Reduced song complexity in founder populations of a widely distributed songbird. Hill, S .D. & Pawley, M. D. M. 2019. IBIS. DOI: 10.1111/ibi.12692. VIEW
When a species colonizes a new location, the founding population can be drastically different from the larger source population. These so-called founder effects can lead to genetic bottlenecks in which a significant amount of genetic diversity is lost (Baker & Moeed 1987, Frankham 1997). But what about other features, such as song? Can a founder effect lead to a vocal bottleneck, resulting in reduced song diversity? Two ornithologists tested this idea in the Common Myna (Acridotheres tristis), a widespread Asian songbird that has been introduced in Australia, New Zealand, South Africa and the USA.
When a small population establishes itself a new area, there will be less adults to learn from (Baker & Jenkins 1987). Based on this reasoning, we can predict less song diversity in the introduced populations. Moreover, the birds might also lose particular song features (e.g., syllables), leading to less complex songs (Hamao & Ueda 2000). To test these hypotheses, the researchers compared songs between native and founder populations of the Common Myna. They focused on the duration of songs, the diversity and number of syllables per song, and the transitions between syllables.
Figure 1 The songs of introduced Common Mynas are less complex. The first spectrogram (a) shows the song of a bird from Abu Dhabi, United Arab Emirates where the Common Myna is introduced. The second spectrogram (b) depicts the song of a native bird from Guyarat India.
The analyses of these songs supported the predictions. Introduced birds had significantly fewer unique songs in their repertoire. In addition, the songs of native birds were more complex with a higher number of syllables and more syllable transitions per song. Taken together, these results point to a vocal bottleneck in the Common Myna. But what does this mean for the introduced populations? Over time, these birds might develop a different song repertoire compared to the native populations. This might set the stage for speciation: the origin of a new Myna species.
Baker, A. J. & Jenkins, P. F. 1987. Founder effect and cultural evolution of songs in an isolated population of chaffinches, Fringilla coelebs, in the Chatham Islands. Animal Behaviour 35: 1793-1803. VIEW
Baker, A. J. & Moeed, A. 1987. Rapid Genetic Differentiation and Founder Effect in Colonizing Populations of Common Mynas (Acridotheres tristis). Evolution 41: 525-538. VIEW
Frankham, R. 1997. Do island populations have less genetic variation than mainland populations? Heredity 78: 311-327. VIEW
Hamao, S. & Ueda, K. 2000. Simplified song in an island population of the bush warbler Cettia diphone. Journal of Ethology 18: 53-57. VIEW
Featured image: Common Myna Acridotheres tristis | Nihar Gogoi| CC BY-SA 4.0 Wikimedia Commons