Thermal,trophic and metabolic life histories of inaccessible fishes revealed from stable‐isotope analyses: a case study using orange roughy Hoplostethus atlanticus

A time‐resolved record of inhabited water depth, metabolic rate and trophic behaviour of the orange roughy Hoplostethus atlanticus was recovered from combined stable‐isotope analyses of otolith and muscle tissue. The results demonstrate that H. atlanticus from the north‐east Atlantic Ocean have a complex life history with three distinct depth‐stratified life stages. Early juvenile H. atlanticus occupy relatively shallow habitats, juvenile H. atlanticus show a deep‐demersal phase, rising at sexual maturity, and adult H. atlanticus exploit increasingly deep habitats with increasing age. At all sampled sizes, H. atlanticus muscle tissues have an isotopic composition suggesting a benthic rather than benthopelagic or pelagic diet. Isotopic measures of relative metabolic rate provide an insight into energy partitioning throughout ontogeny. Hoplostethus atlanticus have relatively low metabolic rates compared to coexisting deep‐water benthic fishes, consistent with their unusually high longevity. Surprisingly, lifetime fastest growth rates are achieved during juvenile stages when otolith isotopes imply deep‐water residency and relatively low metabolic rates. Fast growth may be sustained during a period of high efficiency associated with reduced metabolic costs of prey capture or predator evasion. The stable‐isotope approach can be applied to any teleost and provides a rapid, cost‐effective technique for studying deep‐water fish communities.     

Ontogenetic approach to assessment of chufa response to culture conditions by the method of chlorophyll fluorescence induction

Application of earlier proposed ontogenetic approach to assessment of chufa (Cyperus esculentus L.) response to artificial-light culture growing conditions differing in illuminance and type of mineral nutrition is described. It was shown that, on biological soil-like substrate, plant productivity did not increase as a result of PAR level rising, and life time of chufa leaves was reduced to 11 days as compared with 18 days on the neutral substrate. Changes in the parameters of chlorophyll fluorescence induction (F _v/F _m, Yield = (F _m − F _t)/F _m, and ETR = 0.5 × 0.84 × Yield × PAR) analyzed on the basis of ontogenetic approach show that it can disclose nonoptimal culture conditions.     

Support for the thermal coadaptation hypothesis from the growth rates of Sceloporus jarrovii lizards

The thermal coadaptation hypothesis posits that ectotherms thermoregulate behaviorally to maintain body temperatures (T_b) that maximize performance, such as net energy gain. Huey's (1982) energetics model describes how food availability and T_b interact to affect net energy gain. We tested the thermal coadaptation hypothesis and Huey's energetics model with growth rates of juvenile Yarrow's spiny lizards (Sceloporus jarrovii). We compared the preferred (selected) T_b range (T_sel) of lizards in high and low energy states to their optimal temperature (T_o) for growth over nine weeks, and determined whether the T_o for growth depended on food availability. We also measured the same lizards’ resting metabolic rate at five T_bs to test the energetics model assumptions that metabolic cost increases exponentially with T_b and does not differ between energy states. The T_sel of lizards on both diets overlapped with the T_o for growth. The assumptions of the energetics model were verified, but the T_o for net energy gain did not depend on food availability. Therefore, we found support for the thermal coadaptation hypothesis. We did not find support for the energetics model, but this may have been due to low statistical power.     

Assessment of photosynthetic performance in the two life history stages of Alaria crassifolia (Laminariales,Phaeophyceae)

Understanding of the physiological responses of kelp to environmental parameters is crucial, especially in the context of environmental change that may have contributed to the decline of kelp forests all over the world. The current study presents the photosynthetic characteristics of the macroscopic sporophyte and microscopic gametophyte stages of the brown alga Alaria crassifolia from Hokkaido, Japan, as determined by examining their photosynthetic responses over a range of temperature and irradiance using dissolved oxygen and chlorophyll fluorescence measurements. Net photosynthetic rates of the sporophyte were consistently higher than those of gametophyte across temperature gradients and irradiance levels. Photosynthesis–irradiance curves at 8°C, 16°C, and 20°C revealed similar initial slopes (α = 0.4–0.9) on the two life history stages, but higher compensation (E _c = 4–7 μmol photons m^?2 s^?1) and saturation irradiances (E _k = 53–103 μmol photons m^?2 s^?1) for the sporophyte than for the gametophyte (E _c = 0–7 μmol photons m^?2 s^?1; E _k = 7–10 μmol photons m^?2 s^?1). Both stages exhibited chronic photoinhibition, as shown by the failure of recovery in their maximum quantum yields (F _v/F _m) following high irradiance stress, with greater possibility of photodamage at low temperature. Gametophytes were less sensitive to low temperatures than sporophytes, given their relatively stable F _v/F _m response. Nevertheless, temperature optima for photosynthesis of both stages coincide with each other at 20–23°C, which correspond to the growth and maturation periods of A. crassifolia in Japan. This species is also likely to suffer from thermal inhibition as both GP rates and F _v/F _m decreased above 24°C.     

