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115 results for “aposematism”
Data from: How to fight multiple enemies: target-specific chemical defences in an aposematic moth
Animals have evolved different defensive strategies to survive predation, among which chemical defences are particularly widespread and diverse. Here we investigate the function of chemical defence diversity, hypothesising that such diversity has evolved as a response to multiple enemies. The aposematic wood tiger moth (Arctia plantaginis) displays conspicuous hindwing colouration and secretes two distinct defensive fluids, from their thoracic glands and abdomen. We presented fluids from lab-reared moths to two biologically relevant predators, birds and ants, and measured their reaction in controlled bioassays (no information on colour was provided). We found that defensive fluids are target-specific: thoracic fluids, and particularly the 2-sec-butyl-3-methoxypyrazine (SBMP) which they contain, deterred birds, but caused no aversive response in ants. In contrast, abdominal fluids were particularly deterrent to ants, while birds did not find them repellent. Our study is the first to show evidence of a single species producing separate chemical defences targeted to different predator types, highlighting the importance of taking into account complex predator communities in studies on the evolution of prey defence diversity.
Data from: Multi-trait aposematic signal in Batesian mimicry
Batesian mimics can parasitize Müllerian mimicry rings mimicking the warning color signal. The evolutionary success of Batesian mimics can increase adding complexity to the signal by behavioral and locomotor mimicry. We investigated three fundamental morphological and locomotor traits in a Neotropical mimicry ring based on Ithomiini butterflies and parasitized by Polythoridae damselflies: wing color, wing shape, and flight style. The study species have wings with a subapical white patch, considered the aposematic signal, and a more apical black patch. The main predators are VS-birds, visually more sensitive to violet than to ultraviolet wavelengths (UVS-birds). The white patches, compared to the black patches, were closer in the bird color space, with higher overlap for VS-birds than for UVS-birds. Using a discriminability index for bird vision, the white patches were more similar between the mimics and the model than the black patches. The wing shape of the mimics was closer to the model in the morphospace, compared to other outgroup damselflies. The wing-beat frequency was similar among mimics and the model, and different from another outgroup damselfly. Multitrait aposematic signals involving morphology and locomotion may favor the evolution of mimicry rings and the success of Batesian mimics by improving signal effectiveness toward predators.
Data from: Appearance before performance? Nutritional constraints on life-history traits, but not warning signal expression in aposematic moths
1. Trade-offs have been shown to play an important role in the divergence of mating strategies and sexual ornamentation, but their importance in explaining warning signal diversity has received less attention. In aposematic organisms, allocation costs of producing the conspicuous warning signal pigmentation under nutritional stress could potentially trade-off with life-history traits and maintain variation in warning colouration. 2. We studied this with an aposematic herbivore Arctia plantaginis (Arctiidae), whose larvae and adults show extensive variation in aposematic colouration. In larvae, less melanic colouration (i.e. larger orange patterns) produces a more efficient warning signal against predators, whereas high amounts of melanism (smaller orange pattern) enhance thermoregulation, correlate with better immunity and make individuals harder to detect for naïve predators. 3. We conducted a factorial rearing experiment with larvae originating from lines selected for either small or large orange signal size, which were reared on an artificial diet that had either low or high protein content. Protein content of the diet is critical for melanin production. We measured the effects of diet on individual colouration, life-history traits, immune defence and reproductive output. We also compared the responses to dietary conditions between the small and large larval signal genotypes. 4. Protein content of the diet did not affect warning colouration in the larval stage, but larval signal sizes differed significantly among selection lines, confirming that its variation is mainly genetically determined. In adults, signal line or diet did not affect colouration in hindwings, but males' forewings had more melanin on the high than on low protein diet. Contrary to colouration, diet quality had a stronger impact on life-history traits: individuals developed for longer, had smaller hindwing sizes in females and lower immune defence on the low protein content diet compared to the high. These costs were higher for more melanic larval signal genotypes in terms of development time and female hindwing size. 5. We conclude that low plasticity in warning signal characteristics makes signal expression robust under varying dietary conditions. Therefore, variation in diet quality is not likely to constrain signal expression, but can have a bigger impact on performance.
