Promiscuous squid fatigued after mating: study

Jul 18, 2012
Southern dumpling squid. Credit: Mark Norman

(Phys.org) -- In order to pass on their genes, southern dumpling squid engage in up to three hours of mating with each partner, but University of Melbourne researchers have found that this results in a reduced ability to swim for up to 30 minutes afterwards.

The research provides new insight into the evolution of and and is the first time that the energetic costs of mating have been shown to affect after mating.

The research was conducted by Master of Science student Ms Amanda Franklin with Ms Zoe Squires and Dr Devi Stuart-Fox from the Department of Zoology at the University of Melbourne, and is published today in the international journal Biology Letters.

The team studied dumpling (Euprymna tasmanica) that live in waters of including Port Phillip Bay and Tasmania and reach about 7cm long at adult size.

Dumpling squid engage in up to three hours of mating and males appear to initiate mating whenever the opportunity arises. The male grabs the female from underneath, and holds her in place throughout copulation. Both can change colour from a sandy yellow to dark purple with green and orange highlights. They can also produce a cloud of ink as a decoy to help them escape from predators. 

Ms Franklin said 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 from St Leonards in south-eastern 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,” 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.” 

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 on female lifespan. We’re hoping to report the results of this experiment very soon.” 

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User comments : 3

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Picard
1 / 5 (1) Jul 18, 2012
I'm also tired after sex.

Maybe I'm doing it wrong.
Squirrel
1 / 5 (1) Jul 18, 2012
Looks like a form of sexual selection. It's not clear whether the female force the males to have such long copulation or the males are responsible. In the former case it would select (given repeated matings and predators eliminating easily tired males) for males with the best genes to cope with fatigue.

Alternatively, males might competing with other males by making fertilization dependent upon a male's ability to sustain multiple long matings and survive.
antialias_physorg
not rated yet Jul 18, 2012
"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."

Initiation of foraging is not determined by chance of success/predation but by how hungry the individual is (in predominantly instinct driven species). And I could imagine that after 30 minutes of strenuous excercise these suckers (Ha!) are hungry.

Ms Franklin said the team was keen to understand the impact of such an extensive mating ritual

Well, this part of the study might provide a clue:
Dumpling squid engage in up to three hours of mating and males appear to initiate mating WHENEVER THE OPORTUNITY ARISES.
(Caps mine)

Read: They are sex addicts (which makes for a very good survival strategy).