The bilayer enhances rhodopsin kinetic stability in bovine rod outer segment disk membranes

Rhodopsin is a kinetically stable protein constituting >90% of rod outer segment disk membrane protein. To investigate the bilayer contribution to rhodopsin kinetic stability, disk membranes were systematically disrupted by octyl-β-D-glucopyranoside. Rhodopsin kinetic stability was examined under subsolubilizing (rhodopsin in a bilayer environment perturbed by octyl-β-D-glucopyranoside) and under fully solubilizing conditions (rhodopsin in a micelle with cosolubilized phospholipids). As determined by DSC, rhodopsin exhibited a scan-rate-dependent irreversible endothermic transition at all stages of solubilization. The transition temperature (T_m) decreased in the subsolubilizing stage. However, once the rhodopsin was in a micelle environment there was little change of the T_m as the phospholipid/rhodopsin ratio in the mixed micelles decreased during the fully solubilized stage. Rhodopsin thermal denaturation is consistent with the two-state irreversible model at all stages of solubilization. The activation energy of denaturation (E_act) was calculated from the scan rate dependence of the T_m and from the rate of rhodopsin thermal bleaching at all stages of solubilization. The E_act as determined by both techniques decreased in the subsolubilizing stage, but remained constant once fully solubilized. These results indicate the bilayer structure increases the E_act to rhodopsin denaturation.     

Chloroplasts require glutathione reductase to balance reactive oxygen species and maintain efficient photosynthesis

Thiol‐based redox‐regulation is vital for coordinating chloroplast functions depending on illumination and has been throroughly investigated for thioredoxin‐dependent processes. In parallel, glutathione reductase (GR) maintains a highly reduced glutathione pool, enabling glutathione‐mediated redox buffering. Yet, how the redox cascades of the thioredoxin and glutathione redox machineries integrate metabolic regulation and detoxification of reactive oxygen species remains largely unresolved because null mutants of plastid/mitochondrial GR are embryo‐lethal in Arabidopsis thaliana. To investigate whether maintaining a highly reducing stromal glutathione redox potential (E_GSH) via GR is necessary for functional photosynthesis and plant growth, we created knockout lines of the homologous enzyme in the model moss Physcomitrella patens. In these viable mutant lines, we found decreasing photosynthetic performance and plant growth with increasing light intensities, whereas ascorbate and zeaxanthin/antheraxanthin levels were elevated. By in vivo monitoring stromal E_GSH dynamics, we show that stromal E_GSH is highly reducing in wild‐type and clearly responsive to light, whereas an absence of GR leads to a partial glutathione oxidation, which is not rescued by light. By metabolic labelling, we reveal changing protein abundances in the GR knockout plants, pinpointing the adjustment of chloroplast proteostasis and the induction of plastid protein repair and degradation machineries. Our results indicate that the plastid thioredoxin system is not a functional backup for the plastid glutathione redox systems, whereas GR plays a critical role in maintaining efficient photosynthesis.     

