Fig 6. Passively ingested nematodes but not skin-penetrating nematodes show experience-dependent modulation of CO₂-response valence.

A. Passively ingested H. contortus iL3s are neutral to CO₂ when cultured on feces, but attracted to CO₂ when cultured off feces in dH₂O. CO₂ attraction occurs within 1 week following removal from feces, and is maintained for at least 5 weeks. Nematodes were allowed to develop on feces for at least 7 days. They were then either tested immediately, or stored in dH₂O for up to 5 weeks and then tested. The “on-feces” group included iL3s aged up to 9 weeks, confirming that CO₂ attraction occurred as a result of removal from feces rather than increased iL3 age. *p<0.05, **p<0.01, ***p<0.001, Kruskal-Wallis test with Dunn’s post-test. n = 8–16 trials for each condition. B-C. Skin-penetrating S. stercoralis (B) and A. ceylanicum (C) iL3s do not show experience-dependent modulation of CO₂-response valence. Nematodes were allowed to develop on feces for 7 days (B) or 10 days (C) until they reached the iL3 stage. iL3s were then either tested immediately, stored in BU saline [64] for 7 days and then tested, or stored in BU saline for 14 days and then tested. CO₂ response was slightly attenuated in S. stercoralis iL3s cultured off feces, but did not shift from repulsion to attraction (B); CO₂ response was unchanged in A. ceylanicum iL3s cultured on vs. off feces (C). *p<0.05, Kruskal-Wallis test with Dunn’s post-test (B) or one-way ANOVA with Dunnett’s post-test (C). n = 8–10 trials for each condition. Graphs show medians and interquartile ranges.