Journal of Experimental Biology最新文献

Fish schooling depends on social interactions between animals. Studies on schooling overwhelmingly focus on a single species, which challenges our ability to resolve what features of this collective behavior are universal and how it has diversified over the course of evolution. Here, we studied interspecific variation in schooling behavior among five species of Neotropical tetras to examine how social networks relate to schooling kinematics among species. We quantified differences in speed, polarization, spacing, mutual information, and network properties within, and between, species. Our results demonstrate substantial interspecific variation in schooling behavior, with polarized species exhibiting higher speeds and more cohesive social networks. In contrast, shoaling species showed greater variability in their spatial arrangement and a less cohesive social structure. This comparison demonstrates how closely-related species are capable of exhibiting distinct forms of schooling that reflect divergent traits in sensing, motivation, and locomotor control.

Safely navigating variable terrains requires animals to balance competing demands of speed, stability, maneuverability, and injury avoidance. Straight-line locomotion has been extensively studied, but less is known about how animals coordinate turning maneuvers. The physics of turning creates a coupling between speed, turn sharpness and ground reaction force (GRF) demands, resulting in a trade-off between speed and maneuverability. Here we investigated locomotor strategies as guinea fowl navigated turns in high and low friction substrates. We measured center of mass trajectories and GRF in four conditions: control straight, control turns, slippery straight, and slippery turns. We hypothesized that guinea fowl would slow down in turns to maintain peak GRF similar to steady, straight conditions, and that slippery terrain would lead to a shift towards slower speeds and shallower turn angles for slip avoidance. We found that guinea fowl slowed down by 14% in high friction turns and 27% in slippery turns compared to straight running and maintained GRF peaks within the 95% prediction interval for straight runs. Contrary to predictions, guinea fowl used similar turn strategies in low and high friction terrain, executing gradual turns with ∼7° change in heading per step, shifting from aerial to grounded running and leaning into the turn. Substantial individual variation in preferred speeds persisted across terrains, and preferred speed correlated with slip and fall rates (faster birds fell more frequently), suggesting individual variation in risk tolerance. Our findings support the hypothesis that animals modulate speed and ground reaction forces to balance competing mechanical demands in unsteady maneuvers, though the underlying control mechanisms remain to be determined.

The relationship between morphology and ecology is mediated by behavior. We explore this relationship by assessing the link between trophic ecology and the use of prey-specific feeding behaviors in a cichlid fish system. Cichlid diversification features repeated transitions between free-moving prey and attached benthic prey, requiring predators to evolve prey-specific approaches to feeding. Using 2000 Hz video, we characterized feeding behavior on an experimental attached benthic prey in seven species of Mesoamerican heroine cichlid spanning three independent transitions to specialized piscivory and two to specialized benthic-feeding ecology. We investigated the effect of feeding ecology on the behavior and kinematics of benthic grazing, a derived, specialized mode of cichlid feeding. Surprisingly, all species readily fed on benthic prey, regardless of their feeding ecology. Nearly all non-benthic species used the same benthic-feeding behaviors as ecological benthic-feeders. Our findings demonstrate an unexpected level of behavioral versatility among cichlid species in exploiting functionally demanding prey outside their typical diets. We propose that this repertoire of latent feeding behaviors supports trophic versatility and facilitates niche diversification. We also show that two benthic-feeding lineages of Neotropical cichlids evolved distinct approaches to benthic feeding, exhibiting the highest and lowest total feeding-strike kinesis, respectively. Together, our findings highlight the importance of behavior in linking morphology and ecology and motivate further study into the diversity and evolutionary context of benthic feeding across the Cichlidae.

