Rapid color change in a group-hunting pelagic predator attacking schooling prey.

A major challenge for group-hunting predators is coordinating movement at high speed. Billfish - large predators with an elongated rostrum (bill) - include some of the fastest animals in the ocean and often form groups when hunting. This presents a challenge: how do fast-moving predators wielding dangerous weaponry reliably coordinate their attacks to avoid injury? We report a possible solution to this problem through rapid colour change in group-hunting striped marlin (Kajikia audax) as they hunt schools of Pacific sardines (Sardinops sagax). By analysing high-resolution drone footage of marlin attacks, we found that individual marlin intensified the contrast of their body stripes immediately prior to striking prey schools, before rapidly decreasing intensity after their attack. This suggests that color change may be a reliable signal of motivation to attack, potentially deterring conspecifics from attacking.

Spatial memory predicts home range size and predation risk in pheasants.

Most animals confine their activities to a discrete home range, long assumed to reflect the fitness benefits of obtaining spatial knowledge about the landscape. However, few empirical studies have linked spatial memory to home range development or determined how selection operates on spatial memory via the latter's role in mediating space use. We assayed the cognitive ability of juvenile pheasants (Phasianus colchicus) reared under identical conditions before releasing them into the wild. Then, we used high-throughput tracking to record their movements as they developed their home ranges, and determined the location, timing and cause of mortality events. Individuals with greater spatial reference memory developed larger home ranges. Mortality risk from predators was highest at the periphery of an individual's home range in areas where they had less experience and opportunity to obtain spatial information. Predation risk was lower in individuals with greater spatial memory and larger core home ranges, suggesting selection may operate on spatial memory by increasing the ability to learn about predation risk across the landscape. Our results reveal that spatial memory, determined from abstract cognitive assays, shapes home range development and variation, and suggests predation risk selects for spatial memory via experience-dependent spatial variation in mortality.

An extreme cold event leads to community-wide convergence in lower temperature tolerance in a lizard community.

Extreme climate events are predicted to increase in frequency and severity due to contemporary climate change. Recent studies have documented the evolutionary impacts of extreme events on single species, but no studies have yet investigated whether such events can drive community-wide patterns of trait shifts. On 22 January 2020, subtropical south Florida experienced an extreme cold episode during which air temperatures dropped below the lower thermal limit of resident lizard populations. In the week immediately after the cold event, we documented decreased lower thermal limits (CTmin) of six co-occurring lizard species that vary widely in ecology, body size and thermal physiology. Although cold tolerance of these species differed significantly before the cold snap, lizards sampled immediately after had converged on the same new, lower limit of thermal tolerance. Here, we demonstrate that extreme climate events can drive substantial and synchronous community-wide trait changes and provide evidence that tropical and subtropical ectotherms-often characterized as unable to withstand rapid changes in climatic conditions-can endure climatic conditions that exceed their physiological limits. Future studies investigating the mechanisms driving these trait shifts will prove valuable in understanding the ability of ectotherm communities to mitigate climate change.

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

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.

Evolution of non-kin cooperation: social assortment by cooperative phenotype in guppies.

Cooperation among non-kin constitutes a conundrum for evolutionary biology. Theory suggests that non-kin cooperation can evolve if individuals differ consistently in their cooperative phenotypes and assort socially by these, such that cooperative individuals interact predominantly with one another. However, our knowledge of the role of cooperative phenotypes in the social structuring of real-world animal populations is minimal. In this study, we investigated cooperative phenotypes and their link to social structure in wild Trinidadian guppies (Poecilia reticulata). We first investigated whether wild guppies are repeatable in their individual levels of cooperativeness (i.e. have cooperative phenotypes) and found evidence for this in seven out of eight populations, a result which was mostly driven by females. We then examined the social network structure of one of these populations where the expected fitness impact of cooperative contexts is relatively high, and found assortment by cooperativeness, but not by genetic relatedness. By contrast, and in accordance with our expectations, we did not find assortment by cooperativeness in a population where the expected fitness impact of cooperative contexts is lower. Our results provide empirical support for current theory and suggest that assortment by cooperativeness is important for the evolution and persistence of non-kin cooperation in real-world populations.

Dynamic eye colour as an honest signal of aggression.

