Damage and protection of the photosynthetic apparatus from UV-B radiation. I. Effect of ascorbate

In this work, the effect of the exogenously added ascorbate (Asc) against the UV-B inhibition of the photosystem II (PSII) functions in isolated pea thylakoid membranes was studied. The results reveal that Asc decreases the UV-B induced damage of the donor and the acceptor side of PSII during short treatment up to 60 min. The exogenous Asc exhibits a different UV-protective effect on PSII centers in grana and stroma lamellae, as the effect is more pronounced on the PSIIβ centers in comparison to PSIIα centers. Data also suggest that one of the possible protective roles of the Asc in photosynthetic membranes is the modification of the oxygen-evolving complex by influence on the initial S₀–S₁ state distribution in the dark.     

Validation of a Chronotype Questionnaire Including an Amplitude Dimension

The aim of this paper was to validate a French version of the Chronotype Questionnaire (Ogińska, 2011, Pers. Individ. Dif. 50:1039–1043), which represents an interesting novelty in the psychometric assessment of chronotype, because it comprises not only an assessment of the morningness-eveningness (ME) dimension, but also a distinctness (DI) dimension (i.e., amplitude), which represents the range of diurnal variation. In study 1, we aimed to confirm the structure of the Chronotype Questionnaire, with two different samples, young adults (n?=?338, mean?±?SD?=?18.70?±?1.12?yrs, 244 men and 94 women) and old adults (n?=?477, mean?±?SD?=?55.92?±?11.9?yrs, 168 men and 310 women). The confirmatory factor analysis (CFA) indicated a poor fit in both samples as well as in the whole sample, which could be due to some inconsistencies in the original instrument, above all in the distinctness dimension. We therefore decided to revise the Chronotype Questionnaire, keeping the ME dimension, but refining the DI dimension. In study 2, with a new sample of 197 participants (mean?±?SD?=?22.71?±?2.23?yrs, 105 men and 92 women), we examined the factor structure of the revised scale containing 18 items. The resulting questionnaire contained 16 items (i.e., 8 items on each scale), with item factor loadings higher than .45. In study 3, we aimed to confirm the factor structure of the instrument developed in study 2 as well as to examine its convergent validity, with a new sample of 158 participants (mean?±?SD?=?55.92?±?11.9?yrs, 97 men and 61 women). Results of the CFA showed that a good fit of the model could be obtained with 16 items in the questionnaire. The new questionnaire derived from the original Chronotype Questionnaire was from now on called the Caen Chronotype Questionnaire (CCQ). Convergence validity was obtained with the Horne and Östberg questionnaire and the ME scale of the CCQ, showing a negative significant relationship (r?=??.82). The CCQ showed promising psychometric qualities, and further research should aim to combine it with physiological variables.     

Succession and physiological health of freshwater microalgal fouling in a Tasmanian hydropower canal

Freshwater microalgal biofouling in hydropower canals in Tarraleah, Tasmania, is dominated by a single diatom species, Gomphonema tarraleahae. The microfouling community is under investigation with the aim of reducing its impact on electricity generation. Species succession was investigated using removable glass slides. Fouled slides were examined microscopically and for chlorophyll a biomass. Chl a biomass increased steeply after 8 weeks (0.09–0.87 mg m^?2), but increased much earlier on slides surrounded by a biofouled inoculum. Succession began with low profile diatoms such as Tabellaria flocculosa, progressing to stalked diatoms such as Gomphonema spp. and Cymbella aspera. Few chlorophytes and no filamentous algae were present. Pulse amplitude modulated fluorometry was used to measure the physiological health of fouling on the canal wall. Maximum quantum yield (F _v/F _m) measurements were consistently <0.18, indicating that the fouling mat consisted of dead or dying algae. The succession and physiological health of cells in the fouling community has broad implications for mitigation techniques used.     

Intact rat superior mesenteric artery endothelium is an electrical syncytium and expresses strong inward rectifier K+ conductance

Background and purpose

Vascular endothelial and smooth muscle cell phenotypes may change dramatically after isolation and in cell cultures. This study was designed to investigate gap junctions coupling in an integrated intact preparation and to test if K_IR channels modulate resting membrane conductance in “in situ” endothelial cells (EC), and acetylcholine (ACh)-evoked relaxation of the rat superior mesenteric artery.

