Introduction:

Whole genome sequencing uncovered a signal of hybridisation between the two species on Norfolk Island. Using paired-end 150bp sequencing with 5X depth, Sonya and her team ended up with 15 million SNPs for downstream analysis to determine if introgression had occurred after the contact of these two species. Using imputation methods to identify SNPs, and D statistics and analysis of ABBA/BABA patterns, they asked the question “have the hybrids back crossed with parental populations resulting in introgression?”. The answer was yes. A positive D value, indicating an elevation of ABBA allele patterns rather than BABA patterns supports introgression. The next question was “where in the genome is introgression evident?”. Using a sliding window approach with 50kb windows and a 10kb sliding step, they showed that introgressed windows occurred widely across the genome, with interesting candidate genes for features such as plumage colouration and bill size and shape being highlighted in these windows. This genetic evidence aligned with phenotypic features of some museum specimens that are thought to be hybrid individuals.