A TRIBUTE TO TOM WOOD

Abstract

Review of Specialization, speciation, and radiation: the evolutionary biology of insects. Tilmon, K. J. 2008. University of California Press, Berkley, CA. xv+ 341 pp. HC $65, ISBN 978-0-52025132-8. Understanding the evolutionary biology of any organismal group is a daunting task. The complexity of intertwining factors such as ecological processes, life-history, population genetics, geography, and macroevolutionary patterns is enough to keep any evolutionary ecologist happily occupied for at least one, if not several, careers. This is particularly true for diverse groups in which developing generalized “rules” may be more problematic due to an increased chance of exceptions arising. If we add biotic interactions to the mix—as we rightfully should if we are to understand the evolutionary biology of any taxon—the challenge requires a true jack-of-all-trades approach. An important role model in this regard was the fearless Thomas K. Wood (1942–2002). Tom spent his career studying the evolutionary biology of membracid treehoppers and his love for this group propelled his research in a myriad of directions. Although he is well known for his studies of sympatric speciation in Enchenopa treehoppers, Tom’s interests were diverse and his research included among other things, morphological, phylogenetic, genetic, ecological, and physiological work (Tilmon 2002; Deitz and Bartlett 2004). In Tom’s spirit of striving to understand the evolutionary history of a group of organisms, Kelley Tilmon organized a symposium for the Entomological Society of America which culminated in a multiauthored volume on Specialization, Speciation, and Radiation: The Evolutionary Biology of Herbivorous Insects. As the book is dedicated to the memory of Tom Wood, we would expect no less than a comprehensive and substantive accounting of the evolution of plant-feeding insects. Readers will not be disappointed; the book is text-like in appearance and contains 23 chapters that span the gamut of disciplines and techniques involved in the study of herbivorous insects. The overarching theme of the book centers on understanding why phytophagous insects are so species rich. What attributes of these insects have facilitated their divergence? Their feeding niche is an obvious trait that sets this group apart, and clearly adaptation to host plants has long been considered an important diversifying force (Hutchinson 1959). Ehrlich and Raven’s (1964) seminal paper on butterflies and their host plants identified reciprocal speciation events between interacting plant and insect groups as a major mode of speciation. Given the voluminous literature on this subject, what do we have left to learn? Haven’t we long since beaten this dead horse? One might think so; however, Tilmon’s book may just change the minds of even the most skeptical readers. Rather than simply asking why these insects are so diverse, the book succeeds in highlighting what we can learn about speciation by studying herbivorous insects. Some of the most dramatic examples of explosive species radiations occur within Insecta and these have been generated by a number of processes. For instance, Hawaiian crickets have been identified as one of the fastest evolving organismal groups and their rate of evolution is attributed to sexual selection (Mendelson and Shaw 2005). Blepharida leaf beetles have radiated in accordance to their host plant’s chemistry rather than with patterns of host plant diversification (Becerra 1997). The pollinating fig wasps (e.g., Herre et al. 1996; Machado et al. 2001; Weiblen 2004) and yucca moths (Pellmyr et al. 2008) have diversified at least in part due to their intimate and mutualistic interactions with their host plants. Furthermore, insects can also be used to examine evolution in action. An excellent example of sympatric speciation has occurred within the last 150 years in