{"id":"861a2499-863b-406e-bf13-e31ab55c00d8","arxiv_id":"2506.13299","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":8,"one_line_summary":"Non-reciprocal forces between a vesicle and attached particles generate shape-dependent activity that produces membrane protrusions, invaginations, cyclic blebs, and polar motion in simulations.","lead":"The authors model a host cell as a fluid membrane vesicle and its symbionts as sticky spheres that pull on the membrane with unequal, non-reciprocal forces. The simulations show this asymmetry alone can grow branching protrusions, invaginations, and transient bulges that do not appear with symmetric forces or with a constant external pull.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The abstract's uniqueness claim is untested: no simulation with reciprocal interactions plus constant activity is performed; SI Fig. S5 only compares non-reciprocal forces to an external tether pull.","rationale":"I considered the reader's weakest_assumption, that Eq. (1) is an un-derived coarse-graining of host-symbiont interactions that relies on the Langevin bath to absorb momentum imbalance. I do not regard that as the most load-bearing concern, because the paper explicitly frames the model as generic (Section IV: 'we have not explicitly defined the nature of the non-reciprocal force'), and non-reciprocal pairwise couplings are a standard active-matter coarse-graining in the literature, including phoretic interactions. The paper's internal claim does not require a specific microscopic derivation. The sharper gap is the missing active-reciprocal baseline. The abstract's headline distinction is a comparative statement, and the only control offered, SI Fig. S5, is a constant tether pull, not a system with reciprocal interactions plus constant activity. The claim that cyclic blebbing and polar vesicle motion are absent in self-propelled-particle systems is based solely on refs. [17-19], not on a simulation using the same membrane model. This is directly testable with the provided TriLMP/LAMMPS code. The fixed-topology concern for 'budding' is real but mitigated by the one-particle-thick model reproducing the single-symbiont diagram; the multi-symbiont phases would also benefit from a topology-changing cross-check, but the missing active-reciprocal baseline is the more consequential test because it addresses the central uniqueness claim. If the reciprocal-active baseline produces the same morphologies, the paper's significance would need reframing; if it does not, the central claim is strengthened. The reader already flagged the novelty baseline issue in the rationale, so I partially agree with the reader's overall assessment, and the verdict remains CONDITIONAL.","tokens_in":14581,"tokens_out":17045,"duration_ms":177599,"concrete_test":"Run the same TriLMP vesicle and symbiont sizes used in Figs. 2 and 5, with the non-reciprocal pair style replaced by a reciprocal interaction of equal strength epsilon = epsilon_hs = epsilon_sh and with each symbiont given a constant self-propulsion force along its orientation (active Brownian particle, with translational and rotational diffusion from the same Langevin thermostat). Sweep the propulsion speed to match the protrusion activity levels and repeat 10 replicas at the key parameter points: epsilon/kBT = 10, Delta-epsilon = 0 (protrusion region) and epsilon_sh/kBT = 2, Delta-epsilon = -2 and -6 with NS = 5 (cyclic blebbing and polar vesicle). Classify morphologies with the paper's own criteria. If the cyclic blebbing or polar vesicle phase appears in the reciprocal-active baseline, the 'not reported' claim fails; if no such phases appear, the concern is settled.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim in the Abstract includes a uniqueness statement: the morphologies are 'not reported in reciprocal systems with constant activity,' and cyclic blebbing is 'not previously been reported in the context of self-propelled particles interacting with lipid membranes' (Sec. III C). The paper's only quantitative control against reciprocal driving is SI Fig. S5, where the symbiont is tethered to a membrane bead and pulled by an external constant force. That is not a reciprocal active system: the membrane-symbiont pair interaction is reciprocal and the activity is an external force applied to one particle, not a constant self-propulsion. It tests whether fS exceeds the tether-pulling threshold fP, but not whether reciprocal interactions with constant activity (e.g., active Brownian symbionts) can generate the same cyclic blebbing, polar vesicle motion, or branched protrusions. The uniqueness assertion therefore rests entirely on a literature comparison to refs. [17-19], not on a same-model baseline. A direct simulation with reciprocal forces plus constant self-propulsion is needed to support the claim that non-reciprocity is responsible for the reported morphologies.