Multiple spectral inputs improve motion discrimination in the Drosophila visual system

Color and motion information are thought to be channeled through separate neural pathways, but it remains unclear whether and how these pathways interact to improve motion perception. In insects, such as Drosophila, it has long been believed that motion information is fed exclusively by one spectral class of photoreceptor, so-called R1 to R6 cells; whereas R7 and R8 photoreceptors, which exist in multiple spectral classes, subserve color vision. Here, we report that R7 and R8 also contribute to the motion pathway. By using electrophysiological, optical, and behavioral assays, we found that R7/R8 information converge with and shape the motion pathway output, explaining flies' broadly tuned optomotor behavior by its composite responses. Our results demonstrate that inputs from photoreceptors of different spectral sensitivities improve motion discrimination, increasing robustness of perception.     

Co-optimal distribution of leaf nitrogen and hydraulic conductance in plant canopies

Leaf properties vary significantly within plant canopies, due to the strong gradient in light availability through the canopy, and the need for plants to use resources efficiently. At high light, photosynthesis is maximized when leaves have a high nitrogen content and water supply, whereas at low light leaves have a lower requirement for both nitrogen and water. Studies of the distribution of leaf nitrogen (N) within canopies have shown that, if water supply is ignored, the optimal distribution is that where N is proportional to light, but that the gradient of N in real canopies is shallower than the optimal distribution. We extend this work by considering the optimal co-allocation of nitrogen and water supply within plant canopies. We developed a simple 'toy' two-leaf canopy model and optimized the distribution of N and hydraulic conductance (K) between the two leaves. We asked whether hydraulic constraints to water supply can explain shallow N gradients in canopies. We found that the optimal N distribution within plant canopies is proportional to the light distribution only if hydraulic conductance, K, is also optimally distributed. The optimal distribution of K is that where K and N are both proportional to incident light, such that optimal K is highest to the upper canopy. If the plant is constrained in its ability to construct higher K to sun-exposed leaves, the optimal N distribution does not follow the gradient in light within canopies, but instead follows a shallower gradient. We therefore hypothesize that measured deviations from the predicted optimal distribution of N could be explained by constraints on the distribution of K within canopies. Further empirical research is required on the extent to which plants can construct optimal K distributions, and whether shallow within-canopy N distributions can be explained by sub-optimal K distributions.     

Defining the forest landowner’s utility–loss compensative subsidy level for a biodiversity object

New, cost efficient and voluntary biodiversity protection tools may require bidding price definition on part of the seller. Both the seller and the buyer can withdraw from negotiations if they find that the conditions of the protection contract are unacceptable. However, it can be very difficult for non-industrial, private landowners to define the bidding price demand for their biodiversity objects. The terms of the protection contract, the production possibilities of the forest holding, the forest owner’s multiple forest management goals and their substitutability, and the possible monetary subsidy paid for biodiversity protection should all be simultaneously taken into account when estimating the owner’s price demand for protecting the biodiversity object. This study strives to provide relief in resolving this problem by presenting an approach in which the landowner’s utility–loss compensative subsidy can be defined based on the owner’s forest-holding level utility function and the production possibilities of the holding. The properties of the approach are illustrated by four planning cases in which the length of the protection period (permanent or 20-year temporary protection) and the holding-level goals were varied. The utility functions of the cases were derived by selecting numeric goal variables for the goals, and by defining weights and sub-utility functions for these variables. Varying subsidies for protecting an old-growth spruce stand were included into the simulation of “No treatment” schedules for the examined stand, and the holding-level total utility was maximized for every price level. The utility–loss compensative subsidy was found when the holding-level total utility equaled the total utility achieved in the plan where the stand was regenerated. This subsidy, however, is not necessarily the exact price that the owner should ask from the buyer; all prices above the defined subsidy level will increase owner’s utility if the buyer accepts them. It was concluded that the presented approach provided consistent results in the four cases and that it thus offers valuable decision support for current biodiversity-protection programs.     

Temperature sensitivity of soil organic matter decomposition in southern and northern areas of the boreal forest zone

Much effort has been made to improve understanding of factors controlling the temperature dependence of soil organic matter (SOM) decomposition. The question of how soils formed in different geographical locations and conditions respond to temperature changes is still open. In addition to climate, residence times of soil organic matter are controlled by its decomposability and microbial community. In this work we hypothesized that the decomposition of SOM is adapted to the prevailing SOM quality and climatic conditions. This should result in different temperature vs. decomposition curves for northern and southern soils. We studied short-term temperature dependence of SOM decomposition near the northern and southern borders of the boreal forest zone using a Gaussian model. As carbon mineralization rate is driven by microbial activity, we focused on organic carbon fractions available to microbes and the size, composition and functioning of microbial communities in the soil. Despite differences in microbial community structure and behavior, similar amounts and qualities of the microbially available carbon led to similar temperature dependences of carbon mineralization in the north and south. The overall soil respiration rate level was higher in spruce forest sites than in pine forest sites irrespective of climate conditions. Our results do not mean that there is no risk of carbon losses from northern soils due to warming climate conditions. As temperature sensitivity of the decomposition increases with decreasing temperature regime, the proportional increase in the decomposition rate in northern latitudes might lead to significant carbon losses from the soils.     

