Observability Asymmetry Determines the Fate of Cross-Domain Signal Reuse in Evolved Communicators

When evolved agents communicate about multiple environmental dimensions using a limited signal vocabulary, cross-domain signal reuse emerges as a natural consequence of communicative pressure. But what determines whether such reuse remains context-dependent and novel (metaphor-like) or conventionalizes into stable polysemy? We present an artificial life simulation in which populations of neural-network-controlled agents evolve communication strategies in a dual-domain foraging environment where one dimension (resource quality) is directly observable and the other (danger) is partially hidden. This observability asymmetry creates a natural source-to-target directionality: agents develop rich signal conventions for the observable domain and face pressure to borrow those signals for the elusive domain. Across 9 ablation conditions with 5–10 independent evolutionary runs each (500 generations, 50 agents), we find that observability asymmetry between domains determines the character of cross-domain signal reuse. When both domains are equally observable, cross-domain signals conventionalize at rates equal to novel usage (novel-to-conventionalization ratio of 1.1:1). When the target domain is partially hidden, novel cross-domain usage dominates over conventionalization at ratios of 4:1 to 13:1 (Mann-Whitney U = 0, p < 0.001 for all pairwise comparisons against the symmetric condition). Additionally, positive structural correspondence between domains elevates dual-correct transfer events by an order of magnitude (p < 0.01). Baseline correction via domain-shuffled permutation tests reveals that absolute cross-domain transfer rates do not exceed chance, but the distribution of transfer types (novel vs. conventionalized) is robustly condition-dependent. These findings suggest that the elusiveness of a target domain is a structural precondition for the persistence of metaphor-like signal usage, and that observable target domains promote conventionalization into polysemy.