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"Muñoz-Basagoiti et al. introduce a coarse-grained model in which a host vesicle (dynamically triangulated membrane) and symbiont particles interact via pairwise forces that violate action–reaction symmetry. The force on a particle of species j from species i is given by Eq. (1), with strength ε_ij; the asymmetry is parameterized by Δε = ε_sh − ε_hs. The authors show by molecular dynamics/HMC simulations that a single symbiont produces stable protrusions for Δε > 0 and invaginations, catenoids, or budding for Δε < 0, and that the net 'symbiotic force' fS on the interacting cluster is proportional to |Δε| and depends on the cluster geometry, establishing a feedback between membrane shape and drive. With multiple symbionts, they report cooperative and suppressed protrusions for Δε > 0, and for Δε < 0 cyclic blebbing, ballistic polar vesicles, and 'inside-out' protrusions. Results are checked with a second membrane model (one-particle-thick) and against an equilibrium wrapping limit (γ=7, φ=6/σ̃, Δε=0) and a tether-pulling control.","tokens_in":14878,"tokens_out":9686,"duration_ms":94304,"significance":"If the results hold, the paper offers a minimal mechanism—non-reciprocal interaction alone—for generating a rich set of membrane morphologies relevant to symbiosis, and may inspire synthetic cell experiments. Strengths: explicit non-reciprocal pair style in LAMMPS; two independent membrane models; multiple replicas for the single-symbiont phase diagram; clear definition of fS and its shape feedback; code availability. The central open issue is the abstract's uniqueness claim relative to reciprocal active systems, which is not tested with a same-model baseline.","major_comments":[{"comment":"The claim that the observed morphologies are 'not reported in reciprocal systems with constant activity' and 'not accessible to systems which rely on intrinsic force production via motile filaments or other self-propelled agents' is not supported by a same-model control. The only quantitative control (SI Fig. S5) uses a reciprocal interaction plus an external constant pulling force on a tethered symbiont; this is not equivalent to a self-propelled (active Brownian) particle. No simulation with ε_hs = ε_sh and a constant self-propulsion force on the symbionts is reported. Please add such simulations (e.g., active Langevin dynamics of symbionts with reciprocal membrane interactions) at overlapping parameters, or soften the claims to 'not observed in our reciprocal control' and 'differ from previously reported active-membrane studies.' Without this, the abstract's novelty statement is not verifiable from the presented data.","section":"Abstract and Sec. III.C"},{"comment":"The protrusion region is defined by heuristic thresholds (p ≥ 30% protrusion probability, acylindricity a ≤ 1, cutoff d = 5σ) and the phase boundaries are only guides for the eye. The sensitivity of the phase diagram to these thresholds is not characterized. Since the existence of a distinct protrusion regime is a central result, please report the underlying probability distributions or a threshold-sensitivity analysis so the reader can judge whether the boundaries correspond to sharp or gradual crossovers.","section":"Sec. III.A and Fig. 2A"},{"comment":"The multi-symbiont phase diagrams are based on only three replicas per parameter set, yet they identify several dynamical phases (cyclic blebbing, polar vesicle, inside-out protrusions). For stochastic classification of transient morphologies, three replicas is low, especially for distinguishing cyclic blebbing from stochastic membrane fluctuations. Please provide additional replicas for the dynamic phases or give quantitative order parameters with error bars, and state explicitly how 'cyclic' blebbing is defined and measured.","section":"Sec. III.C, Figs. 4B and 5"},{"comment":"The model relies on the Langevin thermostat to absorb the momentum imbalance produced by the non-reciprocal forces. The sensitivity of the results to the thermostat damping coefficient and to simulation box size is not reported, and these choices could affect the persistence or magnitude of the symbiotic force fS. Please add a short parameter check (e.g., two damping values and two box sizes) to show that the morphologies and the fS scaling in Fig. 3B are robust to the thermostatting protocol.","section":"Sec. II.C and Sec. III.B"}],"minor_comments":[{"comment":"The caption of Fig. 5 states ε_sh/kBT = 2 while Sec. III.C states ε_hs/kBT = 2; please clarify which interaction strength is held fixed in the Δε < 0 multi-symbiont simulations, since the wrapping state and hence the available symbiotic force depend on it.","section":"Sec. III.C and Fig. 5 caption"},{"comment":"The caption refers to 'white data points' while the text later refers to 'white diamond symbols' for the same region; please make the symbol terminology consistent.","section":"Fig. 2A caption and Sec. III.A"},{"comment":"The caption calls the control 'reciprocal and non-reciprocal