Biomedical subjects

J D Congdon

Publications and source records attributed to J D Congdon.

31 records · Page 2Linked to original sources

PubMed2000

Chemical and thermal effects on the viability and motility of spermatozoa from the turtle epididymis.

The viability and motility of spermatozoa harvested from the epididymides of turtles were estimated to elucidate properties that might enable them to be stored over long periods of time. Spermatozoa from the painted turtle, Chrysemys picta, were analysed and compared with spermatozoa from two other turtles, Trachemys scripta and Sternotherus odoratus using the Cellsoft analysis system for videotaped images. Spermatozoa from C. picta and T. scripta, suspended in F-10 medium, showed low motility (3-6% motile) and motion velocities, whereas the motility of spermatozoa from S. odoratus was higher (40% motile). Spermatozoa from C. picta and S. odoratus, but not T. scripta, had higher motilities and motion velocities when incubated at 2 degrees C before analyses. C. picta spermatozoa were unresponsive to calcium concentrations ranging from 10(-8) to 10(-1) mol l(-1), potassium concentrations ranging from 0. 1 to 10 mmol l(-1), and to pH values in the range 5.9-8.4. Spermatozoa from C. picta were sensitive to hypo-osmotic media, and showed reduced motility at 25% of normal osmolarity and no motility at 10% of normal osmolarity. Distorted cells and missing flagellae were noted at 50% of normal osmolarity. C. picta spermatozoa were viable up to 40 days after harvest when incubated at 4 degrees C; during this time, both motility and motion velocity were increased in response to 0.5 mmol 3-isobutyl-1-methylxanthine l(-1). Spermatozoa from turtles have osmotic properties and resistance to changing chemical environments similar to spermatozoa from other vertebrates that have internal fertilization, and appear to be stable over long periods of time compared with spermatozoa from other vertebrate species.

1-Methyl-3-isobutylxanthine↗

PubMed2000

Chromosome translocations in turtles: a biomarker in a sentinel animal for ecological dosimetry.

Nonhuman organisms are being exposed to ionizing radiations at radionuclide-contaminated sites around the world. Direct methods are seldom available for measuring biologically relevant doses received by these organisms. Here we extend biological dosimetry techniques, which are much better developed for humans and a few other mammalian species, to a nonmammalian species. Turtles were chosen because a long-lived animal would best serve the need for low-level, chronic exposure conditions. We chose the yellow-bellied slider turtle (Trachemys scripta), which is known to have a maximum life span of at least 22 years. As reported elsewhere, we first isolated an embryonic fibroblast cell line and constructed whole-chromosome-specific DNA libraries for chromosome 1 by microdissection and PCR. A FISH painting probe was prepared and used to establish a dose-response curve for ionizing radiation-induced chromosome interchange aberrations in turtle fibroblasts. This was compared to the dose response for human fibroblasts treated under similar conditions in our laboratory. With respect to induction of chromosome interchange aberrations, human fibroblasts were approximately 1.7 times more sensitive than the T. scripta fibroblasts. To the extent that symmetrical interchanges are persistent over long periods, this approach could eventually provide a measure of the integrated lifetime dose these organisms receive from radionuclides in their environment and give a measure of the extent of relevant genetic damage over that time.

Animals↗

PubMed1999

Responsiveness of the hypothalamo-pituitary-interrenal axis in an amphibian (Bufo terrestris) exposed to coal combustion wastes.

To assess the responsiveness of the interrenal axis to stress, we injected toads exposed to coal combustion wastes and toads from an unpolluted reference site with adrenocorticotropic hormone (ACTH), as well as the vehicle alone (saline). Initial circulating levels of corticosterone in toads captured at the polluted area were significantly higher than levels in toads from the reference site. Corticosterone levels in toads from the polluted site remained high even after 2 weeks of laboratory acclimation and injection with saline. The results may suggest disruption of hepatic enzymes responsible for the metabolic clearance of steroid hormones. Injection of toads from the polluted site with ACTH had no effect on plasma corticosterone levels, whereas a similar treatment of toads from the reference site stimulated a marked increase in corticosterone. Our study provides evidence that toads exposed to coal combustion wastes may be less efficient at responding to additional environmental stressors.