Experimental approach

Whole cell blind patch recordings of ionic currents from in situ EC, dye-coupling experiments, and functional studies were performed in rat superior mesenteric artery.

Key results

EC were dye-coupled through gap junctions. 18β-glycyrretinic acid (25 μM) decreased outward and inward currents, the 80% decay of time and time constant of the capacitative transients, capacitance, and increased input resistance. Barium chloride (30 μM) decreased resting and ACh-evoked inward currents, the sensitivity of ACh-evoked relaxation, and decreased both the sensitivity and the maximal relaxation to S-nitroso-N-acetyl penicillamine in arteries with, but not in arteries without endothelium.

Conclusions

The present results suggest that the EC layer of this large artery is electrically coupled, and that K_IR channels regulate resting inward conductance, hence suggesting that they are of importance for resting membrane potential in in situ EC. Moreover, EC K_IR channels are involved in ACh-evoked relaxation.     

Exploring the relationship between flapping behaviour and accelerometer signal during ascending flight,and a new approach to calibration

We understand little about the energetic costs of flight in free-ranging birds, in part because current techniques for estimating flight energetics in the wild are limited. Accelerometry is known to estimate energy expenditure through body movement in terrestrial animals, once calibrated using a treadmill with chamber respirometry. The flight equivalent, a wind tunnel with mask respirometry, is particularly difficult to instigate, and has not been applied to calibrate accelerometry. We take the first steps in exploring a novel method for calibrating accelerometers with flight energy expenditure. We collected accelerometry data for Harris's Hawks Parabuteo unicinctus flying to varying heights up to 4.1 m over a small horizontal distance; the mechanical energy expended to gain height can be estimated from physical first principles. The relationship between accelerometry and mechanical energy expenditure was strong, and while a simple wing flapping model confirmed that accelerometry is sensitive to both changes in wing beat amplitude and frequency, the relationship was explained predominately by changes in wing beat frequency, and less so by changes in amplitude. Our study provides initial, positive evidence that accelerometry can be calibrated with body power using climbing flights, potentially providing a basis for estimating flapping flight metabolic rate at least in situations of altitude gain.     

Photosynthetic activity in two heteromorphic life‐history stages of a freshwater red alga,Thorea gaudichaudii (Thoreales) from Japan,in response to an irradiance and temperature gradient

We determined the effect of irradiance and temperature on the photosynthesis of two heteromorphic life‐history stages of an endangered freshwater red alga, Thorea gaudichaudii (Thoreales) by laboratory and field measurements. Net oxygenic photosynthesis–irradiance models of macroscopic and microscopic life‐history stages revealed similar low irradiance‐adapted responses, with a compensation irradiance (E_c) of 6.71 and 2.56 μmol photons m^?2 s^?1 (4.30–9.13 and 0.13–7.19, 95% Bayesian prediction interval, BPI) and saturating irradiance (E_k) of 26.6 and 30.0 μmol photons m^?2 s^?1 (19.0–37.4 and 12.1–63.0, BPI), respectively. A temperature‐dependent model of net photosynthesis and dark respiration in macroscopic and microscopic stages also showed similar temperature responses, and the gross photosynthetic rate (GP_max), 3.54 and 6.34 μg O₂ g_ww^?1 min^?1 (3.10–3.99 and 5.31–8.21, BPI), was highest at 32.1 and 35.7°C (29.8–34.0 and 29.5–48.6, BPI). The maximum quantum yields (F _v/F _m) in macroscopic and microscopic stages were also similar in response with respect to temperature; however, it was somewhat steady at low temperatures with the highest value of 0.54 and 0.62 (0.54–0.55 and 0.61–0.63, BPI) at 17.8 and 15.0°C (16.7–18.8 and 12.3–17.1, BPI). The effective quantum yield (Φ _PSII) in macroscopic and microscopic stages was also negatively correlated with irradiance, which decreased after 12 h of continuous exposure to 50 (low) and 1000 (high) μmol photons m^?2 s^?1 at 12 and 22°C. Large declines of Φ _PSII and subsequent failure of F _v/F _m recovery were particularly enhanced at high irradiance, signifying photoinhibition. Diurnal change of Φ _PSII and incident irradiance of the macroscopic stage under the field measurement revealed the midday depression of Φ _PSII; however, there was little direct sunlight due to shading by the trees, and algae were occurring in the shaded locations in the freshwater spring.     

