A central question of biology is how new traits evolve when there are no obvious precursors among relatives or ancestors. Acoustic communication, with its great diversity of signal traits, serves as a model system to study this question. Because acoustic communication functions in the context of reproduction, it has been widely assumed that female preferences for particular attributes of male signals are responsible for shaping male signals and for driving the diversification of signals among different species. Models based on this assumption require that males and females are tightly linked, such that a gradual shift in the preferences of females will be paralleled by a corresponding shift in the signals of males. Recent studies indicate that this linkage might not be as tight as expected, however, and that female preferences and male signals may evolve independently of each other.
This project tests the hypothesis that genetic drift (i.e. evolution due to chance events) plays a stronger role in signal evolution than has been previously acknowledged and could account for the lack of parallel evolution between males and females. According to this hypothesis, males, rather than females, lead the way in the divergence of signals between species. The project includes five species of katydids that all exhibit a new call trait (double pulse rhythm, in which the pulses of the call are grouped into pairs) and five closely related species with the older call trait (single pulse rhythm, in which pulses are evenly spaced). The aims of the project are 1) to determine the evolutionary relationships among the species in this group of insects, 2) to analyze the call patterns of males, in order to look for geographical differences and to identify species that are in the process of evolving the new call pattern, and 3) to identify the attributes of male calls that females use for recognizing males of their own species. Call recognition will be determined using a walking compensator, or spherical treadmill, that measures the attractiveness of different male calls to listening females. By comparing the patterns of males calls with the set of attributes used by females to recognize those calls, it will be possible to identify the evolutionary mechanisms responsible for the diversification of signals among species.
The number of species included in this project places it among the largest comparative studies of the evolution of communication. This project will provide a better understanding of the evolution of new traits, and of the patterns that emerge between males and females in communication systems.
Broader impacts of this study include the training of undergraduate and graduate students in comprehensive, multi-approach research. The infrastructure developed for this project will also be used for instruction in both informal and formal course settings. Furthermore, the walking compensator, which is among the most powerful tools for behavioral analysis, will be maintained and made available to other researchers.
