| Description |
Understanding how reproductive barriers between species arise and are maintained is paramount to the study of speciation and evolutionary biology. The contribution of avian vocal learning to the process of speciation has been the subject of considerable debate, with some suggesting that vocal learning has strongly promoted rapid speciation in the speciesrich oscine passerines. Furthermore, vocal learning has been characterized through the focused study of a small and closely-related group of taxa and so the common understanding of vocal learning in birds may reflect this narrow taxonomic coverage. While the evolutionary origin of this complex trait remains mysterious, I address the complexities of the evolution and evolutionary implications of vocal learning in songbirds through three lines of research. In a meta-analysis of isolate studies, through comparison of isolate to normal song for 16 species, I find that the learned components of song vary significantly among species, in line with literature that finds different degrees of genetic guidance in the development of song production modules. These findings form the basis for the theory of modular vocal learning. In a Setophaga hybrid zone, I investigate the potential for differential evolution in response to secondary contact for song traits according to their degree of genetic guidance by pairing a production-based acoustic analysis with a geographic cline analysis. I find that song rhythm shows a cline that resembles that of a quantitative trait under moderate iv selection while other song traits do not. In the same system, female response to song differs according to song rhythm in a way that reflects the cline shape for song rhythm uncovered previously; this suggests that this song trait, which is presumably under stricter genetically guided development than other aspects of song production, is important in mate attraction. In contrast, males do not respond differently to song based on any measured song trait. Together, my research results show that vocal learning contributes variably to the acoustic features of song across diverse species and that this contribution may not necessarily be informative during mating decisions. In contrast, components of song more likely to be under genetic control appear to function in mate attraction and evolve accordingly. From my results, vocal learning does not appear to function in accelerating speciation rates, and so the details of the origin and maintenance of vocal learning in songbirds remain open for investigation. |