Causes of slowing‐down seasonal CO2 amplitude at Mauna Loa

Changing amplitude of the seasonal cycle of atmospheric CO₂ (SCA) in the northern hemisphere is an emerging carbon cycle property. Mauna Loa (MLO) station (20°N, 156°W), which has the longest continuous northern hemisphere CO₂ record, shows an increasing SCA before the 1980s (p < .01), followed by no significant change thereafter. We analyzed the potential driving factors of SCA slowing‐down, with an ensemble of dynamic global vegetation models (DGVMs) coupled with an atmospheric transport model. We found that slowing‐down of SCA at MLO is primarily explained by response of net biome productivity (NBP) to climate change, and by changes in atmospheric circulations. Through NBP, climate change increases SCA at MLO before the 1980s and decreases it afterwards. The effect of climate change on the slowing‐down of SCA at MLO is mainly exerted by intensified drought stress acting to offset the acceleration driven by CO₂ fertilization. This challenges the view that CO₂ fertilization is the dominant cause of emergent SCA trends at northern sites south of 40°N. The contribution of agricultural intensification on the deceleration of SCA at MLO was elusive according to land–atmosphere CO₂ flux estimated by DGVMs and atmospheric inversions. Our results also show the necessity to adequately account for changing circulation patterns in understanding carbon cycle dynamics observed from atmospheric observations and in using these observations to benchmark DGVMs.     

THE SIGNIFICANCE OF MULTI-NOTE ADVERTISEMENT CALLS IN A REED FROG,HYPEROLIUS TUBERILING UIS

ABSTRACT

The reed frog Hyperolius tuberilinguis is a prolonged breeder with an advertisement call that varies in complexity from one to six click notes. Call complexity increases with chorus size, but calls containing more than three notes are rare. In playback experiments to males, subjects responded by increasing the complexity of their calls, without closely matching the stimulus and rarely exceeding the stimulus in complexity. Stimuli less complex than their own evoked a reduction in complexity. Call repetition rate remained unchanged in the responses. In two-choice phonotaxis experiments, females discriminated against one-note calls, and two- and three-note calls were the most attractive. Males thus adjust their calling in the presence of neighbours to a pattern most preferred by females. Calls of higher complexity may be more easily detected or located by females in the noisy environment of a chorus.     

Intertidal population genetic dynamics at a microgeographic seascape scale

The intertidal community is among the most physically harsh niches on earth, with highly heterogeneous environmental and biological factors that impose strong habitat selection on population abundance, genetic connectivity and ecological adaptation of organisms in nature. However, most genetic studies to date have concentrated on the influence of basin-wide or regional marine environments (e.g. habitat discontinuities, oceanic currents and fronts, and geographic barriers) on spatiotemporal distribution and composition of intertidal invertebrates having planktonic stages or long-distance dispersal capability. Little is known about sessile marine organisms (e.g. seaweeds) in the context of topographic tidal gradients and reproductive traits at the microgeographic scale. In this issue of Molecular Ecology, Krueger-Hadfield et al. ( 2013a ) implemented an elaborate sampling strategy with red seaweed (Chondrus crispus) from a 90-m transect stand near Roscoff and comprehensively detected genome-scale genetic differentiation and biases in ploidy level. This study not only revealed that tidal height resulted in genetic differentiation between high- and low-shore stands and restricted the genetic exchange within the high-shore habitat, but also demonstrated that intergametophytic nonrandom fertilization in C. crispus can cause significant deviation from Hardy–Weinberg equilibrium. Such new genetic insights highlight the importance of microgeographic genetic dynamics and life history characteristics for better understanding the evolutionary processes of speciation and diversification of intertidal marine organisms.