Data from: Not everything is black and white: color and behavioral variation reveal a continuum between cryptic and aposematic strategies in a polymorphic poison frog
Aposematism and crypsis are often viewed as two extremes of a continuum of visual conspicuousness to predators. Theory predicts that behavioral and coloration conspicuousness should vary in tandem along the conspicuousness spectrum for antipredator strategies to be effective. Here we used visual modeling of contrast and behavioral observations to examine the conspicuousness of four populations of the granular poison frog, Oophaga granulifera, which exhibits almost continuous variation in dorsal color. The patterns of geographic variation in color, visual contrast, and behavior support a gradient of overall conspicuousness along the distribution of O. granulifera. Red and green populations, at the extremes of the color distribution, differ in all elements of color, contrast, and behavior, strongly reflecting aposematic and cryptic strategies. However, there is no smooth cline in any elements of behavior or coloration between the two extremes. Instead populations of intermediate colors attain intermediate conspicuousness by displaying different combinations of aposematic and cryptic traits. We argue that coloration divergence among populations may be linked to the evolution of a gradient of strategies to balance the costs of detection by predators and the benefits of learned aversion.
Data from: Multiple origins of sexual dichromatism and aposematism within large carpenter bees
The evolution of reversed sexual dichromatism and aposematic coloration have long been of interest to both theoreticians and empiricists. Yet despite the potential connections between these phenomena, they have seldom been jointly studied. Large carpenter bees (genus Xylocopa) are a promising group for such comparative investigations as they are a diverse clade in which both aposematism and reversed sexual dichromatism can occur either together or separately. We investigated the evolutionary history of dichromatism and aposematism and a potential correlation of these traits with diversification rates within Xylocopa, using a newly-generated phylogeny for 179 Xylocopa species based on ultraconserved elements (UCEs). A monochromatic, inconspicuous ancestor is indicated for the genus, with subsequent convergent evolution of sexual dichromatism and aposematism in multiple lineages. Aposematism is found to co-vary with reversed sexual dichromatism in many species; however, reversed dichromatism also evolved in non-aposematic species. Bayesian Analysis of Macroevolutionary Models (BAMM) did not show increased diversification in any specific clade in Xylocopa, whereas support from Hidden State Speciation and Extinction (HiSSE) models remained inconclusive regarding an association of increased diversification rates with dichromatism or aposematism. We discuss the evolution of color patterns and diversification in Xylocopa by considering potential drivers of dichromatism and aposematism.
Data from: Diversification and convergence of aposematic phenotypes: truncated receptors and cellular arrangements mediate rapid evolution of coloration in harlequin poison frogs
Aposematic signals represent one of the classical systems to study evolution and, as such, they have received considerable empirical and theoretical investigation. Despite the extensive literature on aposematic coloration, much uncertainty remains about genetic changes responsible for the repeated evolution of similar signals in multiple lineages. Here, we study the diversification and convergence of coloration among lineages of aposematic harlequin poison frogs (O. histrionica complex). Our results suggest that different background phenotypes, showing different color and/or luminance contrast, have evolved independently at least twice in this group. We suggest that cellular arrangements are behind the striking diversity of color and patterns in this group and propose that differences in dorsal background color may be related to either or both, the presence/absence of xanthophores and the dispersion of melanosomes. Our genetic analyses support a role for the melanocortin receptor MC1R in melanosome aggregation, and we show evidence that two different mutations (∆433 and C432A) are responsible for the darker phenotypes that may display a more detectable, easier to learn, aposematic signal.
