That's me with a 13-foot Florida Yard Dog--3.96 meters for the scientists in the crowd

Click on the following links or simply scroll down to find out more about my research.

          Research CV                Publication List                 Ship Captain and the other Swabbies            

Here are a few research-adventure images to start with.

I am interested in how developmental programs are modified over both evolutionary and ecological timescales and the similarities or differences between these modifications.

I am studying the spadefoot group because they show a tremendous amount of developmental labiality.  The North American spadefoot toads show at least three forms of developmental program modification, larval period plasticity, developmental polyphenism, and the evolution of fixed, rapid development.

The focus of my PhD research is understanding the developmental program modifications underlying spadefoot toad polyphenism, specifically, modifications of the muscle developmental program.  Larvae of at least two spadefoot species (Spea multiplicata and Spea bombifrons) show a striking environmentally-induced polyphenism in which a “typical” filter-feeding tadpole is transformed, in both morphology and behavior, into a carnivore (Fig. 1) that actively preys on microcrustaceans and cannibalizes conspecifics (Pomeroy 1981; Pfennig 1990).  The phenotypes are so dissimilar that they were originally classified as different subspecies (Turner 1952).  All tadpoles hatch with the same phenotype but some larvae soon transform into carnivores, which are fully recognizable, including myoenlargement of the jaw musculature, as little as three days after hatching (Fig. 1, premetamorphosis).  By mid-development (Fig. 1, prometamorphosis), larvae are strikingly distinct in both morphology and behavior and show fully recognizable myoenlargement of the jaw and tail musculature.  Finally, at metamorphosis the phenotypes begin to converge (Fig. 1, metamorphosis) and upon emergence from the pond, show no phenotypic differences. 

Carnivores have a number of traits that show growth rate modifications, both up and down regulation (Table 1).  In addition, the trait growth-rate modification occurs as two, temporally dissociated modules, which primarily consist of an increase in growth rate of the jaw musculature just after hatching (Figs. 2, 3a, Storz 2004, Storz and Travis 2007) and an increase in the growth rate of tail musculature at mid-development (Figs. 2, 3b, Storz and Travis 2007).

Table 1.  Compilation of studies investigating larval polyphenism in spadefoot toads.  Each trait shows either an increased (↑), decreased (↓) growth rate or no difference (-) in carnivores, relative to omnivores.

Given that the biggest difference between carnivore and omnivore phenotypes is due to trait-specific increases in muscle growth, I am using the spadefoot toad system to investigate the mechanistic regulation of myosatellite cell proliferation and differentiation.  Myosatellite cells are quiescent, undifferentiated, premyoblastic precursors to myotubes and are found in both the developing fetus and among myofibers of adult muscle.  Myosatellite cells remain quiescent in the embryonic primary myotome or adult skeletal muscle until activated.  After which, they begin to proliferate by mitogenic cycling through the cell cycle and upon leaving the cell cycle, can fuse to existing myofibers, or fuse to other myosatellite cells and differentiate into a new multinucleate myotube, or theoretically differentiate individually into a new uninucleate myotube.  Understanding spadefoot toad polyphenism is important for the study of myosatellite cell system regulation because the interactions among the factors regulating myosatellite cell quiescence, proliferation, and differentiation and their appropriate concentrations have been refined by the process of evolution and natural selection in this system for the past 20–29 million years (Garcia-Paris et al. 2003).  Thus, these animals are able to respond to a specific environmental cue and up-regulate muscle growth without the corresponding maladies, such as tumor formation, found in other studies (Morgan et al. 2002).  Hence, rather than attempting to recreate a perfect system in the lab––in which muscle growth can be stimulated without repercussions, as many labs are currently attempting to do via in vitro and in vivo myosatellite cell assays––it is important to fully exhaust this system to understand how spadefoot larvae have evolved the ability to increase muscle growth in response to a specific environmental cue.

Integrative studies, which incorporate information from multiple organizational levels, are the most powerful means by which to study biology (Marden et al. 1998).  Hence, I have developed a research program to study muscle developmental biology in spadefoot toad larvae that integrates across trait-growth allometry, histology, and molecular biology in hopes that these different organizational levels will provide reciprocal illumination.

 In my previous research I quantified muscle growth-rate differences between the carnivore phenotypes and found that muscles of the carnivore can increase growth rate as much as two fold relative to omnivores.  In addition, the increase of muscle growth rate shown by carnivores occurs as two temporarily dissociated modules, the jaw musculature just after hatching and the tail musculature at mid-development (Storz and Travis 2007).  I intend to follow this research with both histological and molecular analyses of muscle differences between the two phenotypes and between the two temporarily dissociated modules within the carnivore phenotype.  My ultimate goal is to understand how these tadpoles convert an environmental cue into an increase in growth rate of their jaw and tail musculature and why this occurs as two modules.  My preliminary evidence suggests that carnivore myoenlargement occurs by way of hyperplasia rather than hypertrophy in both the early muscle module and the mid-development muscle module (Fig. 4). 

The specific aims of my research are four fold.

(1)         To continue my histology studies to determine whether myoenlargement is occurring by way of hyperplasia, hypertrophy, or a combination of the two.

(2)         To determine which fiber type, type I or II, predominates each phenotype and each muscle module.

(3)         To conduct a candidate gene analysis of three general factors know to control somatic growth in larval anurans, Prolactin (PRL), Growth Hormone (GH), and Insulin-like Growth Factor (IGF-1).

(4)         To conduct tissue specific subtractive hybridization assays of both the orbitohyoideus jaw muscle and tail muscle, which are representative of the early and mid-development muscle modules, respectively, in order to gauge the qualitative and/or quantitative transcriptome differences underlying the muscle growth-rate differences.