Aposematism in mammals

Mesozoic mammaliaforms illuminate the origins of pelage coloration

Pelage coloration, which serves numerous functions, is crucial to the evolution of behavior, physiology, and habitat preferences of mammals. However, little is known about the coloration of Mesozoic mammaliaforms that coevolved with dinosaurs. In this study, we used a dataset of melanosome (melanin-containing organelle) morphology and quantitatively measured hair colors from 116 extant mammals to reliably reconstruct the coloration of six Mesozoic mammaliaforms, including a previously undescribed euharamiyidan. Unlike the highly diverse melanosomes discovered in feathered dinosaurs, hairs in six mammaliaforms of different lineages and diverse ecomorphotypes showed uniform melanosome geometry, corresponding to dark-brown coloration consistent with crypsis and nocturnality. Our results suggest that the melanosome variation and color expansion seen in extant mammals may have occurred during their rapid radiation and diversification after the Cretaceous-Paleogene extinction.

Parasitism as a potential driver of aposematism

Aposematic animals couple unprofitability to predators, such as toxicity, with a warning signal, such as conspicuous coloration. Although toxicity and coloration can provide effective protection against predation, these traits also play a major role in the context of parasitism. Many of the color pigments used by aposematic animals are components of anti-infection immunity. Moreover, toxic compounds are used by conspicuous animals as defenses against parasites and pathogens. Parasites and pathogens not only pose selection on coloration through immunity and toxicity, they also play a major role in sexual selection, with mate choice often depending on conspicuous coloration and anti-infection toxicity. Consequently, parasitism is likely an important component in the evolution of traits that provide predator protection through aposematism.

Experimental evidence of aposematic signal in black tadpoles

Aposematism is a widespread defense mechanism in animals. Anuran amphibians are known for their extensive repertoire of defenses, especially in the adult stage. Color-based mechanisms are particularly common in this group, although their use during the larval stage is still understudied. The hypothesis of aposematism in tadpoles has been suggested for several species that present conspicuous coloration and unpalatability. Tadpoles of some bufonid toads have been considered aposematic for decades, as they have a conspicuous black color, are unpalatable, and form aggregations that make them even more visible. However, few empirical studies have tested aposematism in these larvae against visually oriented predators, such as birds. In this paper, we tested whether the uniform black coloration acts as an aposematic signal in anuran larvae. The research was conducted through field predation experiments using artificial replicas of tadpoles of different colors (brown, gray, and black). The survival of black replicas was significantly higher than that of control groups, supporting the aposematism hypothesis. Given that the replicas varied only in color, we conclude that the differential attacks among treatments were carried out by visually oriented predators, probably birds, that had learned to recognize and avoid black tadpoles.

The Evolution of Rodent Tail Morphology

AbstractPopulation-level variation in rodent tail structures has been variously attributed to facilitating social communication, locomotion, thermoregulation, and predator avoidance. Little is known, however, about the applicability of these ecological and social correlates to explaining the tremendous interspecific diversity of this appendage. To investigate the potential drivers of rodent tail morphology at a macroevolutionary level, we first carefully reviewed the literature and constructed a list of major hypotheses regarding this variation. We then compiled a database of 11 different tail traits related to length, color, texture, and ecological characteristics for 2,101 species of rodents (order Rodentia) and examined their key evolutionary correlates. Using Bayesian phylogenetic mixed models across the entire order and additionally within the five rodent suborders, we found that tail length is correlated with both temperature (Allen's rule) and locomotory mode, that black tips are more common in brightly lit environments, that naked tails are often found in warmer climates, that fluffy-tipped tails are more common in smaller and/or arboreal species, that prehensility is predominant in arboreal species and/or species with longer tails, and that tail autotomy is more common in open environments. Most of our tested predictions, largely drawn from population-level studies, are not recapitulated across the entire order, potentially indicating a role of local ecological context in shaping tail morphology.

