Time course of color induction in the honeybee

Color induction in the honeybee is investigated in color discrimination experiments. An individual bee walks in a dark arena and is trained to a self-luminant stimulus presented from below. In the dual-choice tests the dark background is replaced by a colored induction stimulus. Choice behavior is recorded by TV camera and analyzed by computer. Successive color induction is separated from simultaneous induction by analysis of the walking paths. Only successive color induction occurs. Simultaneous effects are not observed. That is a stimulus acts as a color inducing stimulus only when the bee crosses this stimulus. Thus, the color perceived by a given eye region is found to be dependent on the viewing history, but not on the stimuli presented simultaneously on neighboring parts of the retina. Color induction in the honeybee described in terms of selective sensitivity decrease (adaptation) does not explain all behavioral effects induced by the stimulus. The time course of successive color induction is calculated from the exposure times to the induction stimulus and from the choice behavior. The data suggest that color induction is complete after a few seconds. Photoreceptor adaptation is sufficient to explain the observed time course.     

Evaluating regional water security through a freshwater ecosystem service flow model: A case study in Beijing-Tianjian-Hebei region,China

Freshwater ecosystem service is essential to human’s survival and development. Many studies have documented the spatial differences in the supply and demand of ecosystem services and proposed the concept of ecosystem services flows. However, few studies characterize freshwater ecosystem service flow quantitatively. Therefore, our paper aims to quantify the effects of freshwater ecosystem service flow on downstream areas. We developed a freshwater ecosystem service flow model and applied it in the Beijing–Tianjin–Hebei (BTH) region, China, for the year of 2000, 2005, and 2010. We assessed the regional water security with an improved freshwater security index by integrating freshwater service provision, consumption and flow; and found that most areas of the BTH region (69.2%) were affected by upstream freshwater flows. The areas achieving water security in the region also expanded to 66.9%, 66.1%, and 71.3%, which were 6.4%, 6.8% and 5.7% increments compared to no-flow situation, in 2000, 2005 and 2010, respectively. Setting quota for human water consumption is suggested to further improve water security. These results highlight the need to fully understand the connections between distant freshwater ecosystem service provision and local freshwater ecosystem service consumption. This approach may also help managers to choose more sustainable strategies for critical freshwater resource management across different regions.     

Spectral shifts of mammalian ultraviolet-sensitive pigments (short wavelength-sensitive opsin 1) are associated with eye length and photic niche evolution

Retinal opsin photopigments initiate mammalian vision when stimulated by light. Most mammals possess a short wavelength-sensitive opsin 1 (SWS1) pigment that is primarily sensitive to either ultraviolet or violet light, leading to variation in colour perception across species. Despite knowledge of both ultraviolet- and violet-sensitive SWS1 classes in mammals for 25 years, the adaptive significance of this variation has not been subjected to hypothesis testing, resulting in minimal understanding of the basis for mammalian SWS1 spectral tuning evolution. Here, we gathered data on SWS1 for 403 mammal species, including novel SWS1 sequences for 97 species. Ancestral sequence reconstructions suggest that the most recent common ancestor of Theria possessed an ultraviolet SWS1 pigment, and that violet-sensitive pigments evolved at least 12 times in mammalian history. We also observed that ultraviolet pigments, previously considered to be a rarity, are common in mammals. We then used phylogenetic comparative methods to test the hypotheses that the evolution of violet-sensitive SWS1 is associated with increased light exposure, extended longevity and longer eye length. We discovered that diurnal mammals and species with longer eyes are more likely to have violet-sensitive pigments and less likely to possess UV-sensitive pigments. We hypothesize that (i) as mammals evolved larger body sizes, they evolved longer eyes, which limited transmittance of ultraviolet light to the retina due to an increase in Rayleigh scattering, and (ii) as mammals began to invade diurnal temporal niches, they evolved lenses with low UV transmittance to reduce chromatic aberration and/or photo-oxidative damage.     

