Inter-individual variability and thigmotaxis-like spatial phenotypes in Tenebrio molitor

Abstract

Aim: To establish Tenebrio molitor as a viable model for studying thigmotaxis, as the physiological simplicity and practical advantages of these invertebrates make them ideal for pharmacological screening.

Methods: Adult mealworms (Tenebrio molitor, n = 13) were tested individually in a circular Petri dish arena during a 5-minute free-exploration period. Behavioral sessions were video-recorded, and locomotor trajectories were extracted using ToxTrac software. Three metrics were computed: total distance traveled, center occupancy, and wall occupancy. Data were analyzed in Python using unsupervised k-means clustering (k = 2) on z-score standardized metrics to identify distinct behavioral phenotypes, with cluster validity assessed via silhouette coefficients.

Results: Subjects were partitioned by k-means clustering into two subtypes as Cluster 0 (n = 7) and Cluster 1 (n = 6). Distance traveled differed significantly between clusters (t = 4.42, p = .003, d = 2.59), with thigmotaxis associated with greater distances traveled. Wall occupancy also differed significantly (t = 3.33, p = .015, d = 1.98), reflecting pronounced variation in peripheral spatial preference. Center occupancy showed a large effect size (d = 1.16) but lacked statistical significance (p = .063). Results suggest the clusters capture substantial behavioral heterogeneity despite the small sample size (n = 13).

Conclusion: These findings validate Tenebrio molitor as a viable thigmotaxis model, reflecting structured behavioral heterogeneity vertebrate-like. This species provides a high-throughput, cost-effective foundation for future research into the evolutionary conservation and pharmacological modulation of anxiety-related traits.