Animal eyes are some of the most widely recognisable structures in nature. Due to their salience to predators and prey, most research has focused on how animals hide or camouflage their eyes [1]. However, across all vertebrate Classes, many species actually express brightly coloured or conspicuous eyes, suggesting they may have also evolved a signalling function. Nevertheless, perhaps due to the difficulty with experimentally manipulating eye appearance, very few species beyond humans [2] have been experimentally shown to use eyes as signals [3]. Using staged behavioural trials we show that Trinidadian guppies (Poecilia reticulata), which can rapidly change their iris colour, predominantly express conspicuous eye colouration when performing aggressive behaviours towards smaller conspecifics. Furthermore, using a novel, visually realistic robotic system to create a mismatch between signal and relative competitive ability, we show that eye colour is used to honestly signal aggressive motivation. Specifically, robotic 'cheats' (that is, smaller, less-competitive robotic fish that display aggressive eye colouration when defending a food patch) attracted greater food competition from larger real fish. Our study suggests that eye colour may be an under-appreciated aspect of signalling in animals, shows the utility of our biomimetic robotic system for investigating animal behaviour, and provides experimental evidence that socially mediated costs towards low-quality individuals may maintain the honesty of dynamic colour signals.

Fear of predation drives stable and differentiated social relationships in guppies.

Social relationships can have important consequences for fitness in animals. Whilst numerous studies have shown that individuals often join larger groups in response to perceived predation risk (i.e. fear of predation), the importance of predation risk in driving the formation and stability of social relationships within groups has been relatively ignored. We experimentally tested how predation threat influenced fine-scale social network structure using Trinidadian guppies (Poecilia reticulata). When perceived predation risk was high, individuals developed stable and more differentiated social ties compared to when perceived risk was low. Intriguingly, social differentiation coincided with shoals being somewhat smaller under high-perceived risk, suggesting a possible conflict between forming stable social relationships and larger social groups. Individuals most at risk of predation (large and bold individuals) showed the most exaggerated responses in several social measures. Taken together, we provide the first experimental evidence that proximate risk of predation can increase the intensity of social relationships and fine-scale social structure in animal populations.

Sexual selection drives asymmetric introgression in wall lizards.

Hybridisation is increasingly recognised as an important cause of diversification and adaptation. Here, we show how divergence in male secondary sexual characters between two lineages of the common wall lizard (Podarcis muralis) gives rise to strong asymmetries in male competitive ability and mating success, resulting in asymmetric hybridisation upon secondary contact. Combined with no negative effects of hybridisation on survival or reproductive characters in F1-hybrids, these results suggest that introgression should be asymmetric, resulting in the displacement of sexual characters of the sub-dominant lineage. This prediction was confirmed in two types of secondary contact, across a natural contact zone and in two introduced populations. Our study illustrates how divergence in sexually selected traits via male competition can determine the direction and extent of introgression, contributing to geographic patterns of genetic and phenotypic diversity.

The role of experience in problem solving and innovative tool use in crows.

Creative problem solving and innovative tool use in animals are often seen as indicators of advanced intelligence because they seem to imply causal reasoning abilities [1]. However, complex behavior can also arise from relatively simple mechanisms [2, 3], and the cognitive operations underlying seemingly "insightful" behavior are rarely examined [4]. By controlling and varying prior experience, it is possible to determine the minimum information animals require to solve a given problem [5]. We investigated how pretesting experience affects the performance of New Caledonian crows (Corvus moneduloides) when facing a novel problem. The task (developed by Bird and Emery [6]) required dropping stones into a vertical tube to collapse an out-of-reach platform in a transparent box and release a food reward. After establishing that the birds had no preexisting tendency to drop stones into holes, subjects were assigned to two experimental groups that were given different kinds of experience with the affordances of the apparatus. Crows that had learned about the mechanism (collapsibility) of the platform without the use of stones passed the task, just like the subjects that had previously been trained to drop stones. This demonstrates that successful innovation was also possible after acquaintance with just the functional properties of the task.

Habitat stability and predation pressure affect temperament behaviours in populations of three-spined sticklebacks.

1. There is growing interest in the causes and consequences of animal temperaments. Temperament behaviours often have heritable components, but ecological variables can also affect them. Numerous variables are likely to differ between habitats, and these may interact to influence temperament behaviours. 2. Temperament behaviours may be correlated within populations (behavioural syndromes), although the underlying causes of such correlations are currently unclear. 3. We analysed three different temperament behaviours and learning ability in three-spined sticklebacks, Gasterosteus aculeatus, to determine how different ecological variables influence them both within and between populations. We selected populations from four ponds and four rivers that varied naturally in their exposure to predators. 4. High-predation river populations were significantly less bold than a high-predation pond and low-predation river populations, and low-predation pond populations were significantly less bold than a high-predation pond population. Within populations, temperament behaviours were correlated in one high-predation river population only. 5. These results suggest that multiple ecological factors can interact to affect temperament behaviours between populations, and also correlations in those behaviours within populations.