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Genetic Bottlenecks as Gloomy Octopus Drifts South

A species of octopus previously confined to eastern Australian waters is extending its range south, riding a new wave of warm water as ocean currents change. In a study published in Scientific Reports (https://goo.gl/tLH5Hk), researchers have examined the genetic processes associated with the gloomy octopus’ range shift.

The octopus was first spotted in Tasmanian waters by local fishers and citizen scientists from the Redmap project. “The octopus’ real name is the common Sydney octopus, or Octopus tetricus, but it’s known as the ‘gloomy’ octopus because it appears to have a rather downcast expression,” explained Dr Jorge Ramos of the University of Tasmania, who led the study.

“In recent years researchers have identified an increasing trend for both marine and terrestrial animals to shift their distributions, extending their ranges in response to climate change as new areas become warm enough or other ecosystem changes take place. As citizen science projects such as Redmap are revealing, range shifts are one of the most common responses of marine species to oceanic warming.

“The gloomy octopus provided a good opportunity to examine what genetic process may allow marine range-shifting species to establish and persist in recently colonised areas due to oceanic warming,” Ramos said.

The study’s senior author, A/Prof Jan Strugnell of James Cook University, said the octopus is drifting south with the East Australian Current. “As the seas have warmed, the current has been transporting warmer waters than before into the temperate Tasmanian marine ecosystem, and with it dozens of marine species that are new to the area,” Strugnell said. “Our study took the opportunity to look at the genetic make-up of the new arrivals.”

The research found that populations along the range extension suffered “genetic bottlenecks” – a loss of genetic diversity. “Surprisingly, even though genetic bottlenecks were detected, genetic diversity was moderate and comparable between populations from their usual home and the new place,” Strugnell said.

One of the possible reasons is that the bulk of the octopi came from one location that has relatively similar temperatures to Tasmania.