March 14, 2011
Red may generally be considered an "aggressive" color but researchers at Indiana State University are studying blue, which signals aggression in some male lizards.
Research led by Diana Hews, associate professor of biology, centers on four species of lizards where males lack a blue patch of skin that, in most other species in the same group of lizards, serves as a key signal of territorial aggression.
But animal communication signals are complex and Hews and her colleagues have secured a nearly $1 million National Science Foundation grant to look into what role different components of color, motion and chemicals play in shaping and signaling aggression, and studying some of the physiological differences underlying these traits.
Male lizards in the species without the blue patch are less aggressive, respond less to visual signals and more to chemical signals, and have fewer brain cells sensitive to testosterone, according to Hews' previous research. These males also have lower levels of a key skin pigment and a larger sensory organ for detecting chemicals.
The four-year NSF grant will allow Hews and Emilia Martins, professor of biology at Indiana University-Bloomington, to study in more detail the evolution change in the lizards' visual and chemical sensory systems over evolutionary time.
"What is neat about this system is that it's an entire suite of correlated traits," Hews said. "What we are interested in is, when you see one of those traits that is different in a species, do we similarly see the whole ‘package' switch over too? It's an evolutionary change coded by genes, and we think genes related to hormones may be acting like a "master switch"."
Hews said the one "oddball" species she has intensively studied has not only lost the distinctive blue patch and has fewer receptors that mediate aggression, but it also smells things more and uses visual displays less.
"In this group of lizard species, we have two examples of an older occurrence of this loss of the blue and two examples of a more recent occurrence of the loss, based on a molecular clock," she said. "The simple prediction is that, in the species that have had the change for a longer time, we will see more of the "package" of traits being pulled apart. We also are interested in how it gets pulled apart - meaning which traits specifically can become uncoupled from the package."
Hormones, including testosterone, often play key roles in the development of the traits involved in aggression, and so species differences in how the hormones are acting are one area that will be closely studied. Another colleague, Erica Rosenblum who is an assistant professor at the University of Idaho, will be characterizing changes in the DNA sequences for genes coding for key hormone receptors.
The NSF grant also will allow for inter-disciplinary collaboration by funding detailed analyses of the lizards' secretions by Richard Fitch, associate professor of chemistry at Indiana State.
"That's a new angle because people have not really looked at how differences in hormone levels might give you differences in what you smell like in reptiles," Hews said. "Males will rub the secretions on rocks in their territory, just like mammals that mark with secretions, so we expect that the chemical cues may signal more things in these species without the color signal, and that they may have chemical components that allow the secretions to persist in the environment longer."
The grant will also support field research by undergraduate and graduate students and high school teachers. Yet another element of the grant will allow Martins to develop statistical methods required to conduct the analyses of the suites of interrelated traits in related species.
Those methods will be shared online with other researchers and the project will connect K-12 science teachers with ongoing research via collaboration with two Indiana science museums that will feature displays about the research.
So far, Hews has conducted most of her field research in southeastern Arizona, home to one of the "oddball" species of lizards and also home to a research station operated by the American Museum of Natural History. The grant funding will allow study of other examples of these unusual species, and their closest relatives, all of which are found in Texas and in Mexico.
"This project is attractive to the National Science Foundation for a variety of reasons. It is inter-disciplinary and will develop statistical methods that will be shared with other researchers and educators," Hews said.
Kit Murphy, professor and chair of the department of biology at Indiana State, said, "What makes this grant especially important for ISU is the involvement of undergraduate and graduate students in cutting-edge research. These opportunities provide our students with invaluable experiences that can shape their scientific careers."
Photo: http://isuphoto.smugmug.com/photos/1216281582_gfjpj-L.jpg - Males of Sceloporus virgatus are an example of a lizard species without blue abdominal patches that are the focus of research led by Diana Hews, associate professor of biology at Indiana State University. (© 2001 by David Sanders)
Contact: Diana Hews, associate professor of biology, Indiana State University, 812-237-8352 or firstname.lastname@example.org
Writer: Dave Taylor, media relations director, Office of Communications and Marketing, Indiana State University, 812-237-3743 or email@example.com
The National Science Foundation has awarded a grant to study factors that contribute to low aggression in certain male lizards. Undergraduate and graduate students and classroom teachers will be involved in the research.