THE SEPARATE AND COMBINED EFFECTS OF HARMONIC STRUCTURE, PHASE, AND FM ON FEMALE PREFERENCES IN THE BARKING TREEFROG (HYLA-GRATIOSA)

In natural advertisement calls of the barking treefrog, Hyla gratiosa, a small amount of incoherent frequency modulation (FM) is present. In coherency in the FM of a call creates inharmonicity and phase changes between its frequency components. In this study, the combined and sepa rate effects of the harmonic structure, phase spectrum, and FM of an a dvertisement call on female choice were tested. The harmonic structure of a call can have a direct effect on female preference; females show ed a significant preference for static-inharmonic calls over static-ha rmonic calls. Neither differences in phase or FM alone conferred a pre ference in two choice tests. However, when FM is present in both calls it does influence female preference for harmonic structure -namely ha rmonic calls become preferable to inharmonic calls. This reversal of f emale preference for inharmonicity in a call by the presence of FM sug gests that call parameters may interact, and thereby effect mate choic e.