Polymorphic mating signals and female choice in an Amazonian frog

Abstract

Sexual selection, more specifically mate choice, is one of the most important mechanisms responsible for signal evolution and assortative mating. My thesis integrates genetic analysis, behavioral assays and morphological observations to understand the evolution of polymorphic male mating signals in the frog Peters’ Dwarf Frogs (Physalaemus petersi). In this frog, different populations form distinct genetic clades that coincide with the type of advertisement call males produce. My thesis has four chapters: the first chapter investigates the role of sexual selection in the origin and maintenance of polymorphic mating signals and its consequences for reproductive isolation. I demonstrate strong female mate choice for male signals at a sympatric site. I propose that sexual selection is responsible for the maintenance of different call morphs in sympatric populations, and it likely contributed to the origin of polymorphic male signals. Males of P. petersi form choruses. Males that produce different call morphs are found calling together in sympatric populations. This set up the question if Peters’ Dwarf Frogs use acoustic cues to join choruses in nature. In the second chapter, I demonstrated that the males perform phonotaxis to choruses of similar call frequency. Along with the previous studies of female phonotaxis, the results suggest the pattern of discrimination of males and females are similarly based on the frequency of the call. Evolution of some behaviors results from changes in morphology; for instance, advertisement calls are normally restricted to males, which have larger larynges and muscles than females. In the third chapter, I investigate the ontogenetic morphological differences between males and females of a model in animal communication and close relative of P. petersi, the túngara frog, Physalaemus pustulosus. The results constitute the first comparison between males and females in the ontogeny of the vocal apparatus of a common frog, and contribute to the general knowledge of developmental differences in sound-producing organs. Lastly, in the fourth chapter, I investigated the developmental differences between males of two populations of Peters’ Dwarf Frog that produce different types of calls. I found the laryngeal growth is significantly different between P. petersi males that produce different types of calls.