Sex change in clownfish as an ARCH-governed biological decision

Single causal factors rarely govern biological transitions that are rapid, discrete, and largely irreversible. Instead, they emerge from the coordinated alignment of multiple regulatory domains that collectively determine whether execution occurs. Here, we apply the ARCH framework—a multiplicative, threshold-based model of biological decision-making—to socially controlled sex change in clownfish ( Amphiprion spp.). The ARCH model formalizes execution as requiring convergence across four jointly necessary domains: Archetype (latent structural readiness), Drive (endocrine activation favoring ovarian differentiation), Context (social and environmental permissiveness), and Phase (temporal, developmental, and physiological gating). Using evidence from behavioral, endocrine, molecular, and developmental studies, we show that sex change in clownfish exhibits defining properties of ARCH-governed decisions, including zero-term veto effects, persistence of metastable intermediate states, non-linear interactions among regulatory inputs, and hysteresis following commitment. Removal of the dominant female is necessary but insufficient for transition; endocrine manipulations can veto execution despite social permissiveness, and stress and developmental constraints modulate the timing and probability of commitment. Framing sex change as an ARCH-governed biological decision unifies disparate empirical findings and generates explicit, falsifiable predictions regarding how perturbations across domains interact to control the probability, timing, and stability of sexual transition. More broadly, this work positions sequential hermaphroditism as a model system for studying threshold-governed decision architectures linking social context, endocrine signaling, and irreversible behavioral change. Socially controlled sex change in clownfish operates as a threshold-governed, multiplicative biological decision. Transition from the male to female phenotype occurs only when four jointly necessary domains converge: Archetype (latent structural readiness of gonadal and neural substrates), Drive (endocrine bias toward estrogenic signaling), Context (social permissiveness following loss of the dominant female), and Phase (developmental, temporal, and physiological gating). Partial activation of individual domains stabilizes metastable intermediate states without commitment, while suppression of any single domain vetoes execution. Sustained alignment above a critical threshold (A × D × C × Φ ≥ Θ) produces irreversible commitment to the female phenotype, consistent with bistability and hysteresis characteristic of major biological transitions. • Socially controlled sex change is framed as a threshold-governed biological decision. • Male-to-female transition requires conjunctive alignment of structural, endocrine, social, and temporal domains. • Suppression of any single domain vetoes sex change despite permissive conditions in others. • Partial domain alignment stabilizes metastable intermediate sexual states without commitment. • Sustained alignment produces irreversible commitment with hysteresis characteristic of hormone-dependent behaviors.