Data from: Differential predation drives the geographical divergence in multiple traits in aposematic frogs
Prey have evolved a range of traits to enhance their survival against predators. These traits often show geographical variation due to the differences in local predation pressure. To date, there exists ample evidence of the geographical variation in single anti-predator traits such as coloration induced by differential predation. However, predation pressure often induces the shift in a suite of (correlated) prey traits, such as coloration and behavior, rather than a single trait in nature. In this study, we investigated the nature and extent of geographical variation in both color and behavioral traits in the oriental fire-bellied toad, Bombina orientalis, testing whether the frogs experience different predation pressure in different sites and evaluating how this might affect a range of traits associated with predator avoidance. Specifically, we quantified dorsal/ventral coloration, daytime resting place (i.e. the place where each frog was first spotted), and activity levels of natural populations of the frogs in 9 geographically distinct sites distributed across South Korea. We found the clearest differences in these traits between mainland and Jeju Island populations, with Jeju Island frogs exhibiting 1) less bright and less chromatic aposematic ventral coloration than mainland frogs, 2) lower activity during both day and night, and 3) a tendency to rest underwater. Follow-up predation experiments using clay frog models found that frogs in Jeju Island suffer higher predation pressure than mainland frogs, which readily explains the divergence in behavioral and morphological traits among populations.
Data from: Hybridization promotes color polymorphism in the aposematic harlequin poison frog, Oophaga histrionica
Whether hybridization can be a mechanism that drives phenotypic diversity is a widely debated topic in evolutionary biology. In poison frogs (Dendrobatidae), assortative mating has been invoked to explain how new color morphs persist despite the expected homogenizing effects of natural selection. Here, we tested the complementary hypothesis that new morphs arise through hybridization between different color morphs. Specifically, we (1) reconstructed the phylogenetic relationships among the studied populations of a dart-poison frog to provide an evolutionary framework, (2) tested whether microsatellite allele frequencies of one putative hybrid population of the polymorphic frog O. histrionica are intermediate between O. histrionica and O. lehmanni, and (3) conducted mate-choice experiments to test whether putatively intermediate females prefer homotypic males over males from the other two populations. Our findings are compatible with a hybrid origin for the new morph and emphasize the possibility of hybridization as a mechanism generating variation in polymorphic species. Moreover, because coloration in poison frogs is aposematic and should be heavily constrained, our findings suggest that hybridization can produce phenotypic novelty even in systems where phenotypes are subject to strong stabilizing selection.
Data from: The role of predators in maintaining the geographic organization of aposematic signals
Selective predation of aposematic signals is expected to promote phenotypic uniformity. But while uniform within a population, numerous species display impressive variations in warning signals among adjacent populations. Predators from different localities learning to avoid distinct signals while performing intense selection on others are thus expected to maintain such a geographic organization. We tested this assumption by placing clay frog models, representing distinct color morphs of the Peruvian poison-dart frog Ranitomeya imitator and a non conspicuous frog, reciprocally between adjacent localities. In each locality, avian predators were able to discriminate between warning signals; the adjacent exotic morph suffered up to four times more attacks than the local one and two times more than the non conspicuous phenotype. Moreover, predation attempts on the exotic morph quickly decreased to almost nil, suggesting rapid learning. This experiment offers direct evidence for the existence of different predator communities performing localized homogenizing selection on distinct aposematic signals.
Data from: Too hard to swallow: a secret secondary defence of an aposematic insect
Anti-predator strategies are significant components of adaptation in prey species. Aposematic prey are expected to possess effective defences that have evolved simultaneously with their warning colours. This study tested the hypothesis of the defensive function and ecological significance of the hard body in aposematic Pachyrhynchus weevils pioneered by Alfred Russel Wallace nearly 150 years ago. We used predation trials with Japalura tree lizards to assess the survivorship of 'hard' (mature) vs. 'soft' (teneral) and 'clawed' (intact) vs. 'clawless' (surgically removed) weevils. The ecological significance of the weevil's hard body was evaluated by assessing the hardness of the weevils, the local prey insects, and the bite forces of the lizard populations. The existence of toxins or deterrents in the weevil was examined by gas chromatography-mass spectrometry (GC-MS). All 'hard' weevils were instantly spat out after being bitten once and survived attacks by the lizards. In contrast, the 'soft' weevils were chewed and subsequently swallowed. The results were the same regardless of the presence or absence of the weevil's tarsal claws. The hardness of 'hard' Pachyrhynchus weevils was significantly higher than the average hardness of other prey insects in the same habitat and the mean bite forces of the local lizards. The four candidate compounds of the weevil identified by GC-MS had no known toxic or repellent functions against vertebrates. These results reveal that the hardness of aposematic prey functions as an effective secondary defence, and they provide a framework for understanding the spatio-temporal interactions between vertebrate predators and aposematic insect prey.
