Biomass compensation: Behind the diversity gradients of tidepool fishes

Species richness is unevenly distributed on the Earth, with biodiversity gradients of various spatial scales supposedly being affected by abiotic as well as biotic factors including community traits such as body size spectra and relative abundance patterns. To explore large-scale spatial variation in species diversity and their processes, tidepool fish communities were investigated through an intensive field work conducted on 55 shore sites in south-western Japan. Multiple ecological measures were taken into account to assess changes in local community structures with changes in the number of species. Biomass (total fish wet weight) per unit area showed no systematic change with latitude, while taxa richness and number of individuals tended to increase toward lower latitudes. In addition, median fish body weight scaled positively with latitude, which was more conspicuous in Blenniidae than in Gobiidae. The latitudinal gradient of diversity in tidepool fish assemblages appears to be characterized by partitioning of total biomass that tends to stay constant across latitudes, suggesting the phenomenon of “biomass compensation” whereby body size and abundance/diversity change in opposite directions with latitude. Our study highlights that biomass compensation can be part of processes involved in generating gradients of species richness even without an apparent energy/resource gradient.     

Biosynthesis of mono- and sesqui-terpenes in peppermint from glucose-C and CO2

Labeled glucose and CO₂ are more efficient precursors of monoterpenes in peppermint (Mentha piperita L.) cuttings than is mevalonate, which is the best precursor of sesquiterpenes in this plant. Metabolic turnover of the labeled monoterpenes was observed, in agreement with previous observations. Pulegone derived from ¹⁴CO₂ after 1, 3, 6, 9 and 12 hr of incubation was chemically degraded, and in every case at least 90% of the ¹⁴C-label was found in the seven-carbon fragment containing the isopentenyl pyrophosphate-derived portion of the molecule. The isopropylidene side chain, containing three carbons hypothetically derived from dimethylallyl pyrophosphate, was found to be essentially unlabeled. The results suggest that an endogenous dimethylallyl pyrophosphate pool participates in monoterpene biosynthesis, much as earlier work had suggested that a similar pool participates in sesquiterpene biosynthesis in this plant. These findings are of particular interest because it appears, based on the differential utilization of labeled precursors, that monoterpenes and sesquiterpenes are produced at separate sites in the plant.     

Size-assortative nest preference in a paternal brooding blenny Rhabdoblennius ellipes (Jordan & Starks)

Field and laboratory studies were conducted to clarify the processes contributing to the size-assortative nest use by males of a paternal brooding blenny Rhabdoblennius ellipes . The use of natural and artificial nests by males in the field was highly size-assortative; males used smaller nests even when larger nests were available. Aquarium nest choice experiments without a competitive male strongly suggested that the size-assortative nest use by males is not the result of male–male competition for larger nests, but male preference for size-matched nests. Males were likely to choose nests on the basis of the nest entrance size rather than nest length and volume, suggesting that the size-assortative nest preference in this species is an adaptation to predation pressure against eggs and resident males.     

The Role of Allochthonous Inputs of Dissolved Organic Carbon on the Hypolimnetic Oxygen Content of Reservoirs

Hypolimnetic oxygen content in lentic ecosystems has traditionally been modeled as a function of variables measured at the epilimnion, or that are supposed to drive epilimnetic processes, like total phosphorus load. However, in man-made reservoirs the river inflow can plunge into deep layers, directly linking the hypolimnion with the surrounding watershed. In these circumstances, organic matter carried by the river can influence the hypolimnetic oxygen content without important intervention of epilimnetic processes. Taking long-term data from two reservoirs in Spain, we applied an empirical regression approach to show that the dissolved organic matter carried by the river is the main driver shaping the hypolimnetic oxygen content. By contrast, typical variables commonly included in the modeling of the oxygen content in the hypolimnion (nutrient concentrations, chlorophyll a, and dissolved organic carbon measured in the water column) did not show any significant correlation. Interpretations from this regression approach were supported by a comparison between the monthly oxygen consumption in the hypolimnion and the monthly dissolved organic carbon load from the river inflow. We also revisited the prediction of the year-to-year variability of the Nürnberg’s anoxic factor in four reservoirs from Spain and the USA, explicitly including the allochthonous sources in the equations. These sources were significant predictors of the anoxic factor, especially in those systems subject to relatively high human impact. Thus, effects of allochthonous dissolved organic carbon should always be considered in empirical modeling and management of reservoir hypolimnetic processes related to oxygen content (for example, anoxia, nutrient internal loading, or phosphorus cycle resilience).     

