Stress facilitated SDC evolution in structured environments. (A) Experimental data of the yields at varying stress levels (6-APA concentrations). The yield of SDC in the homogeneous group (solid line with circle symbols) remained constant, whereas the yield of the cheater in the homogeneous group (solid line with triangular symbols) remained null. The yield of SDC in heterogeneous groups (dash line with circle symbols) remained null, and the yield of cheater decreased with stress intensity (dash line with triangular symbols). Homo. SDC, homogeneous SDC group; Het. SDC, heterogeneous SDC group; Homo. Cheater, homogeneous cheater group; Het. Cheater, heterogeneous cheater group. (B) The|$\Delta R$| increased with stress intensity when |$\lambda$| = 2.|$\Delta R$|  |$\ge$| 0 signified an increase in SDCs, whereas|$\Delta R$| < 0 denoted an increase in cheaters. The error bar in panels A-B represented the standard deviation of three biological replicates. (C) Illustration of how high stress facilitated SDC evolution. The reduced yield of heterogeneous cheater groups under high stress created selective pressure that favored the survival and proliferation of SDCs. Because SDCs produced public goods that alleviated stress, they were better equipped to survive and reproduce in stressful environments.