HOWARD LAB - PROJECTS

Ecological Risk Assessment and GMO's | Toad Vocalization Behavior
Ontogeny of Sexual Dimorphism

Ecological risk assessment and genetically modified organisms

This study addresses ecological concerns resulting from an accidental or intentional release of a genetically modified organism (GMO) into nature and is conducted in collaboration with Dr. William Muir (Animal Sciences Department at Purdue University). Theoretical aspects involve devising a computer model to predict the consequences of a GMO release based on differences in basic features of survival and reproduction (fitness components) between the GMO and its wild counterparts. If released, a GMO could pose no risk either because if fails to flourish or is indistinguishable from its wild relatives in its ecology. Alternatively, a released GMO could pose one of two risks: an invasion risk in which it flourishes, replaces its wild counterparts, and increases the chance that other species go extinct; or an extinction risk in which the GMO replaces its natural counterparts before going extinct itself, resulting in the local extinction of its species. We termed the latter possibility the Trojan Gene Hypothesis. The empirical aspects of our study involve documenting differences in fitness components between the GMO and its wild counterparts, and setting up populations of the wild type in the lab and introducing GMOs to test model predictions. We use two fish species, Japanese medaka and Nile tilapia, for this study.

Image: Predicted time to extinction of a wild-type medaka population as a function of the mating advantage (numbers above curves) of transgenic males relative to wild-type males and the relative viability of transgenic offspring.

Vocalization behavior in American toads

     This study follows a long-term project on the mating behavior of American toads that I began in 1982. In my previous work, I found that males lower the pitch of their calls when another calling male is nearby; I also found that females have a preference for lower-pitched calls. In the current investigation, I have conducted field playback experiments on males in which I played back synthesized toad calls differing in pitch and timed my playbacks to either alternate or overlap (and precede) the calls of focal males. I have also been conducting call choice experiments on females in a sound chamber in the lab. The goals in this research are to determine why male toads engage in vocal competition and how these interactions influence mate choice by females.

The ontogeny of sexual dimorphism in tiger salamanders

This study also follows an earlier study on the mating behavior of tiger salamanders that I conducted with two students. Two sexually dimorphic tail characters (tail height and tail length) influenced male success in mate competition and mate choice, respectively. In the present study, I reared about 100 tiger salamanders from zygotes to adulthood and monitored their growth and tail development. My goal was to determine when and how the sexual dimorphism occurred during ontogeny. The tail length difference occurred after the young metamorphosed into the terrestrial form but before individuals could be sexed externally. In this case the dimorphism resulted from an increased rate of tail growth in males relative to females. The tail height dimorphism never manifested itself.