Abstract
Geographic variation in bird song has received much attention in evolutionary studies, yet few consider components within songs that may be subject to different constraints and follow different evolutionary trajectories. Here, we quantify patterns of geographic variation in the socially transmitted “whistle” song of Albert's lyrebirds (Menura alberti), an oscine passerine renowned for its remarkable vocal abilities. Albert's lyrebirds are confined to narrow stretches of suitable habitat in Australia, allowing us to map likely paths of cultural transmission using a species distribution model and least cost paths. We use quantitative methods to divide the songs into three components present in all study populations: the introductory elements, the song body, and the final element. We compare geographic separation between populations with variation in these components as well as the full song. All populations were distinguishable by song, and songs varied according to the geographic distance between populations. However, within songs, only the introductory elements and song body could be used to distinguish among populations. The song body and final element changed with distance, but the introductory elements varied independently of geographic separation. These differing geographic patterns of within‐song variation are unexpected, given that the whistle song components are always produced in the same sequence and may be perceived as a temporally discrete unit. Knowledge of such spatial patterns of within‐song variation enables further work to determine possible selective pressures and constraints acting on each song component and provides spatially explicit targets for preserving cultural diversity. As such, our study highlights the importance for science and conservation of investigating spatial patterns within seemingly discrete behavioral traits at multiple levels of organization.
Highlights
Geographic variation in bird song is often used as a framework to examine patterns and processes of evolution in nature (Podos & Warren, 2007)
Knowledge of such spatial patterns of within-song variation enables further work to determine possible selective pressures and constraints acting on each song component and provides spatially explicit targets for preserving cultural diversity
Knowledge of such spatial patterns of within- song variation enables further work to determine possible selective pressures and constraints acting on each song component
Summary
Geographic variation in bird song is often used as a framework to examine patterns and processes of evolution in nature (Podos & Warren, 2007) This is in part because, as a learnt trait, it has the potential to evolve faster than purely genetic traits, and so exhibits considerable spatiotemporal variation both within and between species (Lynch, 1996; Mason et al, 2017), and may even lead to eventual speciation (Danner et al, 2011, 2017). In order to better understand processes of cultural variation in the Albert's lyrebird, we investigated the geographic variation in a distinctive, socially transmitted, species-specific song we call the “whistle song” (after Dalziell & Welbergen, 2016; Zann & Dunstan, 2008). If there are different patterns of spatial variation within each song component, the song components cannot be under the same selection pressures or constraints and are following independent evolutionary trajectories
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