Squid sex... it's just so tiring

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Men aren't the only ones who want to go to sleep after sex. After three hours of going at it, squids are too tired to do much either, new research has shown.

Researcher Amanda Franklin, a science masters student at the University of Melbourne's Department of Zoology, said being worn out from sex could keep squids from finding food or avoiding predators.

In the study, Ms Franklin and her colleagues looked at the southern dumpling squid (Euprymna tasmanica), a small cephalopod which grows up to 7cm and lives only one year.

The southern dumpling squid mates with multiple partners, with intercourse lasting up to three hours.

The male grabs the female from underneath, and holds her in place throughout copulation.

In order to find out how exhausting these sexual encounters were, the researchers captured wild dumpling squid off the coast of southeast Australia, and placed them in tanks of flowing water. The flowing water forced the squid to swim, so the researchers could measure how long it took before the squids were exhausted.

The squids were then paired up for mating and placed back in the tanks.

"We found that after mating, both male and female dumpling squid took up to thirty minutes to recover to their previous swimming ability," Ms Franklin said.

"This suggested that the squid were suffering from temporary muscle fatigue.

"Our results were a little surprising as the degree of fatigue was similar in both genders even though mating looks more strenuous for males.

"We predict that during this phase of muscle fatigue, squid may hide in the sand to avoid predators until they have recovered. The cost to them in doing this of course is that they cannot forage for food or search for other mates at this time."

The findings, published in the journal Biology Letters, highlights the risks of mating for some species. Franklin suggested the high-intensity mating may even explain the squids short lifespans.

Dumpling squid are closely related to about 10 bobtail squid species found around the world, including the waters around Hawaii and the South China Sea. These species have similar mating habits to the southern dumpling squid.

"Dumpling squid live for less than a year, and may engage in the energetic activity of mating many times within their short breeding period. This reproductive strategy may have other costs to individuals besides energy loss and we have investigated this further by assessing the effect of mating on female lifespan. We're hoping to report the results of this experiment very soon."