Poster Presentation Society for Molecular Biology and Evolution Conference 2016

A genomic approach to examining two avian hybrid zones (#534)

Ashlee Shipham 1 , Daniel J Schmidt 1 , Leo Joseph 2 , Jane M Hughes 1
  1. Australian Rivers Institute, Griffith School of Environment, Griffith University, Nathan, Queensland, Australia
  2. Australian National Wildlife Collection, CSIRO National Facilities and Collections, Canberra, ACT, Australia

Hybrid zones provide a unique opportunity to examine the strength and nature of species boundaries. The occurrence of hybridization can have wide-ranging implications for the taxa involved, depending on the strength of pre- and post-zygotic barriers to gene flow between them. Rosellas are a group of colourful and charismatic Australian parrots, with a number of morphologically distinct species and subspecies exhibiting zones of intergradation where their ranges overlap. Two zones that have been examined morphologically, but which lack an analysis of their underlying genetic composition are studied here. The first is between two non-sister species, the pale-headed (Platycercus adscitus) and eastern (P. eximius) rosellas, which hybridize in the border region between Queensland and New South Wales. The second is a broad zone between the two currently recognized P. adscitus sub-species, located in Queensland. Here, we have taken a genomic approach to advance the understanding of these two zones. We aim to distinguish whether they represent hybrid zones or geographic clines in morphology, and examine the presence and pattern of gene flow across them. We employ restriction site-associated DNA (RAD) sequencing to generate thousands of loci. Using a combination of assignment tests and genomic cline analyses, we find different patterns of variation in the P. adscitus /P. eximius hybrid zone and that between P. adscitus subspecies. The former appears to be largely bimodal, with some support for introgression of P. eximius alleles into P. adscitus. The latter appears less structured, and we consider (1) that this may represent a geographic cline in plumage rather than a hybrid zone, or (2) that weak/absent barriers to reproductive isolation may have resulted in genomic introgression extending beyond that which is readily identifiable based on plumage characteristics. The potential causes and implications of our findings are discussed.