Evolution of signal frequency in Neoconocephalus (Orthoptera: Tettigoniidae) : a study of perceptual and environmental sources of selection

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Mate-attraction signals offer an ideal opportunity to examine the sources of selection that shape traits and trait diversity, as they are very diverse and are hypothesized to evolve rapidly. Mate-attraction signals of an organism are likely to be under selection from several sources under natural conditions. Despite this few studies have examined multiple sources of selection in a given system. The sensory drive model is unique in that it outlines several selective forces that are likely to be important in shaping mate-attraction signals in a given system. In this study I characterized the potential impact of several sources of selection emphasized in the sensory drive model on the evolution of carrier frequencies of acoustic advertisement signals of katydids of the genus Neoconocephalus. In the first part of my study I characterized sensory properties, specifically I described the function of the two main frequency components of male N. bivocatus calls in attracting females. I also proposed two alternative call processing mechanisms for N. bivocatus, as the existing call processing model of katydids (i.e. serial processing) does not adequately explain call processing observed in N. bivocatus. In the second part of my study I described the selection that is likely to be imposed by female spectral tuning, call localization properties, habitat-effects and acoustically orienting parasitoids on the carrier frequency of male N. retusus calls using bio-acoustic, behavioral and field-based experiments.