Too much mating fatigues oversexed squid

U. MELBOURNE (AUS) — After mating for up to three hours, the southern dumpling squid is often too tired to swim for up to 30 minutes afterwards.

Published in the journal Biology Letters, the research provides new insight into the evolution of reproductive strategies and is the first time the energetic costs of mating have been shown to affect physical abilities after mating.

Researchers studied dumpling squid (Euprymna tasmanica) that live in waters of Southern Australia and grow to about 7 cm (almost 3 inches) long as adults. Both males and females can change color from a sandy yellow to dark purple with green and orange highlights. They produce a cloud of ink as a decoy to help them escape from predators.


Both males and females can change color from a sandy yellow to dark purple with green and orange highlights. They produce a cloud of ink as a decoy to help them escape from predators. (Credit: University of Melbourne)

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Dumpling squid engage in up to three hours of mating that is seemingly initiated by males whenever the opportunity arises. The male grabs the female from underneath, and holds her in place throughout copulation.

The team was keen to understand the impact of such an extensive mating ritual because although traditionally thought to be trivial, the energetic costs of mating could reduce an animal’s survival if it decreased the ability to avoid predators and forage for food.

The researchers collected dumpling squid in southeastern Australia and tested their swimming endurance against a constant current of water in the lab. The squid were then allowed to mate and their swimming ability re-tested.

“We found that after mating, both male and female dumpling squid took up to thirty minutes to recover to their previous swimming ability,” says Amanda Franklin, master of science student at the University of Melbourne. “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.”

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.”

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