Biomedical subjects

C J Limpus

Publications and source records attributed to C J Limpus.

12 recordsLinked to original sources

PubMed2002

Patterns of lipid storage and mobilisation in the female green sea turtle ( Chelonia mydas).

Reproductive data from southern Queensland indicate that vitellogenesis in female Chelonia mydas takes approximately 8 months and is followed by a migration to a breeding area. At Heron Island, females lay multiple clutches over approximately 3 months. To investigate how females mobilise and store lipid during the breeding season we collected plasma, yolk, and fat tissue samples from females at a variety of stages during the nesting season. In breeding females, concentrations of plasma triglyceride increased seasonally. They reached peak concentrations during vitellogenesis and courtship, remained high throughout the nesting season, and then declined to a nadir after the last clutch. Plasma protein concentration increased throughout the breeding season, peaking following the last clutch for the season. Yolk lipids were highest during courtship and were similar throughout the nesting season, suggesting that uptake of lipid by ovarian follicles is completed prior to the beginning of the nesting season. Plasma triglyceride decreases in females with prolonged periods of unsuccessful nesting, and total lipid levels in adipose tissue and follicle yolks were significantly lower in atretic females. It appears that: (1) endogenous energy reserves can be reduced by stochastic environmental events (such as those reducing nesting success), and (2) a metabolic shift signalling the end of the nesting season is characterised by a drop in plasma triglycerides and slight increase in total plasma protein.

Adipose Tissue↗

PubMed2001

Quantitative analysis of herpesvirus sequences from normal tissue and fibropapillomas of marine turtles with real-time PCR.

Quantitative real-time PCR has been used to measure fibropapilloma-associated turtle herpesvirus (FPTHV) pol DNA loads in fibropapillomas, fibromas, and uninvolved tissues of green, loggerhead, and olive ridley turtles from Hawaii, Florida, Costa Rica, Australia, Mexico, and the West Indies. The viral DNA loads from tumors obtained from terminal animals were relatively homogeneous (range 2-20 copies/cell), whereas DNA copy numbers from biopsied tumors and skin of otherwise healthy turtles displayed a wide variation (range 0.001-170 copies/cell) and may reflect the stage of tumor development. FPTHV DNA loads in tumors were 2.5-4.5 logs higher than in uninvolved skin from the same animal regardless of geographic location, further implying a role for FPTHV in the etiology of fibropapillomatosis. Although FPTHV pol sequences amplified from tumors are highly related to each other, single signature amino acid substitutions distinguish the Australia/Hawaii, Mexico/Costa Rica, and Florida/Caribbean groups.

Amino Acid Sequence↗

PubMed2000

Evidence for a hormonal tactic maximizing green turtle reproduction in response to a pervasive ecological stressor.

Mortality of breeding sea turtles due to excessive heat exposure after nesting activities is an unusual feature of the Raine Island green turtle rookery. Breeding turtles that fail to return to the ocean after oviposition can experience increasing body temperatures that exceed lethal limits (>39 degrees C) as ambient temperatures rise after sunrise. We investigated how acute increases in body temperature influenced plasma corticosterone (B) concentrations of individual turtles. Furthermore, interactions between progesterone (P) and testosterone (T) and increasing body temperature and the glucocorticoid corticosterone were examined for negative correlations. Breeding green turtles exhibited a 16-fold mean increase in plasma corticosterone concentration as body temperature (cloacal) rose from 28.2 to 40.7 degrees C in less than 6 h. However, the absolute increase in plasma B was small and much less than expected, despite the lethal stressor. Comparatively, the maximal B response to lethal heat stress was similar to plasma B concentrations obtained from breeding female turtles exposed to 8 h of capture stress. However, the maximal B response of breeding turtles exposed to heat and capture stressors was significantly less than the B response of nonbreeding adult female turtles subjected to an 8-h capture stressor. No negative correlations were observed between plasma T and plasma B, between plasma T and body temperature, between plasma P and plasma B, or between plasma P and body temperature. Our findings provide further evidence that reduced adrenocortical function operates in breeding green turtles in the presence of even the most pervasive of environmental stressors.

Adrenal Cortex↗

PubMed1999

Plasma steroid interactions during high-density green turtle nesting and associated disturbance.

