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Dumpling squid (Euprymna tasmanica) have marathon sex sessions that leave them incapacitated. (Credit: M Norman)

Sex makes squid exhausted, say scientists

  • BY Emma Davis |
  • July 19, 2012

Australia's dumpling squid are unable to swim after bouts of mating, increasing their risk of being eaten by predators.

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SOUTHERN DUMPLING SQUID spend up to three hours mating, but become so exhausted they struggle to float or swim for up to half an hour afterwards, researchers have found.

"We found that after mating, both male and female dumpling squid took up to 30 minutes to recover to their previous swimming ability," says Amanda Franklin, zoologist behind the study at the University of Melbourne. "This suggested that the squid were suffering from temporary muscle fatigue."

Native to Australian southern coastal waters, the dumpling squid live for less than one year and are sexually mature for the last four months. Amanda and her colleagues discovered that despite the risk of predation, males will mate at nearly every opportunity they get. 

Marathon mating sessions

To initiate mating the male squid grab the females from underneath and holds them in place. It then takes 1-3 hours for the mating process to occur, and a further 3-7 days for the female to lay her fertilised eggs.

"The male uses that whole time to transfer the sperm to the female," Amanda says. "That's why it's so long. At the end, he pretty much throws her off with violent, shaking movements to detach himself from her and then they swim in different directions."

At this point both the male and female typically bury themselves in the sand to recover.

The lengthy mating time and the prolonged period of exhaustion afterwards makes them an easy target for predators, however.

"They're a little species, and they don't have any bones, so they're basically a bite-size meal for any animal bigger than them," she says. "[Despite this] it looks like they pretty much just mate whenever they get the chance."

Sexual selection for sneaky males

Associate Professor Cullum Brown, a marine biologist at Macquarie University in Sydney, says the mating tactics observed are surprising.

"It's clearly a very physical thing for the male," says Cullum, who was not involved in the study. "He's grasping on to a girl who's pretty much the same size as him, and she doesn't seem to struggle all that much, but maybe she doesn't have a choice."

"He's tired afterwards because he's been physically fighting with the girl for however long it takes, and the female is largely exhausted not because she's struggling...but largely because her ability to breathe is reduced with the grip the male has on her. She's actually getting asphyxiated."

"It seems to me that the females not getting a choice at all, the males are ambushing them and that has all sorts of interesting evolutionary implications," says Cullum. "From the males' perspective maybe there is the selection on being as stealthy and strong and sneaky as possible."

The study was published this week in the journal Biology Letters.

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