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Abstract When terrestrial organisms locomote in natural settings, they must navigate complex surfaces that vary in incline angles and substrate roughness. Variable surface structures are common in arboreal environments and can be challenging to traverse. This study examines the walking gait of katydids (Tettigoniidae) as they traverse a custom-built platform with varying incline angles (30○, 45○, 60○, 75○, 90○) and substrate roughness (40, 120, and 320 grit sandpaper). Our results show that katydids walk more slowly as the incline angle increases and as katydid mass increases, with a decrease of around 0.3 body lengths per second for every 1○ increase in incline. At steeper inclines and larger sizes, katydids are also less likely to use an alternating tripod gait, opting instead to maintain more limbs in contact with the substrate during walking. Katydids also increased average duty factor when climbing steeper inclines and with increasing body mass. However, substrate roughness did not affect walking speed or gait preference in our trials. These findings provide insights into how environmental factors influence locomotor strategies in katydids and enhance our understanding of effective locomotor strategies in hexapods. 

Abstract In aquatic ecosystems, freshwater planarians (Dugesia spp.) function as predators, employing specialized adaptations for capturing live prey. This exploratory study examines the predatory interactions between the freshwater planarian Dugesia spp. and the California blackworm (Lumbriculus variegatus). Observations demonstrate that Dugesia is capable of capturing prey more than twice its own length. The predation process involves a dual adhesion mechanism whereby the planarian adheres simultaneously to the blackworm and the substrate, effectively immobilizing its prey. Despite the rapid escape response of blackworms, characterized by a helical swimming gait with alternating handedness, planarian adhesion frequently prevents successful escape, with no significant effect of worm size. Subsequently, Dugesia employs an eversible pharynx to initiate ingestion, consuming the internal tissues of the blackworm through suction. Blackworm injury significantly increased vulnerability to predation, suggesting that chemical cues from wounds may aid planarians in prey detection. This study provides insights into the biomechanics and behaviors of predation involving two interacting muscular hydrostats, highlighting the critical adaptations that enable planarians to subdue and consume relatively large, mobile prey. 

Synopsis Seventy percent of mammals copulate using repeated pelvic thrusting, while the transfer of sperm requires just a single intromission. Why did thrusting evolve to be the dominant form of sexual intercourse? In this study, we investigate how the rate of sexual pelvic thrusting changes with body size. By analyzing films of copulating mammals, from mice Mus musculus to elephants Elephantidae, we find that bigger animals thrust slower. The rate of pelvic thrusting decreases from 6 Hz for the pocket mouse Pergonathus to 1.3–1.8 Hz for humans to an absence of thrusting for the rhino Rhinocerotidae and elephant Elephantidae families. To understand this dependence on body size, we consider the spring-like behavior of the legs, which is associated with the elasticity of the body's muscles, tendons, and ligaments. For both running and thrusting, greater displacment and energy savings can be achieved if the system is oscillated at its resonant or natural frequency. Resonant frequencies, as measured through previous studies of running in dogs Canis familiaris and horses Equus ferus caballus, show good agreement with sexual thrusting frequencies. Running and sexual thrusting have nothing in common from a behavioral perspective, but from a physical perspective, they are both constrained by the same musculoskeletal systems, and both take advantage of resonance. Our findings may provide improved treatments for human sexual dysfunction as well as improving breeding strategies for domestic mammals. 

Abstract Bacterial biofilms, surface-attached microbial communities, grow horizontally across surfaces and vertically above them. Although a simple heuristic model for vertical growth was experimentally shown to accurately describe the behavior of diverse microbial species, the biophysical implications and theoretical basis for this empirical model were unclear. Here, we demonstrate that this heuristic model emerges naturally from fundamental principles of active fluid dynamics. By analytically deriving solutions for an active fluid model of vertical biofilm growth, we show that the governing equations reduce to the same form as the empirical model in both early- and late-stage growth regimes. Our analysis reveals that cell death and decay rates likely play key roles in determining the characteristic parameters of vertical growth. The active fluid model produces a single, simple equation governing growth at all heights that is surprisingly simpler than the heuristic model. With this theoretical basis, we explain why the vertical growth rate reaches a maximum at a height greater than the previously identified characteristic length scale. These results provide a theoretical foundation for a simple mathematical model of vertical growth, enabling deeper understanding of how biological and biophysical factors interact during biofilm development. 

Synopsis Rhagovelia oriander is a freshwater water strider native to the rivers and streams of North and South America, known for its distinctive skating movement on the water’s surface. This movement resembles the correlated random-walk pattern seen in microorganisms such as Escherichia coli. Previous studies have primarily focused on limb adaptations and biomechanics, leaving the ecological significance inadequately addressed. We combine field observations with controlled laboratory experiments using a flow mill to investigate the dynamics of R. oriander under typical flow conditions. Our findings indicate that this insect exhibits a two-dimensional run-and-tumble motion, often incorporating lateral tumbles following straight runs (run distance: $$30.7\pm 9.3$$ mm). We find that this behavior is resilient to changes in flow speed. In-silico simulations of particle interception demonstrated that this locomotion method enhances encounter rates compared to linear movement, particularly when the simulated food particle is following a rapid flow field. Our results document run-and-tumble locomotion in a millimeter-scale organism, showcasing a unique example of convergent behavior across diverse taxonomic groups and providing valuable insights into locomotion ecology while serving as a source of inspiration for bioinspired robotics and environmental exploration algorithms. 

