Explore the vast range of titles available.

\"Optics--a field of physics focusing on the study of light--is also central to many areas of biology, including vision, ecology, botany, animal behavior, neurobiology, and molecular biology. The Optics of Life introduces the fundamentals of optics to biologists and nonphysicists, giving them the tools they need to successfully incorporate optical measurements and principles into their research. S©œnke Johnsen starts with the basics, describing the properties of light and the units and geometry of measurement. He then explores how light is created and propagates and how it interacts with matter, covering topics such as absorption, scattering, fluorescence, and polarization. Johnsen also provides a tutorial on how to measure light as well as an informative discussion of quantum mechanics. The Optics of Life features a host of examples drawn from nature and everyday life, and several appendixes that offer further practical guidance for researchers. This concise book uses a minimum of equations and jargon, explaining the basic physics of light in a succinct and lively manner. It is the essential primer for working biologists and for anyone seeking an accessible introduction to optics\"--Provided by publisher.

Recently, it has been shown that animals such as jumping spiders, birds, and butterflies have evolved ultra-black coloration comparable to the blackest synthetic materials. Of these, certain papilionid butterflies have reflectances approaching 0.2%, resulting from a polydisperse honeycomb structure. It is unknown if other ultra-black butterflies use this mechanism. Here, we examine a phylogenetically diverse set of butterflies and demonstrate that other butterflies employ simpler nanostructures that achieve ultra-black coloration in scales thinner than synthetic alternatives. Using scanning electron microscopy, we find considerable interspecific variation in the geometry of the holes in the structures, and verify with finite-difference time-domain modeling that expanded trabeculae and ridges, found across ultra-black butterflies, reduce reflectance up to 16-fold. Our results demonstrate that butterflies produce ultra-black by creating a sparse material with high surface area to increase absorption and minimize surface reflection. We hypothesize that butterflies use ultra-black to increase the contrast of color signals. Nature has developed the ability to produce a wide range of optical effects most notably in the butterfly wing. Here, the authors report on the analysis of the structures responsible for ultra-black coloration across different butterflies and combine this with modelling to identify the key characteristics

يقدم هذا الكتاب في الحقيقة، كل ما يحتاجه المرء لمعرفة البصريات البيولوجية، بدءا من طبيعة الضوء وانتقاله في المحيط البيئي وصولا إلى كيفية تكثيفه ولونه وخصائص الاستقطاب وعواقبه، فبساطة الطرح في هذا الكتاب تجعل مواضيعه في متناول كل شخص مهتم ببصريات الحياة البيولوجية والبصريات البيئية والحيوانية وحتى الرؤية البشرية من الصفات التي يتميز بها هذا الكتاب عن غيره من الكتب المتخصصة، هو أن فصوله تعطي مقدمة لفهم الفيزياء وقياسات الضوء.

One classic explanation for the remarkable diversity of flower colors across angiosperms involves evolutionary shifts among different types of pollinators with different color preferences. However, the pollinator shift model fails to account for the many examples of color variation within clades that share the same pollination system. An alternate explanation is the competition model, which suggests that color divergence evolves in response to interspecific competition for pollinators, as a means to decrease interspecific pollinator movements. This model predicts color overdispersion within communities relative to null assemblages. Here, we combine morphometric analyses, field surveys, and models of pollinator vision with a species-level phylogeny to test the competition model in the primarily hummingbird-pollinated clade lochrominae (Solanaceae). Results show that flower color as perceived by pollinators is significantly overdispersed within sites. This pattern is not simply due to phylogenetic history: phylogenetic community structure does not deviate from random expectations, and flower color lacks phylogenetic signal. Moreover, taxa that occur in sympatry occupy a significantly larger volume of color space than those in allopatry, supporting the hypothesis that competition in sympatry drove the evolution of novel colors. We suggest that competition among close relatives may commonly underlie floral divergence, especially in species-rich habitats where congeners frequently co-occur.

Senses connect organisms to both the world and to each other, yet there is much we don’t know about them. Using examples drawn primarily from the author’s subfield of vision research, this article discusses five major open questions.

It has been recognized for decades that animals sense light using photoreceptors besides those that are devoted strictly to vision. However, the nature of these receptors, their molecular components, their physiological responses, and their biological functions are often obscure. Only recently have researchers begun to learn how critical these non-visual or very simple visual responses are to organismal function. New approaches, including high-throughput molecular genetic techniques, have led to a revolution in our understanding of the evolution, anatomical distribution, physiology, and—in some cases—function of non-visual photoreception in diverse organisms. In the following papers, we bring together specialists from throughout the field to review the current state of knowledge regarding extraocular, non-visual, and simple photoreceptors in a large diversity of organisms ranging from protists through vertebrates and invertebrates.