Raine Island in the Northern Great Barrier Reef constitutes an extremely high-density green turtle (Chelonia mydas) rookery. On this island, competitive interactions for nesting space and subsequent disturbance of individual nesting are widespread. High-density nesting often delays successful oviposition by one or more nights. There is little information on how hormones in female reptiles interact during competitive reproductive events in such high-density nesting populations. In this three-part study we investigated the interactions between density (within and between rookery/ies), nesting success and failure, and plasma steroid profiles in green turtles. First, we compared levels of plasma corticosterone (B) and combined testosterone + 5alpha-dihydrotestosterone (T + DHT) in turtles during five stages of oviposition in both a high-nesting-density sector (1 turtle/m2) and a low-nesting-density sector (0.1 turtle/m2). Second, we investigated the relationship between increasing delays (0, 1, 2, 3, and 6 days) in successful oviposition and the plasma steroids B and T + DHT. Third, we assessed a comparative measure of steroid hormone levels of females at low-density sites on Raine Island (high-density rookery) and Number Seven Sandbank (low-density rookery). Despite a significant trend suggesting high-density nesting turtles elaborated more plasma B than turtles in low-density sectors, the magnitude of this increase was small. We suggest that this increase may be an artifact of increased metabolic demand and hence catabolism of energy substrates associated with high-density nesting. Plasma T + DHT remained stable in response to density-dependent effects associated with nesting. Furthermore, prolonging successful oviposition because of multiple nightly disturbance failed to elicit any change in either plasma B or T + DHT. These data suggest that green turtles may be exhibiting adrenal desensitization to prevent both physical and behavioral disturbances interfering with reproduction. We suspect that down-regulating the acute adrenocortical response may represent an adaptive trade-off mechanism for optimizing current reproductive success at the potential expense of survivorship.

Animals↗

PubMed1999

Interactions between behavior and plasma steroids within the scramble mating system of the promiscuous green turtle, Chelonia mydas.

We measured plasma androgen (combined testosterone and 5alpha-dihydrotestosterone) (A) and corticosterone (B) in the promiscuous green turtle (Chelonia mydas) during courtship in the southern Great Barrier Reef. This study examined if reproductive behaviors and intermale aggression induced behavioral androgen and adrenocortical responses in reproductively active male and female green turtles. Associations between reproductive behavior and plasma steroids were investigated in green turtles across the population and within individuals. Levels across a range of both asocial and social behaviors were compared including (a) free swimming behavior; (b) initial courtship interactions; (c) mounted behavior (male and female turtles involved in copulatory activities); (d) intermale aggression (rival males that physically competed with another male turtle or mounted males recipient to these aggressive interactions); and (e) extensive courtship damage (male turtles that had accumulated excessive courtship damage from rival males). Behavioral androgen responses were detected in male turtles, in that plasma A was observed to increase with both attendant and mounted behavior. Male turtles who had been subjected to intermale aggression or who had accumulated severe courtship damage exhibited significantly lower plasma A than their respective controls. No pronounced adrenocortical response was observed after either intermale aggression or accumulation of extensive courtship damage. Female turtles exhibited a significant increase in plasma B during swimming versus mounted behavior, but no change in plasma A. We discuss our results in terms of how scramble polygamy might influence behavioral androgen interactions differently from more typical combative and territorial forms of male polygamy.

Aggression↗

PubMed1998

The environmental contaminant DDE fails to influence the outcome of sexual differentiation in the marine turtle Chelonia mydas.

In many turtles, the temperature experienced during the middle of egg incubation determines the sex of the offspring. The implication of steroid sex hormones as the proximate trigger for sex determination opens the possibility that endocrine-disrupting contaminants may also influence the outcome of sexual differentiation. In this study we investigate the potential effects of DDE (a common DDT metabolite) on sexual differentiation of Chelonia mydas (green sea turtle). Four clutches of eggs collected from Heron Island, Queensland, Australia, were treated with DDE at the beginning of the thermosensitive period for sexual determination. An incubation temperature of 28 degrees C or less produces male hatchlings in this species, whereas 30 degrees C or more produces female hatchlings. Dosed eggs were consequently incubated at two temperatures (27.6 degrees C and 30.4 degrees C) on the upper and lower boundaries of the sex determination threshold for this species. DDE, ranging from 3.3 to 66.5 microg, was dissolved in 5, 10, and 25 microl ethanol and applied to eggshells above the embryo. Less than 2.5 ng/g DDE was present in eggs prior to dosing. Approximately 34% of the applied DDE was absorbed in the eggs, but only approximately 8% of applied DDE was found in embryos. Thus, treated eggs, corrected for background DDE, had up to 543 ng/g DDE. The sex ratio at these doses did not differ from what would be expected on consideration of temperature alone. Incubation time, hatching success, incidence of body deformities, hatching size, and weight were also within the limits of healthy developed hatchlings. This indicates that the eggs of C. mydas in the wild with concentrations of DDE less than 543 ng/g should produce hatchlings with relatively high hatching success, survival rate, and normally differentiated gonads.

