High Evolutionary Rates in Nuclear Genes of Squamates

We compared nonsynonymous substitution rates (Ka) of nuclear coding genes between four major groups of living sauropsids (reptiles): birds, squamates, crocodiles, and turtles. Since only 9 orthologous genes are known in all the four taxonomic groups, we searched for orthologous genes known in chicken and at least one of any representative of poikilotherm sauropsids. Thus, we analyzed three additional data sets: 28 genes identified in chicken and various squamates, 24 genes identified in chicken and crocodilians, and 20 genes identified in chicken and turtles. To compare nonsynonymous substitution rates between all lineages of sauropsids, we used the relative-rate test with human genes as the outgroup. We show that 22/28 nuclear coding genes of squamates, especially snakes (15/16), have an higher evolutionary rate than those in chicken (in mean, 30–40% faster). However, no such difference is detected between crocodiles, turtles and chicken. Higher substitution rate in squamates nuclear coding genes than in chicken, and probably than in other sauropsids, could explain some of the difficulties in resolving the molecular phylogeny of reptiles. Received: 5 July 2000 / Accepted: 13 February 2001     

Reptile freeze tolerance: metabolism and gene expression

Terrestrially hibernating reptiles that live in seasonally cold climates need effective strategies of cold hardiness to survive the winter. Use of thermally buffered hibernacula is very important but when exposure to temperatures below 0 degrees C cannot be avoided, either freeze avoidance (supercooling) or freeze tolerance strategies can be employed, sometimes by the same species depending on environmental conditions. Several reptile species display ecologically relevant freeze tolerance, surviving for extended times with 50% or more of their total body water frozen. The use of colligative cryoprotectants by reptiles is poorly developed but metabolic and enzymatic adaptations providing anoxia tolerance and antioxidant defense are important aids to freezing survival. New studies using DNA array screening are examining the role of freeze-responsive gene expression. Three categories of freeze responsive genes have been identified from recent screenings of liver and heart from freeze-exposed (5h post-nucleation at -2.5 degrees C) hatchling painted turtles, Chrysemys picta marginata. These genes encode (a) proteins involved in iron binding, (b) enzymes of antioxidant defense, and (c) serine protease inhibitors. The same genes were up-regulated by anoxia exposure (4 h of N2 gas exposure at 5 degrees C) of the hatchlings which suggests that these defenses for freeze tolerance are aimed at counteracting the injurious effects of the ischemia imposed by plasma freezing.     

A review of thermoregulation and physiological performance in reptiles: what is the role of phenotypic flexibility?

Biological functions are dependent on the temperature of the organism. Animals may respond to fluctuation in the thermal environment by regulating their body temperature and by modifying physiological and biochemical rates. Phenotypic flexibility (reversible phenotypic plasticity, acclimation, or acclimatisation) in rate functions occurs in all major taxonomic groups and may be considered as an ancestral condition. Within the Reptilia, representatives from all major groups show phenotypic flexibility in response to long-term or chronic changes in the thermal environment. Acclimation or acclimatisation in reptiles are most commonly assessed by measuring whole animal responses such as oxygen consumption, but whole animal responses are comprised of variation in individual traits such as enzyme activities, hormone expression, and cardiovascular functions. The challenge now lies in connecting the changes in the components to the functioning of the whole animal and its fitness. Experimental designs in research on reptilian thermal physiology should incorporate the capacity for reversible phenotypic plasticity as a null-hypothesis, because the significance of differential body temperature–performance relationships (thermal reaction norms) between individuals, populations, or species cannot be assessed without testing that null-hypothesis.     

龟鳖动物疾病的研究进展

随着养殖规模的扩大,龟鳖动物的疾病日益增多,许多养殖场遭受了巨大的经济损失。为此,一些学者对龟鳖动物的疾病进行了大量研究。本文总结了龟鳖动物疾病的致病因素、诊断及防治等应用方面的研究,指出了龟鳖动物疾病研究中存在的主要问题并提出了相应的建议。     

Post-nesting migrations patterns of Green Turtles (Chelonia mydas) from the Egyptian Red Sea

In order to identify the migratory pathways and foraging grounds of post-nesting Green Turtles (Chelonia mydas) in the Red Sea, we attached satellite transmitters to four females immediately after egg deposition and tracked them between 207 and 647 days. We identified four geographically distinct post-nesting habitat areas and migration paths from Zabargad Island, Egypt which was remarkable given our small sample size. Our shortest migration was 140?km and the longest 940?km, with the migrations and post-nesting habitat encompassing the boundaries of four of the seven Red Sea countries (Egypt, Sudan, Eritrea, and Saudi Arabia). The post-nesting habitats were located in shallow coastal habitat and three consisted of near-shore archipelagos. Two turtles moved past areas of suitable post-nesting habitat that was occupied by other turtles, which suggests that these turtles may be exhibiting fidelity to certain feeding and nesting sites. Our results suggest that regional and multi-national cooperation will be needed to protect sea turtles that nest on Zabargad Island, a nesting site that is important for Egypt and other Red Sea nations.     

