Proceedings of the Royal Society B: Biological Sciences最新文献

Pelagic fishes must obtain resources in prey-sparse habitats and may be considered energy speculators with maximization, gambling high energy costs (e.g. metabolism) for a high rate of return (prey capture). As such, they may have to carefully use their energy seascape to obtain the resources necessary for high growth rates. For diving animals, their energy seascape will also have a vertical component in addition to a horizontal one, which is rarely considered. Dolphinfish, Coryphaena hippurus, embody the maximization strategy as they have high metabolic rates and fast growth rates. We coupled biologging on wild individuals with lab-based respirometry to estimate dolphinfish swimming metabolic rates and vertical energy seascapes. Dolphinfish performed continuous yo-yo dives with deeper dives at night but higher activity during the day. Dive descents were approximately 27% less costly than the ascents. Fish modulated their behaviour so that metabolic costs during the descent/ascent phases of deeper dives were less than those for shallow dives. While temperature is likely the primary limit of dive depth, the vertical energy seascape may be secondary and limit maximum dive depths. Studies of pelagic animal energy seascapes should consider the vertical component that will help determine their ability to access and utilize prey.

Lepidosaurs are an ecologically diverse and speciose group with more than 11 000 living species (squamates and the tuatara). Stem lepidosaurs are known from the Early Triassic onwards, but primarily from very incomplete specimens. Therefore, we have little information on their ecological diversity or the ecological context of deep evolutionary divergences of Lepidosauria. Marmoretta oxoniensis, from the Middle Jurassic of the UK, is one of the most completely known candidate stem lepidosaurs. Previous studies proposed that it may have been semi-aquatic, based primarily on its abundance in marginal marine rocks. We show here that Marmoretta was adapted for climbing, based on the post-cranial anatomy of a partial skeleton, visualized using micro-computed tomography (µCT)-in particular, the steep angles of thoracic zygapophyses, ungual phalanx morphology and elongate penultimate manual phalanges that curve distoventrally along their lengths. Linear discriminant analysis of the partial hand, using a training dataset of hand skeleton measurements and habitat use in extant squamates, returns strong evidence for clinging arboreality and Marmoretta clusters among scansorial/arboreal iguanians in manus shape space. Evidence of arboreality in Marmoretta provides the first information about habitat use in a probable stem lepidosaur and illuminates the vertical structure of ecological communities of the mid-Mesozoic.

To buffer the effects of local environmental changes, organisms may modify their phenotypic traits (i.e. phenotypic plasticity) or disperse towards other potential habitats (i.e. dispersal plasticity). Despite extensive work studying either 'local phenotypic plasticity' or 'dispersal plasticity' independently, little is known about their potential covariation and interplay. These strategies are classically viewed as alternatives. However, this expectation has been challenged by theoretical work suggesting that they may instead evolve together under some environmental contexts. Here, we experimentally quantified morphological, movement and dispersal plasticity in response to thermal changes in 12 strains of the ciliate Tetrahymena thermophila. We showed that phenotypic and dispersal plasticity are not alternative strategies, with half of the strains expressing simultaneously all dimensions of plasticity in response to thermal changes. Furthermore, the extent of morphological and movement plasticity weakly but significantly differed between residents and dispersers. Interestingly, we found no covariation between these different plasticity dimensions, suggesting that they may evolve independently, which pleads for studying which environmental contexts favour the evolution of each. The fact that phenotypic and dispersal plasticity are not alternative strategies and may affect the expression of one another opens interesting perspectives about their joint evolution and the potential consequences of their interplay.

Humans have developed a sophisticated system of cultural transmission that allows for complex, non-genetically specified behaviours to be passed on from one generation to the next. This system relies on understanding others as social and communicative partners. Some theoretical accounts argue for the existence of domain-specific cognitive adaptations that prioritize social information, while others suggest that social learning is itself a product of cumulative cultural evolution based on domain-general learning mechanisms. The current paper explores the contribution of humans' unique ontogenetic environment to the emergence of social learning in infancy. It suggests that the prolonged period of post-natal dependency experienced by human infants contributes to the development of social learning. Because of motor limitations, infants learn to interact with and act through caregivers, establishing social learning abilities and skills that continue to develop as children become less dependent. According to this perspective, at least some key aspects of social development can be attributed to a developmental trajectory guided by infants' early motor development that radically alters how they experience the world.

