P2.188 Thursday, Jan. 5 The effect of temperature on running in the tarantula, Aphonopelma hentzi BOOSTER, N.; SU, F.Y.*; ADOLPH, S.C.; AHN, A.N.; Pitzer College; Harvey Mudd College; Harvey Mudd College; Harvey Mudd College firstname.lastname@example.org
Tarantulas lack extensor muscles in some of their leg joints but still need to extend their limbs. Instead of muscles, extension in the leg joints is mediated by a hydraulic mechanism, where hemolymph is pumped from the prosoma (or thorax) into the legs. Our study examined tarantulas sprinting in a temperature-controlled environmental chamber at four temperatures: 15, 24, 32, and 40°C. Using a high-speed video camera (Allied Vision Technologies; Pike model), we quantified the three-dimensional joint angle changes of the femur-patella (proximal) and tibia-metatarsus (distal) on the first (front) and fourth (hind) legs in four animals. Since muscle activity increases with temperature, we examined the hydraulic mechanism using extension fraction, or the fraction of the stride devoted to extension. Stride frequency, as expected, increased from 3.7 to 9.4 Hz at 15 and 40°C, respectively. Stride length, however, did not change with temperature at 1.3 ± 0.1 body lengths (7.1 ± 1.6 cm). Extension fraction remained constant with temperature at 0.48 ± 0.003. Additionally, the joint angle range for each of the four joints remained constant with temperature. Interestingly, the joint angle ranges of the proximal joints exceeded that of the distal joints by 39.1 ± 4.0° (front leg) and 31.7 ± 6.9° (hind leg). The much smaller joint angle range for the distal joints suggests the distal joints may act more like struts during running in tarantulas. The kinematics during running indicate that hemolymph viscosity does not seem to limit joint movement as temperature increases from 15 to 40°C, which includes ecologically relevant temperatures. We thank HHMI, Barbara Stokes Dewey, and the Biology Department of HMC for funding.