Feedback regulation of photosynthetic electron transport by NADP(H) redox poise

When plants experience an imbalance between the absorption of light energy and the use of that energy to drive metabolism, they are liable to suffer from oxidative stress. Such imbalances arise due to environmental conditions (e.g. heat, chilling or drought), and can result in the production of reactive oxygen species (ROS). Here, we present evidence for a novel protective process — feedback redox regulation via the redox poise of the NADP(H) pool. Photosynthetic electron transport was studied in two transgenic tobacco (Nicotiana tabacum) lines — one having reduced levels of ferredoxin NADP⁺-reductase (FNR), the enzyme responsible for reducing NADP⁺, and the other reduced levels of glyceraldehyde 3-phosphate dehydrogenase (GAPDH), the principal consumer of NADPH. Both had a similar degree of inhibition of carbon fixation and impaired electron transport. However, whilst FNR antisense plants were obviously stressed, with extensive bleaching of leaves, GAPDH antisense plants showed no visible signs of stress, beyond having a slowed growth rate. Examination of electron transport in these plants indicated that this difference is due to feedback regulation occurring in the GAPDH but not the FNR antisense plants. We propose that this reflects the occurrence of a previously undescribed regulatory pathway responding to the redox poise of the NADP(H) pool.     

Pathways controlling dNTP pools to maintain genome stability

Artificially modified nucleotides, in the form of nucleoside analogues, are widely used in the treatment of cancers and various other diseases, and have become important tools in the laboratory to characterise DNA repair pathways. In contrast, the role of endogenously occurring nucleotide modifications in genome stability is little understood. This is despite the demonstration over three decades ago that the cellular DNA precursor pool is orders of magnitude more susceptible to modification than the DNA molecule itself. More recently, underscoring the importance of this topic, oxidation of the cellular nucleotide pool achieved through targeting the sanitation enzyme MTH1, appears to be a promising anti-cancer strategy. This article reviews our current understanding of modified DNA precursors in genome stability, with a particular focus upon oxidised nucleotides, and outlines some important outstanding questions.     

Mitochondrial superoxide mediates labile iron level: evidence from Mn-SOD-transgenic mice and heterozygous knockout mice and isolated rat liver mitochondria

Superoxide is the main reactive oxygen species (ROS) generated by aerobic cells primarily in mitochondria. It is also capable of producing other ROS and reactive nitrogen species (RNS). Moreover, superoxide has the potential to release iron from its protein complexes. Unbound or loosely bound cellular iron, known as labile iron, can catalyze the formation of the highly reactive hydroxyl radical. ROS/RNS can cause mitochondrial dysfunction and damage. Manganese superoxide dismutase (Mn-SOD) is the chief ROS-scavenging enzyme and thereby the primary antioxidant involved in protecting mitochondria from oxidative damage. To investigate whether mitochondrial superoxide mediates labile iron in vivo, the levels of labile iron were determined in the tissues of mice overexpressing Mn-SOD and heterozygous Mn-SOD-knockout mice. Furthermore, the effect of increased mitochondrial superoxide generation on labile iron levels was determined in isolated rat liver mitochondria exposed to various electron transport inhibitors. The results clearly showed that increased expression of Mn-SOD significantly lowered the levels of labile iron in heart, liver, kidney, and skeletal muscle, whereas decreased expression of Mn-SOD significantly increased the levels of labile iron in the same organs. In addition, the data showed that peroxidative damage to membrane lipids closely correlated with the levels of labile iron in various tissues and that altering the status of Mn-SOD did not alter the status of other antioxidant systems. Results also showed that increased ROS production in isolated liver mitochondria significantly increased the levels of mitochondrial labile iron. These findings constitute the first evidence suggesting that mitochondrial superoxide is capable of releasing iron from its protein complexes in vivo and that it could also release iron from protein complexes contained within the organelle.