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.