Data from: Batesian mimics influence the evolution of conspicuousness in an aposematic salamander
Conspicuousness, or having high contrast relative to the surrounding background, is a common feature of unpalatable species. Several hypotheses have been proposed to explain the occurrence of conspicuousness, and while most involve the role of conspicuousness as a direct signal of unpalatability to potential predators, one hypothesis suggests that exaggerated conspicuousness may evolve in unpalatable species to reduce predator confusion with palatable species (potential Batesian mimics). This hypothesis of antagonistic coevolution between palatable and unpalatable species hinges on the 'cost of conspicuousness,' in which conspicuousness increases the likelihood of predation more in palatable species than in unpalatable species. Under this mimicry scenario four patterns are expected: 1) mimics will more closely resemble local models than models from other localities, 2) there will be a positive relationship between mimic and model conspicuousness, 3) models will be more conspicuous in the presence of mimics, and 4) when models and mimics differ in conspicuousness, mimics will be less conspicuous than models. We tested these predictions in the salamander mimicry system involving Notophthalmus viridescens (model) and one color morph of Plethodon cinereus (mimic). All predictions were supported, indicating that selection for Batesian mimicry not only influences the evolution of mimics, but also the evolution of the models they resemble. These findings indicate that mimicry plays a large role in the evolution of model warning signals, particularly influencing the evolution of conspicuousness.
Data from: No evidence of quantitative signal honesty across species of aposematic burnet moths (Lepidoptera: Zygaenidae)
Many defended species use conspicuous visual warning signals to deter potential predators from attacking. Traditional theory holds that these signals should converge on similar forms, yet variation in visual traits and the levels of defensive chemicals is common, both within and between species. It is currently unclear how the strength of signals and potency of defences might be related: conflicting theories suggest that aposematic signals should be quantitatively honest, or, in contrast, that investment in one component should be prioritised over the other, while empirical tests have yielded contrasting results. Here, we advance this debate by examining the relationship between defensive chemicals and signal properties in a family of aposematic Lepidoptera, accounting for phylogenetic relationships and quantifying coloration from the perspective of relevant predators. We test for correlations between toxin levels and measures of wing colour across 14 species of day-flying burnet and forester moths (Lepidoptera: Zygaenidae), protected by highly aversive cyanogenic glucosides, and find no clear evidence of quantitative signal honesty. Significant relationships between toxin levels and coloration vary between sexes and sampling years, and several trends run contrary to expectations for signal honesty. Although toxin concentration is positively correlated with increasing luminance contrast in forewing pattern in one year, higher toxin levels are also associated with paler and less chromatically salient markings, at least in females, in another year. Our study also serves to highlight important factors, including sex-specific trends and seasonal variation, that should be accounted for in future work on signal honesty in aposematic species.
Dataset for: Numbers, neighbours and hungry predators: what makes chemically defended aposematic prey susceptible to predation?
