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A Matador-like Predator Diversion Strategy Driven by Conspicuous Coloration in Guppies

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Abstract

Understanding the adaptive function of conspicuous coloration has been a major focus of evolutionary biology for much of the last century. Although considerable progress has been made in explaining how conspicuous coloration can be used in functions as diverse as sexual and social signaling, startling predators, and advertising toxicity [1], there remain a multitude of species that display conspicuous coloration that cannot be explained by existing theory. Here we detail a new “matador-like” divertive antipredator strategy based on conspicuous coloration in Trinidadian guppies (Poecilia reticulata). Guppies encountering predatory fish rapidly enhance the conspicuousness of their eyes by blackening their irises. By pitting biomimetic robotic guppies against real predatory fish, we show this conspicuous eye coloration diverts attacks away from the guppies’ center of mass to their head. To determine the function of this seemingly counterintuitive behavior, we developed a method for simulating escape probabilities when live prey interact with ballistic attacking predators, and find this diversion effect significantly benefits black-eyed guppies because they evade capture by rapidly pivoting away from the predator once it has committed to its attack. Remarkably, this antipredator strategy reverses the commonly observed negative scaling relationship between prey size and evasive ability, with larger fish benefiting most from diverting predators. Taken together, our results introduce a new antipredator divertive strategy that may be widely used by conspicuously colored prey that rely on agility to escape their predators.

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Avoiding Attack discusses the diversity of mechanisms by which prey avoid predator attacks and explores how such defensive mechanisms have evolved through natural selection. It considers how potential prey avoid detection, how they make themselves unprofitable to attack, how they communicate this status, and how other species have exploited these signals. Using carefully selected examples of camouflage, mimicry, and warning signals drawn from a wide range of species and ecosystems, the authors summarise the latest research into these fascinating adaptations, developing mathematical models where appropriate and making recommendations for future study. This second edition has been extensively rewritten, particularly in the application of modern genetic research techniques which have transformed our recent understanding of adaptations in evolutionary genomics and phylogenetics. The book also employs a more integrated and systematic approach, ensuring that each chapter has a broader focus on the evolutionary and ecological consequences of anti-predator adaptation. The field has grown and developed considerably over the last decade with an explosion of new research literature, making this new edition timely.
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Fast-starts are brief, sudden accelerations used by fish during predator-prey encounters. The kinematics and performance of fish during fast-start manoeuvres have received a lot of attention since they may determine the outcome of predator-prey interactions in terms of feeding success or survival. We will discuss recent progress on (1) the kinematics of escape responses and feeding strikes, (2) the fast-start performance of species with different body morphologies and from different habitats, and (3) the functional significance of fast-start kinematics and performance within the context of predator-prey interactions.
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Experiments with teleosts attacking fathead minnow (Pimephales promelas) prey showed that piscivore locomotor tactics vary with body/fin morphology. Predators were tiger musky (Esox sp.), rainbow trout (Salmo gairdneri), smallmouth bass (Micropterus dolomieui), and rock bass (Ambloplites rupestris) representing several morphological series from more flexible to more rigid bodies, elongate to gibbose bodies, soft-rayed to acanthopterygian median/paired fin patterns, and more to less myotomal muscle. Two predicted optimal tactics were common to the four predators: (1) strike at the prey center of mass and (2) strike prey from the side. Other tactics varied among the predators. Tiger musky always used S-start fast-starts, rainbow trout used steady swimming with body/caudal fin movements, and smallmouth and rock bass used steady swimming with body/caudal fin movements for closer prey and started attacks on distant prey with pectoral propulsion. Tiger musky overshot prey, this being prevented by the use of paired fins as brakes in the two centrarchids. Rainbow trout regularly chased prey, but effective braking coupled with suction feeding appeared to make chases less necessary for smallmouth and rock bass. Speeds in strikes increased according to rock bass < smallmouth bass < rainbow trout < tiger musky consistent with expectations based on morphology. Each species used attack speeds likely to minimize closure times, which is the general optimal strategy for interceptors. Tiger musky attacked at maximum speeds but rainbow trout and smallmouth and rock bass attacked at speeds very much lower than their maximum potential. The prey has a low response threshold for these three species compared with tiger musky when high speeds and associated large prey reaction distances would increase closure times.
