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A recent study led by the University of Otago has shed light on the origins of a rare lineage of mergansers, fish-eating ducks, in New Zealand. Mergansers are typically found in the Northern Hemisphere, with only a few rare species located in the Southern Hemisphere, such as the critically endangered Brazilian merganser and two extinct species that were previously found in New Zealand’s Auckland and Chatham Islands. The Auckland Island merganser was the last surviving population until its extinction in 1902, leaving the evolutionary history of mergansers in New Zealand a mystery.

Associate Professor Nic Rawlence, the lead author of the study, explains that there has been a lack of a deep-time fossil record for mergansers in the Southern Hemisphere, making it challenging to understand their evolutionary relationship and origins. The research findings, published in the Zoological Journal of the Linnean Society, reveal that mergansers arrived in the New Zealand region over seven million years ago from the Northern Hemisphere, in a separate colonization event from that of the Brazilian merganser. This discovery has significant implications and highlights the diverse origins of New Zealand’s bird species beyond just Australia.

The study utilized advanced ancient DNA techniques to extract DNA from historical specimens of the extinct Auckland Island merganser and critically endangered Brazilian merganser, providing valuable insights into the evolutionary history of mergansers in the region. By sequencing the mitochondrial genome of these species and constructing a family tree, researchers were able to determine when their ancestors arrived in New Zealand and how they diversified across the Auckland and Chatham Islands. They hope future research will further uncover unexpected lineages through palaeontological and ancient DNA studies in the Southern Hemisphere.

Associate Professor Rawlence emphasizes the significance of this discovery, noting that it aligns with theories proposed by renowned New Zealand palaeontologist Sir Charles Fleming in the 1960s. The collaboration between researchers from various institutions, including Manaaki Whenua Landcare Research, the Museum of New Zealand Te Papa Tongarewa, and the University of Adelaide, highlights the importance of multidisciplinary approaches in uncovering the mysteries of New Zealand’s unique bird species. By combining genetics and palaeontology, scientists are able to paint a more complete picture of the evolutionary history of these enigmatic birds.

The research not only reveals the ancient origins of mergansers in New Zealand but also underscores the interconnectedness of bird species across different regions, including Madagascar, Africa, South America, and now the Northern Hemisphere. As genetic and palaeontological technologies continue to advance, more unexpected lineages and evolutionary relationships are likely to be uncovered. This study represents a step towards a deeper understanding of New Zealand’s avian biodiversity and the complex evolutionary processes that have shaped the country’s unique fauna.

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