EVOLUTIONARY CHANGE IN CRICKET ACOUSTICAL COMMUNICATION

Abstract

The principal questions asked so far with regard to the acoustical communication of crickets have been analytical: what are the causes and effects of the different kinds and amounts of variation in cricket stridulations; and how is the hierarchy of the nervous system related to the hierarchy of parameters in the song pattern? My problem, in contrast, is chiefly one of synthesis: how has cricket acoustical behavior evolved? Obviously there are no fossil cricket songs, and so all evidence must come from comparative study of modern species, supplemented by what we know about cricket relationships from fossil orthopteroids. Cricket acoustical communication is a good subject for evolutionary analysis. It seems to represent the most complicated invertebrate acoustical system, with some species repertoires including four to six different signals; and we probably know more about it than we do about any other invertebrate acoustical system-from all of the several points of view which include signal structure and function, differences and similarities among species, differences and similarity among signals within species repertoires, and neurophysiological basis. Most of the information cited in the reconstruction attempted here comes from evidence accumulated by the participants in this symposium, and from a comparative examination of the various stridulatory patterns of about 100 cricket species, representing eight subfamilies, 20 genera, and 30 species groups (tape recordings in the University of Michigan Museum of Zoology). This accumulation of evidence is more impressive than one might at first suspect. For example, we understand fairly well the acoustical behavior of all but two