Intra-specific color variation is often underestimated by researchers, and among mammals, intra-specific differences in coloration are poorly documented for most species. The main goal of this study was to apply an objective color measurement methodology to the study of a specific problem: the detection, if any, of patterns of changes in the fur color of specimens of Akodon budini in relation to biological (i.e., sex) and environmental (i.e., season) variables. We hypothesize that coat color will be more homogeneous in males than in females and that coat color will be darker in winter than in summer, the latter being orange. We measured the pelage color on five points over the dorsal surface of 26 A. budini museum specimens using a spectroradiometer and a diffuse illumination cabin. We used Principal Component Analysis to describe the association between the color variables, sex and season, and each of the observations. We then used general linear models of Analysis of Variance to examine relationships between color data, season, and sex. The results clearly confirm the hypothesis related to seasonal coat color change but do not directly confirm the hypothesis related to changes in coat color in relation to sex, and we show the complexity of the studied pattern.In conclusion, undoubtedly, the studied variables should accordingly be considered when studying the coloration of specimens for characterization, identification and discrimination of different taxonomic units based on color.Keywords: Akodon budini, CIELab colour space, season, sex, spectroradiometer.Variação intraespecífica da cor da pelagem de uma espécie de pequeno roedor sul-americano ResumoVariação de cor intra-específica é muitas vezes subestimada pelos pesquisadores, e entre espécies de mamíferos, as diferenças intra-específicas na coloração são pouco conhecidas para a maioria das espécies. O principal objetivo deste estudo foi aplicar uma metodologia objetiva de medição de cor para o estudo de um problema específico: a detecção de padrões de mudanças na cor da pele de espécimes de Akodon budini em relação a variáveis biológicas (i.e., sexo) e ambientais (i.e., temporada), se houver. Nossa hipótese é que a cor da pelagem do sexo masculino será mais homogênea do que a de fêmeas e que a cor da pelagem do inverno vai ser mais escura do que a de verão, sendo esta última mais laranja. Medimos a cor da pelagem em cinco pontos sobre a superfície dorsal de 26 espécimes de museu de A. budini usando um espectroradiômetro e uma cabine de iluminação difusa. Usamos Análise de Componentes Principais para descrever a associação entre as variáveis de cor, sexo e temporada, e cada uma das observações. Em seguida, usamos modelos lineares gerais da Análise de Variância para verificar as relações entre os dados de cor, temporada, e sexo. Os resultados confirmam claramente a hipótese relacionada à mudança sazonal de cor da pelagem, mas não confirmam diretamente a hipótese relacionada com alterações na cor da pelagem em relação ao sexo, e vamos mostrar a complex...
The role of color in taxonomic and systematic studies of several taxa is central. Color data are more valuable if they permit comparisons. We aimed to provide pelage objective color measurements of a series of Akodon budini and to use those color data to test and to quantitatively analyze the infl uence of both the lighting source and the measuring point, in the determination of pelage color of museum skins. We used a spectroradiometer to measure the pelage color at fi ve points over the dorsal midline of 54 Akodon budini museum skins. PCAs and ANOVAs were conducted over the color data. The characteristics of the studied series also allowed us to include and assess the potential effects of some main sources of intraspecifi c variation. Determinations of fur color strongly depend on the lighting source, and therefore it is essential that lighting conditions are controlled during color measurements and then made explicit when communicating the color characterization of particular taxonomic units. Furthermore, color determinations strongly depend on the measuring point, even on the same body area, and therefore it is critical that the color characterization of a taxon includes the variation between different points of the different body parts of the studied specimens.
Based on the experimental visual data obtained for self-luminous stimuli surrounded by a dark background, a new colour appearance model (CAM) for unrelated self-luminous stimuli, CAM15u, was previously developed. To extend the model to related self-luminous stimuli, the colour appearance of coloured self-luminous stimuli surrounded by a luminous background was evaluated using the magnitude estimation method. Experiments have been performed in Belgium and in Argentina using two different experimental setups. With a LED setup in the Belgian laboratory, visual data on the perception of brightness, hue and amount of white of 30 coloured self-luminous stimuli surrounded by a luminous background were collected. Luminance levels of the stimuli and the background were respectively 50 cd/m 2 and 28 cd/m 2 (positive contrast condition). With a projector setup in the Argentinian laboratory, visual data on the perception of brightness and amount of white of 32 coloured self-luminous stimuli surrounded by a luminous background were collected. Luminance levels of the stimuli and the background were respectively 10 cd/m 2 and 5.6 cd/m 2 (positive contrast condition). For both experiments; the brightness scaling shows a clear and prominent Helmholtz-Kohlrausch effect. This effect describes the impact of the saturation of a stimulus on the perceived brightness and has been seriously underestimated in earlier CAMs. Both brightness, hue and amount of white are found to be well predicted by CAM15u, for this positive contrast condition.
ObjectiveDetermination of color and evaluating its variation form the basis for a broad range of research questions. For studies on taxonomy, systematics, etc., resorting to mammal specimens in museum collections has a number of advantages over using field specimens. However, if museum specimens are to be for studying color, they should accurately represent the color of live animals, or we should understand how they differ. Basically, this study addresses this question: How does coat color vary when dealing with specimens of Akodon budini (Budin’s grass mouse, Thomas 1918), stored in one museum collection for different periods of time?ResultsWe measured color values through a spectroradiometer and a diffuse illumination cabin and used the reflectance values in the form of CIELab tri-stimulus values, considering CIE standard illuminant A. We observed that there is a relationship between specimen storage antiquity and pelage color and it seems that it is general for at least a number of small mammals and this could indicate a universal phenomenon across several mammal species and across several storage conditions. Our results, as others, emphasize the importance of considering storage time, among other circumstances, in research studies using mammal skins and where color is of importance.Electronic supplementary materialThe online version of this article (10.1186/s13104-018-3544-x) contains supplementary material, which is available to authorized users.
Many students do not link optics with images perceived in labs and everyday life. As a direct consequence, they don’t understand the physical behavior of the optical systems involved. We present three problematic situations useful to promote better geometrical optics learning.
Research on the correlation between the initial pupillary light reflex, the perceptual brightness, and the excitations of the photoreceptors was performed for unrelated self-luminous 10 stimuli at low photopic light levels (5 to 80 cd/ m 2). All stimuli were optically characterized using a spectroradiometer. For determining the pupillary diameter, an Eye Tracker was used. The perceived brightness was evaluated with the magnitude estimation method. Test stimuli were presented alternating with a reference stimulus and the Michelson contrast of the pupillary diameter between test and reference conditions was calculated. Six observers (three female and three male) participated, with ages between 30 and 39 years (with an average of 34.5 years). It was found that the coefficient of determination between the pupillary response and the perceived stimulus brightness was higher than the corresponding value for luminance, allowing the suggestion that brightness has a greater effect on pupillary size than luminance. Nevertheless, this is not the complete story: highly saturated red and blue stimuli both induce a high brightness perception but the pupil contraction induced by the blue stimuli is much greater than for the red stimuli. Pupillary diameter was also studied as a function of the relative excitations of the five photoreceptors. The effect of rod and ipRGC excitations on pupillary size variation seems to be larger than that of the other photoreceptors. However, for the working conditions prevailing in this research, it could be expected that rods are not very active and that the ipRGC response might be the major driving mechanism.
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