Inequity aversion (IA) is the resistance to unequitable rewards given similar investments. It has been postulated as an important mechanism by which human cooperation thrives. To understand the evolutionary origin of human IA and its distribution across the animal kingdom, many species have been tested on IA, with mixed results. Whereas chimpanzees were originally found to show IA, more recent studies showed that their IA response could be explained by social disappointment. We conducted two studies on IA in bonobos using established paradigms: a token-exchange task and the social disappointment task. Bonobos could exchange tokens for equal or less-preferred food rewards than their partners (Study 1) and were tested with humans and machines to control for social disappointment effects (Study 2). We found that bonobos responded aversively to unequal food distributions in both studies, which was reflected by more refusals to participate when disadvantaged. Notably, and contrary to chimpanzees, this effect could not be explained by social disappointment, although Study 2 was only partially consistent with an IA explanation. Overall, our findings indicate that bonobos possess the sensitivity to recognize and respond to unfair treatment, which supports the notion that IA may have coevolved as a stabilizing mechanism for cooperation.

We report on a decade of research on elephant impacts in equatorial evergreen forests in Gabon and Malaysia, comparing sites with (+) and without (-) elephants and documenting major differences in forest structure, tree species composition and tree species diversity. In both regions, we compared sites supporting natural densities of elephants with otherwise undisturbed sites from which elephants had been absent for several decades. Elephant (+) sites supported low densities of seedlings and saplings relative to elephant (-) sites. In Lope National Park, Gabon, 88% of saplings and small trees (<20 cm dbh) were of species avoided by elephants, implicating forest elephants as powerful filters in tree recruitment. In Malaysia, Asian elephants showed strong preferences for monocots over dicots, as we found through both indirect and direct means. Loss of elephants from both Asian and African forests releases diversity from top-down pressure, as preferred forage species increase in abundance, leading to increased density of small stems and tree species diversity. In contrast, loss of other major functional groups of animals, including top carnivores, seed predators and seed dispersers, often results in negative impacts on tree diversity.

Animals communicate using multiple sensory channels, including via vision. The colourful plumage of birds is a model system to study visual communication, having evolved through a complex interplay of processes, acting not only on the ability of a plumage patch to convey information, but also in response to physiological and environmental factors. Although much research on inter-specific variation in bird plumage has concentrated on sexual selection, much less has considered the role of non-sexual selection and how it is affected by the joint effects of avian viewing conditions and receiver vision. Here, we combined a taxonomically diverse database of avian plumage reflectance measurements with bird vision models, habitat and behavioural data to test the effect of three factors that affect viewing conditions-habitat openness, migratory preference and diel activity-on avian plumage contrast, accounting for shared evolutionary history and variation in avian visual systems. We find that habitat structure and migratory preference predicted plumage visual contrast, especially for females. Our study therefore demonstrates the important role of non-sexually selected traits, viewing conditions and bird vision, in shaping avian plumage contrast.

Leaf-cutter ants cut fresh leaves to grow a symbiotic fungus as crop. During cutting, one mandible is typically anchored onto the leaf lamina while the other slices through it like a knife. When initiating cuts into the leaf edge, however, foragers sometimes deviate from this behaviour and instead use their mandibles symmetrically, akin to scissors. In vivo behavioural assays revealed that the preference for either of the two cutting strategies depended on leaf edge geometry and differed between natural leaf margins that were straight or serrated with notch-like folds: leaf-cutter ants displayed a strong preference for scissor-cutting when leaf edges were straight or had wide notches. This preference, however, reversed in favour of knife-cutting when notches were narrow. To investigate whether this behavioural difference had a mechanical origin, we mimicked knife-cutting in ex vivo cutting experiments: for wide notches, all but the sharpest mandibles failed to initiate cuts, or only did so at large forces, caused by substantial leaf buckling and bending. This increased force demand would substantially limit the ability of foragers to cut leaves, and so reduce the colony's access to food sources. Scissor-cutting may thus be an adaptation to the mechanical difficulties associated with bending and buckling of thin leaves.

The motor system is known to process temporal information, and moving rhythmically while listening to a melody can improve auditory processing. In three interrelated behavioural experiments, we demonstrate that this effect translates to speech processing. Motor priming improves the efficiency of subsequent naturalistic speech-in-noise processing under specific conditions. (i) Moving rhythmically at the lexical rate (~1.8 Hz) significantly improves subsequent speech processing compared to moving at other rates, such as the phrasal or syllabic rates. (ii) The impact of such rhythmic motor priming is not influenced by whether it is self-generated or triggered by an auditory beat. (iii) Overt lexical vocalization, regardless of its semantic content, also enhances the efficiency of subsequent speech processing. These findings provide evidence for the functional role of the motor system in processing the temporal dynamics of naturalistic speech.