Bird song, ecology and speciation

Abstract

The study of bird song dialects was once considered the most promising approach for investigating the role of behaviour in reproductive divergence and speciation. However, after a series of studies yielding conflicting results, research in the field slowed significantly. Recent findings, on how ecological factors may lead to divergence in both song and morphology, necessitate a re-examination. We focus primarily on species with learned song, examine conflicting results in the literature and propose some potential new directions for future studies. We believe an integrative approach, including an examination of the role of ecology in divergent selection, is essential for gaining insight into the role of song in the evolution of assortative mating. Habitat-dependent selection on both song and fitness-related characteristics can lead to parallel divergence in these traits. Song may, therefore, provide females with acoustic cues to find males that are most fit for a particular habitat. In analysing the role of song learning in reproductive divergence, we focus on post-dispersal plasticity in a conceptual framework. We argue that song learning may initially constrain reproductive divergence, while in the later stages of population divergence it may promote speciation.

On the maintenance of bird song dialects

“…Studies are still mostly divided into those with a focus either on dialect or on environmental impact and change in acoustic structure (Slabbekoorn & Smith, 2002). There are, however, some interesting exceptions.…”

“…Interspecific variation often plays a critical role as a pre-zygotic barrier to hybridization between closely related taxa. Under specific conditions, geographic variation within species can be regarded as a precursor of reproductively isolating variation between species, as divergent signals do not have to but can promote speciation through an impact on male settlement success and assortative mating (Slabbekoorn & Smith, 2002;Edwards et al, 2005;Price, 2008, p. 470).…”

“…Geographically distinct acoustic clusters yield sharp transitions in vocal parameters across localities and are referred to here as dialects (Marler & Tamura, 1962;Baker & Cunningham, 1985;Slabbekoorn & Smith, 2002;Podos & Warren, 2007). The best studied dialectal bird species is the white-crowned sparrow (Zonotrichia leucophrys) for which there is ample field data on different subspecies (e.g., Baptista & King 1980;Baker & Cunningham 1985;Cunningham et al 1989;Nelson et al 2004).…”

Distinct song parts of the endemic marsh grassbird of China vary with latitude and climate among migratory and sedentary populations

“…Consequently, a pattern of isolation by distance in geographic song variation is likely to emerge through both individual dispersal and song learning processes, which opens up potential for acoustically guided population divergence (Ellers and Slabbekoorn 2003;Podos and Warren 2007). This may be especially the case if such variation is linked to a heritable trait of ecological relevance such as migratory tendency (Winker 2000;Slabbekoorn and Smith 2002;Rolland et al 2014). Species confined to fragmented habitats may be a special case in this respect as they occur in separated populations in habitat islands (c.f.…”

“…Geographic variation in birdsong can affect gene flow among populations and play an important role in avian speciation (Slabbekoorn and Smith 2002;Edwards et al 2005;Price 2008). Song variation and associated acoustic response patterns by potential mates and competitors are well-accepted as descriptors of species boundaries and key factors in intra-specific population divergence.…”