Analysis of the electrochemistry of hemes with Ems spanning 800 mV

The free energy of heme reduction in different proteins is found to vary over more than 18 kcal/mol. It is a challenge to determine how proteins manage to achieve this enormous range of E_ms with a single type of redox cofactor. Proteins containing 141 unique hemes of a‐, b‐, and c‐type, with bis‐His, His‐Met, and aquo‐His ligation were calculated using Multi‐Conformation Continuum Electrostatics (MCCE). The experimental E_ms range over 800 mV from ?350 mV in cytochrome c₃ to 450 mV in cytochrome c peroxidase (vs. SHE). The quantitative analysis of the factors that modulate heme electrochemistry includes the interactions of the heme with its ligands, the solvent, the protein backbone, and sidechains. MCCE calculated E_ms are in good agreement with measured values. Using no free parameters the slope of the line comparing calculated and experimental E_ms is 0.73 (R² = 0.90), showing the method accounts for 73% of the observed E_m range. Adding a +160 mV correction to the His‐Met c‐type hemes yields a slope of 0.97 (R² = 0.93). With the correction 65% of the hemes have an absolute error smaller than 60 mV and 92% are within 120 mV. The overview of heme proteins with known structures and E_ms shows both the lowest and highest potential hemes are c‐type, whereas the b‐type hemes are found in the middle E_m range. In solution, bis‐His ligation lowers the E_m by ≈205 mV relative to hemes with His‐Met ligands. The bis‐His, aquo‐His, and His‐Met ligated b‐type hemes all cluster about E_ms which are ≈200 mV more positive in protein than in water. In contrast, the low potential bis‐His c‐type hemes are shifted little from in solution, whereas the high potential His‐Met c‐type hemes are raised by ≈300 mV from solution. The analysis shows that no single type of interaction can be identified as the most important in setting heme electrochemistry in proteins. For example, the loss of solvation (reaction field) energy, which raises the E_m, has been suggested to be a major factor in tuning in situ E_ms. However, the calculated solvation energy vs. experimental E_m shows a slope of 0.2 and R² of 0.5 thus correlates weakly with E_ms. All other individual interactions show even less correlation with E_m. However the sum of these terms does reproduce the range of observed E_ms. Therefore, different proteins use different aspects of their structures to modulate the in situ heme electrochemistry. This study also shows that the calculated E_ms are relatively insensitive to different heme partial charges and to the protein dielectric constant used in the simulation. Proteins 2009. © 2008 Wiley‐Liss, Inc.     

Mechanosensitive ion channels in chara: influence of water channel inhibitors, HgCl2 and ZnCl2, on generation of receptor potential

Characean internodal cells generate receptor potential (ΔE _m) in response to mechanical stimuli. Upon a long-lasting stimulus, the cells generated ΔE _m at the moment of both compression and decompression, and the amplitude of ΔE _m at the moment of decompression, (ΔE _m)_E, was larger than that at compression. The long-lasting stimulus caused a membrane deformation (ΔD _m) having two components, a rapid one, (ΔD _m)_rapid, at the moment of compression and a slower one, (ΔD _m)_slow, during the long-lasting compression. We assumed that (ΔD _m)_slow might have some causal relation with the larger ΔE _m at (ΔE _m)_E. We treated internodal cells with either HgCl₂ or ZnCl₂, water channel inhibitors, to decrease (ΔD _m)_slow. Both inhibitors attenuated (ΔD _m)_slow during compression. Cells treated with HgCl₂ generated smaller (ΔE _m)_E compared to nontreated cells. On the other hand, cells treated with ZnCl₂ never attenuated (ΔE _m)_E but, rather, amplified it. Thus, the amplitude of (ΔD _m)_slow did not always show tight correlation with the amplitude of (ΔE _m)_E. Furthermore, when a constant deformation was applied to an internodal cell in a medium with higher or lower osmotic value, a cell having higher turgor always showed a larger (ΔE _m)_E. Thus, we concluded that changes in tension at the membrane may be the most important factor to induce activation of mechanosensitive Ca²⁺ channel.     

Ontogenetic trajectories in the ornithischian endocranium

Understanding ontogenetic and developmental patterns is critical for reconstructing the life history of fossil vertebrates. In dinosaurs, ontogenetic studies have nearly exclusively focused on changes in the cranial and post‐cranial skeleton, whereas ontogenetic changes in the endocranium have received little attention. Here, we present digital reconstructions of the brain and inner ear anatomy of two ontogenetic stages of the Jurassic ornithischian dinosaur Dysalotosaurus lettowvorbecki. Results show that the endocranial anatomy underwent considerable changes during growth, including a rostrocaudal elongation of the olfactory apparatus, a reduction in the cephalic and pontine flexure and an increase in cerebellum size. Functional elements, such as the cerebral hemispheres and the inner ear, were already well developed in early ontogenetic stages, indicating a large degree of precociality. The anisotropic pattern of size and shape changes in the endocranium further indicates that ontogenetic trajectories may be controlled by functional and environmental demands in the different growth stages in Dysalotosaurus lettowvorbecki. The occurrence of similar ontogenetic patterns in the endocranial anatomy of derived ornithopod dinosaurs suggests a more widespread distribution of this growth trajectory.     