Waves of larch budmoth outbreaks in the European alps

Spatially extended population models predict complex spatiotemporal patterns, such as spiral waves and spatial chaos, as a result of the reaction-diffusion dynamics that arise from trophic interactions. However, examples of such patterns in ecological systems are scarce. We develop a quantitative technique to demonstrate the existence of waves in Central European larch budmoth (Zeiraphera diniana Gn.) outbreaks. We show that these waves travel toward the northeast-east at 210 kilometers per year. A theoretical model involving a moth-enemy interaction predicts directional waves, but only if dispersal is directionally biased or habitat productivity varies across the landscape. Our study confirms that nonlinear ecological interactions can lead to complex spatial dynamics at a regional scale.     

Influence of age, site, and degenerative state on the speed of sound in equine articular cartilage

OBJECTIVE: To determine the speed of sound (SOS) in equine articular cartilage and investigate the influence of age, site in the joint, and cartilage degeneration on the SOS. SAMPLE POPULATION: Cartilage samples from 38 metacarpophalangeal joints of 38 horses (age range, 5 months to 22 years). PROCEDURE: Osteochondral plugs were collected from 2 articular sites of the proximal phalanx after the degenerative state was characterized by use of the cartilage degeneration index (CDI) technique. The SOS was calculated (ratio of needle-probe cartilage thickness to time of flight of the ultrasound pulse), and relationships between SOS value and age, site, and cartilage degeneration were evaluated. An analytical model of cartilage indentation was used to evaluate the effect of variation in true SOS on the determination of cartilage thickness and dynamic modulus with the ultrasound indentation technique. RESULTS: The mean SOS for all samples was 1,696 +/- 126 m/s. Age, site, and cartilage degeneration had no significant influence on the SOS in cartilage. The analytical model revealed that use of the mean SOS of 1,696 m/s was associated with maximum errors of 17.5% on cartilage thickness and 70% on dynamic modulus in an SOS range that covered 95% of the individual measurements. CONCLUSIONS AND CLINICAL RELEVANCE: In equine articular cartilage, use of mean SOS of 1,696 m/s in ultrasound indentation measurements introduces some inaccuracy on cartilage thickness determinations, but the dynamic modulus of cartilage can be estimated with acceptable accuracy in horses regardless of age, site in the joint, or stage of cartilage degeneration.     

Maintenance of flying squirrel habitat and timber harvest: a site-specific spatial model in forest planning calculations

Spatial and temporal continuity of resources often benefits both ecological and economic goals in landscape management. Consideration of multiple and conflicting goals is also needed to view the future production possibilities of forests in successful forest management. Our aim was to estimate the production potential of a planning area in Finland by examining different forest management strategies from ecological and economic perspectives using long-term forest planning calculations. Economic objectives referred to timber production, whereas ecological objectives were based on suitable habitats for arboreal Siberian flying squirrel (Pteromys volans). Suitable habitats were defined using an empirical site-specific model, which includes a spatial variable reflecting the availability of habitat within an individual’s activity area. Five alternative forest plans were worked out with different objectives for flying squirrel habitat and timber production. The alternative plans were compared with respect to values of objective variables at the end of the planning period of 60 years and against a production possibility frontier among net present value and flying squirrel habitat. Varying objective values in our analyses resulted from different utilization of production possibilities, and the changes were in line with the objectives used. The formation of flying squirrel habitat clusters in the landscape was enhanced, and it did not always incur severe reductions in harvestable timber volume. Possibilities to combine ecological and economic goals, both spatial and aspatial, in the planning process seems to be an encouraging alternative for the long-term forest management in the future.     

A literature-based study on the loss tangent of wood in connection with mechanical pulping

In mechanical pulping, wood is dynamically loaded, which causes large heat losses due to wood viscoelasticity. The heat losses depend on the loss tangent (tan δ) of wood. The loss tangent has a temperature-dependent behaviour, especially in the lignin glass transition region. The glass transition softens wood, and is therefore necessary for gentle mechanical pulping, but at the same time, the loss tangent shows a maximum called the α-peak. The transient peak depends on temperature, loading frequency and moisture content. The temperature where the peak is found can be lowered with chemical treatments, but they also increase the magnitude of the peak. Thermal treatment in the presence of water also increases the magnitude. The loss tangent of wood depends, amongst other things, on the chemical structure of lignin, width of cellulose crystals, microfibril angle, and extractives in the cell wall.