pulling'; the control is actually a reciprocal interaction plus an external force, which is a different driving protocol. Please rephrase to avoid implying that it is an active self-propulsion baseline.","section":"SI Fig. S5 caption"},{"comment":"The sentence 'The shape of a cell influences, and it is influenced by its interactions with its neighbours' is grammatically awkward; consider rephrasing for clarity.","section":"Abstract and Introduction"},{"comment":"The initial placement of symbionts (distance from the vesicle, equilibration protocol) is not fully specified; please add the exact initialization details used for the single- and multi-symbiont simulations.","section":"Sec. II and SI Sec. I"}],"recommendation":"major_revision","confidential_remarks":"This is an exploratory simulation study with a clear and useful model, but the advertised novelty relative to reciprocal active systems is not yet backed by a same-model control. I would like to see the authors either add a reciprocal-plus-active-self-propulsion simulation or explicitly retract the uniqueness claim. The low replica count in the multi-symbiont diagrams and the inconsistency in ε_hs/ε_sh notation in Sec. III.C/Fig. 5 should also be fixed. I do not think the lack of a microscopic derivation for Eq. (1) is a flaw, since the model is explicitly coarse-grained and the mapping to phoretic interactions is stated."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a solid simulation study that introduces a genuinely new mechanism — non-reciprocal pairwise forces between a fluid vesicle and attached particles generate a shape-dependent 'symbiotic force' that can extrude protrusions, invaginations, blebs, and polar vesicle motion. The modeling is careful and the main phenomenon is real, but the abstract's uniqueness claim (that these morphologies are not accessible to reciprocal systems) is not directly tested. I'd ask for a same-model control before believing that specific claim.\n\nWhat's new: the idea that asymmetry in pairwise interactions alone, without intrinsic self-propulsion, is enough to create a feedback loop between membrane deformation and driving force. The fS force is proportional to |Δε| and its direction and persistence depend on the cluster geometry — that's the core mechanism, and it's well supported by the data in Fig 3. The morphology diagrams in Fig 2 and Fig 5 are rich and largely reproduced with a second membrane model that allows topology changes, which is a genuine check. The comparisons to reciprocal adhesion and to constant tether pulling are appropriate baselines for the force threshold, and the team runs multiple replicas.\n\nWhere I'd push back: the claim that these morphologies are 'not reported in reciprocal systems with constant activity' is, as far as I can tell, supported only by a literature comparison (refs 17–19) and by the tether-pulling control. The tether-pulling setup is not a reciprocal active system: the membrane-symbiont pair interaction is reciprocal and the activity is an external constant force on one tethered particle. That's a different animal from, say, active Brownian symbionts with reciprocal pairwise forces. Without a direct simulation of a reciprocal system with constant self-propulsion, I can't tell if non-reciprocity is truly essential for cyclic blebbing, polar vesicle motion, or the branched protrusions. I'd like to see that baseline added, or the uniqueness language softened.\n\nOther soft spots: the morphology thresholds are heuristic (30% protrusion probability, d=5σ, acylindricity ≤1) with no sensitivity analysis. The 'budding' in the triangulated model is inferred from neighbor-count saturation because the topology is fixed, and the one-particle-thick model often ruptures instead — so budding is the least certain region of the phase diagram. The code is promised but not linked in the text, which I'd also fix.\n\nOverall: the mechanism is interesting, the simulations are careful, and the main claim of shape-dependent activity holds. The overclaim in the abstract and the missing reciprocal+activity control are addressable, not fatal. This deserves peer review; I'd send it back asking for that baseline and a fuller sensitivity analysis, but it's a legitimately new idea in active soft matter.","headline":"New non-reciprocal membrane-remodeling mechanism with solid simulations, but the abstract's uniqueness claim needs a same-model reciprocal-active control before publication.","tokens_in":15407,"tokens_out":3088,"would_cite":true,"duration_ms":29723,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A fluid vesicle and hard-sphere symbionts with unequal two-way interaction strengths generate protrusions, invaginations, budding, cyclic blebs, and a ballistically moving polar vesicle.","keywords":["non-reciprocal interactions","membrane remodeling","symbiosis","active matter","coarse-grained simulation","fluid vesicles","morphogenesis","symbiotic force"],"falsifier":"Re-run the