Seasonal fluctuations in energy demand pose major energetic challenges to temperate small mammals. Photoperiod was regarded as a highly reliable and anticipatory environmental cue, enabling animals to redistribute their energetic resources and prepare for upcoming seasonal stressors. However, the integrative mechanisms by which photoperiodic changes drive inguinal white adipose tissue (iWAT) browning to achieve this energetic redistribution remain poorly understood. Here, we investigated whether photoperiod alone can induce browning of iWAT and modulate thermogenic capacity in the Brandt's vole (Lasiopodomys brandtii). Combining field sampling across seasons and an 8-week controlled photoperiod experiment, we investigated how seasonal photoperiod regulates morphological and molecular remodeling of iWAT in Brandt's voles. In autumn, iWAT showed marked reductions in adipocyte size accompanied by increased expression of browning-related genes. Short-day exposure similarly decreased iWAT mass and adipocyte area while elevating UCP1 levels, indicating enhanced browning capacity in response to reduced day length. Transcriptomic analysis revealed that photoperiod-dependent molecular regulation was centered on the calcium signaling pathway, with Ca²⁺-mediated activation of CaMKII and CREB emerging as key drivers initiating the browning program. Our findings demonstrate that photoperiod alone is sufficient to induce functional browning of white adipose tissue, providing experimental evidence for a photoperiod-driven thermogenic program for the seasonality of physiological adaptation in temperate small mammals.

Selective oviposition is a behavioral trait that requires detection and discrimination of potential sites followed by appropriate, sometimes spatially precise placement of eggs. In several lineages of stick and leaf insects (Phasmatodea) selective oviposition has evolved from a non-selective ancestral state, in which animals simply drop eggs to the ground. We herein describe such a selective behavior for Lobofemora sp. which places single eggs into small holes in front of its head and between the antennae, despite belonging to a lineage whose ancestral state has been reconstructed as dropping eggs. In order to test the hypotheses that such an egg placement involves antennal tactile detection and discrimination of site properties, we combine an oviposition assay with long-term motion tracking. We show that Lobofemora sp. employs its antennae for size-dependent site preference and postural adjustment according to directional properties of the site. Furthermore, we hypothesized and demonstrated that females refrain from egg-laying when no holes are available. We conclude that antennal tactile cues are sufficient to stimulate and inform targeted oviposition in Lobofemora. Since related egg-dropping species of the same lineage are unknown to use their short antennae for tactile exploration, we suggest that recruitment of the antennae for substrate probing was key to evolve this oviposition behavior.

Harmonic hopping has been described in mammals, birds and insects as a phenomenon by which acoustic character states change in discrete steps in a form of punctuated evolution rather than in a gradual manner. In these cases, acoustic signals appear to 'jump' from low-frequency ancestral states to higher - harmonically linked - frequencies in closely related species, without apparent intermediate forms. Male crickets (Orthoptera, Gryllidae) usually produce low-frequency acoustic signals (2-8 kHz) to attract distant mating partners by rubbing their wings together. However, many species in the subfamily Eneopterinae have evolved calls with uncharacteristically high frequencies, some even reaching the ultrasonic range (>20 kHz). Here, we document for the first time high-frequency calls in the cricket genus Pseudolebinthus (Eneopterinae). Using laser Doppler vibrometry, microcomputed tomography and finite element modelling, we present acoustic evidence that the calls are indeed a result of harmonic frequency hopping from an ancestral low-frequency fundamental to its fourth harmonic. We also provide morphological and biomechanical support for a mechanism explaining the apparent frequency jump through gradual changes to the morphology of the sound-production system. Using phylogenetic analyses, we further show that harmonic hopping events in eneopterine crickets occurred multiple times in various acoustical and morphological contexts independently, thereby constituting an example of convergent evolution of an acoustic trait.

Flying animals face very high instantaneous costs of locomotion (flight metabolic rate ∼16x basal metabolic rate in bats). However, the effect of flight duration is poorly studied. We hypothesized there is a metabolic transition from short burst to longer duration flights, and predicted higher metabolic rate in short flights. We adapted the sodium bicarbonate isotopic tracer method to measure flight metabolic rate for durations up to 11 min in big brown bats (Eptesicus fuscus). We observed a ∼3 fold decrease in metabolic rate (V̇CO2 over the first ∼6 min of flight with predicted minimum V̇CO2 = 2.48±0.65 ml/min. We discuss other aspects of the metabolic transition with flight duration as important avenues for further investigation. Implications include understanding evolutionary trade-offs among foraging strategies, revising energetic budget models, and incorporating these aspects of the physiology of volant mammals into the mammalian exercise model.