Many animals convergently evolved photosynthetic symbioses. In bivalves, giant clams (Cardiidae: Tridacninae) gape open to irradiate their symbionts, but heart cockles (Cardiidae: Fraginae) stay closed because sunlight passes through transparent windows in their shells. Here, we show that heart cockles ( Corculum cardissa and spp.) use biophotonic adaptations to transmit sunlight for photosynthesis. Heart cockles transmit 11–62% of photosynthetically active radiation (mean = 31%) but only 5–28% of potentially harmful UV radiation (mean = 14%) to their symbionts. Beneath each window, microlenses condense light to penetrate more deeply into the symbiont-rich tissue. Within each window, aragonite forms narrow fibrous prisms perpendicular to the surface. These bundled “fiber optic cables” project images through the shell with a resolution of >100 lines/mm. Parameter sweeps show that the aragonite fibers’ size (~1 µm diameter), morphology (long fibers rather than plates), and orientation (along the optical c-axis) transmit more light than many other possible designs. Heart cockle shell windows are thus: (i) the first instance of fiber optic cable bundles in an organism to our knowledge; (ii) a second evolution, with epidermal cells in angiosperm plants, of condensing lenses for photosynthesis; and (iii) a photonic system that efficiently transmits useful light while protecting photosymbionts from UV radiation. Some bivalves have evolved photosynthetic symbioses. Here, the authors show that heart cockles transmit light through their upper shell to internal photosynthetic symbionts, using mineral fiber optic cables to maximize light transmission.

Many vertebrates have distinctive blue-green bones and other tissues due to unusually high biliverdin concentrations—a phenomenon called chlorosis. Despite its prevalence, the biochemical basis, biology, and evolution of chlorosis are poorly understood. In this study, we show that the occurrence of high biliverdin in anurans (frogs and toads) has evolved multiple times during their evolutionary history, and relies on the same mechanism—the presence of a class of serpin family proteins that bind biliverdin. Using a diverse combination of techniques, we purified these serpins from several species of nonmodel treefrogs and developed a pipeline that allowed us to assemble their complete amino acid and nucleotide sequences. The described proteins, hereafter named biliverdinbinding serpins (BBS), have absorption spectra that mimic those of phytochromes and bacteriophytochromes. Our models showed that physiological concentration of BBSs fine-tune the color of the animals, providing the physiological basis for crypsis in green foliage even under near-infrared light. Additionally, we found that these BBSs are most similar to human glycoprotein alpha-1-antitrypsin, but with a remarkable functional diversification. Our results present molecular and functional evidence of recurrent evolution of chlorosis, describe a biliverdin-binding protein in vertebrates, and introduce a function for a member of the serpin superfamily, the largest and most ubiquitous group of protease inhibitors.

Key Points Behavioural experiments have shown that diverse animals can detect the Earth's magnetic field and use it as a cue for guiding movements over both long and short distances. However, whereas receptors for most other sensory systems have been characterized and studied, primary receptors involved in detecting magnetic fields have not yet been identified with certainty. This article reviews the three main mechanisms that have been proposed to underlie magnetoreception (electromagnetic induction, chemical magnetoreception and biogenic magnetite) and evaluates the evidence for each. Electromagnetic induction involves detecting small electrical currents that are generated when an animal moves through the Earth's magnetic field. This requires a well-developed electrosense. Most induction models also require the animal to live in a conductive medium such as sea water. Although sharks and a few other electrosensitive marine fishes might plausibly rely on induction, no direct evidence has yet been obtained that they do so. Chemical magnetoreception involves molecular reactions, the yields of which are modified by the direction and intensity of Earth-strength magnetic fields. All proposed reactions involve electron spins in pairs of radicals. At present, however, no radical pair reaction has been identified that is affected by magnetic fields as weak as the Earth's. Evidence consistent with a radical pair mechanism includes effects of light and radio-frequency fields on magnetic orientation behaviour. The magnetite hypothesis posits that crystals of the magnetic mineral magnetite transduce magnetic field energy into physical forces that can be detected by the nervous system. In several animals, magnetite has been detected in anatomical locations that have been linked to magnetoreception, but unequivocal morphological or neurophysiological evidence for magnetite-based receptors has not yet been obtained. All three of the proposed mechanisms are plausible from the standpoint of physics and, at present, the available data are insufficient to confirm or refute any of them. Different animals might rely on different mechanisms. Moreover, at least a few animals might use two different magnetoreception systems, one for sensing field direction and the other for sensing field elements useful for determining geographic position. Each system might be based on separate receptors with different underlying mechanisms. Most magnetoreception research has been based on behavioural studies. Sustained efforts are now needed to exploit a wider range of modern neuroscience techniques. Such undertakings might be facilitated by the discovery that magnetic sensitivity exists in several favorable model systems, including zebrafish, the fruitfly Drosophila melanogaster and the mollusc Tritonia diomedea . Diverse animals can detect magnetic fields but little is known about how they do so. Three main hypotheses of magnetic field perception have been proposed. Electrosensitive marine fish might detect the Earth's field through electromagnetic induction, but direct evidence that induction underlies magnetoreception in such fish has not been obtained. Studies in other animals have provided evidence that is consistent with two other mechanisms: biogenic magnetite and chemical reactions that are modulated by weak magnetic fields. Despite recent advances, however, magnetoreceptors have not been identified with certainty in any animal, and the mode of transduction for the magnetic sense remains unknown.

Aggregation is a common life-history trait in open-water taxa. Qualitative understanding of how aggregation by prey influences their encounter rates with predators is critical for understanding pelagic predator–prey interactions and trophic webs. We extend a recently developed theory on underwater visibility to predict the consequences of grouping in open-water species in terms of increased visual detection of groups by predators. Our model suggests that enhanced visibility will be relatively modest, with maximum detection distance typically only doubling for a 100-fold increase in the number of prey in a group. This result suggests that although larger groups are more easily detected, this cost to aggregation will in many cases be dominated by benefits, especially through risk dilution in situations where predators cannot consume all members of a discovered group. This, in turn, helps to explain the ubiquity of grouping across a great variety of open-water taxa.