Ultrastructural study of different types of callus from leaf expiants ofAesculus hippocastanum L.

Summary The cell ultrastructure in three types of callus obtained from leaf explants ofAesculus hippocastanum L. has been studied. Remarkable differences have been shown between the cells of the forerunner E₁ callus and those of the callus arising from it, according to the culture conditions.The peculiar characteristics of E₁ are the scarcity of intercellular spaces and the occurrence of autophagic vacuoles in the cells.An embryogenic friable callus (E₂) is formed in time when E₁ is maintained on solid culture medium. The E₂ cells show cytological features typical of a higher metabolic level and contain starch. Diffused middle lamella digestion leads to the detachment of small embryogenic cell aggregates consisting of vacuolated parenchymatous-like cells and small meristematic cells which may be regarded as embryoids initials.Shaking E₁ in the same liquid medium and subsequent culture on solid medium lead to the differentiation of a non-embryogenic callus (NE), whose cells are very large and highly vacuolated, devoid of starch and with organelle-rich cytoplasm. The NE callus shows a high degree of growth, but does not attain embryogenic competence in time.Abbreviations c cell - cr crystal - cw cell wall - d dictyosome - er endoplasmic reticulum - m mitochondrion - mb microbody - n nucleus - p plastid - s starch - v vacuole     

Stage-structured ontogeny in resource populations generates non-additive stabilizing and de-stabilizing forces in populations and communities

Demographic heterogeneity influences how populations respond to density dependent intraspecific competition and trophic interactions. Distinct stages across an organism's development, or ontogeny, are an important example of demographic heterogeneity. In consumer populations, ontogenetic stage structure has been shown to produce categorical differences in population dynamics, community dynamics and even species coexistence compared to models lacking explicit ontogeny. The study of consumer–resource interactions must also consider the ontogenetic stage structure of the resource itself, particularly plants, given their fundamental role at the basis of terrestrial food webs. We incorporate distinct ontogenetic stages of plants into an adaptable multi-stage consumer–resource modeling framework that facilitates studying how stage specific consumers shape trophic dynamics at low trophic levels. We describe the role of density dependent demographic rates in mediating the dynamics of stage-structured plant populations. We then investigate how these demographic rates interact with consumer pressure to influence stability and coexistence in multiple stage-specific consumer–resource interactions. Results detail how density dependent effects across distinct ontogenetic stages in plant development produce non-additivity in the drivers of dynamic stability both in single populations and in consumer–resource settings, challenging the ubiquity of certain traditional ecological dynamic paradigms. We also find categorical differences in the population variability induced by herbivores consuming separate plant stages. Consumer–resource models, such as plant–herbivore interactions, often average out demographic heterogeneity in populations. Here, we show that explicitly including plant demographic heterogeneity through ontogeny yields distinct dynamic expectations for both plants and herbivores compared to traditional consumer–resource formulations. Our results indicate that efforts to understand the demographic effect of herbivores on plant populations may need to also consider the effects of plant demographics on herbivores and the reciprocal relationship between them.     

Short-and long-term effects of cadmium on transmembrane electric potential (E m) in maize roots

