Fig. 3.
Effect of body orientation on heart and ventilation rates of grasshoppers. (A) Heart rates for grasshoppers placed into head-down, head-up, or prone position (in random order). Heart movements were observed with a microscope through the dorsal cuticle after removal of wings. Heart rate fell with time in the head-down but not other orientations (linear mixed effect model with individual as a random variable, significant orientation*time effect; F4,112 = 2.92; P = 0.024). Note that the large confidence limits in 3A reflect large interindividual variation; within animals, trends were more consistent (SI Appendix, Table S8). After 5 min, heart rate was significantly lower in the head-down than the head-up position (F2,118 = 3.42; P = 0.036). (B) Body orientation significantly affected heart rates of 4 locusts measured using synchrotron X-ray video of the pulses of the cardiac tracheae (paired t test, t1,3 = 3.52; n = 4; P = 0.036). (C) Ventilation rates were significantly affected by orientation (F2,96 = 4.23; P = 0.017, ANOVA with individual as random factor), with higher rates for animals in the head-down position.