<p>Many chemically defended aposematic species are characterised by relatively low toxin levels, which enables predators to include them in their diets under certain circumstances. Knowledge of the conditions governing the survival of such prey animals – especially in the context of the co-occurrence of similar but undefended prey, which may result in mimicry-like interactions – is crucial for understanding the initial evolution of aposematism.</p> <p>In a one-month outdoor experiment using fish (the common carp<em> Cyprinus carpio</em>) as predators, we examined the survival of moderately defended aposematic tadpole prey (the European common toad <em>Bufo bufo</em>) with varying absolute densities in single-species prey systems or varying relative densities in two-species prey systems containing morphologically similar but undefended prey (the European common frog <em>Rana temporaria</em>). The density effects were investigated in conjunction with the hunger levels of the predator, which were manipulated by means of the addition of alternative (non-tadpole) food.</p> <p>The survival of the <em>B. bufo</em> tadpoles was promoted by increasing their absolute density in the single-species prey systems, increasing their relative density in the two-species prey systems, and providing ample alternative food for the predator. Hungry predators eliminated all <em>R. temporaria </em>individuals regardless of their proportion in the prey community; in treatments with ample alternative food, high relative <em>B. bufo</em> density supported <em>R. temporaria</em> survival.</p> <p>The results demonstrated that moderately defended prey did benefit from high population densities (both absolute and relative), even under long-term predation pressure. However, the physiological state of the predator was a crucial factor in the survival of moderately defended prey. While the availability of alternative prey in general should promote the spread and maintenance of aposematism, the results indicated that the resemblance between the co-occurring defended and undefended prey may impose mortality costs on the defended model species, even in the absence of actual mimicry.</p>
Red coloration and the evolution of aposematism in arboreal sciurids
<p>An animal's coloration is associated with a variety of processes and is therefore subjected to multiple selective pressures. Mammals, especially, are typically inconspicuously colored, or cryptic, to avoid detection by predators. Alternatively, an animal may use conspicuous coloration to advertise the presence of an anti-predator defense. The association between signal and defense is called aposematism. Conspicuous black and white coloration has recently been associated with a range of defenses in mammals, including body size (Howell et al. 2021), however red coloration as a potentially aposematic signal has yet to be investigated in mammals. Squirrels, like most mammals, are unable to perceive red for use as a social signal. Here we use a comparative framework to test whether redness could be a means of background matching, serve a thermoregulatory function or be an honest warning of anti-predator defenses across a global distribution of tree squirrels which vary in size from 16g to 2.2kg in this study. We measured redness of the dorsum, the venter and of red accents of study skin specimens of 57 tree squirrel species (N=257) representing 25 genera. We then associated these phenotypic variables with environmental variables using phylogenetic generalized least squares regression. We find that increasing dorsal redness is associated with more humid environments and closed canopies, consistent with prior work that coloration on this body region under selection for crypsis (Sheets and Chavez 2020). However, we find that ventral redness and maximum redness is associated with large body sizes. Our findings suggest that crypsis and aposematism are not mutually exclusive, and that aposematism may be more widespread in mammals than is currently appreciated.<u></u></p>
Ecological and metabolic traits of non-aposematic species challenge the crypsis-aposematic duality of Neotropical poison frogs
<p>Within the context of animal defence strategies, most species are believed to be either cryptic or aposematic. In this sense, dendrobatid frogs are among the best-studied vertebrate systems in terms of colouration, behaviour, and chemical defence. Though a dual criterium, cryptic-palatable and conspicuous-toxic, was used to classify species within this clade, there are notorious exceptions that do not fit into this duality. In particular, some species assigned to the cryptic-palatable category possess colourful spots that markedly contrast the rest of the body's dark coloration and contain toxic substances. Here, we investigate whether two pairs of syntopic dendrobatids, in which one of the members within each pair has colour spots and the other a homogeneous dark colour, differ in the activity pattern, dietary specialization, foraging activity, and metabolic rate. In agreement with our prediction, we found that the coloured species in one of the pairs is more active and has a higher dietary selectivity and prey accumulation capacity. However, no association was not found for the other species pair. Furthermore, contrary to our prediction, species with coloured spots have a lower metabolic rate than their syntopic homogenous peers. Overall, our findings suggest that species with coloured spots could be classified in a different category based on ecological and metabolic traits while opening exciting perspectives for understanding the evolution of aposematism in amphibians.</p>
FIGURES 14–25 in New species of Ischalia Pascoe, 1860 (Coleoptera: Ischaliidae), with a key to aposematically coloured species from continental Asia, and new notes on their mimicry
FIGURES 14–25. General view of Ischaliidae, Lycidae, Cantharidae and Anthicidae (mimicry complex). 14—Ischalia (s. str.) anhuiensis Kazantsev et Young, 2010; 15—I. (s. str.) lama Kazantsev et Young, 2010; 16—I. (s. str.) martensi Paulus, 1971; 17—I. (s. str.) laosensis sp. nov.; 18— Libnetisia latrunculus (Kazantsev, 2000) (Lycidae); 19—Libnetus piceovittatus Kazantsev, 1992 (Lycidae); 20—Dihammatus brancuccii Kazantsev, 1992 (Lycidae); 21—Plateros suturalis (Pic, 1926) (Lycidae); 22—P. macrosuturalis Kazantsev, 1991 (Lycidae); 23—Lycocerus sp. (Cantharidae) 24—Anthicomorphus himalayanus Telnov, 2010 (Anthicidae); 25—A. pasteuri Pic, 1901 (Anthicidae). Not reproduced to the same scale.
