What's so exhausting about squid sex?

For dumpling squid like the ones pictured up top, sex is serious business. Mating sessions can last as long as three hours, and involve plenty of strenuous physical activity. Afterwards, the mating squid are left feeling so exhausted that their swimming endurance is halved, and it can take them up to 30 minutes to recover.

It's worth pointing out, by the way, that mating halves the swimming endurance of both sexes — not just the males. Yeah... the researchers were surprised, too:

"We expected males to be more strongly affected than females," writes Amanda Michelle Franklin, a zoologist at the University of Melbourne and first author on the study, "because males are more active during copulation. The males physically restrain the female, pump jets of water into her mantle and jet, change colour and ink more than females do." Females, on the other hand, appear "relatively quiescent, only occasionally jetting or visibly elongating the mantle. "

And yet, the researchers note, "swimming endurance was clearly reduced by mating and the magnitude of this effect was similar for both sexes."

The researchers hypothesize that the downside to squid feeling knackered after a round of sex is that it leaves them ill-equipped to handle basic functions important to their survival — things like predator-avoidance. How's that for a tradeoff?

Check out the full study, free of charge, over at Biology Letters.

Top image by Mark Norman