Upon continued submersion in water, the glabrous skin on human hands and feet forms wrinkles. The formation of these wrinkles is known to be an active process, controlled by the autonomic nervous system. Such an active control suggests that these wrinkles may have an important function, but this function has not been clear. In this study, we show that submerged objects are handled more quickly with wrinkled fingers than with unwrinkled fingers, whereas wrinkles make no difference to manipulating dry objects. These findings support the hypothesis that water-induced finger wrinkles improve handling submerged objects and suggest that they may be an adaptation for handling objects in wet conditions.

Recent research has explored links between cognition and personality, with prominent hypotheses proposing that personality drives consistent individual differences in cognitive function. These hypotheses particularly expect bolder individuals to be faster, but less accurate, as a trade‐off in cognitive function. However, cognitive processes are typically interconnected and defined in more complex terms than simply speed and accuracy. Here, we present evidence that personality‐based differences in learning rates are a result of differences in decision‐making during training in a two‐alternative forced‐choice spatial memory task. This was examined in the mormyrid fish Gnathonemus petersii in the presence of light, where both vision and the electric sense are available, and in the dark, where visibility is limited and fish rely mostly on electrosensing. The species is adapted for the dark to avoid visual predators; thus, the presence of light can induce high‐risk and the dark low‐risk. We show that light conditions had little effect on learning, with bolder fish learning faster both in the light and in the dark conditions. Yet the relationship between learning rates and error rates indicates that the effect on learning is indirectly influenced by accuracy during training. Speed‐accuracy trade‐offs were not found in decision‐making, with bolder individuals deciding faster and more accurately both in the light and in the dark. Only learning strategy was affected by light conditions, with significantly more fish preferring response to place learning in the dark than in the light, where distal cues were not visible. We conclude that other than effects from the integration of visual information, bolder individuals show a consistently greater tendency to explore and find food rewards during training. This affects their decision‐making and in turn their learning performance. We highlight the complexity by which personality‐based effects are exhibited in spatial associative learning.

BackgroundThe expression of animal personality is indicated by patterns of consistency in individual behaviour. Often, the differences exhibited between individuals are consistent across situations. However, between some situations, this can be biased by variable levels of individual plasticity. The interaction between individual plasticity and animal personality can be illustrated by examining situation-sensitive personality traits such as boldness (i.e. risk-taking and exploration tendency). For the weakly electric fish Gnathonemus petersii, light condition is a major factor influencing behaviour. Adapted to navigate in low-light conditions, this species chooses to be more active in dark environments where risk from visual predators is lower. However, G. petersii also exhibit individual differences in their degree of behavioural change from light to dark. The present study, therefore, aims to examine if an increase of motivation to explore in the safety of the dark, not only affects mean levels of boldness, but also the variation between individuals, as a result of differences in individual plasticity.ResultsBoldness was consistent between a novel-object and a novel-environment situation in bright light. However, no consistency in boldness was noted between a bright (risky) and a dark (safe) novel environment. Furthermore, there was a negative association between boldness and the degree of change across novel environments, with shier individuals exhibiting greater behavioural plasticity.ConclusionsThis study highlights that individual plasticity can vary with personality. In addition, the effect of light suggests that variation in boldness is situation specific. Finally, there appears to be a trade-off between personality and individual plasticity with shy but plastic individuals minimizing costs when perceiving risk and bold but stable individuals consistently maximizing rewards, which can be maladaptive.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-016-0154-0) contains supplementary material, which is available to authorized users.

Contests are largely driven by resource value, but their outcome also depends on asymmetries in fighting ability between contestants. Consequently, individuals benefit from assessing these asymmetries when deciding to engage opponents or retreat. Yet, there is much about these assessments that we do not know. First, it is often difficult to discriminate if individuals only assess their own fighting ability or if they compare it to that of their opponents by mutual assessment. Second, the extent to which assessment improves over the course of a contest, as predicted by theory, has remained largely unexplored. We addressed these questions by studying assessment during territorial contests between male Siamese fighting fish, Betta splendens. Findings show the consistent use of mutual assessment when deciding to engage opponents, with a progressive increase in assessment accuracy over sequential contest phases by reducing the use of dishonest signals. Importantly, contrary to theoretical expectations, we find evidence of a novel form of mutual assessment in which fight motivation increases (rather than decreases) when contestants assess their opponents as more formidable than themselves. Although contestants shifted to opponent-only assessment when adjusting display and attack, the collective evidence shows greater aggressive intent towards more threatening opponents. We argue that explanations for this form of assessment may be provided by considering territorial dynamics related to reproductive success and parental investment.

Background Competition is considered to rely on the value attributed to resources by animals, but the influence of extrinsic stressors on this value remains unexplored. Although natural or anthropogenic environmental stress often drives decreased competition, assumptions that this relies on resource devaluation are without formal evidence. According to theory, physiological or perceptual effects may influence contest behaviour directly, but motivational changes due to resource value are expected to manifest as behavioural adjustments only in interaction with attainment costs and resource benefits. Thus, we hypothesise that stressor-induced resource devaluations will impose greater effects when attainment costs are high, but not when resource benefits are higher. Noise may elicit such effects because it impacts the acoustic environment and imposes physiological and behavioural costs to animals. Therefore, we manipulated the acoustic environment using playbacks of artificial noise to test our hypotheses in the territorial male Siamese fighting fish, Betta splendens. Results Compared to a no-playback control, noise reduced defense motivation only when territory owners faced comparatively bigger opponents that impose greater injury costs, but not when territories also contained bubble nests that offer reproductive benefits. In turn, nest-size decreases were noted only after contests under noise treatment, but temporal nest-size changes relied on cross-contest variation in noise and comparative opponent size. Thus, the combined effects of noise are conditional on added attainment costs and offset by exceeding resource benefits. Conclusion Our findings provide support for the hypothesised modulation of resource value under extrinsic stress and suggest implications for competition under increasing anthropogenic activity.