The world in color presents a dazzling dimension of phenotypic variation. Biological interest in this variation has burgeoned, due to both increased means for quantifying spectral information and heightened appreciation for how animals view the world differently than humans. Effective study of color traits is challenged by how to best quantify visual perception in nonhuman species. This requires consideration of at least visual physiology but ultimately also the neural processes underlying perception. Our knowledge of color perception is founded largely on the principles gained from human psychophysics that have proven generalizable based on comparative studies in select animal models. Appreciation of these principles, their empirical foundation, and the reasonable limits to their applicability is crucial to reaching informed conclusions in color research. In this article, we seek a common intellectual basis for the study of color in nature. We first discuss the key perceptual principles, namely, retinal photoreception, sensory channels, opponent processing, color constancy, and receptor noise. We then draw on this basis to inform an analytical framework driven by the research question in relation to identifiable viewers and visual tasks of interest. Consideration of the limits to perceptual inference guides two primary decisions: first, whether a sensory-based approach is necessary and justified and, second, whether the visual task refers to perceptual distance or discriminability. We outline informed approaches in each situation and discuss key challenges for future progress, focusing particularly on how animals perceive color. Given that animal behavior serves as both the basic unit of psychophysics and the ultimate driver of color ecology/evolution, behavioral data are critical to reconciling knowledge across the schools of color research.

~ A number of taxonomically diverse species of araneoid spiders adorn their orb-webs with conspicuous silk structures, called decorations or stabilimenta. The function of these decorations remains controversial and -several explanations have been suggested. These include: (1) stabilising and strengthening the web; (2) hiding and concealing the spider from predators; (3) preventing web damage by larger animals, such as birds; (4) increasing foraging success; or (5) providing a sunshield. Additionally, they may have no specific function and are a consequence of stress or silk regulation. This review evaluates the strength of these --^~-•-^. explanations-based on the evidence. The foraging function has received most supporting-evidence, derived -from both correlative field studies and experimental'-manipulations. This contrasts with the evidence provided for other functional explanations, which have not been tested as-extensively. A phylogenetic analysis of the different decoration patterns suggests that the different-types of decorations are as -evolutionary labile as the decorations themselves: the analysis shows little homology and numerous convergences and independent gains. Therefore, it., is possible that different types of decorations have different functions, and this can only be resolved by improved species phylogenies, and a combination of experimental and ultimately comparative analyses.

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In many animal groups genital structures appear to have evolved extremely rapidly, prompting enduring interest in why this is so. Throughout this literature there remains a bias towards studying male genitalia; here we examine the extent of that bias and its possible causes.

Our understanding of selection in nature stems mainly from whole-season and cross-sectional estimates of selection gradients.These estimates suggest that selection is relatively constant within, but fluctuates between seasons. However, the strength of selection depends on demographics, and because demographics can vary within seasons, there is a gap in our understanding regarding the extent to which seasonal fluctuations in demographics may cause variation in selection. Here we use two populations of the golden orb-web spider (Nephila plumipes) that differ in density to examine how demographics change within a season and whether there are correlated shifts in selection. We demonstrate that there is within-season variation in sex ratio and density at multiple spatial and temporal scales. This variation led to changes in the competitive challenges that males encountered at different times of the season and was correlated with significant variation in selection gradients on male size and weight between sampling periods. We highlight the importance of understanding the biology of the organism under study to correctly determine the relevant scale in which to examine selection. We also argue that studies may underestimate the true variation in selection by averaging values, leading to misinterpretation of the effect of selection on phenotypic evolution. K E Y W O R D S : Demographic variation, Nephila plumipes, selection gradients, sexual selection.The strength and direction of selection pressures acting on heritable traits can predict the evolution of phenotypic distributions (Fisher 1930;Lande and Arnold 1983;Kingsolver et al. 2001). The advent of statistical methods to quantify phenotypic selection (Arnold and Wade 1984a,b;Lande and Arnold 1983;Brodie et al. 1995) has led to a better understanding of how selection shapes phenotypes through time. By using estimates of selection gradients derived from cross-sectional sampling or average fitness (longitudinal estimates) across a breeding season, a number of studies have provided information on variation in the strength of selection on a variety of traits associated with fitness (see Kingsolver et al. 2001 for a review). Comparisons of spatially 4 Current address:

Sexual selection, through female choice and/or male–male competition, has influenced the nature and direction of sexual size dimorphism in numerous species. However, few studies have examined the influence of sperm competition on size dimorphism. The orb‐web spider Nephila edulis has a polygamous mating system and extreme size dimorphism. Additionally, the frequency distribution of male body size is extremely skewed with most males being small and few large. The duration of copulation, male size and sexual cannibalism have been identified as the significant factors determining patterns of sperm precedence in spiders. In double mating trials, females were assigned to three treatments: either they mated once with both males or the first or the second male was allowed to mate twice. Paternity was strongly associated with the duration of copulation, independent of mating order. Males that were allowed to mate twice not only doubled the duration of copulation but also their paternity. Small males had a clear mating advantage, they copulated longer than large males and fertilized more eggs. Males of different sizes used different tactics to mate. Large males were more likely to mate through a hole they cut into the web, whereas small males approached the female directly. Furthermore, small males usually mated at their first attempt but large males required several attempts before mating took place. There was no obvious female reaction towards males of different sizes.

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