Evidence for Hybridisation Between the New Zealand Magpie Moth Nyctemera annulata (Boisduval, 1832) (Lepidoptera: Erebidae) and Its Australian Sister Taxon Nyctemera amicus (White, 1841)

ABSTRACT Hybridisation is a natural evolutionary process, but in recent decades, it has increased between previously geographically separated species due to international transport, land modification and climate change. Nyctemera annulata (Boisduval, 1832), the New Zealand magpie moth, one of only four arctiine tiger moth species endemic to New Zealand, is potentially threatened by hybridisation with its colonising Australian sister taxon, Nyctemera amicus (White, 1841). Previous studies identified putative hybrids based on intermediate morphological traits, but molecular evidence for hybridisation between these taxa has been lacking. In this study, we investigated hybridisation between N. annulata and N. amicus using the mitochondrial gene cytochrome c oxidase subunit I (COI) and nuclear genes RpS5 and Histone H3. We identified two COI haplotypes of N. annulata , differing from N. amicus by 13 nucleotides (2.5% divergence). Nineteen putative hybrids were sequenced, 14 with the N. annulata COI haplotype and five with the N. amicus haplotype, providing molecular evidence consistent with hybridisation. Putative hybrids displayed combinations of colour traits from both parental taxa, which were biased towards N. amicus . Two individuals with the colour traits and morphology of N. amicus had the N. annulata mitochondrial haplotype, demonstrating that hybridisation can occur cryptically and that morphology alone is insufficient for reliable identification. Two putative hybrids from Norfolk Island provide the first evidence of possible hybridisation between these taxa outside New Zealand. Phylogenetic analyses confirmed that N. annulata and N. amicus are closely related sister taxa while remaining genetically distinct from other sampled Nyctemera Hübner, 1820 species. These findings demonstrate incomplete reproductive isolation between these taxa and highlight potential conservation risks to endemic N. annulata populations. Continued monitoring and genomic studies are recommended to determine the extent and evolutionary consequences of hybridisation.