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Considerable emphasis has, in the past, been placed on the eye camouflage of a wide variety of animals, including fishes. Evidence from those fishes inhabiting Caribbean reefs indicates that eye ornamentation is much more common than their obliteration; this is probably due mainly to the ease with which reef fishes can avoid predators and the importance of the eyes as signals in intraspecific interactions. The similarities between eye ornamentation of these fishes and the concept of poster-coloration are discussed.ZusammenfassungObwohl bisher die Augentarnung der Fische viel beachtet wurde, zeigt ein Vergleich der Arten, die karibische Riffe bewohnen, daß Hervorhebung der Augen haufiger ist als Tarnung:1. In den meisten Fllen ist eine dunkle Pupille von einer stark kontrastie-renden hellen Iris umrandet.2. Viele Arten haben außerdem noch andere Augenmarkierungen, wie Ringe oder ‘Brauen’ von abstechender Farbe.3. Die Hauptfarben der Umgebung der Augen (schwarz, blau und gelb) erhöhen noch den Kontrast.Die beiden Faktoren, die wahrscheinlich zur Entwicklung der Augen als Farbsignale führten, sind die Unfhigkeit eines Raubfisches, kleine Korallenfische bei Tageslicht zu erbeuten, wenn Farbsignale am aufflligsten sind, und die gut belegte Tatsache, daß Fischaugen in der arteigenen Verstndigung eine Rolle spielen.
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Blue tail coloration in hatchling skinks (Eumeces fasciatus and E. laticeps) appears to be an antipredatory adaptation that distracts attention away from the body to the tail. The tail itself serves as a decoy that may be autotomized as a final defense against capture. The effectiveness of intact tails in deflecting attacks from the body was 50% against scarlet kingsnakes in the experimental conditions used. Brightness rather than hue presumably accounts for the higher attack frequency on blue than black tails in this study, but the blue color may have evolved in response to avian predation.Repeated predation without ill effects by several predators allows rejection of the hypothesis that the blue tail is aposematic for the predators tested. The hypothesis that blue tails provide stimuli inhibiting aggression or predation by adult male conspecifics is untenable for E. laticeps because adult males readily eat intact hatchlings. Although this study provides no statistical evidence that blue tail coloration inhibits attack by female E. laticeps on hatchlings, the trend of predation rates on blue- and black-tailed hatchlings is in the direction predicted for inhibition.
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Size-selective predation has been proposed to be one important evolutionary force shaping life-history traits in guppies (Poecilia reticulata). Populations living in the presence of the ring-tailed pike cichlid (Crenicichlasaxatilis) are smaller, mature earlier, allocate more energy to offspring and get more and smaller young than guppies in localities without Crenicichla. We investigated if Crenicichlasaxatilis is a size-selective predator, if the selectivity is a result of active choice and if the optimal prey size can be explained according to an optimal foraging model. In single-prey experiments we quantified the predators’ pre-capture costs (time), capture success, and post-capture costs (time) for four different prey sizes spanning from 10 to 40 mm total length. To see which of the components of the prey cycle the predator takes into account for its choice, we then predicted prey values and optimal prey size with 6 different models that included one or more of the prey cycle components. In two multiple prey experiments, the cichlids were given the choice of the two and four different prey sizes simultaneously. Crenicichlasaxatilis actively selected the largest guppies in both cases. The three prey-value functions that included handling time (post-capture cost) did not accurately predict the prey choice. Instead the prey-value functions that took into account pre-capture cost (approach and attack time) were able to correctly predict the choice of the largest guppy size, suggesting that pre-capture costs may be more important than post-capture costs for prey choice in Crenicichlasaxatilis. The study confirms that Crenicichlasaxatilis is a size-selective predator selecting large guppies, while earlier evidence for selectivity for large prey in Crenicichla cichlids has been weak and equivocal. Our result strengthen the possibility that size-selective predation is a mechanism in life-history evolution in guppies.
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This paper discusses some of the ethical issues raised by studies of predator-prey and aggressive interactions when these involve artificially-staged encounters. Such experiments call for special care in ensuring that a maximum of information is gained and a minimum of suffering caused. On the one hand, we should consider critically the theoretical importance of the question at issue, make sure that the behaviour is recorded accurately and explore the possibility of collaborative experiments. On the other hand, field studies of natural encounters should be used wherever possible. Where staged encounters are necessary, the use of model predators should be considered, the number of subjects kept to a minimum and the experiments made as short as possible.
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The level of predatory threat encountered by fish may vary from population to population. In Trinidad, for example, guppies in the Lower Aripo River encounter a range of fish predators. Guppies from the Paria River, by contrast, encounter few fish predators but probably experience a high degree of predation from freshwater prawns, Macrobrachium spp. Predation risk from all types of aquatic predators is low for guppies from the Upper Aripo River. Inspection behaviour allows prey fish to recognize and assess potential predators. The risk associated with this behaviour can be minimized if the attack cone around the predator's jaws is avoided. This experiment investigated attack-cone avoidance behaviour during inspection of either a fish predator, Rivulus hartii or a macrobrachium, M. crenulatum, by wildcaught guppies. Inspecting Lower Aripo guppies kept a large distance between themselves and the rivulus. They also selectively avoided the dangerous mouth region. These Lower Aripo guppies did not, however, display attack-cone avoidance in the presence of the macrobrachium. Guppies from the Paria population were most wary when inspecting the macrobrachium. Upper Aripo guppies showed no attack-cone avoidance and displayed poor recognition of both predators. The results demonstrate that fish skilled at dealing with one type of predator gain no automatic advantage when faced with a novel predator. They also show that fish exposed to high levels of predation in the wild will not necessarily be more cautious in circumstances where the level of danger is unknown.
