar changes in all measured parameters, but the rates of change were greater in dorsalis than in bellii. By day 46, the plasma pH of dorsalis had fallen to 6.96, a change that required °180 d in bellii. By day 38, the acidosis was entirely due to lactate formation in both groups, and it had induced compensatory changes in ionic concentrations, particularly large increases in total Ca and total Mg in the blood. We conclude that the only adaptation required of bellii to enable it to endure longer winters than dorsalis is an ability to limit lactate accumulation, by having either a lower metabolic rate and/or a great ability to eliminate lactate. It is known that hibernation in a normoxic environment would be less stressful physiologically than in an anoxic one, but turtles apparently choose the latter. We suggest that the physiological stress of prolonged anoxia and the requirements of subsequent recovery in the spring are outweighed by considerations of predator avoidance during the winter. Tolerance of the physiological perturbations resulting from prolonged anoxia may limit the northern distribution of freshwater turtles.

Incubation temperature is known to determine the sex of hatchlings in many species of turtles, including the map turtles, Graptemys ouachitensis, G. pseudogeographica, G. geographica, and painted turtle, Chrysemys picta. This paper presents a study of sex ratio and nest ecology in natural populations of these species in Wisconsin, but largely for G. ouachitensis and G. pseudogeo- graphica. Nesting was monitored during June, and hatchlings were obtained from 236 nests during August and September 1980. The distribution of nest sex ratios in samples of the two common species was bimodal, tending to be all-female or all-male within a nest, with an overall excess of females. Nests with males were located amid vegetation, with cool temperatures, and nests with females were located in open sand exposed to the sun, with high temperatures. The sex ratio differed significantly between nesting beaches, apparently because of differences in the availability of warm vs. cool nest sites. All-female nests hatched in less time than all-male nests, and the sex ratio of emerging hatchlings consequently changed from nearly all female early in August to all male in September. The data indicate major environmental influences on the hatchling sex ratio in map turtles.

A mark—recapture study of a population of painted turtles, Chrysemys picta, started by O. J. Sexton between 1953 and 1957 was continued between 1968 and 1973. Life tables are constructed and a demographic history of the population is suggested. Males mature during their 4th yr and first breed at age five. Females mature at age seven and lay two clutches of about 6 to 7 eggs each year. Mortality is about 92% between laying and the arrival of the hatchlings at the pond. Juvenile and adult mortality is at a constant exponential rate of about 0.15 for males and 0.18 for females each year. Raccoons, Procyon lotor, are an important predator during spring migrations. There is no indication of senescence; females over 30 yr old are still reproductive. Between 1954 and 1972 the population's size has been reduced from an estimated 981 to about 186 animals. This has been accompanied by a decrease in mean generation time from 12.35 to 10.70 yr. Survivorship from laying to arrival at the pond has more than doubled, but adult survivorship has decreased. These changes are attributed to an increased predation rate resulting from a reduction in the number of safe basking sites. A hypothetical population was simulated by recurrent use of a population projection matrix, derived from the 1954 life table, to demonstrate the stability characteristics of this long—lived, iteroparous species. The evolution of this life history is interpreted as an adaptation to a highly uncertain probability of nest success and an effective predator defense in the adult stage.

Behavioral characteristics and microhabitat distributions of individuals may cause heterogeneity in their risk of capture in field studies of the dynamics of natural populations. The number of recaptures of marked individuals can be used to test for equicatchability by their fit to a Poisson distribution. If the null hypothesis of equal risk of capture is rejected the number of captures per individual may follow a negative binomial distribution. The use of truncated distributions to estimate the number of transients in the population, or the number of animals never caught is found to be of very limited value. These methods are applied to an original set of capture histories from a study of a population of the painted turtle, Chrysemys picta. See full-text article at JSTOR

That certain algae occasionally grow on the carapaces of turtles is a fact wellknown to many persons, scientists and laymen alike; hardly a person has not heard of "mossback" turtles, and the term "mossback" has been incorporated into our language. In view of the wide familiarity with the phenomenon it is remarkable that there apparently never has been a systematic study of this interesting relationship, either on the part of the phycologists or the herpetologists. In the preparation of the present study many herpetological papers that mention epizo6phytic algae (or "moss") have been examined; only three of these (Evermann and Clark 1916; Lagler 1943; Walker, Green and Jones 1953) even give generic determinations of the algae. Neither of the two recent major works on North American turtles (Pope 1939; Carr 1952) gives this relationship more than passing remarks. Of eleven herpetological works which note the presence of algae on turtles, four involve the musk turtle, Sterno therus odorat us Latreille, seven the snapping turtle, Chelydra serpentina Linnaeus; one the painted turtle, Chrysemys picta Schneider; and one Blanding's turtle, EmMYs blandingii Holbrook (Carr 1940; Conant 1938; Lagler 1943; Pope 1939; Cahn 1937; Ruthven, Thompson and Thompson 1912; Brim

Statistically significant differences were found in body length, body weight and clutch size between three southern Michigan populations of the painted turtle (Chrysemys picta) occupying differing habitats. The clutch size differences were as great as those reported from different parts of the range of this and other species. Diet, rather than body weight or shell length, is suggested as being the factor responsible for observed differences in reproductive potential. See full-text article at JSTOR