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Mating Games Squid Play<< Cephalopod Articles | By , Department of Psychology and Neuroscience, University of Lethbridge
In the summer of 1998 I began a long-term field research project in Bonaire to evaluate the skin colours andpatterns of Sepioteuthis sepiodea, and understand their communication. Evaluating this system is going to take a lot of time. Along the way, I and my many volunteer assistants were able to watch squid mating strategies. This is a first report of what we saw.
Like most Cephalopods, Sepioteuthis squid leave the best to the last. For most of their lifespan they are not interested in sex. They hunt by themselves at night and gather in schools or shoals in the daytime. They swim in a kind of lineout, keeping together, watching for predators and staying in the same bay or shore area. During the last weeks of their lifespan, however, that all changes. Sex, and status, becomes the center of their days.
As they have permanent separate sexes and male sperm is cheaper than female eggs to produce, mating theory predicts that males should be more eager and more managing in the business of pairing and mating than females, who should be more choosey about who they accept. This aspect of courtship seems to be true for squid. Moynihan and Rodaniche (1982) and other researchers have pointed out the variety and importance of visual displays on the skin of Sepioteuthis, so they should use these in courtship. What else shapes the system?The third important influence is the social group. Squid court and mate in groups of from four to fifty, so during interaction with the other sex they are susceptible to a lot of influences from each other. It's quite an open system.
The first visible sign of interest in sex is a subtle division of the group into male-female pairs. Males and females seem to prefer larger partners, and eventually they sort into same-size pairs. This sign of interest is often accompanied by an exchange of skin signals. The male does Stripe, a pair of wide black longitudinal stripes on either side of the mantle, with paler areas in between. The female does what we called Saddle, which is probably the same as what Moynihan and Rodaniche (1982) called Pied. We used this name because it's such a good description of the pattern. All the female's mantle goes white, except for a thin line of dark brown on the very anterior like a saddle over her body. Often the dark line extends a bit mid-dorsally towards the anterior end of the mantle. When they did the nearly 300 Saddle-Stripes we recorded, the pair were nearly always positioned with the female directly over the male.
These displays seem to show interest but not more than that (like the exchange of a long kiss in humans). We saw Saddle-Stripe in smaller squid who showed no other sexual behavior, and we saw it in a pair after they had mated or attempted mating. More interesting, we saw it in newly formed pairs after a take-over and inlonger-term pairs after the male had challenged another male. Sometimes a pair would match up for a minute, exchange a Saddle-Stripe and then go away (or back) to others. Maybe it's a kind of testing, or level-setting.
The next signal we saw did indicate much more than passing interest in partnering. When a male went pale and started Flickering the intensity on and off, a VERY visible signal in the shallow water, it showed a serious intent to mate. Males pass spermatophores to the female by sticking them onto her skin just below the eyes. A willing female often turns pale herself and the pair swim fairly quickly side-by-side back and forth in a Rocking motion, with him still Flickering, for a minute or so. Then he darts around in front of her and sticks the spermatophores in place; the probability of this transition is 0.3. The female can then take them and puts them in her mantle cavity, where the sperm are stored for later fertilization of her eggs.
All this depends on the female being willing. If she isn't, she has a bag of tricks up her sleeve (well, mantle). First, she may just jet away, and if this jet isn't too fast the male may Chase her. Sometimes the chase turns into Rocking and then they mate; it could be that females are testing males for fitness by doing this. If she's only mildly resistant, she may put an agonistic pattern of rough vertical Zebra stripes on her skin. If she's really serious she can dodge when the male chases, go down to the bottom near the sand or coral, and do a linear arms-up posture with dark skin that seems to really mean business. If she does these things, the probability of a mating attempt drops to near zero.
More than this refusal can go wrong when a male tries to mate. As they are all in the group together, other males see the signal and challenge him over 50% of the time. Challenges tend to be accompanied by a very obvious Zebra striped display on the skin. As one male starts to Flicker, another will put rough vertical stripes on the skin over a white or yellow background and come at him. This challenge can result in a takeover and formation of a new pair or just disrupt the mating. I watched once for forty minutes as a male started Flicker, a juvenile swam at him in Zebra, and the male replied in Zebra and chased him away. This happened over and over;eventually the male gave up and the pair never did mate.
Sometimes this challenge escalated into the Formal Zebra challenge (James Wood coined the phrase Full Assed Zebra for it). A pair of males take an over-under position, put a Zebra on the skin, and often push each other at the posterior end of the mantle. The Zebra looked different depending on position; it was on white and the arms were widely spread if the squid was Under, on dark brown and arms less spread if he was Over. There was sometimes jockeying for position, useful because when we analyzed 21 displays the Under squid not only had brighter Zebra, it won the contest. This exchange took a full minute on average and the two males were oblivious to anything else happening at the time, which puts an open-ocean animal in danger. It was one activity that was easy to film, and we could even reach out to touch squid during a Formal Zebra, impossible otherwise. Still, understanding what squid mean by these signals will take a lot of time. See Owings et al, 1997, for a good detailed discussion of animal communication.
