Relating song to morphology, ecology, and phylogeny in the avian genus Vireo

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Linnea N. Schaefer, Integrative Biology, University of California, Berkeley, Berkeley, CA, Carla Cicero, Phred M. Benham and Rauri Bowie, Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, CA, Lauryn Benedict, Biological Sciences, University of Northern Colorado, Greeley, CO

Background/Question/Methods
Evolutionary relationships and adaptive radiation within the avian family Vireonidae have intrigued ornithologists for decades. Studies using molecular data have investigated phylogenetic relationships and song evolution, but questions remain about vireo diversification in the context of phylogeny, behavior (including song), and ecology. We used a phylogenetic framework to explore song variation among 28 of the 33 Vireo species and to study the effects of morphological and ecological traits on song. Song has been hypothesized to vary in frequency, length, and complexity based on habitat, and has been correlated to body size across vireonids and other groups and may evolve via sexual selection. Here, we tested three specific hypotheses: (1) Vireo song will follow expectations of the acoustic adaptation hypothesis: longer duration, lower frequency, and less complex in closed habitats; (2) Song frequency will decrease with body size; (3) Both phenotypic and song traits will reflect shared ancestry and have strong phylogenetic signal.
Results/Conclusions
We present a new vireonid phylogeny based on multilocus DNA sequences and examine trait evolution with a focus on the genus Vireo. In agreement with prior data, we found Vireo to be split into three clades that conform to phenotypic traits. We also found the genus Hylophilus to be polyphyletic, with “canopy” Hylophilus nested weakly within Vireo. We found a significant association between habitat and song minimum frequency that has not been documented previously in Vireo. Contrary to our predictions, species that occupy open habitats, regardless of whether exclusively or in addition to forests, have lower minimum frequencies than species that occupy only closed habitats. In accordance with previous research, we found a negative correlation between mean body mass and song low frequency and center frequency. Five of the eleven song measurements showed significant phylogenetic signal. These findings contradict the acoustic adaptation hypothesis, but fit with research suggesting that body size and evolutionary history have stronger effects than habitat on song.