Biomechanics and the Ontogeny of Feeding in the American Alligator (Alligator Mississippiensis): Reconciling Factors Contributing to Intraspecific Niche Differentiation in a Large Bodied Vertebrate

• Other Authors: Gignac, Paul Michael (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Biology; Life sciences
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-7143

As vertebrates attain a larger body size, the relative growth of various body parts results in differential rates of growth across the organism and may result in substantial impacts on mechanical performance. To deal with this problem, shape changes often accompany somatic growth, and the nature of these changes is thought to reflect a tight relationship between the morphological form of an organism's anatomy and its function within a given environment. In this context, the feeding anatomy of vertebrates is a consummate form-function relationship. An extreme example of a taxon that undergoes ontogenetic dietary shifts is the American alligator, Alligator mississippiensis, which traverses a 5000-fold increase in mass during its lifetime. As a consequence, this species must cope with changes in its feeding functional morphology (i.e., size and shape of dental and musculoskeletal attributes) while exploiting varying ecological feeding niches. Hatchlings start out as insectivorous neonates but abandon that feeding niche as larger body size allows them access to a wider range of prey items, first frogs and fish and other small, compliant prey before finally reaching the adult ecomorphology where they access more robust quarry. Absolute body size and bite-force positive allometry play an important role in these transitions. Therefore, to understand the nature of the anatomical changes that underpin these factors and thus facilitate dietary niche transitions, I dissected a growth series of wild A. mississippiensis. I standardized the topology, attachment points, and naming scheme for the jaw adductor musculature and quantified the growth of the cranial skeleton, jaw adductor muscle system, and dental form throughout ontogeny. I derived mathematical models of bite-force and hold-force generation based on these data, and tested them against additional developmental series of known bite-force A. mississippiensis. I developed and implemented a novel technique to identify the aerobic capacity of the jaw adductor muscles, called Muscle Oxidative Inference Analysis (MOIA). Finally, dental pressures were quantified using bite forces and dental morphology. These data demonstrate that after hatching, larger body size (25 cm snout-vent length, SVL) initially allows A. mississippiensis access to increasingly larger, compliant prey. At 45 cm SVL positive allometry in the post-orbital growth of the skull and M. Pterygoideus ventralis muscles in addition to substantial changes in the aerobic capacity of some jaw adductor muscles facilitates access elusive terrestrial prey such as birds and small mammals. By 75 cm SVL, subtle changes in dental form along with bite-force positive allometry make it possible for this taxon to generate tooth pressures that can fracture and mechanically fail the bony carapaces of turtles. Finally, large adult body size (150+ cm SVL) and continued positive allometry in the musculoskeletal attributes of its jaw adductor system and further augmented oxidative capacity of its adductor muscles allow A. mississippiensis to secure large game mammals such as deer, boar, and cattle. === A Dissertation submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === Spring Semester, 2010. === March 26, 2010. === Includes bibliographical references. === Gregory Erickson, Professor Directing Dissertation; William Parker, University Representative; P. Bryant Chase, Committee Member; Brian Inouye, Committee Member; Emily DuVal, Committee Member; Patrick Hollis, Committee Member.