Wednesday, 27 February 2013

DNA barcoding reveals secrets of ancient cephalopod

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shellNautilusThe ornamental shell trade targets Nautilus and, as a result, many populations are being overexploited, leading to population fragmentation and isolation, which contributes to diversification. Image: Nautilus shell, David BygottA RECENT study has not only shed light on the charismatic Nautilus pompilius, but has also illustrated the success of using DNA barcoding as a tool to identify geographic origins, and to study population genetics and evolutionary biology.

N. pompilius (Mollusca: Cephalopoda) also known as the chambered nautilus, is the last living genera of externally shelled cephalopods and is considered a ‘living fossil’, as it dates back nearly 500 million years. 

However, according to the study “DNA barcoding in Nautilus pompilius: evolutionary divergence of an ancient species in modern times”, the ornamental shell trade targets Nautilus and, as a result, many populations are being overexploited, leading to population fragmentation and isolation, which contributes to diversification.

Department of Fisheries scientist Dr Stephen Newman says Nautilus is an ancient animal with a unique life history.

“They lay eggs as discreet units attached to benthic substrate, and the resulting zygote is one of the largest known invertebrate eggs, taking approximately 11 months to hatch,” he says.

“They have no planktonic stage [most other marine species do] and newly hatched individuals resemble miniature adults and are able to feed independently of any parental care.”

Dr Newman says the study focuses on the evolutionary-history and dispersal-history of current populations of N. pompilius to develop a greater understanding of their biology, movement and the relationships between different groups or populations.

The paper reveals three distinct clades for N. pompilius; one clade is from Western Australia, Indonesia and the Philippines.

Phylogenetic analyses were conducted on N. pompilius, and it was found that population similarity reflects oceanic topographic features, with divergence between populations across the N. pompilius range mirroring geographical separation.

“Our results show a significant degree of genetic divergence between the three proposed evolutionary clades, indicative of both movement between reefs, and ancient evolution history,” Dr Newman says.

However, populations of Nautilus from Western Australia were linked with populations from Indonesia and the Philippines, indicating migration between populations that is potentially mediated by movement of individuals via the Indonesian throughflow.

“The West Australian populations [from Ahsmore, Imperieuse, Clerke, and Scott Reefs] are all represented as one large intermixed population, indicating the extent of connectivity between the reefs,” Dr Newman says.

“The Philippine and Indonesian accessions are also interspersed and resolved within the clade which indicates that Nautilus from the surrounding seas of the Indonesian archipelago are still, or have been in their recent evolutionary history, sympatrically distributed with the Nautilus surrounding West Australia.”

Dr Newman says studies such as these aids in the monitoring, assessment and management of fish resources.

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