Meeting Abstract
Understanding the mechanics behind morphological systems offers insights into their evolution. Recent work on linkage systems in fish and crustaceans has suggested that the evolution of such systems may depend on mechanical sensitivity, where geometrical changes to different parts of a system can have variable influence on mechanical outputs. While examined at the evolutionary level, no study has tested directly for mechanical sensitivity within a biological linkage system at the mechanical level. In this study, we analyze the mechanical sensitivity of three mechanical outputs of the fish cranial linkage. We examine three measures of kinematic transmission (KT, the ratio of output link to input link rotation) based on a neurocranium input link and three output links: the suspensorium, hyoid, and lower jaw. We investigate two specific questions about the sensitivity of these outputs to changes in linkage geometry: 1) What changes in linkage geometry affect the KT of one output link while keeping the other KTs constant? 2) Which geometry changes result in the largest and smallest changes to each KT? We addressed these questions using a kinematic model based on the cranial linkage of Salmo salar available from the R package linkR. We systematically changed the linkage geometry by altering the positions of each joint and calculating the resulting KTs. Our results show that 1) it is possible to change the geometry such that each KT can be altered without affecting the others, and 2) there are multiple ways to alter link length, some of which influence KTs more than others. These results provide insight into the morphological evolution of the fish skull and highlight which structural features in the system may have more freedom to evolve than others, demonstrating the value of applying mechanics to organismal evolution.
