Surviving the flood: plastron respiration in the non-tracheate arthropod Phrynus marginemaculatus (Amblypygi: Arachnida)

Specimens of Phrynus marginemaculatus can remain responsive when submerged in water for more than 24 hours. Behavioral data indicate that P. marginemaculatus utilizes dissolved oxygen from the surrounding water. Scanning electron miscroscopy and light microscope sections show cuticular modifications for plastron respiration. All previous examples of plastron respiration have involved animals with tracheal systems, but amblypygids respire through the use of two pairs of book lungs. This study provides the first example of plastron respiration not only in the order Amblypygi, but also, in any non-tracheate arthropod.     

The fine structure of the pupal plastron of simuliid flies

The outer surface of the plastron of the pupal spiracular gills of the Simuliidae was previously thought to be the network formed by the apical branches of the vertical struts. It is now shown that this horizontal network supports a thin laminate outer epicuticle and also a fine meshwork, both of which have been previously overlooked. A simple method is described for quickly producing three-dimensional micrographs of great depth with the transmission electron microscope.     

Evidence for the neural crest origin of turtle plastron bones

Summary: The migrating cranial neural crest cells of birds, fish, and mammals have been shown to form the membranous bones of the cranium and face. These findings have been extrapolated to suggest that all the dermal bones of the vertebrate exoskeleton are derived from the neural crest ectomesenchyme. However, only one group of extant animals, the Chelonians, has an extensive bony exoskeleton in the trunk. We have previously shown that the autapomorphic carapacial and plastron bones of the turtle shell arise from dermal intramembranous ossification. Here, we show that the bones of the plastron stain positively for HNK‐1 and PDGFRα and are therefore most likely of neural crest origin. This extends the hypothesis of the neural crest origin of the exoskeleton to include the turtle plastron. genesis 31:111–117, 2001. © 2001 Wiley‐Liss, Inc.     

Regulatory mechanisms of cellular respiration; the role of cell membranes; uranium inhibition of cellular respiration

Uranium as UO(2)(NO(3))(2) combines reversibly with proteins. The degree of dissociation of this combination depends, among other factors, on the H(+) concentration. At pH 7.3 the U-albumin complex was easily dissociated on addition of citrate, while at pH 3.8 it was not. Uranium inhibited reversibly a number of enzyme systems. Uranium enzyme inhibitions could be reversed on addition of certain hydroxypolycarboxylic acids (citric acid, alpha-hydroxyaspartic acid, malic acid); in no case, however, did phosphate have any effect. In cell-free yeast juice, the fermentation of glucose-hexosediphosphate was inhibited by UO(2)(NO(3))(2). Slight reactivation occurred on addition of phosphate. In living yeast cells, the fermentation and oxidation of glucose was inhibited by small amounts of UO(2)(NO(3))(2) (7,7 micrograms per mg. dry weight), while the oxidation of acetic acid, ethyl alcohol, malic and citric acids, was not affected at all. U inhibition in living yeast cells at pH 7.3 was completely released on addition of small amounts of phosphate, adenosinetriphosphate, and citrate, while at pH 3.8 U inhibition was not released by phosphate and citrate. At saturation, one yeast cell contained 7.06 x 10(6) molecules of uranium. Lactic dehydrogenase was not inhibited by U while the oxidation of lactic acid by gonococci was inhibited. Addition of phosphate released this inhibition. The U inhibition of liver succinoxidase was unaffected by phosphate, while the U inhibition of the oxidation of succinate by E. coli was released by phosphate. It has been concluded from these experiments that U inhibition of cell metabolism is due to combination of the metal with the protein portion of the cell membrane. Uranium is presented as an example of surface inhibition.     

A test of an antipredatory function of conspicuous plastron coloration in hatchling turtles

Bright colorations in animals are sometimes an antipredatory signal meant to startle, warn, or deter a predator from consuming a prey organism. Freshwater turtle hatchlings of many species have bright ventral coloration with high internal contrast that may have an antipredator function. We used visual modeling and field experiments to test whether the plastron coloration of Chrysemys picta hatchlings deters predators. We found that bird predators can easily distinguish hatchling turtles from their backgrounds and can easily see color contrast within the plastron. Raccoons cannot easily discriminate within-plastron color contrast but can see hatchlings against common backgrounds. Despite this, we found that brightly-colored, high contrast, replica turtles were not attacked less than low contrast replica turtles, suggesting that the bright coloration is not likely to serve an antipredatory function in this context. We discuss the apparent lack of innate avoidance of orange coloration in freshwater turtles by predators and suggest that preference and avoidance of colors are context-dependent. Since the bright colors are likely not a signal, we hypothesize that the colors may be caused by pigments deposited in tissue from maternal reserves during development. In most species, these pigments fade ontogenetically but they may have important physiological functions in species that maintain the bright coloration throughout adulthood.     