Adrenocorticotropic Hormone↗

PubMed1998

Elevated trace element concentrations in southern toads, Bufo terrestris, exposed to coal combustion waste.

A number of recent studies have linked developmental, physiological, and behavioral abnormalities in amphibians to coal combustion wastes (coal ash). Few studies, however, have determined trace element concentrations in amphibians exposed to coal ash. In the current study we compare total body concentrations of 20 trace elements in adult southern toads, Bufo terrestris, inhabiting coal ash settling basins with toads that were not exposed to the combustion wastes (reference). In addition, we document the accumulation of trace elements in toads transplanted from reference sites to field enclosures in an ash settling basin for 7 and 12 weeks. Arsenic, selenium, and vanadium levels were significantly elevated in toads captured at the ash-contaminated site in comparison to toads from the reference site. All three of these elements were also significantly elevated in toads exposed to the contaminated habitat for only 7 weeks. Our study suggests that adult anurans can bioaccumulate particularly high levels of selenium and may be useful bioindicators in agricultural and coal ash-impacted habitats.

Animals↗

PubMed1998

Egg components and hatchling lipid reserves: parental investment in kinosternid turtles from the southeastern United States.

We measured egg components and pre-ovulatory parental investment in kinosternid turtles (Kinosternon baurii, Kinosternon subrubrum, Sternotherus minor, and Sternotherus odoratus) from the southeastern USA. Allocation patterns were determined by comparing lipid content of eggs and hatchlings, to determine whether females of species with hatchlings that exhibit a delayed nest-emergence strategy: (1) allocate higher proportions of energy storage lipids to eggs, (2) produce hatchlings with higher levels of storage lipids, and (3) have higher levels of pre-ovulatory parental investment in comparison to species whose hatchlings exhibit immediate emergence. Whereas total non-polar lipid (NPL) proportions by dry mass of eggs varied significantly among species, NPL proportions of hatchlings were not significantly different. Pre-ovulatory parental investment in care (proportion of hatchling NPL to egg NPL) was 40, 50, and 55% for K. subrubrum, S. minor, and S. odoratus, respectively. Lipid class composition of eggs and hatchlings was studied to distinguish lipids allocated for energy storage from those allocated to other functions. For both eggs and hatchlings, individual lipid classes (triacylglycerol, triacylglycerol fatty acid, cholesterol, cholesterol ester, and phospholipid) as proportions of total lipid, were similar among species. The major lipid class component of eggs and hatchlings of all species was triacylglycerol (> 83%), an energy storage lipid. Substantial changes in lipid classes during embryogenesis were similar among species and included: (1) depletion of triacylglycerol, (2) increase in cholesterol esters, and (3) changes in phospholipid composition. Incubation time varied significantly among species, and appeared to be responsible for differential energy utilization during embryogenesis. Our results are inconsistent with the previously observed pattern that hatchlings exhibiting a delayed nest-emergence strategy are allocated higher proportions of energy storage lipids than those that exhibit immediate emergence. However, because the species that overwinters in the nest (K. subrubrum) hatches approximately 40 days later than the species that typically does not (S. odoratus), hatchling K. subrubrum may contain higher non-polar lipid proportions than hatchling S. odoratus during similar winter time periods. Kinosternid hatchlings contain enough stored lipids to support basal maintenance costs for substantial time periods. We suggest that such reserves may be critical to hatchling survival during a period of negative energy balance, regardless of nest emergence strategy.

Animals↗

PubMed1997

Increased circulating levels of testosterone and corticosterone in southern toads, Bufo terrestris, exposed to coal combustion waste.

This study describes an interrenal stress response in adult toads, Bufo terrestris, after exposure to coal combustion waste (characterized by a variety of trace elements). In the first portion of this study, free-ranging male toads captured at the coal ash polluted site exhibited significantly higher circulating levels of corticosterone (B) in both June/July and August than conspecifics captured at uncontaminated sites. In addition, both calling and noncalling males from the polluted site had higher B levels than conspecifics engaged in the same behaviors at reference sites. Testosterone levels were elevated in toads from the polluted site, regardless of capture month or behavioral state, suggesting altered androgen production, utilization, and/or clearance. In the second portion of this study, male toads from reference sites were transplanted to enclosures at the polluted site or an uncontaminated site. Toads held at the polluted site exhibited significant increases in B after 10 days of exposure compared to toads held at the reference site. B levels remained significantly elevated in toads transplanted to the polluted site after 12 weeks. We hypothesize that high concentrations of various trace elements in the polluted site are responsible for these hormonal responses.