Quantitative Chemical Analysis of Defensive Secretion of Megacrania tsudai (Phasmatidae) and Effect of Actinidine on its Potential Predators

Insects avoid predation in various ways, and some use multiple ways to avoid predation. However, the effects of comprehensive avoidance methods and the differences in avoidance methods among different life stages of insects have not been sufficiently discussed. The big head stick insect Megacrania tsudai uses background matching as its primary defense and chemical defense as its secondary defense. The aims of this study were to identify and isolate the chemical components of M. tsudai using repeatable methods, determine the amount of the main chemical compound, and reveal the effect of the main chemical compound on its predators. We established a repeatable gas chromatography-mass spectrometry (GC-MS) method to identify the chemical compounds of these secretions, and identified actinidine as the main compound. Actinidine was identified by nuclear magnetic resonance (NMR), and the amount of actinidine in each instar was calculated by constructing a calibration curve using pure actinidine. Mass ratios did not drastically change among instars. Furthermore, experiments involving dropping an aqueous solution of actinidine demonstrated removal behavior in geckos, frogs, and spiders. These results indicated that M. tsudai conducts secondary defenses using defensive secretions consisting mainly of actinidine.

Spatially differential regulation of ATF2 phosphorylation contributes to warning coloration of gregarious locusts

Warning coloration are common defense strategies used by animals to deter predators. Pestilential gregarious locusts exhibit a notable black-brown pattern as a form of warning coloration. However, the mechanisms regulating this distinctive pattern remain largely unknown. Here, we revealed that the black and brown integuments of locusts are governed by varying amounts of β-carotene and β-carotene-binding protein (βCBP) complexes. βCBP expression is regulated by the bZIP transcription factor activation transcription factor 2 (ATF2), which is activated by protein kinase C alpha in response to crowding. Specifically, ATF2 is phosphorylated at Ser327 and translocates to the nucleus, where it binds to the βCBP promoter and stimulates overexpression. Differential phosphorylation of ATF2 leads to the divergent black and brown coloration in gregarious locusts. The accumulation of red pigments vital for creating the brown sternum depends on βCBP overexpression. The spatial variation in ATF2 phosphorylation enables locusts to rapidly adapt to changing environment for aposematism.

The Biological Roots of Music and Dance : Extending the Credible Signaling Hypothesis to Predator Deterrence

After they diverged from panins, hominins evolved an increasingly committed terrestrial lifestyle in open habitats that exposed them to increased predation pressure from Africa's formidable predator guild. In the Pleistocene, Homo transitioned to a more carnivorous lifestyle that would have further increased predation pressure. An effective defense against predators would have required a high degree of cooperation by the smaller and slower hominins. It is in the interest of predator and potential prey to avoid encounters that will be costly for both. A wide variety of species, including carnivores and apes and other primates, have therefore evolved visual and auditory signals that deter predators by credibly signaling detection and/or the ability to effectively defend themselves. In some cooperative species, these predator deterrent signals involve highly synchronized visual and auditory displays among group members. Hagen and Bryant (Human Nature, 14(1), 21-51, 2003) proposed that synchronized visual and auditory displays credibly signal coalition quality. Here, this hypothesis is extended to include credible signals to predators that they have been detected and would be met with a highly coordinated defensive response, thereby deterring an attack. Within-group signaling functions are also proposed. The evolved cognitive abilities underlying these behaviors were foundations for the evolution of fully human music and dance.

Contrasting coloured ventral wings are a visual collision avoidance signal in birds

Collisions between fast-moving objects often cause severe damage, but collision avoidance mechanisms of fast-moving animals remain understudied. Particularly, birds can fly fast and often in large groups, raising the question of how individuals avoid in-flight collisions that are potentially lethal. We tested the collision-avoidance hypothesis, which proposes that conspicuously contrasting ventral wings are visual signals that help birds to avoid collisions. We scored the ventral wing contrasts for a global dataset of 1780 bird species. Phylogenetic comparative analyses showed that larger species had more contrasting ventral wings than smaller species, and that in larger species, colonial breeders had more contrasting ventral wings than non-colonial breeders. Evidently, larger species have lower manoeuvrability than smaller species, and colonial-breeding species frequently encounter con- and heterospecifics, increasing their risk of in-flight collisions. Thus, more contrasting ventral wing patterns in these species are a sensory mechanism that facilitates collision avoidance.