Testing the ability of males and females to respond to altered songs in the dueting green lacewing, Chrysoperla plorabunda (Neuroptera: Chrysopidae)
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Green lacewings in the carnea group of Chrysoperla engage in species-specific heterosexual duets using low-frequency substrate-borne signals. Within each species, both sexes sing nearly identical songs. Songs are the principal barriers to hybridization between sympatric species in the complex. Here, we investigated the responsiveness of males and females of Chrysoperla plorabunda to synthesized, prerecorded songs that differed from the species mean in the period between repeated volleys of abdominal vibration. We tested 15–16 males and 15–16 females using playbacks of two signals that gradually increased or decreased in volley period, starting at the species mean. We found that (1) duets during courtship are accurate, interactive, and adjustable by each participant; (2) in staged duets, both sexes respond best to song tempos near the mean volley period of their population, but can nonetheless maintain duets with signals of nearly twice, or half, the normal volley period; (3) individuals fine-tune their adjustments to signals of different volley periods by changing their own volley duration and latent period, or less often by inserting extra volleys or skipping every other volley; (4) males are significantly better at matching signals of changing tempo than females; and (5) the range of song responsiveness of C. plorabunda does not overlap the natural range of volley periods found in Chrysoperla adamsi, an acoustically similar sibling species, thus reaffirming strong behavioral isolation. In sum, the precise, almost unbreakable heterosexual duets characteristic of song species of the carnea group result from tight mutual feedback between partners. Effective reproductive isolation between species can be based on song differences alone.
KeywordsMating signals Plasticity Speciation Behavioral isolation Playback experiments Sexual selection
The work presented here was funded principally by grants from the Research Foundation of University of Connecticut to C. S. Henry and M. M. Wells. Cynthia S. Jones (University of Connecticut) participated in valuable discussions with the authors to improve the manuscript, while Peter Turchin (University of Connecticut) gave us statistical advice. We thank numerous colleagues from around the world for help in collecting and maintaining living lacewings from many geographical locations. Special thanks go to Ding Johnson (University of Idaho, Moscow, ID, USA), both for collecting the enigmatic C. adamsi in western North America and for the many years of collaboration and friendship we have shared. We also appreciate the contributions of three anonymous reviewers. To the best of our knowledge, the experiments described in this study comply with the current laws of the United States and of the relevant states therein, including Connecticut, California, Washington, Oregon, and Arizona.
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