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C. eleganslocomotion is composed of switches between forward and reversal states punctuated by turns. This locomotory capability is necessary for the nematode to move towards attractive stimuli, escape noxious chemicals, and explore its environment. Although experimentalists have identified a number of premotor neurons as drivers of forward and reverse motion, how these neurons work together to produce the behaviors observed remains to be understood. Towards a better understanding ofC. elegansneurodynamics, we present in this paper a minimally parameterized, biology-based dynamical systems model of the premotor network. Our model consists of a recurrently connected collection of premotor neurons (the core group) driven by over a hundred sensory and interneurons that provide diverse feedforward inputs to the core group. It is data-driven in the sense that the choice of neurons in the core group follows experimental guidance, anatomical structures are dictated by the connectome, and physiological parameters are deduced from whole-brain imaging and voltage clamps data. When simulated with realistic input signals, our model produces premotor activity that closely resembles experimental data: from the seemingly random switching between forward and reversal behaviors to the synchronization of subnetworks to various higher-order statistics. We posit that different roles are played by gap junctions and synaptic connections in switching dynamics. Using the model we identify signal neurons that strongly influence switches between behavioral states and core neurons that play an important role in integrating signal information. The model produces switching statistics that underlie behaviors such as dwelling versus roaming as a result of the synaptic inputs received. 

Abstract Horizontal transfer of genetic material in eukaryotes has rarely been documented over short evolutionary timescales. Here, we show that two retrotransposons,ShellderandSpoink, invaded the genomes of multiple species of themelanogastersubgroup within the last 50 years. Through horizontal transfer,Spoinkspread inD. melanogasterduring the 1980s, while bothShellderandSpoinkinvadedD. simulansin the 1990s. Possibly following hybridization,D. simulansinfected the island endemic speciesD. mauritiana(Mauritius) andD. sechellia(Seychelles) with both TEs after 1995. In the same approximate time-frame,Shellderalso invadedD. teissieri, a species confined to sub-Saharan Africa. We find that the donors ofShellderandSpoinkare likely AmericanDrosophilaspecies from thewillistoni,cardini, andrepletagroups. Thus, the described cascade of TE invasions could only become feasible afterD. melanogasterandD. simulansextended their distributions into the Americas 200 years ago, likely aided by human activity. Our work reveals that cascades of TE invasions, likely initiated by human-mediated range expansions, could have an impact on the genomic and phenotypic evolution of geographically dispersed species. Within a few decades, TEs could invade many species, including island endemics, with distributions very distant from the donor of the TE. 

Nanoindentation was performed on individual grains of a polycrystalline Mg sample with c-axis declination angles ranging from parallel (0°) to perpendicular (90°) to the c-axis. Hardness was highest at ∼0°, decreased up to ∼55°, and then increased at ∼90° to an intermediate level. At ∼0°, high-density 〈c + a〉 dislocations extended deep into the crystal, contributing to high hardness. At ∼55°, 〈c + a〉 dislocations were confined near the indent, and occasional extension twinning reoriented the crystal to ∼45°, promoting 〈a〉 slip in both matrix and twin, leading to low hardness. At ∼90°, extension twinning reoriented the crystal to ∼0°, inducing texture hardening and intermediate hardness. Despite the complex stress state in nanoindentation, which fundamentally differs from the uniaxial stress in bulk tensile and compression tests, the combined contributions of dislocation and twinning still give rise to measurable hardness anisotropy, suggesting nanoindentation as a high-throughput technique for probing orientation-dependent mechanical behavior in Mg. 

Recent work suggests combining physical activity with cognitive tasks may have been critical to human evolution and may be beneficial to human brain health today. These combined tasks are key elements of foraging, a lifestyle employed by human ancestors for over 2 My. However, it is unclear whether cognitive engagement during foraging-like tasks impacts endurance, and therefore foraging performance, and whether cognitive adaptations may mitigate these effects. We tested the hypothesis that cognitive engagement during endurance walking increases perceived physical effort without influencing physiological responses, and that enhanced cognition mitigates these effects. Thirty healthy adults (n_female= 17; aged 18 to 53) underwent nonlocomotor cognitive testing and completed two separate randomized endurance tests: one without (Ex) and one with simultaneous executive function tasks (ExCog). For each condition, participants walked on a treadmill for up to 30-min while physiological responses were recorded, and perception of effort was assessed every 2-min using Borg’s rating of perceived exertion (RPE) scale. During the ExCog condition, RPE was significantly greater (P= 0.005), while energy expenditure was significantly lower (P= 0.008) compared to the Ex condition. Additionally, we observed significant interactions between cognitive abilities and endurance performance—for example, individuals with greater visuospatial abilities experienced a smaller increase in perceived effort (RPE) in the ExCog condition compared to the Ex condition (FDRP= 0.039). These results indicate that cognitive demands and cognitive abilities associated with foraging distinctly influence endurance, suggesting that evolutionary shifts in human cognitive capacities may have relaxed constraints on endurance foraging performance.