Animals↗

PubMed1997

Philopatry of male marine turtles inferred from mitochondrial DNA markers.

Recent studies of mitochondrial DNA (mtDNA) variation among marine turtle populations are consistent with the hypothesis that females return to beaches in their natal region to nest as adults. In contrast, less is known about breeding migrations of male marine turtles and whether they too are philopatric to natal regions. Studies of geographic structuring of restriction fragment and microsatellite polymorphisms at anonymous nuclear loci in green turtle (Chelonia mydas) populations indicate that nuclear gene flow is higher than estimates from mtDNA analyses. Regional populations from the northern and southern Great Barrier Reef were distinct for mtDNA but indistinguishable at nuclear loci, whereas the Gulf of Carpentaria (northern Australia) population was distinct for both types of marker. To assess whether this result was due to reduced philopatry of males across the Great Barrier Reef, we determined the mtDNA haplotypes of breeding males at courtship areas for comparison with breeding females from the same three locations. We used a PCR-restriction fragment length polymorphism approach to determine control region haplotypes and designed mismatch primers for the identification of specific haplotypes. The mtDNA haplotype frequencies were not significantly different between males and females at any of the three areas and estimates of Fst among the regions were similar for males and females (Fst = 0.78 and 0.73, respectively). We conclude that breeding males, like females, are philopatric to courtship areas within their natal region. Nuclear gene flow between populations is most likely occurring through matings during migrations of both males and females through nonnatal courtship areas.

Animals↗

PubMed1997

Geographic structure of mitochondrial and nuclear gene polymorphisms in Australian green turtle populations and male-biased gene flow.

The genetic structure of green turtle (Chelonia mydas) rookeries located around the Australian coast was assessed by (1) comparing the structure found within and among geographic regions, (2) comparing microsatellite loci vs. restriction fragment length polymorphism analyses of anonymous single copy nuclear DNA (ascnDNA) loci, and (3) comparing the structure found at nuclear DNA markers to that of previously analyzed mitochondrial (mtDNA) control region sequences. Significant genetic structure was observed over all regions at both sets of nuclear markers, though the microsatellite data provided greater resolution in identifying significant genetic differences in pairwise tests between regions. Inferences about population structure and migration rates from the microsatellite data varied depending on whether statistics were based on the stepwise mutation or infinite allele model, with the latter being more congruent with geography. Estimated rates of gene flow were generally higher than expected for nuclear DNA (nDNA) in comparison to mtDNA, and this difference was most pronounced in comparisons between the northern and southern Great Barrier Reef (GBR). The genetic data combined with results from physical tagging studies indicate that the lack of nuclear gene divergence through the GBR is likely due to the migration of sGBR turtles through the courtship area of the nGBR population, rather than male-biased dispersal. This example highlights the value of combining comparative studies of molecular variation with ecological data to infer population processes.

Alleles↗

PubMed1995

Trans-Pacific migrations of the loggerhead turtle (Caretta caretta) demonstrated with mitochondrial DNA markers.

Juvenile loggerhead turtles (Caretta caretta) have recently been documented in the vicinity of Baja California and thousands of these animals have been captured in oceanic fisheries of the North Pacific. The presence of loggerhead turtles in the central and eastern North Pacific is a prominent enigma in marine turtle distribution because the nearest documented nesting concentrations for this species are in Australia and Japan, over 10,000 km from Baja California. To determine the origin of the Baja California feeding aggregate and North Pacific fishery mortalities, samples from nesting areas and pelagic feeding aggregates were compared with genetic markers derived from mtDNA control region sequences. Overall, 57 of 60 pelagic samples (95%) match haplotypes seen only in Japanese nesting areas, implicating Japan as the primary source of turtles in the North Pacific Current and around Baja California. Australian nesting colonies may contribute the remaining 5% of these pelagic feeding aggregates. Juvenile loggerhead turtles apparently traverse the entire Pacific Ocean, approximately one-third of the planet, in the course of developmental migrations, but mortality in high-seas fisheries raises concern over the future of this migratory population.

