Using Genomic and Plumage Data to Understand Contemporary and Historical Relationships among Australian Rosellas (Genus: Platycercus)

Abstract

It is now widely understood that species boundaries are often semipermeable, and that hybridisation and introgression occur frequently in nature and have the potential to dramatically alter the evolutionary trajectory of the taxa involved. Hybrid zones, regions where genetically distinct populations overlap and produce hybrid offspring, provide a valuable opportunity to gain insight into the speciation process. They can arise without a period of isolation when distributions span environmental gradients or ecotones (primary hybrid zone), or as a result of secondary contact following allopatric divergence (secondary hybrid zone), and their structure and ultimate evolutionary outcome can vary greatly depending on the strength of pre- and post-mating barriers to gene flow, as well as the impact of other evolutionary forces (e.g. selection). The dawn of the age of genomics offers great possibility for the analysis of potentially hybridising taxa. In this thesis, I employ a genomic approach alongside more traditional molecular and non-molecular techniques to examine the presence and influence of hybridisation on two native Australian parrot species, the pale-headed (Platycercus adscitus) and eastern rosellas (P. eximius). Together, these species, which are each composed of readily identifiable subspecies, span the eastern seaboard of Australia, with species and subspecies reportedly hybridising where their ranges overlap.