Analysis of the Form-Function Relationship: Digging Behavior as a Case Study

Abstract

Studies of functional morphology focus on species showing evident specializations, or at least some degree of divergence from the so-called “generalized phenotype.” This may have led to the proposal of the form-function correlation paradigm, which assumes that there is a close relationship between anatomical traits and their biological use. A question that arises in relation to digging is what minimum structural and functional requirements would be needed to carry it out properly regarding a particular biological role? Here, we review the main approaches and results achieved in the study of morphological traits related to the highly mechanically demanding function of digging, especially in the South American subterranean rodents Ctenomys and related caviomorph rodents within the mammalian context. It is seen that whatever the biological role that soil digging will play for a particular group of organisms, they must have the ability to disaggregate a relatively resistant material and, therefore, the magnitude of the produced force is a critical point. Muscles of diggers should not only be able to produce large forces but also to sustain them for long periods of time, for which the muscle architecture is another important issue. Digging tools (e.g., limb bones, claws, incisors, skull) must have the capacity to withstand the concomitant reaction forces without structural failure. In this regard cranial sutures, jaw and skull geometry could play an important role in force dissipation. Examples of species that do not diverge from the generalized surface-dweller phenotype, but are nonetheless capable of constructing complex burrows, are examined regarding some evolutionary scenarios where fulfilling minimum functional requirements would have allowed organisms to adequately perform new biological roles.