Phylogeography and the Role of Hybridization in Speciation

Abstract

Human beings have a strong, innate desire to classify and name things. We like things to be clear-cut. The way we approach classification of birds is as good an example as any of this. So it always comes as something of a surprise to non-ornithologists to learn that how we classify birds at the level of the species around us is still subject of so much at times fiery debate. Various chapters in this book approach this from different perspectives. In this chapter, the focus is on reminding us that evolution is an ongoing, dynamic process and that appreciating this evolution can help us make sense of why it is sometimes so complicated to pin names on birds and indeed many other organisms. This will take us into a few particular aspects of bird evolution. One will be the process of hybridization between populations that may or may not be of the same species or between species that may or may not be each other's closest relatives. Another will concern the study of genetic diversity that exists within a species. In particular, we will examine what we have learned from the way that that diversity has come to be apportioned and distributed across the geographical range and landscapes inhabited by a species. These two areas have opened windows into the dynamics of evolution that give us new understanding of bird species. Genetic boundaries between species and subspecies are frequently very "leaky." Only certain parts of the genome, the entire complement of genetic material in a species, may be contributing to the differences that we can see between bird species. If the chapter can convey to the reader that we must learn to think of birds as continually evolving evolutionary lineages, then it will have had some success.

Robbery in progress: Historical museum collections bring to light a mitochondrial capture within a bird species widespread across southern Australia, the Copperback Quail‐thrush Cinclosoma clarum

“…Literature is growing rapidly on the genomics of speciation and introgression. A facet of this that we focus on here concerns mitochondrial DNA introgression and the mitonuclear discordance it can generate (Rheindt & Edwards, 2011; Winger & Bates, 2015; Roux et al., 2016; Bonnet, Leblois, Rousset, & Crochet, 2017; Gompert, Mandeville, & Buerkle, 2017; Ottenburghs et al, 2015; Ottenburghs et al, 2017;Joseph, 2018; Taylor & Larson, 2019; Peñalba, Joseph, & Moritz, 2019 and references in each). Two principal mechanisms are used to explain a particular form of mitonuclear discordance, that of the capture and replacement of one mitochondrial genome by another: adaptive, mitonuclear interactions, or neutral demographic processes accompanying a range invasion of one taxon or population by another (Currat, Ruedi, Petit, & Excoffier, 2008).…”

Full Issue

“…The western clade included all other sampled populations. Nucleotide divergences between each of the three clades of between 3.01 ± 0.87% and 4.56 ± 1.39% are levels typical of species-rank distinction in birds (Avise & Walker 1998, Joseph & Omland 2009, Hung et al 2016, Joseph 2018. Accordingly, and with statistically validated phenotypic correlation among larger groups, three species and seven distinct populations were identified within the complex, thus: 1.…”

Dissection by genomic and plumage variation of a geographically complex hybrid zone between two Australian non-sister parrot species, Platycercus adscitus and Platycercus eximius

“…Evidence of hybrid zone movement has been identified in a number of species to date (e.g. Buggs 2007; Carling and Zuckerberg 2011; review in Joseph 2018). In the case of the Passerina bunting hybrid zone, movement was accompanied by a narrowing of width (Carling and Zuckerberg 2011), and ecological, demographic and behavioural factors were cited as potential explanations for the change.…”

“…Eastern yellow robin Eopsaltria australis : Morales et al 2017a, b; Red-backed fairy-wren Malurus melanocephalus : Baldassarre et al 2014; Variegated Fairy-wren Malurus lamberti : McLean et al 2017a, b) and regions (Penalba et al 2017). Published genomic studies in general have also been found to focus predominantly on passerines (Joseph 2018; Toews et al 2016).…”