Animals↗

PubMed1987

Morphological constraint on egg size: a challenge to optimal egg size theory?

Some freshwater turtles appear unable to produce eggs large enough to achieve the balance between size and number of eggs predicted by optimal egg size theory. We present evidence that pelvic girdle structure constrains egg size and thus offspring size in females of smaller-bodied species (Chrysemys picta and Deirochelys reticularia). The constraint is demonstrated by the correspondence of slopes of the increase of the pelvic aperture and egg width with increasing body size. This constraint appears to be relaxed in a larger-bodied species (Pseudemys scripta), in which the increase in pelvic aperture relative to body size is greater than the increase in egg width. This type of structural constraint on a reproductive trait should not occur unless there is strong selection on pelvic architecture for other functions, such as locomotion, support, and limb retraction, that prevent expansion of the pelvic aperture. Although other explanations may exist for other groups of organisms that appear to vary egg size, the large variation in egg size associated with body size in some species of turtles can be reconciled with optimal egg size theory only if a pelvic constraint model is accepted.

Animals↗

PubMed1985

Seasonal cycles in testicular activity, gonadotropin, and thyroxine in the painted turtle, Chrysemys picta, under natural conditions.

Plasma levels of testosterone (T), thyroxine (T4) and follicle-stimulating hormone (FSH) were measured in a field population of the painted turtle, Chrysemys picta, in Michigan. All three hormones showed pronounced seasonality; plasma luteinizing hormone (LH) remained nondetectable. Plasma T and FSH concentrations were highly correlated and exhibited biphasic cycles with peaks in spring and fall, whereas T4 showed a single peak in summer, coincident with the nadir in T. Hormone levels were minimal on the day that animals emerged from hibernation at the end of March; T and FSH then increased rapidly (in ca. 1 week after emergence) to a transient peak that persisted for only ca. 2 weeks. Plasma T and FSH rose again in September before the onset of hibernation and shortly after the late summer peak in spermatogenetic recrudescence. Plasma T4 increased more gradually after emergence in spring and did not peak for 1-2 months, coincident with the nadir in T. The profile in plasma FSH is consistent with the view that this gonadotropin may regulate androgen secretion but it did not show the expected relationship to the spermatogenetic cycle. Separate studies indicated that the turtles are sensitive to capture and handling; hormone levels (especially androgen) fall precipitously within a day of capture. These "stress" effects may account for discrepancies with previous studies of plasma T in this species.

Analysis of Variance↗

PubMed1974

Geckos: adaptive significance and energetics of tail autotomy.

Coleonyx variegatus is adapted to readily sacrifice its tail to predators. This adaptation is associated with characteristic tail behavior and rapid tail regeneration. There is no facultative metabolic increase associated with tail regeneration, and energy normally allocated to body growth and maintenance is diverted to tail regeneration. This supports the contention that tail behavior, autotomy, and rapid regeneration evolved as mechanisms promoting survival in terms of predator escape.

Adaptation, Biological↗

PubMedDate not supplied

Intersexual differences in energy expenditure of Anolis carolinensis lizards during breeding and postbreeding seasons.

