Advertisement call complexity in northern leopard frogs, Rana pipiens
In many animal taxa, acoustic signals are commonly used to communicate information to a variety of receivers. In many frogs and toads, males produce advertisement calls to attract females and repel nearby competitors during the breeding season. While these species-specific calls are typically simple (i.e., a single, repeated note), some anurans produce complex calls containing multiple types of notes that vary in number and temporal order. I investigated the complex vocal repertoire of northern leopard frogs (Rana pipiens) as a model system; the main objectives of my dissertation research were: (1) to describe and categorize the advertisement calls of R. pipiens males, (2) to identify the function of these calls (i.e., mate attraction or male-male competition), and (3) to determine female preferences with respect to male call complexity. ^ Based on analysis of advertisement call recordings and acoustic playback experiments, Rana pipiens males possess a large vocal repertoire consisting of three distinct note types that function in advertisement and two additional note types that serve an aggressive function. These note types are produced in a predictable temporal order to generate common patterns of notes, i.e., "call types". In four-speaker choice tests, females preferred complex over simple calls, but only when duration of call alternatives was not controlled. As in anurans with simple calls, duration may be an important cue that females use in selecting potential mates; because calls are energetically expensive to produce, long calls may indicate superior male quality or condition. While complexity per se did not influence female preferences in my trials, complex calls may be easier to detect above the background chorus in natural breeding aggregations. In field playback experiments simulating a nearby vocal competitor, males generally increased the rate, complexity, and diversity of their calls; however, at high playback amplitudes, males reduced advertisement call complexity and increased use of aggressive notes. By partitioning the advertisement call into different components, males may increase the effectiveness of their calls by giving just female-specific notes, male-specific notes, or a mixture of both simultaneously depending on prevailing social conditions. ^
Richard D. Howard, Purdue University.
Biology, Ecology|Biology, Zoology