The strategies underlying different forms of protective coloration are well understood but little attention has been paid to the ecological, life‐history and behavioural circumstances under which they evolve. While some comparative studies have investigated the ecological correlates of aposematism, and background matching, the latter particularly in mammals, few have examined the ecological correlates of other types of protective coloration. Here, we first outline which types of defensive coloration strategies may be exhibited by the same individual; concluding that many protective coloration mechanisms can be employed simultaneously, particularly in conjunction with background matching. Second, we review the ecological predictions that have been made for each sort of protective coloration mechanism before systematically surveying phylogenetically controlled comparative studies linking ecological and social variables to antipredator defences that involve coloration. We find that some a priori predictions based on small‐scale empirical studies and logical arguments are indeed supported by comparative data, especially in relation to how illumination affects both background matching and self‐shadow concealment through countershading; how body size is associated with countershading, motion dazzle, flash coloration and aposematism, although only in selected taxa; how immobility may promote background matching in ambush predators; and how mobility may facilitate motion dazzle. Examination of nearly 120 comparative tests reveals that many focus on ecological variables that have little to do with predictions derived from antipredator defence theory, and that broad‐scale ecological studies of defence strategies that incorporate phylogenetics are still very much in their infancy. We close by making recommendations for future evolutionary ecological research.

Primates are noted for their varied and complex pelage and bare skin coloration but the significance of this diverse coloration remains opaque. Using new updated information, novel scoring of coat and skin coloration, and controlling for shared ancestry, we reexamined and extended findings from previous studies across the whole order and the five major clades within it. Across primates, we found (i) direct and indirect evidence for pelage coloration being driven by protective coloration strategies including background matching, countershading, disruptive coloration, and aposematism, (ii) diurnal primates being more colorful, and (iii) the possibility that pelage color diversity is negatively associated with female trichromatic vision; while (iv) reaffirming avoidance of hybridization driving head coloration in males, (v) darker species living in warm, humid conditions (Gloger’s rule), and (vi) advertising to multiple mating partners favoring red genitalia in females. Nonetheless, the importance of these drivers varies greatly across clades. In strepsirrhines and cercopithecoids, countershading is important; greater color diversity may be important for conspecific signaling in more diurnal and social strepsirrhines; lack of female color vision may be associated with colorful strepsirrhines and platyrrhines; whereas cercopithecoids obey Gloger’s rule. Haplorrhines show background matching, aposematism, character displacement, and red female genitalia where several mating partners are available. Our findings emphasize several evolutionary drivers of coloration in this extraordinarily colorful order. Throughout, we used coarse but rigorous measures of coloration, and our ability to replicate findings from earlier studies opens up opportunities for classifying coloration of large numbers of species at a macroevolutionary scale.

Aposematic coloration is traditionally considered to signal unpalatability or toxicity. In mammals, most research has focused on just one form of defense, namely, noxious anal secretions, and its black‐and‐white advertisement as exemplified by skunks. The original formulation of aposematism, however, encompassed a broader range of morphological, physiological, and behavioral defenses, and there are many mammal species with black‐and‐white contrasting patterns that do not have noxious adaptations. Here, using Bayesian phylogenetic models and data from 1726 terrestrial nonvolant mammals we find that two aspects of conspicuous coloration, black‐and‐white coloration patterns on the head and body, advertise defenses that are morphological (spines, large body size), behavioral (pugnacity), and physiological (anal secretions), as well as being involved with sexual signaling and environmental factors linked to crypsis. Within Carnivora, defensive anal secretions are associated with complex black‐and‐white head patterns and longitudinal black‐and‐white body striping; in primates, larger bodied species exhibit irregular patches of black‐and‐white pelage; and in rodents, pugnacity is linked to sharp countershading and irregular blocks of white and black pelage. We show that black‐and‐white coloration in mammals is multifunctional, that it serves to warn predators of several defenses other than noxious anal secretions, and that aposematism in mammals is not restricted to carnivores.

Natural habitats are increasingly affected by anthropogenically driven environmental changes resulting from habitat destruction, chemical and light pollution, and climate change. Organisms inhabiting such habitats are faced with novel disturbances that can alter their modes of signaling. Coloration is one such sensory modality whose production, perception and function is being affected by human-induced disturbances. Animals that acquire pigment derivatives through diet are adversely impacted by the introduction of chemical pollutants into their environments as well as by general loss of natural habitat due to urbanization or logging leading to declines in pigment sources. Those species that do manage to produce color-based signals and displays may face disruptions to their signaling medium in the form of light pollution and turbidity. Furthermore, forest fragmentation and the resulting breaks in canopy cover can expose animals to predation due to the influx of light into previously dark environments. Global climate warming has been decreasing snow cover in arctic regions, causing birds and mammals that undergo seasonal molts to appear conspicuous against a snowless background. Ectotherms that rely on color for thermoregulation are under pressure to change their appearances. Rapid changes in habitat type through severe fire events or coral bleaching also challenge animals to match their backgrounds. Through this review, we aim to describe the wide-ranging impacts of anthropogenic environmental changes on visual ecology and suggest directions for the use of coloration both as an indicator of ecological change and as a tool for conservation.

Objectives: Neonates of several primate species are born with very different pelage coloration from their parents but then assume adult coat color within weeks or months of birth. We set out to test the three conventional functional hypotheses for this distinctive transient natal coat coloration in primates (infanticide, allomothering, and confusion of paternity) as well as solicitation of maternal care, and across all neonate primates, background matching, and Gloger's rule (dark coats being associated with humid environments). Materials and Methods:To examine the functional significance of neonate pelage coloration, we employed five different measures of distinctive coat coloration, new updated information on primate life histories, and a complete primate phylogeny of 286 species to control for shared ancestry.Results: Across primates, we found a strong association between distinctive natal coats and the prevalence of infanticide but no support for allomothering or confusing paternity. We also found that species in which young have distinct natal coats have relatively shorter interbirth intervals, as well as a tendency to be weaned earlier which is unrelated to allomothering. Darker primate natal coats (whether distinctive or not) are not found in shadier, warmer, or wetter habitats.Discussion: While distinct natal coats in primates are generally found in infanticidal species, we argue on logical grounds that this is not an advertisement to incoming males but instead neonate coloration solicits greater maternal care. This enables infants to pass through this infanticide-induced mortality-prone infant phase more rapidly. Conspicuous neonate coats in comparison to adults appear to act as a supernormal stimulus for mothers to hasten post-natal development of their offspring.