We are interested in the neuroendocrine basis of aggressive behavior: How do various hormones act on the brain to change an individual's behavior and make it more aggressive?  We use an integrative, systems approach combining neuroendocrinology, ecology, behavior and evolution to approach this question.  We also use a nontraditional model species, the tree lizard, which has many advantages over traditional model species.  A major advantage of this species is the presence of alternative phenotypes discussed below.  However, this species also is easy to study in the field, gives discrete aggressive behaviors that are easy to quantify, adapts well to captivity and can be raised in captivity.  This work is currently funded by the National Institute of Mental Health.    

Our primary study organism, the common tree lizard (Urosaurus ornatus).   This male is giving the aggressive Fullshow display which reveals his two primary color badges - the multicolored dewlap or throat fan and the bright blue vental patches on the abdomen.  The color of this males dewlap reveals that he is of the aggressive, territorial behavioral morph (see below).

Photo by Blair Wolf.
 

This is a composite photograph of male tree lizard throats illustrating the variation in dewlap color in one population of tree lizards.  From left to right, the top row illustrates orange-blue and orange males and the bottom row illustrates yellow-blue, yellow and blue males.  At least four other dewlap types have been documented in central and southern Arizona that are not illustrated.  Our main study population has both orange and orange-blue males in about equal numbers with an occasional yellow, yellow-blue or blue male present.  Other nearby populations have completely different morph type frequencies.

We are interested in how hormones regulate differences between these different types of males. We have discovered a role for hormones during early development in the differentiation of the two male types. We have also recently discovered a role for hormones during adulthood in switching the orange males between the two reproductive tactics they practice. These results support the general conclusion that differences within the sexes are controlled by hormonal mechanisms similar to those that produce differences between the sexes.
 

We have recently expanded our interests in the endocrine basis of the difference in aggressiveness between the two morphs of the tree lizard to an interest in the neurobiological basis for this difference.  We have been examining the gross morphology of the brain nuclei in the two morphs and the distribution of various neurochemicals and hormone receptors.  This is a picture of the distribution of arginine vasotocin immunopositive cells in the paraventricular nucleus of the tree lizard hypothalamus.  We think this is a key neuropeptide in causing differences in aggressive behaviors between the morphs.