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During predator–prey encounters, a high locomotor performance in unsteady manoeuvres (i.e. acceleration, turning) is desirable for both predators and prey. While speed increases with size in fish and other aquatic vertebrates in continuous swimming, the speed achieved within a given time, a relevant parameter in predator–prey encounters, is size independent. In addition, most parameters indicating high performance in unsteady swimming decrease with size. Both theoretical considerations and data on acceleration suggest a decrease with body size. Small turning radii and high turning rates are indices of manoeuvrability in space and in time, respectively. Manoeuvrability decreases with body length, as minimum turning radii and maximum turning rates increase and decrease with body length, respectively. In addition, the scaling of linear performance in fish locomotion may be modulated by turning behaviour, which is an essential component of the escape response. In angelfish, for example, the speed of large fish is inversely related to their turning angle, i.e. fish escaping at large turning angles show lower speed than fish escaping at small turning angles. The scaling of unsteady locomotor performance makes it difficult for large aquatic vertebrates to capture elusive prey by using whole-body attacks, since the overall manoeuvrability and acceleration of small prey is likely to be superior to that of large predators. Feeding strategies in vertebrate predators can be related to the predator–prey length ratios. At prey–predator ratios higher than approximately 10−2, vertebrate predators are particulate feeders, while at smaller ratios, they tend to be filter feeders. At intermediate ratios, large aquatic predators may use a variety of feeding methods that aid, or do not involve, whole body attacks. Among these are bubble curtains used by humpback whales to trap fish schools, and tail-slapping of fish by delphinids. Tail slapping by killer whales is discussed as an example of these strategies. The speed and acceleration achieved by the flukes of killer whales during tail slaps are higher and comparable, respectively, to those that can be expected in their prey, making tail-slapping an effective predator behaviour.
Article
Status-based differences in sclera colour in small groups of juvenile Atlantic salmon Salmo salar, held in a semi-natural environment over a 20 day period, became obvious 3 days after the start of the study and persisted for the 20 days. Dominant fish had pale sclera, and this pattern was very stable over the experimental period. In contrast, the sclera colour of subordinate fish (ranks 2–5) fluctuated from day to day. Median sclera colour offish ranked 4–5 darkened on days they received more aggression, and sclera of rank 2 fish were lighter on days on which they initiated more attacks. Changes in sclera colour of fish ranked 2–4 were more frequent during feeding periods than non-feeding periods. This study confirms that the relationship between eye colour and status described in tanks is also seen in more natural environments, and also that colour change in juvenile salmonids is a complex response to local events.
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Fish lens transmission was found to vary depending on the type and concentration of short-wave absorbing compounds present within the lens. Pigments extracted from lenses of ten species were identified as mycosporine-like amino acids (mainly palythine, palythene and asterina-330, lambda maxs around 320-360 nm) which are also thought to be present in the majority of the 120 species examined here. A novel mycosporine-like pigment with lambda max 385 nm was isolated from the lens of the flying fish, Exocoetus obtusirostris, while lenses of several closely related tropical freshwater species were found to have high concentrations of the tryptophan catabolite 3-hydroxykynurenine (lambda max 370 nm). The type of lens pigment a species possesses and its concentration depends upon both the animal's phylogenetic group and its "optical niche".
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To study whether absolute (m/s) or relative (body lengths/s) speed should be used to compare the vulnerability of differently sized animals, we developed a simple computer simulation. Human 'predators' were asked to 'catch' (mouse-click) prey of different sizes, moving at different speeds across a computer screen. Using the simulation, a prey's chances of escaping predation depended on its speed (faster prey were more difficult to catch than slower prey of the same body size), but also on its size (larger prey were easier to catch than smaller prey at the same speed). Catching time, the time needed to catch a prey, also depended on both prey speed and prey size. Relative prey speed (body lengths/s or body surface/s) was a better predictor of catching time than was absolute prey speed (m/s). Our experiment demonstrates that, in contrast to earlier assertions, per unit body length speed of prey may be more 'ecologically relevant' than absolute speed. Copyright 1998 The Association for the Study of Animal Behaviour.
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Several plumage types are found in feral pigeons (Columba livia), but one type imparts a clear survival advantage during attacks by the swiftest of all predators--the peregrine falcon (Falco peregrinus). Here we use quantitative field observations and experiments to demonstrate both the selective nature of the falcon's choice of prey and the effect of plumage coloration on the survival of feral pigeons. This plumage colour is an independently heritable trait that is likely to be an antipredator adaptation against high-speed attacks in open air space.