Sperm Competition and Its Evolutionary Consequences in the Insects

OUR APPRECIATION OF biological diversity owesmuch to the collective efforts of a special cadre of scientists who become thoroughly captivated by particular organisms, recognize those central issues that can be studied with greatest precision in their favorite species, andenthusiastically advertise theirÞndings to the biological community. The Canadian behavioral ecologist Darryl Gwynne is among this breed, and his efforts have put katydids (bush-crickets, should you reside outside the Western Hemisphere) on the behavioral ecology and evolutionmap. True, bymid 20 century, katydids (Tettigoniidae) had already acquired some status in the natural history of North America through their mating songs, especially the variable syllables sung by Pterophylla camellifolia (true katydid). In addition, entomologists were becoming aware of the importance of these songs in species recognition, sexual advertisement, and male rivalry. But it was Darryl GwynneÕs studies of mating systems inNorthAmerican andAustralian tettigoniids over the past 20 years Ð which have taught us so much about the evolution of courtship behavior and how ecological factors may inßuence the roles assumed by the sexes Ð that earned this family a central place in biology. These landmark studies, accompanied by concise reviewsof theevolution, anatomy,physiology, and ecology of tettigoniids, are now presented in an eminently readable book, “Katydids and bush-crickets: reproductive behavior and evolution of the Tettigoniidae” (D.T. Gwynne, 2001, Cornell Univ. Press, 317 pp.). In nine chapters, Gwynne introduces us to the global diversity of the Tettigoniidae and its phylogenetic relationships to other Orthoptera, describes the basic biology of this family, and then focuses on Þve topics in reproductive behavior: pairing of the sexes as facilitated by acoustic and vibratory signals, courtship feeding and the evolution of spermatophore attachments, sexual selection, risks incurred by the signaler and receiver, and sexual roles in courtship. The last topic is given special attention, as some tettigoniids are noteworthy for variation and reversals in sexual roles. Thus, we learn about ardent and aggressive females, coy and discriminating males who donate as much or more material investment to their offspring as their female partners do, and the circumstances under which the insects may revert to habits more beÞtting their gender.Gwynnewrites inapersonal style, almost chatty in places, but he does not treat these observations as mere natural history oddities. Rather, he makes exemplary use of “the exception probes the rule” tactic to test and reÞne our understanding of the relationships between the sexes in animal mating systems. “Katydids and bush-crickets: reproductive behavior and evolution of the Tettigoniidae” is not, nor did its author intend it to be, an encyclopedic coverage of these insects. Readers desiring in-depth treatment of speciÞc subjects including tettigoniid systematics, acoustic behavior, and neurobiology may be better served by consulting the (slightly out-of-date) edited volume “The Tettigoniidae: biology, systematics and evolution”(W.J.Bailey andD.C.F.Rentz, [eds.], 1990, Springer-Verlag, 395 pp.). Instead, Darryl GwynneÕs recent book guides the reader through the complex interplay among ecology, evolution, and behavior that has shapedcourtship interactions,mating systems, and sexual differences. Sexual selection theory is clearly a prevailing theme, and its nuances are carefully explained so that one may evaluate the various hypotheses derived from its application. Such application is particularly well developed for analyzing the evolution of the tettigoniid spermatophore, which is accounted forbyno fewer than10potential explanations based largely on sexual selection. Importantly, the explanation thatemerges fromcurrentanalysis asmost likely in general (ejaculate protection) is not that which the author favored in his initial research (paternal investment). As indicated above, “Katydids and bush-crickets” is not a book about mechanisms. Given its stated focus, this is Þne, but there are several places in which I would have preferred a stronger physiological or genetic approach: biomechanical and neurophysiological factors, in addition to ecological ones, do constrain the sorts of songs that katydids can sing and hear, and genetic aspects of signaling, mating preferences, and changes leading to speciation deserve more attention. Similarly, could better understanding of development and nutritional biochemistry provide new insight to the katydid spermatophore? The book includes a number of valuable comparisons with other insects, but several critical ones were not made. For example, gregarization in the decticine katydidAnabrus simplex (Mormon Cricket) is discussed, but there is scant mention of the “locust phenomenon” in Old World Acrididae. Could information on factors regulating locust populations and their movement help explain how tettigoniid hordes periodically form and march across the Great Basin? These points notwithstanding, Darryl Gwynne has written a book that is both informative and provocative. He has combined his considerable literary panachewith extensive knowledge of tettigoniid biology anda sophisticatedunderstandingofevolution tooffer us an exciting view of a magniÞcent group of insects. Moreover, he demonstrates how tettigoniids have served as organisms par excellence for studying diverse aspects of courtship: acoustic communication, parental investment, sexual role reversals. The book is superbly illustrated with Þgures, line drawings, and colorplatesof tettigoniids fromthevariouscontinents.