Hummingbirds possess many distinct traits that make them stand out among birds. Among those features is the use of high-frequency vocalizations as part of the vocal repertoires of some species. These frequencies are much higher than what most birds are known to produce and hear. However, the mechanisms for the production and perception of these vocalizations are yet to be elucidated. This Review summarizes what we have learned about high-frequency vocalizations in hummingbirds in the past decade, as well as potential mechanistic explanations for this behavior. We aimed to compile a broad understanding of the potential proximate and ultimate mechanisms for such extended vocal production and auditory perception, emphasizing the need for comparative studies. By understanding how hummingbirds have adapted to communicate in complex acoustic environments, we may be able to predict how a rapidly changing environment will influence species with extraordinary sensory capabilities compared with other closely related taxa.

Catecholamines may react with other molecules to produce catecholamine derivatives. For example, nitric oxide may induce nitration of dopamine to form 6-nitrodopamine (6-ND). The endogenous production of such a novel catecholamine has been demonstrated in the mammalian and reptilian cardiovascular system, and in vitro studies demonstrate that 6-ND relaxes pre-contracted aortic rings, and acts as a potent chronotropic agent. So far, however, the in vivo effects of 6-ND remain to be characterised in whole organisms. Using South American rattlesnakes (Crotalus durissus), we measured the endogenous production of 6-ND and other catecholamine derivatives in different tissues of the cardiovascular system and the intercostal muscle. We also used myography to measure the vascular reactivity of the mesenteric artery to 6-ND, and we utilised anaesthetised individuals to measure haemodynamic responses to bolus injections of 6-ND (1 μmol kg-1). Except for blood plasma, 6-ND was detected in all tissues studied, and the addition of l-NAME, a blocker of nitric oxide synthesis, did not alter the production of 6-ND, indicating there are alternative biosynthetic pathways. The isolated mesenteric artery contracted in the presence of adrenaline, dopamine, noradrenaline and 6-ND. We also observed a potentiation of the noradrenergic stimulation in the presence of 6-ND. Finally, injection of 6-ND elicited a small but significant reduction in the mesenteric conductance. It is likely that 6-ND per se exerts small effects on overall haemodynamics, but synergises with noradrenaline and possibly other catecholamines to enhance cardiovascular regulation.

Signal efficacy is crucial to communicative behaviors. To be effective, a signal once broadcast must be capable of being received and interpreted by a receiver or receivers. In addition to maximizing the amount that a signal stimulates receptive organs, the timing of when a signal is broadcast would optimally synchronize with a receiver's peak receptivity. Here, we investigated whether peak timing of male courtship, which includes release of a pheromone required for copulation to occur, is synchronized with female pheromone sensitivity in the butterfly Bicyclus anynana (Lepidoptera: Nymphalidae). To do this, we performed behavioral, pheromone, and electrophysiological assays at dawn, noon and dusk. We also investigated the diel rhythmicity of antennae gene expression by performing RNA sequencing on antennal tissues collected at the same three time points. We found that although males court most often near dusk and produce pheromones at constant levels throughout the day, females are more sensitive to odorants in the morning. Furthermore, female antennae exhibited differential and diurnally rhythmic expression of olfactory receptors and genes associated with learning and sexual receptivity, as well as gene ontology (GO) terms related to fatty acid metabolism and trehalose biosynthesis, supporting our diel electrophysiological results. Previous literature indicates that females form both positive and negative mate preference associations with male pheromones in the morning, regardless of whether males court females. Thus, this asynchrony may enable female B. anynana to learn mate preferences before they are courted by conspecific (or potentially heterospecific) males.