FIGURES 8–13 in New species of Ischalia Pascoe, 1860 (Coleoptera: Ischaliidae), with a key to aposematically coloured species from continental Asia, and new notes on their mimicry
FIGURES 8–13. General view and details of Ischalia spp.: 8—I. (s. str.) holzschuhi sp. nov., holotype female, general view, dorsally, 9—I. (s. str.) martensi Paulus, 1971, male, general view, dorsally, 10—same, invaginated tergite, ventrally, 11—same, aedeagus, ventrally, 12—same, laterally; 13—I. (Eupleurida) sichuanensis Young, 2008, male, aedeagus, ventrally. Scale bars: 1.0 mm.
Data from: Wright's shifting balance theory and the diversification of aposematic signals
Despite accumulating evidence for selection within natural systems, the importance of random genetic drift opposing Wright's and Fisher's views of evolution continue to be a subject of controversy. The geographical diversification of aposematic signals appears to be a suitable system to assess the factors involved in the process of adaptation since both theories were independently proposed to explain this phenomenon. In the present study, the effects of drift and selection were assessed from population genetics and predation experiments on poison-dart frogs, Ranitomaya imitator, of Northern Peru. We specifically focus on the transient zone between two distinct aposematic signals. In contrast to regions where high predation maintains a monomorphic aposematic signal, the transient zones are characterized by lowered selection and a high phenotypic diversity. As a result, the diversification of phenotypes may occur via genetic drift without a significant loss of fitness. These new phenotypes may then colonize alternative habitats if successfully recognized and avoided by predators. This study highlights the interplay between drift and selection as determinant processes in the adaptive diversification of aposematic signals. Results are consistent with the expectations of the Wright's shifting balance theory and represent, to our knowledge, the first empirical demonstration of this highly contested theory in a natural system.
Figure 7. General appearance. A in Sexually dimorphic characters and shared aposematic patterns mislead the morphology-based classification of the Lycini (Coleoptera: Lycidae)
Figure 7. General appearance. A, Lipernes sp. 3, male. B, Lipernes sp. 1, male. C, Lipernes sp. 1, female. D, Lipernes sp. 2, male. E, ditto, female. F, Lipernes sp. 4, male. G, Lipernes sp. 5, male. H, Lipernes sp. 6, male. I, Lipernes sp. 7, male. J, Lipernes sp. 8, male. K, Lipernes sp. 9, male. L, Lipernes sp. 13, male. M, Lipernes sp. 14, male. N, Lipernes sp. 14, male. O,
Figure 4 in Sexually dimorphic characters and shared aposematic patterns mislead the morphology-based classification of the Lycini (Coleoptera: Lycidae)
Figure 4. The dated phylogenetic tree and ancestral area reconstruction recovered by the analysis of the pruned dataset.
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