The evolution of elaborate signals can emerge from changes in anatomical signaling structures. In the male túngara frog, a simple advertisement call (‘whine’) can be ornamented facultatively with a suffix (‘chuck’) to produce a more attractive complex call, or ‘whine-chuck’. A fibrous mass (FM1) supported by the vocal cords plays a role in chuck production. Here, we examine the effects of FM1 ablation on a large set of spectral and temporal features of both the whine and chuck and we test the hypothesis that FM1 ablation reduces call attractiveness to females. Both call components were impacted by FM1 ablation, but especially the suffix. The proportion of energy in the suffix’s odd compared to even harmonics diminished markedly as did the relative amplitude, effectively eliminating the chuck percept. FM1 ablation also reduced the whine’s frequency and its rate of frequency modulation. Moreover, post-surgery chucks no longer enhanced the attractiveness of the simple call and whines also appeared to diminish in attractiveness. Together, our results demonstrate that FM1 plays a role in the production of both call components in a way that stimulates the female auditory system and that the growth of FM1 had potentially positive sexual selection implications for the pre-existing simple call.
Advertisement call, fibrous mass, larynx, mate choice, phonation, phonotaxis