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Fig. 8. Morphological plasticity in pupfish may be driven by differences in
environmental conditions that affect thyroid hormone physiology and,
subsequently, morphological development. This model illustrates a possible
scenario where high water temperatures elevate metabolism and cause a suite of
physiological changes in the thyroid hormone system that are dependent on food
availability and quality. If food resources are abundant or high in
nutritional quality, pupfish develop a normal morphology with small head and
eye sizes, a deep body, and pelvic fins (possibly occurring in the refuges for
C. diabolis). If food resources are scarce or of low quality,
however, thyroid hormone production may be inhibited resulting in development
of the neotenous morphology (large head and eye sizes, small body depth, lack
of pelvic fins) typical of C. diabolis in Devil's Hole.
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