Dumpling squid mate, male on left, female on right. They are sexually promiscuous… (Mark Norman / Biology Letters )
After their three-hour sex sessions, dumpling squid are so exhausted that they can swim only half as long as before their sexual workout, an exhaustion that might limit their search for food and leave them more vulnerable to predators, Australian researchers reported this week. Their study is the first to quantify the energetic costs of mating in this submarine species and may lead to a new understanding of the cephalopods' survival, growth and reproduction.
Dumpling squid, formally Euprymna tasmanica, are typically a little less than three inches long when fully grown and live for less than a year. They are sexually promiscuous and their mating sessions are very vigorous, lasting as long as three hours. The male restrains the female, pumping jets of water into her mantle and jet, releasing ink and changing color repeatedly. The physical activity cannot be sustained by aerobic metabolism alone and generally requires anaerobic metabolism, which produces lactate -- an important agent of muscle fatigue.
By contrast, the female's activity is much less energetic. But the male's constrictive hold on her most likely restricts her oxygen intake, inducing anaerobic metabolism in her as well.
Zoologist Amanda Michelle Franklin of the University of Melbourne in Australia and her colleagues collected dumpling squid from the wild and studied them in the laboratory. After acclimation, they forced the squid, both males and females, to swim to exhaustion in a flume. On a different date, the researchers allowed the squid to mate, then performed the same swimming experiment. The team reported in the journal Biology Letters that, after sex, both males and females could swim only half as long as normal. If they were allowed 30 minutes of recovery time after sex, however, they could swim as far as normal.
The authors noted that squid lay several clutches over their reproductive periods, and the energy invested in mating, combined with lost foraging opportunities, could significantly impair their reproductive success, particularly if there are shortages of food.