triangulated-membrane simulations with $\\Delta\\varepsilon=0$ and apply to the symbiont an external constant traction equal to the steady-state symbiotic force measured at finite $\\Delta\\varepsilon$; if the same morphology diagram (protrusions, cyclic blebs, ballistic polar vesicle) still appears, the claim that shape-dependent non-reciprocal feedback drives these morphologies is falsified.","tokens_in":14341,"feed_emoji":"🧫","tokens_out":12096,"duration_ms":112915,"temperature":0.7,"pith_summary":"This paper tries to establish that the shapes of cells can be changed by the mere asymmetry of their interactions with symbiotic partners, with no internal motors or self-propulsion required. The authors simulate a fluid vesicle (the host) interacting with hard-sphere symbionts through pairwise forces whose strength depends on direction: $\\varepsilon_{sh}$ for symbiont-on-host and $\\varepsilon_{hs}$ for host-on-symbiont. When these strengths differ, parameterized by $\\Delta\\varepsilon=\\varepsilon_{sh}-\\varepsilon_{hs}$, an unbalanced symbiotic force arises on the contact cluster, pointing toward the symbiont for $\\Delta\\varepsilon>0$ and toward the membrane for $\\Delta\\varepsilon<0$. Because the magnitude of this force changes as the membrane wraps, buds, or protrudes, the system feeds its own deformation back into the driving force. The paper reports that this feedback generates branched protrusions, invaginations, budding, cyclic blebs, and a ballistically moving polar vesicle, morphologies it argues are not produced by reciprocal systems with constant activity.","feed_headline":"Unequal partner forces grow protrusions, blebs, and motion","feed_subtitle":"Breaking action-reaction symmetry between a vesicle and its symbionts drives membrane shapes no reciprocal system shows.","key_machinery":"The central object is the symbiotic force $\\vec f_S$, defined as the net force on the cluster of membrane beads and symbiont particles within interaction range. In the reciprocal limit $\\Delta\\varepsilon=0$, this force cancels by action-reaction; when $\\Delta\\varepsilon\\neq 0$, it is nonzero, grows with $|\\Delta\\varepsilon|$ and with cluster size, and carries a direction set by the sign of $\\Delta\\varepsilon$. Its dependence on the wrapping geometry closes the feedback loop: as the membrane deforms, the cluster changes and $\\vec f_S$ changes with it. The machinery is implemented as a dynamically triangulated membrane with constrained area and volume, Monte Carlo bond swaps that make the membrane fluid, and a Langevin thermostat that absorbs the unbalanced momentum.","core_discovery":"The central claim is that the non-reciprocal pairwise force law $\\vec F_{k,i\\to l,j}=-\\phi\\varepsilon_{ij}/r^\\gamma\\,\\hat r_{kl}$ for $r<r_c$, with $\\varepsilon_{sh}\\neq\\varepsilon_{hs}$, turns passive contact into an active shape generator for fluid membranes. For $\\Delta\\varepsilon>0$ the net force on the host-symbiont cluster points toward the symbiont and, once $\\Delta\\varepsilon/k_BT\\gtrsim 5$, extrudes dynamic protrusions; for $\\Delta\\varepsilon<0$ the force instead pushes symbionts into wrapped, invaginated, or budded states, and with several symbionts produces cyclic blebs and a polar vesicle that moves ballistically. The key point is that the symbiotic force $\\vec f_S$ is not fixed: it depends on the geometry of the cluster, so the local membrane deformation alters the very force that drives it. The paper presents this shape-force feedback as the mechanism behind morphologies that are not accessible to reciprocal membranes or to membranes deformed by self-propelled particles.","pith_inferences":["Because $\\gamma=2$ maps the same force law onto phoretic interactions between catalytically coated colloids, the model suggests a direct experimental test: two colloid species with independently tunable surface chemistry paired with a giant vesicle should show protrusion for one sign of $\\Delta\\varepsilon$ and invagination or blebbing for the other; this goes beyond the paper, which does not propo","The shape-dependent $\\vec f_S$ could be coarse-grained into a local active tension or curvature-dependent force in a continuum membrane theory, letting future work predict phase boundaries for cyclic blebbing or polar motion without resolving every particle; the authors do not make this connection.","If the interaction strengths track metabolic exchange rates, the results imply that a biological cell could switch between protrusive, invaginated, and blebbing morphologies purely by tuning what it gives to and receives from a partner, without invoking cytoskeletal machinery; this is an inference from the authors' discussion, not a claim they test."],"forward_implications":["A single symbiont with $\\Delta\\varepsilon/k_BT\\gtrsim 5$ extrudes a persistent membrane protrusion even though no agent explicitly pulls the membrane.","For $\\Delta\\varepsilon<0$, symbionts become wrapped, invaginated, or budded