Many chameleons, and panther chameleons in particular, have the remarkable ability to exhibit complex and rapid colour changes during social interactions such as male contests or courtship. It is generally interpreted that these changes are due to dispersion/aggregation of pigment-containing organelles within dermal chromatophores. Here, combining microscopy, photometric videography and photonic band-gap modelling, we show that chameleons shift colour through active tuning of a lattice of guanine nanocrystals within a superficial thick layer of dermal iridophores. In addition, we show that a deeper population of iridophores with larger crystals reflects a substantial proportion of sunlight especially in the near-infrared range. The organization of iridophores into two superposed layers constitutes an evolutionary novelty for chameleons, which allows some species to combine efficient camouflage with spectacular display, while potentially providing passive thermal protection.

/pdf/photonic-crystals-cause-active-colour-change-in-chameleons-36r8btf3qh.pdf

Photonic crystals cause active colour change in chameleons

Communication involves complex behavior in multiple sensory channels, or “modalities.” We provide an overview of multimodal communication and its costs and benefits, place examples of signals and displays from an array of taxa, sensory systems, and functions into our signal classification system, and consider issues surrounding the categorization of multimodal signals. The broadest level of classification is between signals with redundant and nonredundant components, with finer distinctions in each category. We recommend that researchers gather information on responses to each component of a multimodal signal as well as the response to the signal as a whole. We discuss the choice of categories, whether to categorize signals on the basis of the signal or the response, and how to classify signals if data are missing. The choice of behavioral assay may influence the outcome, as may the context of the communicative event. We also consider similarities and differences between multimodal and unimodal ...

https://www.jstor.org/stable/10.1086/431246

Issues in the classification of multimodal communication signals.

The ubiquity of multiple signalling is a long-standing puzzle in the study of animal communication: given the costs of producing and receiving signals, why use more than a single cue? Focusing on sexually selected signals, I argue that dynamic variation in selection pressures can often explain why multiple signals coexist. In contrast to earlier research, which has taken a largely static view of the world, new insights highlight how fluctuations in ecological and social environments, as well as non-equilibrium dynamics intrinsic to coevolutionary systems, can maintain both multiple redundant and non-redundant signals. Future challenges will include identifying the circumstances under which environmental fluctuations lead to multiple signalling, and the consequences of such fluctuations for speciation in multiple-signalling species.

/pdf/dynamics-of-multiple-signalling-systems-animal-communication-19ri44omn3.pdf

Dynamics of multiple signalling systems: animal communication in a world in flux.

Carotenoids are among the most prevalent pigments used in animal signals and are also important for a range of physiological functions. These concomitant roles havemade carotenoidbased signals a po ...

/pdf/carotenoid-based-signals-in-behavioural-ecology-a-review-3ulg7qfq8h.pdf

Carotenoid-based signals in behavioural ecology : a review

Introduction
Animal colouration is a trade-off between being seen by intended, intra- or inter-specific receivers while not being seen by the unintended. Many fishes solve this problem by adaptive colouration. Here, we investigate whether this also holds for fluorescent pigments. In those aquatic environments in which the ambient light is dominated by bluish light, red fluorescence can generate high-contrast signals. The marine, cryptic fish Tripterygion delaisi inhabits such environments and has a bright red-fluorescent iris that can be rapidly up- and down-regulated. Here, we described the physiological and cellular mechanism of this phenomenon using a neurostimulation treatment with KCl and histology.

/pdf/regulation-of-red-fluorescent-light-emission-in-a-cryptic-3pjqhs1bpd.pdf

Regulation of red fluorescent light emission in a cryptic marine fish

Colour patches are complex traits, the components of which may evolve independently through a variety of mechanisms. Although usually treated as simple, two-dimensional characters and classified as either structural or pigmentary, in reality colour patches are complicated, three-dimensional structures that often contain multiple pigment types and structural features. The basic dermal chromatophore unit of fishes, reptiles and amphibians consists of three contiguous cell layers. Xanthophores and erythrophores in the outermost layer contain carotenoid and pteridine pigments that absorb short-wave light; iridophores in the middle layer contain crystalline platelets that reflect light back through the xanthophores; and melanophores in the basal layer contain melanins that absorb light across the spectrum. Changes in any one component of a chromatophore unit can drastically alter the reflectance spectrum produced, and for any given adaptive outcome (e.g. an increase in visibility), there may be multiple biochemical or cellular routes that evolution could take, allowing for divergent responses by different populations or species to similar selection regimes. All of the mechanisms of signal evolution that previously have been applied to single ornaments (including whole colour patches) could potentially be applied to the individual components of colour patches. To reach a complete understanding of colour patch evolution, however, it may be necessary to take an explicitly multi-trait approach. Here, we review multiple trait evolution theory and the basic mechanisms of colour production in fishes, reptiles and amphibians, and use a combination of computer simulations and empirical examples to show how multiple trait evolution theory can be applied to the components of single colour patches. This integrative perspective on animal colouration opens up a host of new questions and hypotheses. We offer specific, testable functional hypotheses for the most common pigmentary (carotenoid, pteridine and melanin) and structural components of vertebrate colour patches.

/pdf/individual-colour-patches-as-multicomponent-signals-50u6wmerzf.pdf

Karen Nersissian

Papers

Individual colour patches as multicomponent signals.