Are diminutive turtles miniaturized? The ontogeny of plastron shape in emydine turtles

Miniaturization, or the evolution of a dramatically reduced body size compared to related lineages, is an extraordinarily widespread phenomenon among metazoans. Evolutionary biologists have been fascinated by miniaturization because this transition has occurred numerous times, often among close relatives, providing a model system for studying convergent evolution and its underlying mechanisms. Much of the developmental work describing the ontogeny of miniature species suggests that paedomorphosis is the predominant avenue of miniaturization. Nevertheless, specific alterations to ontogeny appear highly variable, so that even related lineages with similar miniaturized traits produce those similarities via distinct ontogenetic paths. One major vertebrate group that has been overlooked in research on miniaturization is turtles. In the present study, we examined patterns of shape change in the plastron (the ventral part of the shell) over the course of ontogeny in a small clade of turtles (Emydinae) aiming to investigate whether two independently evolved diminutive members of the clade (Glyptemys muhlenbergii and Clemmys guttata) should be considered as miniaturized. We employ geometric morphometric methods to quantify the patterns of shape change these potentially miniaturized species and their relatives undergo during ontogeny, and use molecular phylogenetic trees to reconstruct ancestral conditions and provide information on the polarity of shape changes. We find that differing changes in ontogenetic parameters relative to ancestral conditions accompany the evolution of small size in emydines: G. muhlenbergii changes the duration of ontogeny and rate of shape change, whereas C. guttata changes growth rate. The observed ontogenetic repatterning of these species is reminiscent of changes in ontogeny and life history often found in miniaturized taxa. However, we conclude that C. guttata and G. muhlenbergii are not truly miniaturized because they still produce typical adult shell morphologies, and larger emydines display comparable ontogenetic flexibility. Because no emydines carry juvenile shell features forward into adulthood, we speculate that few, if any turtles, will show paedomorphic shell traits without corresponding changes in defensive strategy because such shells may offer insufficient protection. © 2013 The Linnean Society of London     

Structural characterization of the micropatterned egg plastron in the mosquito,Aedes albopictus

Eggs of the Asian tiger mosquito Aedes albopictus are fully covered with an air‐covering plastron network that enables them to stay below the surface of the water. Scanning electron microscopy revealed that the chorionic surface was covered with clusters of globular tubercles of different sizes. Histologically, the eggshell provides a typical water‐repellent microarchitecture consisting of an outer exochorion, a membranous endochorion and an intermediate pillar layer. The eggshell has a distinct chorionic tubercle that increases the surface area for gas exchange to enhance respiration capacity. In particular, the chorionic wall gives rise to a hexagonal pattern with smooth and elevated boundaries. In A. albopictus, a set of micropatterns for each hexagon was specified, and each central tubercle was surrounded by 20 small peripheral tubercles. Our fine structural analysis revealed that the partitioning of the surface into numerous hexagonal chorionic sculptures is associated with the Voronoi partition (tessellation), based on the distance to a point in a specific area of the plane. Therefore, the micropatterned surface of the mosquito eggshell appears to not only resist wetting by hydrostatic pressure but also provide resistance to lysate deposition by the biofouling process.     

Relating annual increments of the endangered Blanding's turtle plastron growth to climate

This research is the first published study to report a relationship between climate variables and plastron growth increments of turtles, in this case the endangered Nova Scotia Blanding's turtle (Emydoidea blandingii). We used techniques and software common to the discipline of dendrochronology to successfully cross‐date our growth increment data series, to detrend and average our series of 80 immature Blanding's turtles into one common chronology, and to seek correlations between the chronology and environmental temperature and precipitation variables. Our cross‐dated chronology had a series intercorrelation of 0.441 (above 99% confidence interval), an average mean sensitivity of 0.293, and an average unfiltered autocorrelation of 0.377. Our master chronology represented increments from 1975 to 2007 (33 years), with index values ranging from a low of 0.688 in 2006 to a high of 1.303 in 1977. Univariate climate response function analysis on mean monthly air temperature and precipitation values revealed a positive correlation with the previous year's May temperature and current year's August temperature; a negative correlation with the previous year's October temperature; and no significant correlation with precipitation. These techniques for determining growth increment response to environmental variables should be applicable to other turtle species and merit further exploration.     

