Doctor of Philosophy (PhD)
In this dissertation I explored variation in vocalizations of the avian genus Synallaxis (Passeriformes: Furnariidae) and the use of vocal characters to determine phylogenetic relationships at the species level. Vocalizations of suboscine passerines have recently gained favor as a proxy for genetic material in systematic studies; however, individual and geographic variation are both widespread in suboscines, complicating the definition and analysis of vocal characters. This is particularly true for species that have simple, phylogenetically conserved vocalizations. Moreover, the use of vocal characters in suboscine systematics depends on the confident assessment of homologous vocalizations, as well as a thorough understanding of their role in the behavioral processes fundamental to reproductive isolation and speciation. My research was based upon a collection of approximately 1200 Synallaxis recordings, representing every species and most subspecies in the genus. I identified presumably homologous vocalizations (“songs”) and analyzed variation within and among individuals, populations, and species. Song playback induced statistically significant changes in character measurements within individuals, although individual diagnosability was generally high even in classifications based on few measurements. Geographic variation was pronounced in a widespread, polytypic Andean species (S. azarae) but nonexistent in a related monotypic lowland form (S. frontalis). In comparisons both within and among species, a high degree of vocal convergence within a limited multivariate space and between geographic and elevational extremes obscured potentially significant patterns of variation in other characters, and underscore the need for large sample sizes and complete geographic sampling in suboscine vocal studies. Little phylogenetic information was recovered when vocal characters were mapped onto a molecular phylogeny of Synallaxis. Only one clade showed a strong pattern of phylogenetic conservatism, and there was no relationship overall between the number of vocal differences and genetic distance. The low incidence of autapomorphies and low consistency index for syntactical vocal characters suggest that vocalizations are constrained by morphology and prone to convergence in distantly related species. My results demonstrate substantial variation in suboscine vocalizations and suggest that vocal characters may not be reliable indicators of phylogenetic relationships at broad taxonomic scales, particularly among behaviorally and ecologically diverse taxa.
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O'Shea, Brian J., "Evolution of vocal signals in a neotropical avian lineage" (2009). LSU Doctoral Dissertations. 3211.
Remsen, J. V., Jr.