Songs of Darwin's finches diverge when a new species enters the community
B. Rosemary Grant1 and
Peter R. Grant
-Author Affiliations
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544
Contributed by B. Rosemary Grant, October 12, 2010 (sent for review August 7, 2010)
Abstract
Bird species sing different songs and as a result rarely breed with each other. Species are not static but can shift in acoustic and morphological space, yet maintain their distinctiveness. Investigating such a situation in a community of Darwin's finches sheds light on the origin and maintenance of premating barriers between species. Explanations for songs divergence generally invoke morphological changes to the sound-producing apparatus, environmental changes influencing transmitting properties of song, avoidance of acoustical interference with other species, and random processes including copying errors. We investigated changes in songs of Geospiza fortis (medium ground finch) andGeospiza scandens (cactus ground finch) from 1978 to 2010 on Daphne Major Island, Galápagos. The habitat did not change significantly; however, the finch community changed. The socially aggressive congener Geospiza magnirostris(large ground finch), singing in the same frequency band (2–4 kHz), colonized Daphne in 1983 and increased in numbers. Temporal features of the songs of G. fortis and G. scandens, especially trill rate and song duration, diverged from G. magnirostris songs as it became increasingly common. Changes in song were not a passive consequence of a change in beak morphology. Instead they arose as a bias during song imprinting and production. Sons of both G. fortis and G. scandens sang faster songs than their respective fathers and thereby differed more from G. magnirostris in their songs than did their fathers. Divergence from an aversive or confusing stimulus during learning illustrates a “peak shift” that may be a common feature of song evolution and speciation.
cultural evolution, premating barriers, sexual imprinting, hybridization, character displacement
Footnotes
1To whom correspondence should be addressed. E-mail:rgrant@princeton.edu.
This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected in 2008.
Author contributions: B.R.G. and P.R.G. designed research, performed research, analyzed data, and wrote the paper.
The authors declare no conflict of interest.
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