Research projects

My current and past research projects are broadly linked, but tend to fall under one of the following four categories.

 

1) Sex ratio dynamics in turtles

 

2) Temperature-dependent sex determination in Australian agamid lizards

 

3) Reproductive allocation strategies in lizards

 

4) Phenotypic effects of the incubation environment

 

Sex ratio dynamics in turtles

 

As a postdoctoral researcher in Fred Janzen’s lab at Iowa State University, I am studying various aspects of life-history evolution, and sex ratio dynamics in a population of painted turtles (Chrysemys picta) on the Mississippi River. By using data collected over the past 15+ years, my work will evaluate long-term effects of climate change and patterns in maternal nesting behavior, as well as their subsequent influence on offspring sex ratios and other aspects of offspring phenotypes and fitness. My research will incorporate new data collected over the next several years, and I intend to complement the observations from the long-term data set with experimental studies.

 

Temperature-dependent sex determination in Australian agamid lizards

 

In 2007, I completed my PhD research in Rick Shine’s lab at the University of Sydney, where I studied various aspects of the ecology and evolution of temperature-dependent sex determination (TSD). The major component of my thesis research involved a long-term experimental test of the differential fitness model proposed by Charnov & Bull (1977). Specifically, I tested the hypothesis that incubation temperature affects the fitness of sons differently than that of daughters, such that male-producing temperatures are optimal for sons and female-producing temperatures are optimal for daughters. To test this hypothesis, I studied a short-lived, early-maturing agamid lizard with TSD, the jacky dragon (Amphibolurus muricatus). For this project, I evaluated the effect of incubation temperatures on male and female fitness by incubating eggs at a variety of temperatures, and using hormonal manipulations to embryos to decouple the confounded effects of sex and incubation temperature. By following individuals throughout their lives in semi-natural field enclosures and using microsatellite markers to assign parentage, I was able to measure the influence of incubation history on sex-specific life-time reproductive success.

Reproductive allocation strategies in lizards

 

I am also very interested in how environmental and social conditions encountered by reproductive females influence investment strategies towards offspring, as well as the fitness consequences of such strategies. My work generally takes an experimental approach (i) to evaluate patterns of resource allocation towards offspring in response to a variety of conditions, (ii) to understand the source of energy used to fuel reproduction, and (iii) to evaluate possible fitness consequences of differential resource allocation towards offspring. My past work has provided new insight towards patterns of reproductive strategies in lizards by experimentally manipulating yolk quantity and steroid hormones, maternal dietary quality, and operational sex ratios. I plan to evaluate how parental and environmental conditions interactively influence maternal allocation of resources into male versus female offspring in lizards.

Phenotypic effects of the incubation environment

 

During my MS research in Robin Andrews’ lab at Virginia Polytechnic Institute and State University, I became particularly interested in how environmental conditions during embryogenesis influence offspring phenotypes and fitness. My work on this topic has focused primarily on how moisture and temperature regimes during embryonic development affect morphology, performance, and survival of juvenile fence lizards (Sceloporus undulatus) in Virginia and Florida. In addition, much of my PhD work on temperature-dependent sex determination has also addressed how incubation conditions affect long-term fitness in lizards. Importantly, the fitness consequences of the incubation environment have implications for the evolution of maternal nest-site selection behaviors. That is, selection is expected to shape maternal nest-site choice such that reproductive females select sites with conditions that optimize egg survival and offspring (and her own) fitness. Hence, maternal nesting behaviors are also an important component of my research.

           To compliment this work, I conducted several field studies to evaluate the ecological relevance of laboratory-based results. I conducted a field-intensive study of maternal nesting behaviors in jacky dragons by radio-tracking gravid females to locate their nests. This work enabled me to understand how natural incubation regimes influence offspring sex ratios and other phenotypic traits of the offspring. I also conducted a release-recapture experiment in the field to understand the phenotypic determinants of offspring fitness under natural conditions.