Pianka, a professor of integrative biology at The University of Texas at Austin, and Vitt, a professor of zoology at the University of Oklahoma, have studied lizards for nearly 40 years each. They’ve nurtured a love of lizards since they were children looking under rocks, in caves and streams for lizards. In the book for lay readers, “Lizards: Windows to the Evolution of Diversity,” each writes about their early love of lizards. Pianka, who grew up in northern California, expresses appreciation for his mother who let him keep a variety of lizards, including a 1.5-meter-long boa constrictor, in the house. “How many mothers would allow a son to chill a live rattlesnake in the family refrigerator to cool it down for photography,” he wrote. Vitt, who grew up in Montana, California and Washington, wrote about starting to collect snakes when he was four years old. He’s probably one of the few teenagers who protested a family move from California to Washington because reptile diversity was much lower in the Pacific Northwest. Giving lizards their dueMaking sure lizards got their due respect inspired them to write “Lizards,” a coffee-table book with vibrant photos and accessible information about lizards. After seeing a coffee-table book about snakes, their reaction was: “Oh man, other lizards deserve the same kind of attention,” according to Pianka. Dr. Harry W. Greene, a biology professor at the University of California, Berkeley, who wrote the snake book, wrote the forward to Pianka and Vitt’s lizard book. The lizard book won the grand prize at the Robert Hamilton awards, the prize for the best book written by University of Texas at Austin faculty or staff.
In their careers Pianka and Vitt have hunted lizards in the United States, Australia, Africa and South America, in environments from deserts to rain forests. “We both started in the U.S. desert southwest with North American lizards,” Pianka said, “but he diverged from me and started studying rain forest lizards and Brazilian lizards in various habitats like some dry, almost semi-desert areas in Brazil. “We’ve studied very different taxa because I’ve worked on monitor lizards. He’s never seen a monitor lizard. He’s worked on a lot of Teiids, including tegus, which are New World equivalents of monitor lizards.” Deep historyThey not only have the scars from bites and scratches to show for their fieldwork, they also have a wealth of data collected throughout their careers. Those data were key to their paper recently published in the Proceedings of the National Academies of Science. Their hypothesis is that the diversity of present-day lizards was determined 200 million years ago when two major lizard groups, Scleroglossa and Iguania, separated. The general thought has been that more recent factors of ecology and competition for food led to the diversity of lizard species. Members of scleroglossa include gekkos, skinks, teiids, lacertids, snakes and monitor lizards. They have prehensile jaws and actively seek out foods with sensory capabilities that help them find it. Iguania, which include iguanas, chameleons and Texas horned lizards, lack these characteristics and wait for the food to come to them. They capture food with their sticky tongues.
“When the tongue evolved in these new ways, scleroglossan lizards became much better at finding prey by chemical means,” Pianka said, by smell or sensing it with their tongues. “This gave these lizards a real leg up. They had access to all kinds of prey that iguanians could never get. That’s why we think they became so diverse. They radiated out into all kinds of new niches.” Pianka and Vitt proposed that those differences allowed scleroglossans access to new resources and might account for why there are about 6,000 species of scleroglossans but only about 1,230 iguanians. “All of our lives we thought that what lizards eat today is due to where they live and who they’re competing with, more modern day pressures,” Pianka said. “We never dreamt that deep history was so important.” They used data on lizard diets they have collected over their careers. The data come from 184 species in 12 families on four continents. ‘Thousands of lizard stomachs’They reached their conclusion by using quantitative analysis software to trace the diets of lizards back to common groupings. The diet data came from their own files. The data were contents of thousands of lizard stomachs: ants, termites, wasps, scorpions, roaches, beetles, earwigs and other creatures. “He’s got families I’ve never seen and I’ve got other families, so between us we’ve got good taxonomic and geographical coverage,” Pianka said. “It’s taken us all of our lives to get this much data.” They’d gone through the laborious process of emptying the contents, identifying them, tagging them and storing each stomach’s contents in vials. “I’ve looked at thousands and thousands of lizard stomachs and so has he,” Pianka said. Their conclusion wasn’t earth shattering among biologists and zoologists, but not many other researchers could have done it. “It’s a very nice quantitative demonstration that not many people could ever come up with because most people don’t have detailed stomach contents,” Pianka said. Now that they’ve written “The Lizard Diet,” what’s their next collaboration? “The Lizard Code”? Not quite. Pianka said he and Vitt probably will construct a database of the measurements of lizard shapes and do a multivariable phylogenetic analysis like the one for diets. “We should be able to identify ecological equivalents from different regions that have converged in evolution to be anatomically similar such as tegus in South America with varanids in Australia,” he said. Another convergent pair is Australia’s thorny devil and the North American horned lizard, both of which eat mostly ants. Related Sites |
Back 200 million years ago, the scleroglossa switched from tongue prehension to jaw prehension. That, in turn, freed their tongues to evolve in new ways. 