The theory of morphological integration states that the genetic architecture has a modular pattern, in which a set of genes influences more strongly a unique character complex that exerts a specific function, affecting in a lesser extent other characters of the organism. In general, the modularity of a phenotypic structure is assessed in a hypothesis testing framework, whereby previous information on the structure development and/or function is used. However, this approach incorporates the system functionality in an indirect manner in order to infer about modularity. An alternative approach is to directly measure the variation in the character complex associated to variation in the function it is expected to execute. Arnold's paradigm, widely used in ecomorphology and ecophysiology studies, provides exactly that measure by means of performance gradients. Performance gradients measure how much variation in performance is explained by variation in morphology/physiology. Yet, functional performance studies do not normally infer about modularity and modularity studies do not explicitly measure the influence of modules on functional performance. The proposition of this project is to integrate the approaches adopted in modularity theory with Arnold's paradigm to study the relationships between the skull and limbs of tropidurinae lizards with bite force and running speed, respectively. We aim to elucidate whether characters detected as modules actually influence a specific function.
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