by the host, and at intermediate symbiont numbers the membrane produces blebs in a cyclic sequence.","The number of symbionts controls the mode: independent protrusions at low coverage, cooperative branched protrusions at intermediate coverage, and suppression by membrane tension at high coverage.","Asymmetric symbiont distributions can create a polar vesicle that moves ballistically.","These regimes are not found in reciprocal systems with constant intrinsic activity, so their observation would indicate a genuinely interaction-derived driving force."],"supporting_citations":[{"why":"Introduces non-reciprocal interactions between catalytically coated colloids and the resulting net force on an interacting cluster, and supplies the $\\gamma=2$ phoretic mapping used to generalize the force law.","marker":"[10]"},{"why":"Supply the dynamically triangulated network model and simulation methodology for the fluid host membrane.","marker":"[20, 21]"},{"why":"Gives the equilibrium theory of colloid wrapping by a fluid membrane, the reciprocal baseline whose morphologies the model departs from at $\\Delta\\varepsilon\\neq0$.","marker":"[22]"},{"why":"Results on self-propelled particles deforming and moving vesicles, the baseline for intrinsic-activity morphologies that the paper says its phases are not reported in.","marker":"[17–19]"},{"why":"One-particle-thick membrane model used to reproduce the single-symbiont morphology diagram and to locate topology-change regions inaccessible to fixed-topology membranes.","marker":"[26]"},{"why":"Provides the tube-formation force threshold $f_P\\sim\\sqrt{\\kappa\\Sigma}$, the theoretical scale the symbiotic force must exceed to extrude a protrusion.","marker":"[27]"}],"fun_headline_variants":["Nonreciprocal forces sculpt membrane shapes unseen in reciprocal systems","Asymmetric symbiont forces drive protrusions, invaginations, and blebs","Membrane shape-force feedback yields nonreciprocal morphogenesis","Unequal partner forces create dynamic membrane morphologies","Symbiotic asymmetry remodels membranes into active shapes"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The model stands on the assumption that a symbiont can push on a host more strongly than the host pushes back, as an instantaneous pairwise force with the surrounding fluid absorbing the missing momentum; if real host-symbiont coupling is mechanically reciprocal or mediated mainly by chemical fields, the predicted shapes would not arise.","fun_headline_variants_meta":{"raw":{"variants":["Nonreciprocal forces sculpt membrane shapes unseen in reciprocal systems","Asymmetric symbiont forces drive protrusions, invaginations, and blebs","Membrane shape-force feedback yields nonreciprocal morphogenesis","Unequal partner forces create dynamic membrane morphologies","Symbiotic asymmetry remodels membranes into active shapes"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001162,"raw_usage":{"total_tokens":4770,"prompt_tokens":867,"completion_tokens":3903,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":483,"completion_tokens_details":{"reasoning_tokens":3818}},"tokens_in":483,"tokens_out":3903,"duration_ms":27880,"temperature":1.0,"reasoning_tokens":3818,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T20:05:42.518011+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Re-run the triangulated-membrane simulations with $\\Delta\\varepsilon=0$ and apply to the symbiont an external constant traction equal to the steady-state symbiotic force measured at finite $\\Delta\\varepsilon$; if the same morphology diagram (protrusions, cyclic blebs, ballistic polar vesicle) still appears, the claim that shape-dependent non-reciprocal feedback drives these morphologies is falsified.","supporting_citations":[{"cited_title":"Self-assembly of catalytically active colloidal molecules: Tailoring activity through surface chemistry","cited_arxiv_id":"1306.6596","evidence_quote":"Introduces non-reciprocal interactions between catalytically coated colloids and the resulting net force on an interacting cluster, and supplies the $\\gamma=2$ phoretic mapping used to generalize the force law."},{"cited_title":"Deserno, Elastic deformation of a fluid membrane upon colloid binding, Physical Review E69, 031903 (2004), publisher: American Physical Society","cited_arxiv_id":null,"evidence_quote":"Gives the equilibrium theory of colloid wrapping by a fluid membrane, the reciprocal baseline whose morphologies the model departs from at $\\Delta\\varepsilon\\neq0$."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"One-particle-thick membrane model used to reproduce the single-symbiont morphology diagram and to locate topology-change regions inaccessible to fixed-topology membranes."},{"cited_title":"Derényi, F","cited_arxiv_id":null,"evidence_quote":"Provides the tube-formation force threshold $f_P\\sim\\sqrt{\\kappa\\Sigma}$, the theoretical scale the symbiotic force must exceed to extrude a protrusion."}],"review_version":1}