Although the amount of energy that males and females invest in reproduction is an integral component of theories explaining the evolution of particular mating strategies, few studies have actually determined the amount of energy that each sex allocates to reproduction. We compared how energy is expended by male and female Anolis carolinensis lizards during both the breeding and postbreeding seasons. We used laboratory respirometry to determine resting metabolic rates (RMRs) of inactive, freshly captured lizards and the doubly labeled water technique to determine field metabolic rates (FMRs) of free-ranging lizards. Both RMRs and FMRs were influenced by body mass but not by sex. Season did not influence FMRs; however, RMRs of both sexes increased approximately 40% from the breeding to the postbreeding season. The seasonal increase in RMRs was attributed to a postreproductive increase in feeding rate and specific dynamic action. We used RMRs, FMRs, and thermal profiles of lizards to calculate energy budgets for breeding and postbreeding seasons. Energy budgets partitioned daily field energy (DFE; calculated from FMRs) into daily activity energy (DAE) and daily resting energy (DRE; calculated from RMRs). Energy expended for reproduction was estimated as DAE during the breeding season plus egg production (for females). Despite males having 40% greater body mass, females expended 46% more energy for reproduction than did males (906 and 619 J/d, respectively). Total metabolizable energy (TME=DFE+egg production for females) expended during the breeding season was similar for males and females (1,280 and 1,365 J/d, respectively). Although TME of females decreased 44% from the breeding to the postbreeding season (1,365 vs. 766 J/d), TME of males was similar during both seasons (1,280 vs. 1,245 J/d). There were both seasonal and sexual differences in DRE and DAE. Compared with most lizards from semiarid/desert habitats, A. carolinensis in a temperate habitat expends more total energy during the breeding season, allocates more energy to eggs, and appears to have more total energy available for reproduction.

Analysis of Variance↗

PubMedDate not supplied

Elevated maintenance costs in an anuran (Rana catesbeiana) exposed to a mixture of trace elements during the embryonic and early larval periods.

We investigated the relationship between maintenance costs (standard metabolic rates, measured as O2 consumption at rest) in tadpoles of the bullfrog, Rana catesbeiana, and exposure to contaminants in a coal ash-polluted habitat (characterized by a variety of trace elements). We compared metabolic rates of tadpoles collected from the polluted site with those from an unpolluted reference pond. Tadpoles collected in the polluted site had 40%-97% higher standard metabolic rates than those collected from the reference pond. We also reciprocally transplanted eggs of the bullfrog between the polluted site and another reference pond and compared standard metabolic rates of tadpoles at 25 and 80 d posthatching. Metabolic rates of tadpoles raised in the polluted site were from 39% to 175% higher than those raised in a reference pond, depending on tadpole age and temperature at which metabolic rates were measured. There were no effects of site of origin of the eggs (polluted or unpolluted) on metabolic rates. Survival to hatching did not differ between sites, although survival to the end of the experiment (80 d posthatching) was lower in the polluted area than in the reference site. Surviving tadpoles were larger in wet body mass in the polluted site than in the reference pond, possibly due to lower survival in the former, but there was no relationship between survival and metabolic rate. It is clear that some feature of the polluted habitat was responsible for causing substantial elevation of standard metabolic rates of tadpoles. We hypothesize that the mixture of trace elements present in sediment and water in the polluted site was responsible for the observed physiological differences.

Analysis of Variance↗

PubMedDate not supplied

Relationships of lipids to ovum size in amphibians.

Relative to small embryos, large embryos may have longer developmental periods and, subsequently, relatively greater maintenance budgets. Because of the potentially increased metabolic costs of maintaining large embryos for long embryonic periods, Salthe and Mecham (1974) suggested that as ovum size increases among amphibians, ovum lipids (the primary stored metabolic energy reserves) should increase at a proportionally greater rate. To test Salthe and Mecham's hypothesis, we quantified egg lipids for 13 amphibian species from the southeastern United States. As ovum size increased among species, total, nonpolar, and polar lipids increased at rates uniform with or relatively lower than rates of increase in ovum size, in contrast to the hypothesis of Salthe and Mecham. However, variation in ovum lipids among species may be related to differences in breeding biology. Our results indicate that the amount of lipids allocated to ova do not merely depend on ovum size, but rather on the selective environments of the embryo and neonate.

Amphibians↗

PubMedDate not supplied

Oviductal sperm storage as a reproductive tactic of turtles.

The oviducts of two species of freshwater turtles were examined throughout the year to determine the distribution of sperm within the oviduct, the locations of stored sperm, and the onset of mating. Sperm were stored in undifferentiated tubules and ducts of submucosal glands at the periphery of large glandular segments of the albumen and uterine regions of the oviduct. Sperm transfer to females commenced in October in Sternotherus odoratus and in January in Trachemys scripta. The role of sperm storage in the annual reproductive cycle of freshwater turtles is evaluated in light of the onset of sperm transfer to females and the timing of ovulation and oviposition. Stored sperm are most likely to be utilized in the fertilization of eggs ovulated in the second and subsequent egg clutches.

Animals↗