Pharyngula

Octopus sex

Category: Organisms • Reproduction
Posted on: February 20, 2006 9:58 AM, by PZ Myers

I rather like this illustration I ran across in some reading. It's a bit risqué, and reminded me of some ukiyo-e…the kind of thing you don't usually expect to find in a biology journal.

This line drawing was made from a photograph of a male H. lunulata (shaded) copulating with a female. The arrow points to the male's hectocotylus, which is being inserted into the female's mantle cavity.

This site gets a lot of hits in searches for tentacle sex, and I'm going to distract a lot of slavering otaku once again by talking about the real thing. Not the fantasies of Hokusai, Teraoka, or Saeki (warning! Those links are not work safe!), but some interesting work on how the blue-ringed octopus, Hapalochlaena lunulata, selects its mate (Cheng and Caldwell, 2000). The short answer is...indiscriminately. Here's the abstract:

We studied the reproductive behaviour of the blue-ringed octopus, Hapalochlaena lunulata, in the laboratory by examining 15 male-male and nine male-female interactions. The initiation of physical contact was independent of sex, size or residency status, and there were no noticeable changes in behaviour such as sexual displays associated with courtship or aggression prior to contact. Males did not distinguish between females or other males and copulated (defined as the insertion of the hectocotylus into the mantle cavity of another octopus) readily with both. Spermatophores were released in all copulations with females but not with males. The duration of copulation was significantly longer in male-female interactions (median 160.5 min) than in male-male interactions (median 30 s). Although male-male copulations ended passively with the withdrawal of the hectocotylus by the initiating animal, male-female copulations were always terminated by the females following an intense struggle. These studies suggest the inability of male H. lunulata to determine the sexual identity of potential mates prior to the insertion of the hectocotylus and demonstrate the active role of the female during copulation.

H. lunulata is a pretty (and poisonous) Asian octopus with lovely iridescent blue rings, and since the octopus has a highly developed visual system, the authors wondered if there were any interesting sexual and courtship behaviors in this species. The experiment was simple: octopuses were paired, and their behavior observed and recorded. There is little obvious sexual dimorphism here other than size and the presence of an enlarged hectocotyl arm in the male, that he uses to insert into the female mantle and deposit a spermatophore. The expectation was that the male might engage in some signalling with that arm, and that the two individuals might do something to assert their sex and negotiate before mating.

But no. These octopuses seem to be able to recognize that the other is a conspecific, but do not recognize whether the other is male or female, at least not until after they begin copulation. Put two octopuses together, and within 3-4 minutes, a male will have pounced on the other, whether it is male or female, and inserted his hectocotyl arm into it's mantle. There didn't seem to be much in the way of perceptible preliminaries.

Once copulation began, the male would figure out whether he was having sex with a male or a female. Male-male copulations typically only lasted 30 seconds and did not culminate in spermatophore release (nor did the aggressive male beg pardon of his partner), although in one instance copulation continued for 44 hours. Male-female copulations were significantly more prolonged, typically lasting over two and a half hours, and did result in release of one to four spermatophores.

Copulations always ended at the female's insistence: she would forcibly reach back with her arms and pull the male away. Furthermore, she didn't seem entirely happy with the event. Half the time, the female would actively attack the male afterwards.

In one instance, the female killed the male by pinning him down against the aquarium wall for over 10 h while cannibalizing most of his arms. This was also the male-female pair in which duration of copulation was noticeably shorter, lasting only 25 min.

The lesson in that is ambiguous. It's not clear whether the mortal insult was the affront itself, or the brevity of the engagement.

The behavior of the blue-ringed octopus does remind me of some guys' dating strategy way back in college, though.

Initiating copulation with any individual encountered, male or female, may be a good strategy, or at least a neutral one, because the costs of the interactions are negligible while the benefits may result in an increase in fitness.

Well, the cost is negligible except for the possibility of ending up a post-coital snack, I would think.

Cheng MW, Caldwell RL (2000) Sex identification and mating in the blue-ringed octopus, Hapalochlaena lunulata. Anim Behav. 60(1):27-33.