The physiology of diving in a north-temperate and three tropical turtle species

We examined changes in blood gases, plasma ions, and acid-base status during prolonged submergence (6 h) of four aquatic turtle species in aerated water at 20 °C. Our objective was to determine whether the temperate species, Chrysemys picta bellii, exhibits greater tolerance to submergence apnea than the tropical species, Pelomedusa subrufa, Elseya novaeguineae, and Emydura subglobosa. Blood was sampled from indwelling arterial catheters for measurements of blood PO₂, PCO₂, pH, and hematocrit and for plasma concentrations of lactate, glucose, Na⁺, K⁺, Cl⁻, total Ca, and total Mg. The pattern of change was similar in all species: a combined respiratory and metabolic acidosis associated with a marked decrease of blood PO₂. The severity of the acidosis developed in the temperate species, however, was significantly less than that of the tropical turtles. Lactate rose significantly and HCO₃ ⁻ fell proportionately in all turtles; changes in other plasma ion concentrations were small but were generally in the directions consistent with compensatory exchanges with other body compartments; i.e., cations (K⁺, Ca, and Mg increased) and anions (Cl⁻ decreased). The results indicate that hypoxia tolerance is a conserved trait in turtles, even in those that do not experience enforced winter submergence, and that the temperate species may be superior in this capacity because of reduced metabolic rate. Accepted: 3 March 1999     

Patterns of growth and sexual size dimorphism in two species of box turtles with environmental sex determination

An adaptive explanation for environmental sex determination is that it promotes sexual size dimorphism when larger size benefits one sex more than the other. That is, if growth rates are determined by environment during development, then it is beneficial to match developmental environment to the sex that benefits more from larger size. However, larger size may also be a consequence of larger size at hatching or growing for a longer time, i.e., delayed age at first reproduction. Therefore, the adaptive significance of sexual size dimorphism and environmental sex determination can only be interpreted within the context of both growth and maturation. In addition, in those animals that continue to grow after maturation, sexual size dimorphism at age of first reproduction could differ from sexual size dimorphism at later ages as growth competes for energy with reproduction and maintenance. I compared growth using annuli on carapace scales in two species of box turtles (Terrapene carolina and T. ornata) that have similar patterns of environmental sex determination but, reportedly, have different patterns of sexual size dimorphism. In the populations I studied, sexual size dimorphism was in the same direction in both species; adult females were, on average, larger than adult males. This was due in part to males maturing earlier and therefore at smaller sizes than females. In spite of similar patterns of environmental sex determination, patterns of growth differed between the species. In T. carolina, males grew faster than females as juveniles but females had the larger asymptotic size. In T. ornata, males and females grew at similar rates and had similar asymptotic sizes. Sexual size dimorphism was greatest at maturation because, although males matured younger and smaller, they grew more as adults. There was, therefore, no consistent pattern of faster growth for females that may be ascribed to developmental temperature. Received: 20 March 1996 / Accepted: 10 March 1998     

The rate of mitochondrial 12S rRNA gene evolution is similar in freshwater turtles and marsupials

Assertions that the ``conventional' rate of mitochondrial DNA (mtDNA) evolution is reduced in poikilotherms in general and turtles in particular were tested for side-necked turtles (Pleurodira: Chelidae). Homologous data sets of mitochondrial 12S rRNA gene sequences were used to compare the average divergence between the Australian and South American species for two Gondwanan groups: the chelid turtles and the marsupials. The mean nucleotide divergences between continental groups for both the turtles and the marsupials are remarkably similar. These data suggest that the rate of evolution of mitochondrial 12S rRNA gene is not substantially slower in turtles than in the homeothermic marsupials. Received: 24 February 1997 / Accepted: 30 June 1997     

An experimental analysis of the water relations of eggs of Blanding's turtles (Emydoidea blandingii)

Eggs of Blanding's turtles ( Emydoidea blandingii ) were incubated in the laboratory under hydric conditions eliciting different patterns of net water exchange between eggs and surrounding air and substrate. Eggs incubated on wet and intermediate substrates increased in mass during the first half of incubation and decreased in mass during the second half, and their mass just before hatching was slightly lower than at oviposition. Eggs incubated on dry substrates and on platforms above substrates declined in mass throughout incubation, with a rate of decline greater in the second half of incubation than in the first. The size of hatchlings was related to the hydric environment in which eggs were incubated and, possibly, to the net flux of water across eggshells. However, variation in size of hatchlings was not as great as has been reported for other species with flexible-shelled eggs, owing presumably to the constraints on water exchange imposed by the more complex eggshells of Blanding's turtles.