STORZ, Brian; Florida State University: Polyphenism, Plasticity, and Canalized Rapid Development; Modifications of the Developmental Program in Spadefoot Toads

Is there a common means by which a developmental program is modified via polyphenism, plasticity, or canalization, or do these modifications of the developmental program represent fundamentally different processes? New World spadefoot toads are an excellent system in which to study this question because they have evolved three apparently adaptive strategies for developing in ephemeral ponds: polyphenism, larval period plasticity, and canalized rapid development. Morphological analyses of Spea multiplicata polyphenism, Spea hammondii larval period plasticity , and Scaphiopus evolution of canalized rapid development suggest that the modifications leading to these developmental phenomena are occurring at different points of the developmental cascade. Both larval period plasticity and the evolution of canalized rapid development almost certainly occur(ed) because of changes in timing of the hypothalamus�pituitary�thyroid axis maturation and thyroid hormone release. Polyphenism, in contrast, occurs by way of trait specific modifications rather than an entire shift in somatic tissues, which suggests that the modifying activity for polyphenism occurs at the specific tissue level rather than earlier in the developmental cascade.