Animals↗

PubMed1994

Mitochondrial DNA control region polymorphisms: genetic markers for ecological studies of marine turtles.

We describe a rapid and sensitive method for the detection of population-specific genetic markers in mitochondrial DNA (mtDNA) and the use of such markers to analyse population structure of marine turtles. A series of oligonucleotide primers specific for the amplification of the mtDNA control region in Cheloniid turtles were designed from preliminary sequence data. Using two of these primers, a 384-385-bp sequence was amplified from the 5' portion of the mtDNA control region of 15 green turtles Chelonia mydas from 12 different Indo-Pacific rookeries. Fourteen of the 15 individuals, including some with identical whole-genome restriction fragment patterns, had sequences that differed by one or more base substitutions. Analysis of sequence variation among individuals identified a total of 41 nucleotide substitutions and a 1-bp insertion/deletion. Comparison with evidence from whole-genome restriction enzyme analysis of the same individuals indicated that this portion of the control region is evolving approximately eight times faster than the average rate and that the sequence analysis detected approximately one fifth of the total variation present in the genome. Restriction enzyme analysis of amplified products from an additional 256 individuals revealed significant geographic structuring in the distribution of mtDNA genotypes among five of the 10 rookeries surveyed extensively. Additional geographic structuring of genotypes was identified through denaturing gradient gel electrophoresis (DGGE) of amplified products. Only two of the 10 rookeries surveyed could not be differentiated, indicating that the Indo-Pacific C. mydas include a number of genetically differentiated populations, with minimal female-mediated gene flow among them. Important applications for genetic markers in the conservation and management of marine turtles include the identification of appropriate demographic units for research and management (i.e. genetically discrete populations) and assessment of the composition of feeding and harvested populations.

Animals↗

PubMed1990

Seasonal changes in serum gonadal steroids associated with migration, mating, and nesting in the loggerhead sea turtle (Caretta caretta).

Adult male loggerhead sea turtles, Caretta caretta, exhibited a "prenuptial" spermatogenic cycle that was coincident with increased concentrations of serum testosterone (T). Serum T was high during the months when migration and mating have been recorded for males. In contrast to females, males appear to be annual breeders. Nine reproductively active female C. caretta (as verified through laparoscopy) were tagged with sonic transmitters and were repeatedly bled prior to migration. Four months prior to the nesting season, the ovaries of reproductively active females had hundreds of vitellogenic follicles of approximately 1.5 cm in diameter (i.e., half the size of ovulatory follicles). Approximately 4-6 weeks prior to migration from feeding grounds to mating and nesting areas, serum estradiol-17 beta (E2) concentrations increased significantly and remained high for approximately 4 weeks, suggesting a period of increased vitellogenesis. During a 1- to 2-week period prior to migration, serum E2 decreased significantly, while serum T concentrations increased (at least) until the time of migration. Serum T, E2, and progesterone (PRO) were elevated during nesting if a turtle was going to nest again during that nesting season. During the last nesting of a season, turtles had low serum concentrations of T, E2, and Pro. The prenuptial pattern of gonadal recrudescence and gonadal steroid production in both male and female C. caretta contrasts with those of many temperate freshwater turtles, and this type of reproductive pattern may have been facilitated by adaptation to a tropical marine environment.

Animals↗

PubMed1989

An evolutionary link for developing mammalian lungs.

Lungs of the human infant and those of other mammals are filled with fluid immediately prior to birth. Studies of the ionic composition of this fluid indicate that active ionic transport processes occur in the epithelial cells of the potential airspaces. The purpose of this study was to see if these active ion pumps were present in developing species other than mammals thus providing a possible evolutionary link to mammals. A series of samples of lung liquid, amniotic fluid, and plasma were taken from embryonic marine turtles gathered from clutches incubating in the beach at Mon Repos, Queensland, Australia during the summer of 1986-87. The concentrations of sodium, potassium and chloride ions and protein measured in these liquids indicated that active pumping processes similar to that seen in the mammalian lung were present in the developing lungs of these marine reptiles and further, circumstantial evidence was gathered to suggest that this liquid was partially reabsorbed prior to hatching. The results support the notion that processes responsible for the normal development of the human lung and lungs of other mammals are also present in the hollow lungs of marine turtles. Thus there is an evolutionary counterpart controlling lung development in more ancient species. It may be possible to generalize this observation to the development of hollow lungs of other species.

Animals↗