In this study, the effects of Cd on root growth, respiration, and transmembrane electric potential (E _m) of the outer cortical cells in maize roots treated with various Cd concentrations (from 1 μM to 1 mM) for several hours to one week were studied. The E _m values of root cells ranged between −120 and −140 mV and after addition of Cd they were depolarized immediately. The depolarization was concentration-dependent reaching the value of diffusion potential (E _D) when the Cd concentration exceeded 100 μM. The values of E _D ranged between −65 to −68 mV (−66 ± 1.42 mV). The maximum depolarization of E _m was registered approx. 2.5 h after addition of Cd to the perfusion solution and in some cases, partial (Cd > 100 μM) or complete repolarization (Cd < 100 μM) was observed within 8–10 h of Cd treatment. In the time-dependent experiments (0 to 168 h) shortly after the maximum repolarization of E _m a continuous concentration-dependent decrease of E _m followed at all Cd concentrations. Depolarization of E _m was accompanied by both increased electrolyte leakage and inhibition of respiration, especially in the range of 50 μM to 1 mM Cd, with the exception of root cells treated with 1 and 10 μM Cd for 24 and 48 h. Time course analysis of Cd impact on root respiration revealed that at higher Cd concentrations (> 50 μM) the respiration gradually declined (∼ 6 h) and then remained at this lowest level for up to 24 h. All the Cd concentrations used in this experiment induced significant inhibition of root elongation and concentrations higher than 100 μM stopped the root growth within the first day of Cd treatment. Our results suggest that Cd does not cause irreversible changes in the electrogenic plasma membrane H⁺ ATPase because fusicoccin, an H⁺ ATPase activator diminished the depolarizing effect of Cd on the E _m. The depolarization of E _m in the outer cortical cells of maize roots was the result of a cumulative effect of Cd on ATP supply, plasmalemma permeability, and activity of H⁺ ATPase.     

Accounting for activity respiration results in realistic trophic transfer efficiencies in allometric trophic network (ATN) models

Allometric trophic network (ATN) models offer high flexibility and scalability while minimizing the number of parameters and have been successfully applied to investigate complex food web dynamics and their influence on food web diversity and stability. However, the realism of ATN model energetics has never been assessed in detail, despite their critical influence on dynamic biomass and production patterns. Here, we compare the energetics of the currently established original ATN model, considering only biomass-dependent basal respiration, to an extended ATN model version, considering both basal and assimilation-dependent activity respiration. The latter is crucial in particular for unicellular and invertebrate organisms which dominate the metabolism of pelagic and soil food webs. Based on metabolic scaling laws, we show that the extended ATN version reflects the energy transfer through a chain of four trophic levels of unicellular and invertebrate organisms more realistically than the original ATN version. Depending on the strength of top-down control, the original ATN model yields trophic transfer efficiencies up to 71% at either the third or the fourth trophic level, which considerably exceeds any realistic values. In contrast, the extended ATN version yields realistic trophic transfer efficiencies ≤?30% at all trophic levels, in accordance with both physiological considerations and empirical evidence from pelagic systems. Our results imply that accounting for activity respiration is essential for consistently implementing the metabolic theory of ecology in ATN models and for improving their quantitative predictions, which makes them more powerful tools for investigating the dynamics of complex natural communities.     

Ontogenetic body-mass scaling of resting metabolic rate covaries with species-specific metabolic level and body size in spiders and snakes

According to common belief, metabolic rate usually scales with body mass to the 3/4-power, which is considered by some to be a universal law of nature. However, substantial variation in the metabolic scaling exponent (b) exists, much of which can be related to the overall metabolic level (L) of various taxonomic groups of organisms, as predicted by the recently proposed metabolic-level boundaries (MLB) hypothesis. Here the MLB hypothesis was tested using data for intraspecific (ontogenetic) body-mass scaling of resting metabolic rate in spiders and boid snakes. As predicted, in both animal groups b varies mostly between 2/3 and 1, and is significantly negatively related to L. L is, in turn, negatively related to species-specific body mass (M_m: estimated as the mass at the midpoint of a scaling relationship), and as a result, larger species tend to have steeper metabolic scaling slopes (b) than smaller species. After adjusting for the effects of M_m, b and L are still negatively related, though significantly only in the spiders, which exhibit a much wider range of L than the snakes. Therefore, in spiders and snakes the intraspecific scaling of metabolic rate with body mass itself scales with interspecific variation in both metabolic level and body mass.     

