Under Chris Brown’s watchful eye, there’s a lot to learn about life’s evolution by closely studying female scorpions giving birth. Brown, a TTU assistant professor of biology, has been named TTU's 2004 Sigma Xi research award winner for his paper, "Offspring Size-Number Trade-Offs in Scorpions: An Empirical Test of the Van Noordwijk and De Jong Model," published in a 2003 issue of Evolution, the international journal of organic evolution.
“The model, which is almost 20 years old, has rarely been tested, but proposes an interesting look at trade-offs in the life history of organisms,” said Brown. “I decided to use research on scorpions to test the model.”
In theory, trade-offs are expected at a fundamental level because an organism’s resources, or energy, cannot be two places at the same time. For instance, it would be expected that if a female scorpion gives birth to a large number of offspring, those offspring would be smaller than those of a scorpion that gave birth to a small number.
Size is the expected trade-off for an increased number, according to basic theory.
But Norrdwijk and De Jong presented a model to explain why trade-offs might not be found. The model points out two ways in which individuals differ. Some individual organisms have more resources than others and allocate their resources differently to reproduction instead of growth and survival.
“As an analogy, think of the people who can afford large homes and expensive cars,” said Brown. “Those same people usually have more resources than the average person and allocate a larger percentage to buying more cars or homes than the average person.
To test the model, Brown collected data on 10 species of scorpions from Texas and Arizona. Scorpions give birth to live young that are carried on the female’s back for a period of time, so Brown measured and weighed those offspring and analyzed the resource investment the females made to the size and number of litters.
“My research is consistent with the model in showing that large female scorpions can produce both a large number of offspring that are big in size because she has more energy to invest in reproduction because of her size,” said Brown.
These results suggest that scientific knowledge of variation in an individual organism’s ability to acquire resources and allocate them is critical to a full understanding of all life histories.
Brown also published an article, “Clutch Size and Offspring Size in the Wolf Spider Pirata Sedentarius,” in a 2003 issue of The Journal of Arachnology. He’s conducted several studies on wolf spiders, commonly found in yards and open areas in Tennessee. These spiders do not spin webs and hunt for food on the ground.
In 2004, he was awarded a TTU faculty research grant to study the effect of leg autonomy, the loss of one or more legs, on wolf spiders running on water or land.
“Because speed equals survival for these and many other species, I’ve studied the running speed in spiders and am continuing to study how that relates to survival,” said Brown.
Brown earned his doctorate in quantitative biology as well as a master’s degree in biology from the University of Texas at Arlington and his bachelor’s degree in physics/astronomy at Texas Christian University. He joined TTU’s biology department in Fall 2002.
Sigma Xi is an international scientific research society. Each year, the Tennessee Tech chapter recognizes excellent scientific research by one faculty member for a research paper published or accepted for publication.