Meeting Abstract
Body size is profoundly important to organisms. Smaller individuals typically face greater predation pressures than larger individuals because they are vulnerable to more predators. In many organisms, juveniles may have higher performance that partly offsets their size disadvantage. However, despite the availability of scaling theory that provides testable hypotheses, the ontogeny of performance is not yet very well studied. We used high-speed video recordings to study the scaling relationships among morphology, muscle cross-sectional area (CSA), and defensive strike performance in nine Texas ratsnakes (Pantherophis obsoletus). We tested the hypotheses that maximum strike velocity is independent of body mass and that strike acceleration decreases with increasing body mass. Larger snakes struck from greater distances (range for all snakes = 3.5–30.1 cm), but all snakes covered the strike distance in similar times (0.04–0.2 s). Hence, maximum strike velocity (1.3–3.4 ms-1) and acceleration (46.1–299.2 ms-2) were positively related to body mass, refuting both hypotheses. Relative head mass decreased in larger snakes whereas relative muscle CSA (at multiple positions along the body) scaled with positive allometry or isometry. The greater relative muscle CSA of larger ratsnakes allows them to produce relatively higher forces, and those forces act on a relatively smaller head mass when it is thrusted forward. This differential scaling of cranial and axial morphology allows larger snakes to strike with higher velocities and accelerations than smaller individuals.