Courtship and mating went on mostly in the early morning and late afternoon. Consortship could be reasonably long-term; we watched one pair form about 7:30 a.m. and they mated throughout the next few hours. They mated quickly twice within an hour, then the male had a prolonged period of Flickering and eventual mating later in the morning. Near noon he Flickered and tried to pass spermatophores, but was rejected—he was more eager than her. We recognized a few individuals by scars on the body, and larger pairs were stable over a few days. On the other hand, I saw a male in a consort pair go off to do a Zebra challenge with others. A smaller male came in to the temporarily single female, they did a Saddle-Stripe and he Flickered and they mated, all in about one minute. Pair stability and thus male access to females probably varies with maturity.
If males are motivated to protect their reproductive investment, we would predict that they would try to isolate a female with whom they had mated and guard her from other males. While males mate guarded, it seemed relatively ineffective in the group. There were a lot of Zebra exchanges, there was a lot of jockeying for position. In the line-out of the group there was frequent interposition and shifting, active attempts at guarding and takeover of females by males. There were also subtle position changes and repulsion by females, much harder to document. Eventually, pairs left the group, though slowly and drifting away and back. When they were more than 2 meters from the other squid, a male would often show a Lateral Silver keep-away signal on his mantle. On the side AWAY from her and TOWARDS the other squid, he would turn a bright silver-white. We used to enjoy watching how he held this pattern as they moved. If he ended up on the other side of her, he switched display sides immediately. Sometimes they got closer to the others and he put a bit of Zebra over top of the white. We could argue he was being two-faced, but could also point out the accomplishment of sending three signals at once, on different areas of the skin!
It's intriguing to think about why they separated and why they didn't separate sooner. It's in the male's best interest to isolate a female if he has mated with her. Maybe the group offers the protection of many eyes to spot fish predators, and there's a tradeoff in benefits. Maybe he balances the advantage of the opportunity to fertilize other females, possible only when they are in the group. Alternately, perhaps it's in the female's best interest to stay with the group and mate with several males. Maybe she only allows herself to be herded into isolation when she has done so, when she has enough sperm or her eggs are mature enough to be ready to lay. Maybe she has settled on her best choice. This is an intriguing question but one that will be difficult to answer.
After they drift apart from the group, the female will begin to spend time investigating the coral on the sea bottom. She searches for a protected niche, a crevice out of the way of the scavenging wrasse that eat anything out in the open. Finding one, she will squeeze down and under, move eggs out past the spermatophoric gland to fertilize them, give them a gel coat and attach them, a few at a time. We only saw this once, and the female turned a deep dark brown while she was doing it. She probably lays a few each time andthe male may leave her to go back to the group. His reproductive investment is over when she stops mating and begins to lay—though of course it pays to make sure she survives to lay the eggs!Once in a while we saw a big solitary male come by the group, Zebra at all the males and then just leave. Maybe this was one of the 'leftover' males from a pair.
After this devotion to the business of reproduction, both male and female squid die. They probably get eaten by predatory fish as they lose strength and vigilance. We saw yellowtail snapper, a small member of the tuna family, constantly patrolling the area. Squid inevitably paled and jetted away at their approach, often before we even saw the fish, and we also saw a couple of capture attempts. Constant vigilance and sudden speed would fail at the end of their lifespan, so that's probably how squid die in the wild. But on the way to their demise, they certainly had a heck of an orgy.
These mating games are not out of the way for the average snorkeler to see—you don't even need to scuba dive. We watched Sepioteuthis in Bonaire but they are found all over the Caribbean. They are an inshore species, swimming in about 2-3 meters of water. A group seems to be place-specific so when you find one you can go back to it for days or even weeks. There are only two rules to keep in mind. First, they were most active in early morning and a little less in late afternoon. Go at noon and it's all over (and they will most likely be taking a siesta). Second, squid spook very easily. To watch them you must float, or hover if you are using scuba, nearly motionless until they habituate to your presence and go back to what they were doing. Wear a wet suit, because even in 28 degree water you get pretty cold when not moving. In return, you can watch great colour changes, chart intricate status moves and get a good view of squid mating games.
To read:Hanlon, R.T. and Messenger, J.B. (1996). Cephalopod Behaviour. Cambridge, Cambridge University Press
Moynihan, M. and Rodaniche, A.F. (1982). The behavior and natural history of the Caribbean reef squid Sepioteuthis sepiodea. With a consideration of social, signal and defensive patterns for difficult and dangerous environments. Advances in Ethology 25, 1-151. Book: This reference has more detail on Sepioteuthis and their skin patterns, posture and behaviour than you may need.
Owings, D.H., Beecher, M.D. and Thompson, N.S. (1997). Perspectives in Ethology 12: Communication. New York, Plenum. Book: A very thorough discussion of the subject, nothing on Cephalopods.
Articles ReferenceMather, J. 1999 Mating Games Squid Play. In: The Cephalopod Page (http://www.thecephalopodpage.org/index.html). Wood, J.B. Ed.
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