Tatiana Gerus/Wikimedia Commons
NEW YORK (GenomeWeb) – An ancient DNA analysis has found that the Australian little blue penguin is a recent colonizer of New Zealand, according to a University of Otago-led team of researchers.
By radiocarbon dating and sequencing stretches of ancient DNA from Eudyptula samples found in New Zealand, researchers led by Otago's Jonathan Waters found that the Australian Eudyptula novaehollandiae likely arrived in New Zealand some 500 years ago, around the time of the decline of the indigenous Eudyptula minor. As they reported yesterday in the Royal Society Proceedings B: Biological Sciences, the researchers found that the decline of a native species could thus be masked by the introduction of a related taxon.
"Our results clearly show that the Australian penguin colonized Otago very recently, between 1500 and 1900 AD, apparently following the decline of the native New Zealand little penguin, which was hunted by early human settlers and introduced predators," first author and Otago researcher Stefanie Grosser said in a statement.
The little penguin genus is endemic to both Australia and New Zealand, and recent genetic analysis of mitochondrial DNA had found that there are two, divergent little penguin lineages: one that's found only in New Zealand and one that's found both on New Zealand's Otago coast and in southern Australia. Initial genetic studies had suggested that the Australian penguin had been in New Zealand for thousands of years, though a more recent study hinted at a later introduction.
Waters, Grosser, and their colleagues collected 146 prehistoric Eudyptula bones from museum and archaeological collections and nine historic Eudyptula samples that represent the full swathe of the little penguin range in New Zealand. They extracted and sequenced a 393-basepair stretch of DNA corresponding to the mitochondrial control region HVRI from 128 of those specimens, though 16 of those could only be partially sequenced.
At the same time, radiocarbon dating of nine of the prehistoric Eudyptula bones traced one sample as far back as 34,000 years before present (BP) — the oldest yet discovered, the researchers noted — though most of the others dated back to 1499 BP and 1112 BP.
The genetic analyses revealed a striking turnover in Otago, the researchers reported: E. minor was nearly completely replaced by E. novaehollandiae. All 119 Holocene samples — older than 1600 AD — were phylogenetically assigned to the endemic New Zealand E. minor lineage, while the more modern penguin samples were mostly E. novaehollandiae. Five of the six museum skin samples from birds collects in 1969 had Australian haplotypes, the researchers added.
Their analysis further found that the prehistoric New Zealand Eudyptula exhibited substantial haplotype diversity. Some of the ancient diversity has been lost as the research found that only two of the 12 detected prehistoric New Zealand haplotypes are represented in the modern samples. This, they added, indicates a haplotype diversity reduction of 35 percent.
Using a Bayesian serial coalescent approach, the researchers examined the demographic history of the Australian little penguin in New Zealand. After modeling a number of scenarios, they found that there was the most support for a two-step model in which an initial invasion of E. novaehollandiae was followed by a population expansion in Otago. Under this model, colonization likely took place about 25 generations ago, or in about 1500 AD to 1890 AD with an effective population size of the colonizers of about 2,900 individuals.
This timing, the researchers noted, broadly coincides with a 40 percent population loss of the endemic E. minor. However, they added that they had insufficient power to determine whether the E. novaehollandiae colonization or decline of E. minor occurred first.
Human colonizers, who arrived a few centuries prior, are thought to have aided in the E. minor decline likely due to hunting and the introduction of predators like the Polynesian rat and dog.
"[O]ur aDNA analyses of little penguins directly document a compelling example of rapid faunal shift coinciding with human expansion into New Zealand," the researchers wrote in their paper. "These data highlight that the decline of a native species can be masked by the cryptic invasion of a related species."