restricted access I.4 Functional Morphology: Muscles, Elastic Mechanisms, and Animal Performance
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I.4 Functional Morphology: Muscles, Elastic Mechanisms, and Animal Performance Duncan J. Irschick and Justin P. Henningsen OUTLINE 1. Techniques and history 2. Examples 3. Future directions Functional morphology is the study of relationships between morphology and organismal function. A simple inspection of animal diversity reveals a remarkable array of phenotypes and concomitant functions. For example, even within a single mammalian group (bats), one observes organisms consuming food of all types, such as blood, fruit, leaves, nectar, insects, and other animals. Accompanying this diversity in diet is a remarkable diversity in morphological structure ranging from vampire bats with fangs for making sharp incisions for drawing blood to leaf-eaters specialized for grinding and mastication. One also observes similar variation for different kinds of animal locomotion. Whereas some organisms have evolved wings for flight, such as in birds, bats, and flying insects, other species have evolved elongated hindlimbs for running or jumping, such as in some lizards and kangaroos. This diversity in form and function forms an essential template for functional morphologists because it provides the ‘‘menu’’ from which researchers can address how function relates to form. GLOSSARY biomechanics. A subfield of functional morphology that applies mathematical and biophysical theory to understand animal movement function. The use, action, or mechanical role of phenotypic features kinematics. Animal movement; the angles, velocities, and rates at which different body parts move throughout space and the study thereof kinetics. Forcesproducedbyorganismsduringdynamic movements and the study thereof morphology. The descriptive features of the external and internal (anatomical) phenotype performance. A quantitative measure of the ability of an organism to conduct an ecologically relevant task such as sprinting, jumping, or biting structure. The configuration of muscles, bones, tendons , and other tissues that allow animals to achieve dynamic movements Functional morphology is inherently mechanistic in that it seeks to understand the basic mechanical principles that explain organismal function. Thus, rather than focus purely on descriptive patterns of organismal function (i.e., the frog jumped 20 cm), functional morphology aims to understand the underlying physiological and morphological principles that allow organisms to conduct physical tasks such as swimming, running, flying, and feeding, among others. In contrast to reductionist research that studies living organisms from the biochemical or biophysical perspective (e.g., cell biology), functional morphology generally focuses on emergent functional properties arising from the whole organism. Whole-organism functional capacities represent the end output from integrated morphological , physiological, and behavioral attributes of organisms , and hence their study requires an integrative approach. For example, cheetahs are known for their remarkable sprinting capacities, and one can study how different aspects of their internal anatomy (i.e., lung and heart function, limb muscular morphology) allow cheetahs to sprint so quickly. However, functional morphology is less focused on functional capacities below the organismal level, such as the effectiveness of an enzyme at catalyzing reactions. This rule is not absolute , as, for example, many researchers study the function of individual muscle fibers to understand how larger muscle units function. The field of functional morphology is built around several key ideas. First and foremost, the morphology of animals provides the foundation for all movement, such as the use of muscles and bones during locomotion. However, although descriptive studies of morphology are essential, by themselves they provide an incomplete picture of animal movement. Consequently, functional morphologistsalsoaimtoquantifyanimalfunction,such as feeding or locomotion. Before the advent of techniques for quantifying animal function, researchers assumed that function followed directly from morphology , but in fact, this relationship is complicated. Although the dimensions and configuration of nerves, bones, and muscle limit certain features of animal function (i.e., how fast an animal can run), they are rarely directly predictive. This is because the level of animal function (performance, see below) is driven not only by morphology but also by behavior, which is poorly understood in terms of anatomical bases. Consider the example of Dick Fosbury, who pioneered the ‘‘Fosbury Flop’’ (jumping head first, with the back to the ground) to win the gold medal for the high-jump event at the 1968 Olympics. Before the advent of the technique, high-jumpers took off from their inside foot and swung their outside foot up and over the bar. By altering the ‘‘behavior’’ of jumping, Fosbury was able to achieve a significantly higher jumping capacity. This example also highlights an important concept in functional morphology, namely, whole-organism performance capacity, which is how well an organism completes an ecologically relevant task, such as maximum sprint speed or maximum bite force...