Sky island bird populations isolated by ancient genetic barriers are characterized by different song traits than those isolated by recent deforestation

Abstract

Various mechanisms of isolation can structure populations and result in cultural and genetic differentiation. Similar to genetic markers, for songbirds, culturally transmitted sexual signals such as breeding song can be used as a measure of differentiation as songs can also be impacted by geographic isolation resulting in population‐level differences in song structure. Several studies have found differences in song structure either across ancient geographic barriers or across contemporary habitat barriers owing to deforestation. However, very few studies have examined the effect of both ancient barriers and recent deforestation in the same system. In this study, we examined the geographic variation in song structure across six populations of the White‐bellied Shortwing, a threatened and endemic songbird species complex found on isolated mountaintops or “sky islands” of the Western Ghats. While some sky islands in the system are isolated by ancient valleys, others are separated by deforestation. We examined 14 frequency and temporal spectral traits and two syntax traits from 835 songs of 38 individuals across the six populations. We identified three major song clusters based on a discriminant model of spectral traits, degree of similarity of syntax features, as well as responses of birds to opportunistic playback. However, some traits like complex vocal mechanisms (CVM), relating to the use of syrinxes, clearly differentiated both ancient and recently fragmented populations. We suggest that CVMs may have a cultural basis and can be used to identify culturally isolated populations that cannot be differentiated using genetic markers or commonly used frequency‐based song traits. Our results demonstrate the use of bird songs to reconstruct phylogenetic groups and impacts of habitat fragmentation even in complex scenarios of historic and contemporary isolation.

Two new genera of songbirds represent endemic radiations from the Shola Sky Islands of the Western Ghats, India

“…Montecincla fairbanki sings at a higher bandwidth and song rate than the other populations, whereas M. meridionalis sings at a lower bandwidth than other species, while M. jerdoni has a higher song complexity with longer phrases than the other populations (Additional file 1: Table S5). Songs of all Sholicola species are also quantitatively distinct, with differences in song length and frequency across different species (more details in Purushotham and Robin [49]). The song of the newly described species of Sholicola is shorter in length and higher in frequency from S. albiventris (Additional file 1: Table S6).

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“…For each song, we collected data on frequency and note length parameters for each note, with multiple songs per individual and multiple individuals per population. A detailed statistical analysis of songs and syllables across multiple populations is presented in Purushotham and Robin [49]. …”

Pilot biodiversity assessment of the Hkakabo Razi passerine avifauna in northern Myanmar – implications for conservation from molecular genetics

“…Moreover, our sampling was biased towards understorey tropical species assemblages of the lower to medium elevations. A more pronounced phylogeographic structure can generally be expected from those species occupying sky island habitats of the upper mountain belt and the mountain summits: birds (McCormack et al 2008, Robin et al 2015, Purushotham and Robin 2016; mammals: He et al (2017). Leaf warbler species of the high-elevation forest belt are typical examples, e.g.…”

Environmental influences on acoustic divergence inRhinolophusbats of the Western Ghats-Sri Lanka region

“…Rhinolophus bats are sensitive to deforestation, fragmentation, and microclimatic changes (Struebig et al, 2008;Wordley et al, 2015). Anthropogenic barriers to gene flow through land-use and climate change could further drive acoustic variation and co-occurrence patterns Purushotham and Robin, 2016;Sedlock and Weyandt, 2009;Xu et al, 2008). Studies on genetic/cultural drift or sexual selection should interpret acoustic differences in Rhinolophus bats by accounting for environmental change impacts in rapidly changing biotopes like the WGSL.…”

“…Gunawardene et al, 2007;Robin et al, 2010;Vijayakumar et al, 2016). From north to south, the Goa Gap, Cauvery valley, and the Palghat and Shenkottah Gaps also form distinctive biogeographic zones (Purushotham and Robin, 2016;Ramachandran et al, 2017;Robin et al, 2010). These zones roughly correspond with latitudinal gradients in humidity, rainfall seasonality, and elevation (Bose et al, 2015).…”