Songs of Darwin's finches diverge when a new species enters the community

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) and Geospiza scandens (cactus ground finch) from 1978 to 2010 on Daphne Major Island, Galápa-gos. 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 A ccounting for the origins, persistence, and ultimate extinction of species is one of the most challenging problems for evolutionary biologists. In most cases the divergence of species from a common ancestor happened a long time ago; therefore the process must be inferred from genetic differences between extant species, and the causes are rarely understood. The smaller are the differences between species, and the more recent is their divergence from a common ancestor, the greater is the potential for discovering how and why one species gives rise to two. There are several model systems for studying speciation across a broad taxonomic range of closely related species, from Drosophila flies

Early song discrimination by nestling sparrows in the wild

“…When closely related species come into contact, courtship signals could diverge as a consequence of reproductive character displacement (Grant and Grant, 2010;Kirschel et al, 2009;Seddon, 2005), or converge when there is no selection against heterospecific copying (Haavie et al, 2004;Laiolo, 2012;Secondi et al, 2003;Sorjonen, 1986;Tobias and Seddon, 2009;Vokurková et al, 2013). We currently lack a mechanistic explanation for these contrasting patterns of song divergence versus convergence; the presence or absence of early song discrimination could be one such mechanism that determines whether cultural traits diverge or converge.…”

Historical contingency affects signaling strategies and competitive abilities in evolving populations of simulated robots

“…The evolutionary divergence of signaling systems is commonly attributed to differences in habitats (5,(36)(37)(38), sexual selection (4, 7), or interspecific interactions (9,39), leading to the common assumption that closely related species inhabiting similar environments will often exhibit similar communication systems (13). However, biologists studying communication have become increasingly aware that contingency in evolutionary history can play an additional important role in shaping animal communication systems (40)(41)(42).…”

Assortative flocking in crossbills and implications for ecological speciation

“…Selection may favour only some minimal level of vocal distinctiveness between co-occurring groups of crossbills that is sufficient for recognition [49], with the variation in response to heterotypic vocalizations being based on learned recognition mechanisms [5,50]. The observed level of divergence in call structure between call types could have arisen if individuals alter their vocalizations away from confusing signals (e.g.…”

“…effects have been detected [41; but see 49], and contact calls, unlike sexually selected songs, are unlikely to be under selection to reach performance limits so that vocalization structure is correlated with bill morphology [43].…”