土壤-玉米系统中土壤呼吸强度及各组分贡献

用特殊设计的气体采集箱法对玉米生长期间潮土呼吸强度进行了测定。结果表明,施用150kgNhm^-2的裸地土壤CO2累积排放量是294g C m^-2,约为种植玉米土壤的一半。用根去除法测得的玉米对土壤呼吸的贡献率,苗期小于20％,拔节到收获期波动在30％-70％之间,全生长期平均为46％。玉米生长期间因土壤有机碳分解而释放出的CO2总量为2．94MgChm^-2,大约是0—40cm土层中土壤有机碳总储存量的8％,因此需要输入7．35Mghm^-2的碳含量40％的作物残留物才能平衡土壤中有机碳的损失,约为玉米收获时残留于土壤中根量的一倍,但与残留根量及玉米生长期间根系分泌到土壤的有机物量的总和相当,因此土壤中有机碳总体处于平衡状态。在玉米生长期间,施用氮肥可使土壤CO2排放量降低10％。土壤排放CO2主要受土壤温度的影响,温度效应Q10为1．90-2．88。     

Interannual variability in global soil respiration, 1980–94

We used a climate‐driven regression model to develop spatially resolved estimates of soil‐CO₂ emissions from the terrestrial land surface for each month from January 1980 to December 1994, to evaluate the effects of interannual variations in climate on global soil‐to‐atmosphere CO₂ fluxes. The mean annual global soil‐CO₂ flux over this 15‐y period was estimated to be 80.4 (range 79.3–81.8) Pg C. Monthly variations in global soil‐CO₂ emissions followed closely the mean temperature cycle of the Northern Hemisphere. Globally, soil‐CO₂ emissions reached their minima in February and peaked in July and August. Tropical and subtropical evergreen broad‐leaved forests contributed more soil‐derived CO₂ to the atmosphere than did any other vegetation type (～30% of the total) and exhibited a biannual cycle in their emissions. Soil‐CO₂ emissions in other biomes exhibited a single annual cycle that paralleled the seasonal temperature cycle. Interannual variability in estimated global soil‐CO₂ production is substantially less than is variability in net carbon uptake by plants (i.e., net primary productivity). Thus, soils appear to buffer atmospheric CO₂ concentrations against far more dramatic seasonal and interannual differences in plant growth. Within seasonally dry biomes (savannas, bushlands and deserts), interannual variability in soil‐CO₂ emissions correlated significantly with interannual differences in precipitation. At the global scale, however, annual soil‐CO₂ fluxes correlated with mean annual temperature, with a slope of 3.3 Pg C y^?1 per °C. Although the distribution of precipitation influences seasonal and spatial patterns of soil‐CO₂ emissions, global warming is likely to stimulate CO₂ emissions from soils.     

Light respiration in <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis>

Respiration and photosynthesis are two important processes in microalgal growth that occur simultaneously in the light. To know the rates of both processes, at least one of them has to be measured. To be able to measure the rate of light respiration of Chlorella sorokiniana, the measurement of oxygen uptake must be fast, preferably in the order of minutes. We measured the immediate post-illumination respiratory O₂ uptake rate (OUR) in situ, using fiber-optic oxygen microsensors, and a small and simple extension of the cultivation system. This method enables rapid and frequent measurements without disturbing the cultivation and growth of the microalgae. Two batch experiments were performed with C. sorokiniana in a short light-path photobioreactor, and the OUR was measured at different time points. The net oxygen production rate (net OPR) was measured online. Adding the OUR and net OPR gives the gross oxygen production rate (gross OPR), which is a measure for the oxygen evolution by photosynthesis. The gross OPR was 35–40% higher than the net OPR for both experiments. The respiration rate is known to be related to the growth rate, and it is suggested that faster algal growth leads to a higher energy (ATP) requirement, and as such, respiratory activity increases. This hypothesis is supported by our results, as the specific OUR is highest in the beginning of the batch culture when the specific growth rate is highest. In addition, the specific OUR decreases toward the end of the experiments until it reaches a stable value of around 0.3 mmol O₂ h⁻¹ g⁻¹. This value for the specific OUR is equal to the maintenance requirement of C. sorokiniana as determined in an independent study of (Zijffers et al. 2010 (in press)). This suggests that respiration could fulfill the maintenance requirements of the microalgal cells.