These Whiptails? No Males
There are female lizards reproducing without male partners in North America, especially in the U.S. southwest and northern Mexico.
Scientists know that it started through hybridization between certain species, but they don’t understand the nature of the mechanism that causes the asexual reproduction.
The phenomenon occurring in about a dozen species of whiptail lizards is called parthenogenesis, reproduction that is common among invertebrate species, such as insects, but has been observed in very few of the many thousands of vertebrate species. Because there are no males that would provide sperm to fertilize the eggs in parthenogenesis, all the offspring are female.
James Walker, a professor in the Department of Biological Sciences, has been studying whiptail lizards since 1962. His major professor, T. Paul Maslin at the University of Colorado, discovered parthenogenesis in the lizards more than 50 years ago.
“We don’t know why parthenogenesis exists in one group of lizards in the southwest and Mexico and why it is not more widespread among the vertebrates,” Walker said. “The knowledge that a group can exist, mostly turning out exact copies of itself, is one of the hooks that keeps us interested.”
Walker said there is evidence that parthenogenetic species of whiptail lizards – which are abundant in parts of Oklahoma, Texas, New Mexico, Colorado, Arizona, Utah, Oregon and Washington – have been around for 10,000 years or less, which isn’t a particularly long time compared to other species that originated hundreds of thousands, even millions of years ago. Homo sapiens – us – dates back at least 100,000 years.
“All these lizards in each whiptail species go back to one animal,” Walker said. “There was one hybrid female that popped out of an egg that founded its parthenogenesis.”
However, Michael Douglas, a professor of biological sciences and 21st Century Chair in Global Change Biology at the U of A, predicts that advanced genomic techniques will lead to the discovery that the clonal offspring aren’t necessarily identical.
“What we’re finding is there are some differences,” Douglas said. “There are some mutations that are occurring in these lizards, and that too is a wrinkle that sparks our interest.”
The American Society of Ichthyologists and Herpetologists honored a research team that included Walker, Douglas, associate professor Marlis Douglas, and postdoctoral fellow Whitney J.B. Anthonysamy, all in the Department of Biological Sciences, with the best herpetology paper in 2014 for their study on whiptail lizards without parthenogenesis. The group, which also included researchers at Arizona State University, Louisiana State University and the University of Illinois, is focusing on parthenogenetic lizards to unravel the mystery how these species evolved.