Correcting for finite spatial scales of self-similarity when calculating fractal dimensions of real-world structures

Fractal geometry is a potentially valuable tool for quantitatively characterizing complex structures. The fractal dimension (D) can be used as a simple, single index for summarizing properties of real and abstract structures in space and time. Applications in the fields of biology and ecology range from neurobiology to plant architecture, landscape structure, taxonomy and species diversity. However, methods to estimate the D have often been applied in an uncritical manner, violating assumptions about the nature of fractal structures. The most common error involves ignoring the fact that ideal, i.e. infinitely nested, fractal structures exhibit self-similarity over any range of scales. Unlike ideal fractals, real-world structures exhibit self-similarity only over a finite range of scales.Here we present a new technique for quantitatively determining the scales over which real-world structures show statistical self-similarity. The new technique uses a combination of curve-fitting and tests of curvilinearity of residuals to identify the largest range of contiguous scales that exhibit statistical self-similarity. Consequently, we estimate D only over the statistically identified region of self-similarity and introduce the finite scale- corrected dimension (FSCD). We demonstrate the use of this method in two steps. First, using mathematical fractal curves with known but variable spatial scales of self-similarity (achieved by varying the iteration level used for creating the curves), we demonstrate that our method can reliably quantify the spatial scales of self-similarity. This technique therefore allows accurate empirical quantification of theoretical Ds. Secondly, we apply the technique to digital images of the rhizome systems of goldenrod (Solidago altissima). The technique significantly reduced variations in estimated fractal dimensions arising from variations in the method of preparing digital images. Overall, the revised method has the potential to significantly improve repeatability and reliability for deriving fractal dimensions of real-world branching structures.     

Photopigments underlying color vision in ringtail lemurs (Lemur catta) and brown lemurs (Eulemur fulvus)

A recent examination of color vision in the ringtail lemur produced evidence that these prosimians could make color discriminations consistent with a diagnosis of trichromatic color vision. However, it was unclear if this behavior reflected the presence of three classes of cone or whether lemurs might be able to utilize signals from rods in conjunction with those from only two classes of cone. To resolve that issue, spectral sensitivity functions were obtained from ringtail lemurs (Lemur catta) and brown lemurs (Eulemur fulvus) using a noninvasive electrophysiological procedure, electroretinographic flicker photometry. Results from experiments involving chromatic adaptation indicate that these lemurs routinely have only a single class of cone photopigment in the middle to long wavelengths (peak sensitivity of about 545 nm); they also have a short-wavelengthsensitive cone pigment with peak of about 437 nm. The earlier behavioral results are suggested to have resulted from the ability of lemurs to jointly utilize signals from rods and cones. The cone pigment complements of these lemurs differ distinctly from those seen among the anthropoids. © 1993 Wiley-Liss, Inc.     

Cephalopod dynamic camouflage: bridging the continuum between background matching and disruptive coloration

Individual cuttlefish, octopus and squid have the versatile capability to use body patterns for background matching and disruptive coloration. We define—qualitatively and quantitatively—the chief characteristics of the three major body pattern types used for camouflage by cephalopods: uniform and mottle patterns for background matching, and disruptive patterns that primarily enhance disruptiveness but aid background matching as well. There is great variation within each of the three body pattern types, but by defining their chief characteristics we lay the groundwork to test camouflage concepts by correlating background statistics with those of the body pattern. We describe at least three ways in which background matching can be achieved in cephalopods. Disruptive patterns in cuttlefish possess all four of the basic components of ‘disruptiveness’, supporting Cott''s hypotheses, and we provide field examples of disruptive coloration in which the body pattern contrast exceeds that of the immediate surrounds. Based upon laboratory testing as well as thousands of images of camouflaged cephalopods in the field (a sample is provided on a web archive), we note that size, contrast and edges of background objects are key visual cues that guide cephalopod camouflage patterning. Mottle and disruptive patterns are frequently mixed, suggesting that background matching and disruptive mechanisms are often used in the same pattern.     

