Bacterial metapopulations in nanofabricated landscapes

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   Fig. 1.

   Sewall Wright's heuristic concept of an adaptive landscape (A) (adapted from ref. 11), and a 1D array of MHPs with landscape parameters [K _i, J _i,i+1, λ_i] (B).

   
   
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   Fig. 2.

   Micro/nanofabricated devices. (A) One-dimensional patchy landscape; full device consisting of the array of 85 MHPs, each coupled (by 10 nanoslits) to two parallel feeder channels seen at the top and bottom. (B) Local neighborhood (scanning electron microscopy of adjacent MHPs). MHP connectivity and array topology is implemented through inter-patch corridors. (C) MHPs with three different supply niches. (D) Zero-dimensional (scanning electron microscopy of two uncoupled MHPs). (Scale bars: 100 μm.)

   
   
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   Fig. 3.

   Resource supply, space limitation, and parameter λ. (A) E. coli population dynamics in a single MHP. The black solid line corresponds to bacterial density in one of our 0D devices with a λ_max niche. The blue dotted line represents the modeled resource (Eq. 2), and the red dash-dotted line is the modeled density (Eq. 1). A strategy's life-history [ε, τ_r, τ_m] and environmental (λ) parameters are here fitted to the bacterial data (see Supporting Appendix). (B) Theoretical dynamics of the scaled system (see Supporting Appendix): The solid red and dashed blue curves correspond to bacteria φ(τ) and food ω(τ), respectively.

   
   
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   Fig. 4.

   E. coli in a flat landscape of habitat patches. (A) Photograph montage (see text) capturing the spatial dynamics of the metapopulation during the phase of spatial expansion of its range of occupancy (spatial-log-phase) in a flat, fully open (λ_i = λ_max) landscape. White pixels (x, y) correspond to GFP fluorescence. δt = 10 min. (B) Global (dashed blue) vs. local (solid black) dynamics. Logistic growth (Eq. 3) fitted to the global average is also shown (dotted red; τ_T ∼ 250 min). Vertical (dashed gray) lines in B mark the spatial-log-phase shown in A.

   
   
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   Fig. 5.

   Adaptation to a B&W landscape. Spatial dynamics ρ_i(t) of an E. coli metapopulation adapting to a simple, two-ecotope landscape. The black and white bar at the top shows the relative values of λ_i for the MHPs. White corresponds to λ_max ∼ 10λ*, and black corresponds to λ_min = 0 (see text). The log number of cells per MHP is color-coded as shown by the scale bar on the right. δt = 10 min. Epochs I–III defined by territorial expansions are indicated in gray. Solid gray bars mark the transition from one epoch to another.

   
   
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   Fig. 6.

   Adaptation to a rugged-landscape spatial dynamics ρ_i(t) of an E. coli metapopulation adapting to a complex, multiecotope landscape. The black and white bar at the top shows the relative values of λ_i for the ith MHP. The average number of cells in the local population ρ_i × K* of each MHP is color-coded as shown by the scale bar on the right. As before, δt = 10 min. Epochs I–III defined by territorial expansions are indicated in gray. Solid gray bars mark the transition from one epoch to another.