Many-to-one form-to-function mapping weakens parallel morphological evolution

Evolutionary ecologists aim to explain and predict evolutionary change under different selective regimes. Theory suggests that such evolutionary prediction should be more difficult for biomechanical systems in which different trait combinations generate the same functional output: “many-to-one mapping”. Many-to-one mapping of phenotype to function enables multiple morphological solutions to meet the same adaptive challenges. Therefore, many-to-one mapping should undermine parallel morphological evolution, and hence evolutionary predictability, even when selection pressures are shared among populations. Studying 16 replicate pairs of lake- and stream-adapted threespine stickleback (Gasterosteus aculeatus), we quantified three parts of the teleost feeding apparatus and used biomechanical models to calculate their expected functional outputs. The three feeding structures differed in their form-to-function relationship from one-to-one (lower jaw lever ratio) to increasingly many-to-one (buc..., main.cole Main R script to run first, to load packages, and set up directory structure, along with other housekeeping.  functions.cole Contains functions for analysis. Is sourced by main.cole  figures.cole Contains figure functions. Is sourced by main.R  analyses.cole_MS_161115 analysis code, used to generate the statistics, analyses, and output in the manuscript. requires main.cole to be run first.  CalculateKTCode Calculates Kinematic Transmission for the Opercular 4-bar system.  Complexity Simulation Code for the simulation that compares levels of many-to-one mapping across biomechanical systems.  03.dietCntnt_fromGitHub_161013 Gut content data.  Results_all_R_SI_KT_sexSL Biomechanical trait measurements.  ,