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Trade-offs in Locomotion Performance Across Ecological Contexts: Turtle Ant Running Speed in the Canopy Open Access

Evolutionary trade-offs in trait function constrain how organisms interact with their environment. The canopy environment is structurally complex, with foraging surfaces of a range of sizes and orientations, and often dominated by ants. Nevertheless, little is known about how ants use canopy structures as they forage, and what trade-offs they might experience. Turtle ants (Cephalotes) are a species-rich genus of canopy ants that have undergone exceptional morphological diversification. In particular, there is a five-fold difference in body length across species, which is likely to have important consequences for locomotion performance. This project examines performance trade-offs in turtle ants across a variety of ecological contexts that occur in the canopy. The focal species for this study were Cephalotes varians, in the laboratory, and Cephalotes pusillus, Cephalotes clypeatus and Cephalotes borgmeiri in the field. Field experiments were conducted in the cerrado region of Brazil. Performance ability was measured by recording peak running speeds across a variety of surface widths and orientations in all experiments. Running performance was only minimally reduced by path width in most species, allowing peak speeds on many structures in the canopy. On larger paths, vertical orientation reduced speeds in most species, possibly impacting the use of vertical paths when maximizing foraging efficiency. Slower species maintained similar running speeds on smaller paths, suggesting they may use smaller paths more frequently. Body size was not a reliable predictor of running speed in Cephalotes, suggesting other morphological and behavioral traits may influence speed. Ongoing laboratory studies are examining leg shape and length in absolute terms and relative to body size, to assess how these morphological features may influence running performance across species. Moreover, newly collected field data will be analyzed to provide contrasts with additional species that have different body sizes and morphology. Broadly, this research contributes to understanding functional trade-offs between organismal structure and environment.

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