Fungal hyphae regulate bacterial diversity and plasmid-mediated functional novelty during range expansion.

The amount of bacterial diversity present on many surfaces is enormous; however, how these levels of diversity persist in the face of the purifying processes that occur as bacterial communities expand across space (referred to here as range expansion) remains enigmatic. We shed light on this apparent paradox by providing mechanistic evidence for a strong role of fungal hyphae-mediated dispersal on regulating bacterial diversity during range expansion. Using pairs of fluorescently labeled bacterial strains and a hyphae-forming fungal strain that expand together across a nutrient-amended surface, we show that a hyphal network increases the spatial intermixing and extent of range expansion of the bacterial strains. This is true regardless of the type of interaction (competition or resource cross-feeding) imposed between the bacterial strains. We further show that the underlying cause is that flagellar motility drives bacterial dispersal along the hyphal network, which counteracts the purifying effects of ecological drift at the expansion frontier. We finally demonstrate that hyphae-mediated spatial intermixing increases the conjugation-mediated spread of plasmid-encoded antibiotic resistance. In conclusion, fungal hyphae are important regulators of bacterial diversity and promote plasmid-mediated functional novelty during range expansion in an interaction-independent manner.

Cognition in moral space: A minimal model.

We describe moral cognition as a process occurring in a distinctive cognitive space, wherein moral relationships are defined along several morally relevant dimensions. After identifying candidate dimensions, we show how moral judgments can emerge in this space directly from object perception, without any appeal to moral rules or abstract values. Our reductive "minimal model" (Batterman & Rice, 2014) elaborates Beal's (2020) claim that moral cognition is determined, at the most basic level, by "ontological frames" defining subjects, objects, and the proper relation between them. We expand this claim into a set of formal hypotheses that predict moral judgments based on how objects are "framed" in the relevant dimensions of "moral space."

Emergent Bistability and Switching in a Nonequilibrium Crystal.

Multistability is an inseparable feature of many physical, chemical, and biological systems which are driven far from equilibrium. In these nonequilibrium systems, stochastic dynamics often induces switching between distinct states on emergent time scales; for example, bistable switching is a natural feature of noisy, spatially extended systems that consist of bistable elements. Nevertheless, here we present experimental evidence that bistable elements are not required for the global bistability of a system. We observe temporal switching between a crystalline, condensed state and a gaslike, excited state in a spatially extended, quasi-two-dimensional system of charged microparticles. Accompanying numerical simulations show that conservative forces, damping, and stochastic noise are sufficient to prevent steady-state equilibrium, leading to switching between the two states over a range of time scales, from seconds to hours.