CLAUSSEN, D.L.*; SNASHALL, J.; BARDEN, C.; Miami Univ., Oxford, OH; Miami Univ., Oxford, OH; Miami Univ., Oxford, OH: Effects of slope, substrate, and temperature on forces associated with locomotion of the ornate box turtle, Terrapene ornata

In spite of several studies of the locomotor performances of turtles, we as yet know relatively little about the mechanical forces involved. The present investigation monitored the pulling forces exerted by ornate box turtles tethered to a force transducer. Each turtle was tested three times under each of the following conditions: on styrofoam, dry sand, wet sand, and pea gravel substrates (horizontally at 25 °C); on slopes ranging from +30 to -30 degrees (at 25 °C on styrofoam); and at temperatures ranging from 20 to 40 °C (horizontally on styrofoam). The median force developed during the three initial surges, the time required for this peak force development, and the maximum force, including “second efforts, developed by the turtle under these specific conditions were determined. Although, based on skeletal muscle geometry and force generation, we had predicted scaling to the 0.67 power of body mass, both median and maximum forces actually increased with increasing body mass in a nearly isometric manner. The forces exerted were significantly affected by substrate type, but the patterns for the two forces were different. Median forces were greatest on styrofoam, whereas maximum forces were greatest on pea gravel. Both forces progressively increased as slope decreased from +30 to -30 degrees. The rate of force generation (N/s) was greatest at intermediate slopes. Contact force tended to increase as normal force increased, and was strongly influenced by slope, increasing from -30 to +30 degrees. Surprisingly, we found no significant effects of temperature on tether forces, contraction times, or rates. This evaluation of pulling forces associated with box turtle locomotion thus revealed some interesting and, at times unexpected, relationships.