Dissertation Research: Phylogenetic Systematics, Historical Biogeography, and the Evolution of Vocalizations in Nearctic Toads

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To the human ear, the calls of birds and frogs distinguish different species and can be used for species identification. To the bird or frog ear, these calls are important mating signals, and the signals and responses to them have major evolutionary ramifications. Frog calls, like the more familiar calls of songbirds, function to attract females and announce presence or territory ownership. Females use the calls of males for selecting suitable mates. Changes in these signals or in how females respond to them may result in some females preferring to mate with certain males over others with a slightly different signal. This preferential mating is one type of reproductive isolation, and if maintained over multiple generations, it may result in speciation. Therefore, divergence in mating signals is critical to the generation and maintenance of species diversity. In western toads, Bufo boreas, production of the major mating signal, termed the advertisement call, only occurs in a small proportion of populations. Species in which some populations have a mating signal and others do not provide excellent opportunities to test for the underlying models of evolution. The evolution of female preferences and male traits will be examined in B. boreas using DNA sequencing/molecular phylogenetic, acoustic, and behavioral analyses. These analyses will also allow testing whether the advertisement call was lost and then re-gained, a scenario not previously documented for an acoustic mating signal. Additionally, morphological analyses will be conducted to assess whether call production requires morphological adaptations in addition to the behavioral decision to produce calls. Finally, acoustic analyses of multiple toad species will be conducted to examine variation in advertisement and a second call type, the release call, to determine if the release call was co-opted for the novel advertisement function in some B. boreas.Broader Impacts: This research involves cross-disciplinary training and collaborations with professors, graduate students, and federal conservation biologists in the United States and Canada. All six of the focal species receive conservation protection at some level (state, provincial, and/or federal), but taxonomic uncertainties have inhibited conservation efforts. This study will help resolve evolutionary relationships and taxonomy. Results will be published in scientific journals, presented at society meetings, and presented as part of public lectures and interviews. DNA sequence data will be made publicly available via the GenBank database.