Speciation in birds: Genes, geography, and sexual selection

Abstract

Molecular studies of speciation in birds over the last three decades have been dominated by a focus on the geography, ecology, and timing of speciation, a tradition traceable to Mayr's Systematics and the Origin of Species. However, in the recent years, interest in the behavioral and molecular mechanisms of speciation in birds has increased, building in part on the older traditions and observations from domesticated species. The result is that many of the same mechanisms proffered for model lineages such as Drosophilamechanisms such as genetic incompatibilities, reinforcement, and sexual selection-are now being seriously entertained for birds, albeit with much lower resolution. The recent completion of a draft sequence of the chicken genome, and an abundance of singlenucleotide polymorphisms on the autosomes and sex chromosomes, will dramatically accelerate research on the molecular mechanisms of avian speciation over the next few years. The challenge for ornithologists is now to inform well studied examples of speciation in nature with increased molecular resolution-to clone speciation genes if they exist-and thereby evaluate the relative roles of extrinsic, intrinsic, deterministic, and stochastic causes for avian diversification.

Phylogeography: its development and impact in Australo-Papuan ornithology with special reference to paraphyly in Australian birds

“…If avian speciation involves selectively driven divergence as much as Price (2008) argued, then decisions based on neutral DNA divergence will tend to be too conservative (i.e. will fail to recognise species if the taxa have recently originated) (see Edwards et al 2005;. It is thus clear that species can be named without a requirement of mtDNA monophyly.…”

“…A major theme we have addressed is that this strongly cladistic view is unrepresentative of biological reality at the species and population level where one deals with incompletely sorted DNA in phenotypically distinct entities. Also, interpretation of monophyly in mtDNA can be confounded by population history and sampling (Crandall et al 2000;Edwards et al 2005;Rosenberg 2007;Edwards 2008b). It is tempting to think that taxa should be underlain by corresponding genetic units.…”

Systematics and the origin of species: An introduction

“…The modern fruits of this enthusiasm are the many studies that detail reconstruction of recent cases where evolution has given rise to new species. The progress, and rapid pace of progress, in this field is clearly shown in the paper by Scott Edwards et al (32) that outlines how present-day studies on speciation in birds are gaining the genetic and theoretical sophistication that had formerly only been associated with the model Drosophila systems. Topics such as the role of sexual selection and the frequency of sympatric speciation are now being addressed genetically in a number of avian systems.…”

On the maintenance of bird song dialects

“…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).…”