Interpopulation trophic niches and ontogenetic shifts of a mangrove fish predator

Fish trophic niches reflect important ecological interactions and provide insight into the structure of mangrove food webs. Few studies have been conducted in mangrove fish predators to investigate interpopulation trophic niches and ontogenetic shifts. Using stable isotope analysis and two complementary approaches, the authors investigated trophic niche patterns within and between two ontogenetic groups (juveniles and sub-adults) of a generalist predator (Acentrogobius viridipunctatus) in four mangroves with heterogeneous environmental conditions (e.g., tidal regimes, salinity fluctuations and mangrove tree community). The authors hypothesized that the trophic niche between populations would vary regionally and trophic position would increase consistently from juvenile to sub-adult stages. The results revealed that both δ¹³C and δ¹⁵N values varied greatly across populations and between ontogenetic groups, and complex spatio-ontogenetic variations were expressed by Layman's metrics. They also found some niche separation in space, which is most likely related to resource availability in spatially diverse ecosystems. In addition, trophic niche position increased consistently from juveniles to sub-adults, indicating ontogenetic feeding shifts. The isotopic plasticity index and Fulton's condition index also showed significant spatial-ontogenetic variation, which is consistent with optimal foraging theory. The findings highlight that trophic plasticity has a high adaptive value for mangrove fish predators in dynamic ecosystems.     

Testing the evolutionary constraints of metamorphosis: The ontogeny of head shape in Triturus newts

In vertebrates with complex, biphasic, life cycles, larvae have a distinct morphology and ecological preferences compared to metamorphosed juveniles and adults. In amphibians, abrupt and rapid metamorphic changes transform aquatic larvae to terrestrial juveniles. The main aim of this study is to test whether, relative to larval stages, metamorphosis (1) resets the pattern of variation between ontogenetic stages and species, (2) constrains intraspecific morphological variability, and (3) similar to the “hour‐glass” model reduces morphological disparity. We explore postembryonic ontogenetic trajectories of head shape (from hatching to completed metamorphosis) of two well‐defined, morphologically distinct Triturus newts species and their F1 hybrids. Variation in head shape is quantified and compared on two levels: dynamic (across ontogenetic stages) and static (at a particular stage). Our results show that the ontogenetic trajectories diverge early during development and continue to diverge throughout larval stages and metamorphosis. The high within‐group variance and the largest disparity level (between‐group variance) characterize the metamorphosed stage. Hence, our results indicate that metamorphosis does not canalize head shape variation generated during larval development and that metamorphosed phenotype is not more constrained relative to larval ones. Therefore, metamorphosis cannot be regarded as a developmental constraint, at least not for salamander head shape.     

Growth energetics in relation to temperature of the larvae of Rhopaea verreauxi (Coleoptera: Scarabaeidae)

Summary Instantaneous energy budgets were constructed at a range of constant temperatures (7.5°–27.5°C) for the larval stages of the scarabaeid Rhopaea verreauxi. It was found that as larvae increased in size the temperature optima/maxima for the components of the energy budget shifted to lower temperatures. Also, as larvae increased in size the instantaneous assimilation efficiency (A/C) decreased and the temperature range over which energy could be assimilated narrowed. Within this narrowing range, temperature was found to have an increasingly greater influence upon A/C. This was attributed to its influence upon the post-consumption energetics processes rather than upon consumption itself. The instantaneous net production efficiency (P/A) also decreased with increasing body size. Also, the temperature range over which assimilated energy could be partitioned to growth production became narrower as body size increased. These findings are discussed in relation to those of other energy budget studies. Some comment is made on the importance of temperature acclimation in studies such as this, and on the relation of energetics conversion efficiencies to ectothermy and endothermy and to trophic status. It was concluded that in terms of instantaneous conversion efficiences R. verreauxi could be described as a typical ectothermic herbivore, a moderately efficient converter.     

Direct Coupling of Action Potential Generation in Cells of a Higher Plant (Cucurbita pepo) with the Operation of an Electrogenic Pump

Changes in membrane potential (E _m) were investigated during action potential (AP) generation by excitable cells in bundle parenchyma of 2-week-old pumpkin (Cucurbita pepo L.) seedlings. APs were evoked by gradual cooling from 21 to 6°C at a rate of 1.3–1.5°C/min. Changes in E _m were measured with standard microelectrode technique. The plots of the function dE _m/dt = f(E _m) were obtained from experimental data by numerical differentiation of E _m records. The depolarization proceeded as a one-stage process. Conversely, AP repolarization comprised two stages, distinguished by specific dynamics of dE _m /dt. The second stage of repolarization occurred on a larger scale of E _m and was more sensitive to temperature than the first one. It is supposed that the second stage of repolarization during AP is related to the operation of electrogenic H⁺-pump in the excitable membrane. The scheme of AP generation in higher plant cells is suggested; it foresees the involvement in AP generation of both passive and active mechanisms of electrogenesis.