Monte Carlo-based assessment of the trade-off between spatial resolution,field-of-view and scattered radiation in the variable resolution X-ray CT scanner

ObjectiveThe purpose of this work is to evaluate the impact of optimization of magnification on performance parameters of the variable resolution X-ray (VRX) CT scanner.MethodsA realistic model based on an actual VRX CT scanner was implemented in the GATE Monte Carlo simulation platform. To evaluate the influence of system magnification, spatial resolution, field-of-view (FOV) and scatter-to-primary ratio of the scanner were estimated for both fixed and optimum object magnification at each detector rotation angle. Comparison and inference between these performance parameters were performed angle by angle to determine appropriate object position at each opening half angle.ResultsOptimization of magnification resulted in a trade-off between spatial resolution and FOV of the scanner at opening half angles of 90°–12°, where the spatial resolution increased up to 50% and the scatter-to-primary ratio decreased from 4.8% to 3.8% at a detector angle of about 90° for the same FOV and X-ray energy spectrum. The disadvantage of magnification optimization at these angles is the significant reduction of the FOV (up to 50%). Moreover, magnification optimization was definitely beneficial for opening half angles below 12° improving the spatial resolution from 7.5 cy/mm to 20 cy/mm. Meanwhile, the FOV increased by more than 50% at these angles.ConclusionIt can be concluded that optimization of magnification is essential for opening half angles below 12°. For opening half angles between 90° and 12°, the VRX CT scanner magnification should be set according to the desired spatial resolution and FOV.     

To aggregate or not? Capturing the spatio-temporal complexity of the thermal regime

Freshwater stream systems are under immense pressure from various anthropogenic impacts, including climate change. Stream systems are increasingly being altered by changes to the magnitude, timing, frequency, and duration of their thermal regimes, which will have profound impacts on the life-history dynamics of resident biota within their home range. Although temperature regimes have a significant influence on the biology of instream fauna, large spatio-temporal temperature datasets are often reduced to a single metric at discrete locations and used to describe the thermal regime of a system; potentially leading to a significant loss of information crucial to stream management. Models are often used to extrapolate these metrics to unsampled locations, but it is unclear whether predicting actual daily temperatures or an aggregated metric of the temperature regime best describes the complexity of the thermal regime. We fit spatial statistical stream-network models (SSNMs), random forest and non-spatial linear models to stream temperature data from the Upper Condamine River in QLD, Australia and used them to semi-continuously predict metrics describing the magnitude, duration, and frequency of the thermal regime through space and time. We compared both daily and aggregated temperature metrics and found that SSNMs always had more predictive ability than the random forest models, but both models outperformed the non-spatial linear model. For metrics describing thermal magnitude and duration, aggregated predictions were most accurate, while metrics describing the frequency of heating events were better represented by metrics based on daily predictions generated using a SSNM. A more comprehensive representation of the spatio-temporal thermal regime allows researchers to explore new spatio-temporally explicit questions about the thermal regime. It also provides the information needed to generate a suite of ecologically meaningful metrics capturing multiple aspects of the thermal regime, which will increase our scientific understanding of how organisms respond to thermal cues and provide much-needed information for more effective management actions.     

Sugar‐feeding status alters biting midge photoattraction

The biting midge Culicoides sonorensis Wirth and Jones (Diptera: Ceratopogonidae) transmits pathogens to both livestock and wildlife. Biting midge surveillance relies heavily on light traps for collection; however, little is known about the light spectra preferences of C. sonorensis midges. A light assay arena was constructed and light‐emitting diodes (LEDs) of various light spectra were used as light sources to evaluate midge photoattraction. A comparison of responses to light spectra indicated the highest proportions of C. sonorensis were attracted to ultraviolet (UV) light and that midges differentiated 10‐nm differences in wavelength. Stronger intensities of UV light resulted in greater attraction. Midges exhibited both sugar‐seeking and escape behaviours under different conditions of sugar supplementation before and during the experiment. These behaviours occurred with lights of 355 nm and 365 nm in wavelength. Based on the results of this study, the attraction of C. sonorensis to light traps can be improved through the use of bright LEDs at 355 nm or 365 nm.