Figure 3. Olfactory responses of mammalian-parasitic nematodes.

A. Str. stercoralis is attracted to a number of human-emitted odorants. Red = attractants for Str. stercoralis that also attract anthropophilic mosquitoes [31], [52]–[58]. n = 6–23 trials per odorant. Str. stercoralis did not respond to the chemotaxis controls (Figure S3). *, P<0.05; ***, P<0.001 relative to control, t-test (CO₂ vs. air and L-lactic acid vs. H₂O) or one-way ANOVA with Bonferroni post-test (all other odorants vs. paraffin oil). B. Olfactory responses across species. Response magnitudes are color-coded according to the scale shown to the right of the heat map, and odorants are ordered based on hierarchical cluster analysis. n = 6–14 trials for each odorant-species combination. Each species exhibited a unique odor response profile (P<0.0001, two-way ANOVA with Tukey's post-test). Data for responses of EPNs and C. elegans to 10% CO₂ are from Dillman et al., 2012 [22]. Red = skin-penetrating; gold = passively ingested; blue = insect-parasitic; green = free-living. C. Responses of Ha. contortus to grass odor. Responses to the odors of two different grass samples were examined. n = 8–17 trials for each sample. D. Olfactory preferences reflect host specificity rather than phylogeny. The behavioral dendrogram was constructed based on the odor response profiles of each species. Hierarchical cluster analysis was performed using UPGMA (Unweighted Pair Group Method with Arithmetic Mean). Euclidean distance was used as a similarity measure. Hosts (humans, ruminants, rodents, or insects) for each species are indicated. Coph. Corr. = 0.96. For all graphs, error bars indicate SEM.