ABSTRACT Almost all integral membrane proteins that reside in the outer membrane (OM) of gram-negative bacteria contain a closed amphipathic β sheet (“β barrel”) that serves as a membrane anchor. The membrane integration of β barrel structures is catalyzed by a highly conserved heterooligomer called thebarrelassemblymachine (BAM). Although charged residues that are exposed to the lipid bilayer are infrequently found in outer membrane protein β barrels, the β barrels of OmpC/OmpF-type trimeric porins produced by Enterobacterales contain multiple conserved lipid-facing basic residues located near the extracellular side of the OM. Here, we show that these residues are required for the efficient insertion of theEscherichia coliOmpC protein into the OMin vivo. We found that the mutation of multiple basic residues to glutamine or alanine slowed insertion and reduced insertion efficiency. Furthermore, molecular dynamics simulations provided evidence that the basic residues promote the formation of hydrogen bonds and salt bridges with lipopolysaccharide, a unique glycolipid located exclusively in the outer leaflet of the OM. Taken together, our results support a model in which hydrophilic interactions between OmpC and LPS help to anchor the protein in the OM when the local environment is perturbed by BAM during membrane insertion and suggest a surprising role for membrane lipids in the insertion reaction.IMPORTANCEThe assembly (folding and membrane insertion) of bacterial outer membrane proteins (OMPs) is an essential cellular process that is a potential target for novel antibiotics. A heterooligomer called thebarrelassemblymachine (BAM) plays a major role in catalyzing OMP assembly. Here, we show that a group of highly conserved lipid-facing basic residues inEscherichia coliOmpC, a member of a major family of abundant OMPs known as trimeric porins, is required for the efficient integration of the protein into the outer membrane (OM). Based on our work and previous studies, we propose that the basic residues form interactions with a unique OM lipid (lipopolysaccharide) that promotes the insertion reaction. Our results provide strong evidence that interactions between specific membrane lipids and at least a subset of OMPs are required to supplement the activity of BAM and facilitate the integration of the proteins into the membrane. 

Abstract A surgeon peers downward into a body cavity when operating. Holding this position for hours across weeks, months, and years may lead to neck pain and musculoskeletal disorders. We were inspired by ungulates such as giraffes and horses, which use dorsal‐ventral flexion to graze for 9–14 h per day without perceivable neck pain. Ungulates evolved a strong nuchal ligament that relieves neck muscles by stretching to support some of the weight of the head during grazing or running. In contrast, humans evolved an upright posture, and like many primates, have a reduced nuchal ligament. The goal of this study is to use the nuchal ligament as inspiration for a neck brace that passively supports the weight of the head while still permitting lateral flexion, ventral‐dorsal flexion, and rotation. We assembled a prototype using an elastic band, headband, and back posture corrector. Our device augments the human nuchal ligament by using a stiff material and greater mechanical advantage. By our calculations, flexing the head ventrally 40 degrees when wearing the brace reduces the torque applied by neck muscles by 21%. Our device is a proof‐of‐concept that a bioinspired device can offload neck muscular tension and prevent injury. 

Abstract The semi‐aquatic North American river otter (Lontra canadensis) has the unique challenge of navigating slippery algae‐coated rocks. Unlike other river otter species, each rear paw of the North American river otter has a series of soft, circular, and keratinized plantar pads similar to the felt pads on the boots of fly fishermen. Surrounding these soft pads is a textured epidermal layer. In this combined experimental and numerical study, we investigate the influence of the plantar pads and surrounding skin on the otter's grip. We filmed an otter walking and performed materials testing and histology on preserved otter paws. We present experiments and numerical modeling of how the otter paw may help evacuate water when contacting the river bed. We hope this study will draw interest into natural amphibious grip mechanisms for use in sports and the military. 

Abstract Studies of folded-to-misfolded transitions using model protein systems reveal a range of unfolding needed for exposure of amyloid-prone regions for subsequent fibrillization. Here, we probe the relationship between unfolding and aggregation for glaucoma-associated myocilin. Mutations within the olfactomedin domain of myocilin (OLF) cause a gain-of-function, namely cytotoxic intracellular aggregation, which hastens disease progression. Aggregation by wild-type OLF (OLF^WT) competes with its chemical unfolding, but only below the threshold where OLF loses tertiary structure. Representative moderate (OLF^D380A) and severe (OLF^I499F) disease variants aggregate differently, with rates comparable to OLF^WTin initial stages of unfolding, and variants adopt distinct partially folded structures seen along the OLF^WTurea-unfolding pathway. Whether initiated with mutation or chemical perturbation, unfolding propagates outward to the propeller surface. In sum, for this large protein prone to amyloid formation, the requirement for a conformational change to promote amyloid fibrillization leads to direct competition between unfolding and aggregation. 

ABSTRACT Flying insects solve a daunting control problem of generating a patterned and precise motor program to stay airborne and generate agile maneuvers. In this motor program, each muscle encodes information about movement in precise spike timing down to the millisecond scale. Whereas individual muscles share information about movement, we do not know whether they have separable effects on an animal's motion, or whether muscles functionally interact such that the effects of any muscle's timing depend heavily on the state of the entire musculature. To answer these questions, we performed spike-resolution electromyography and electrical stimulation in the hawkmoth Manduca sexta during tethered flapping. We specifically explored how flight power muscles contribute to pitch control. Combining correlational study of visually induced turns with causal manipulation of spike timing, we discovered likely coordination patterns for pitch turns, and investigated whether these patterns can drive pitch control. We observed significant timing change of the main downstroke muscles, the dorsolongitudinal muscles (DLMs), associated with pitch turns. Causally inducing this timing change in the DLMs with electrical stimulation produced a consistent, mechanically relevant feature in pitch torque, establishing that power muscles in M. sexta have a control role in pitch. Because changes were evoked in only the DLMs, however, these pitch torque features left large unexplained variation. We found this unexplained variation indicates significant functional overlap in pitch control such that precise timing of one power muscle does not produce a precise turn, demonstrating the importance of coordination across the entire motor program for flight.