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The dynamics of hybridisation between an avian island endemic and a recent coloniser

Research objective:

To determine whether there has been hybridisation between the coloniser, Zosterops lateralis, from New Zealand and
Zosterops tenuirostris, the endemic species of Norfolk Island, and whether this hybridisation has led to introgression
between the species.

Results:

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.

For more information, please download the case study here!