Ecology GroupHOWARD
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.