Lizards in an Evolutionary Tree: Ecology and Adaptive Radiation of Anoles

17. Are the Anoles Special, and If So, Why?

383 17 ARE ANOLES SPECIAL, AND IF SO, WHY? What’s so great about anoles? Why have I written a whole book about them—and spent more than 20 years studying them—and why have you read the book? Of course, they’re attractive and engaging little creatures, with great variety and entertaining behavior. But if that were their only claim to fame, this book would be of limited interested. Quite the contrary, anoles are receiving ever-increasing attention: more and more papers, by more and more research groups, on increasingly diverse topics; even the anole genome is being sequenced. What, if anything, makes them so special? I suggest that the interest in anoles stems from three factors: 1. The exceptional extent to which the adaptive radiation of anoles has been studied. 2. The great diversity and disparity exhibited by anole evolution. 3. The replicated adaptive radiations in the Greater Antilles. In this last, concluding chapter, I will consider whether anoles really are so special and if so, why. I’ll then conclude the book by looking forward to consider what the future holds for the lizards themselves. losos_ch17.qxd 4/11/09 9:46 AM Page 383 ANOLIS AS A MODEL TAXON FOR STUDIES OF BIOLOGICAL DIVERSITY In the Prologue, I suggested that Anolis is nearly unrivalled in the depth and breadth of knowledge about its biological diversity, spanning fields as disparate as phylogenetics, ecology, physiology, behavior and evolution, and including both laboratory and field studies and experimental and observational approaches. After having read through the book, you can decide for yourself whether our knowledge of anoles is broader and more integrated than that of other diverse groups of organisms. Why has so much work been conducted on anoles? The answer is simple. For many types of studies, anoles—particularly Greater Antillean species—are ideal subjects. They are often abundant and easy to observe, they can be manipulated in the field to answer behavioral and ecological questions, they can be brought into the lab for a wide variety of different studies, and they can be marked and followed over reasonably short generation times. Plus, many species co-occur, facilitating studies of interspecific interactions. Finally, the patterns of convergence add statistical replication to evolutionary analyses. The only glaring shortcoming in our knowledge of anoles is our lack of understanding of the genetic basis underlying phenotypic variation, and that is likely to change radically in the near future. For these reasons, anoles have been useful subjects to develop new approaches and to test important and general questions in a wide variety of fields. Moreover, the ability to integrate knowledge concerning so many different aspects of their biology has made them an ideal group for synthetic studies of biodiversity and evolution, an attribute that will only grow in the future as we learn more about them. Anoles are particularly useful for macroevolutionary studies for two additional reasons . Grant (1986), following Lack (1947), suggested that Darwin’s finches are at just the right stage of evolutionary diversification to combine studies of pattern and process; that is, they are diverse enough to illustrate interesting patterns of adaptive radiation, yet they are similar enough that process-based studies in behavioral, ecological and microevolutionary time can provide meaningful insight about how and why adaptive diversification occurred. I would argue that the same can be said about anoles; indeed, that has been the primary theme of this book. We can contrast cases like Darwin’s finches and anoles with case studies at either end of the spectrum. On one hand, studies of closely related species in the process of diverging and speciating provide wonderful insights into these processes. Studies on sticklebacks, walking sticks, and columbines (e.g., Rundle et al., 2000; Nosil et al., 2004; Colosimo et al., 2005; Whittall et al., 2006)—to name just three—are at the cutting edge of evolutionary biology, applying modern methods and approaches to advance our knowledge of the evolutionary process. Nonetheless, groups such as these are not adaptive radiations; they simply don’t display enough ecological and phenotypic diversity. Studies on these groups certainly are informative concerning microevolutionary processes, and 384 • A R E A N O L E S S P E C I A L , A N D I F S O , W H Y ? losos_ch17.qxd 4/11/09 9:46 AM Page 384 the groups themselves may be nascent adaptive radiations,446 but...