Degree

Doctor of Philosophy (PhD)

Department

Biology

Document Type

Dissertation

Abstract

The objective of this research was to relate the form of the map turtle feeding apparatus to its function and digestive physiology. Female map turtles (Genus Graptemys) exhibit pronounced differences in their head shapes and prey bases in the wild. I measured voluntary bite force in megacephalic Pearl River map turtles (G. pearlensis) and microcephalic Sabine map turtles (G. sabinensis) along with a suite of morphological characteristics. I found that many morphological characteristics are good predictors of bite performance in both megacephalic and microcephalic map turtles, and that the commonly used metric of head width noted in other studies of turtle bite force was an appropriate predictor for map turtles. I measured the effort it took for map turtles of different head shapes to ingest the same food items and found that megacephalic turtles used considerably more effort to feed on the same item as their microcephalic congeners. To address an animal’s ability to modulate bite performance when affected by motivation, I externally stimulated the jaw adductor muscles and measured the maximal stimulated bite forces. I then quantified the jaw adductor muscle anatomy of Pearl River map turtles and Sabine map turtles. From those muscle measurements, I was able to estimate theoretical bite force of each map turtle that I measured. I found that voluntary bite forces recorded from map turtles were not significantly different from externally stimulated bite forces and calculated theoretical bite forces. I also found that megacephalic map turtles had a higher degree of muscle pinnation in the major jaw adductor muscle subunits (pars profunda and pars superficialis of the Muscularis Adductor Mandibulae Externus). I measured the standard metabolic rates of Pearl River and Sabine map turtles to estimate the baseline metabolic needs of these animals. I found no significant differences in the standard metabolic rates of map turtles that exhibit different trophic morphologies. I measured specific dynamic action, or energetic cost of digestion, in both species of turtles by feeding them ecologically relevant prey items (earthworms). I found that megacephalic Pearl River map turtles used more energy to digest earthworms than microcephalic Sabine map turtles. I then measured specific dynamic action after I fed Pearl River map turtles Corbicula fluminea mussels, an invasive mollusk that is a major component of their diet in the wild. I found that megacephalic Pearl River map turtles used more energy to digest earthworms than Corbicula mussels. The results from all chapters together provide critical mechanical and physiological information about a scarcely studied group of turtles. Most importantly, I have reinforced the linkages among trophic morphology, performance, diet, and physiology in these map turtles.

Date

29-5-2026

DOI

https://proquest.com/docview/3346768472

First Committee Chair

Brad Moon

First Committee Member

Jimmy Nelson

Second Committee Member

Loren Sackett

Third Committee Member

Paul Leberg

Fourth Committee Member

Peter Lindeman

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