Shining a bright light over the side of the Odyssey at night will usually attract schools of squid
to the surface for closer observation. Squid are the primary
food source of Sperm Whales.
Photo: Joanna Wilson
May 4, 2001
The Mating Patterns of Squid
This is Genevieve Johnson speaking to you from the Solomon Sea, Papua New Guinea.
Cephalopods include the octopuses, cuttlefishes, squids, and the most ancient of this family, the chambered nautiluses. When translated literally cephalopod means 'headfoot' for that is exactly what these creatures are. There are over 700 known species of cephalopods worldwide, all with varying body types and lifestyles. They are the most highly evolved marine invertebrates. They possess large brains, display complex social behaviors and much about their elaborate methods of intraspecific communication is still poorly understood.
Joe Cavanaugh has studied squid for the past 3 years and while he is with us on board the Odyssey, will assist us in understanding at least a little of the fascinating behavior, ecology and physiology of squids.
Today he discussed with us the unique mating patterns of many squid species.
In many of the common squid species there are two alternative mating tactics used by males, which is dependent on their size. Large males generally tend to guard females and they place their sperm, which is encased in a spermatophore inside the females mantle cavity, as near to her oviducal entrance as they can get. This will afford them the best chance of inseminating the female and fertilizing her embryos, which are also encased in a capsule. When she extrudes these capsules out of her mantle cavity they are already fertilized by the male that mated with her 'parallel'. It's called a parallel mating because a large male grabs the female parallel to her, and usually underneath her. He then grabs spermatophores with a modified arm that he has called the hectocotylus, and he places those spermatophores inside her mantle cavity from his own penis.
The interesting alternative to this, are the 'sneaker' males that are smaller males, usually half the size or even smaller than that, from the large males. They are not large enough to guard a female on their own, so what they try to do is they use speed and stealth, and they jet into a female very quickly as she is getting ready to lay her eggs. The small 'sneaker' male places his sperm, again encased inside a spermatophore, and is placed inside the female's small genital opening just below her mouth cavity called the seminal receptacle.
What is interesting about the 'sneaker' method is that the sperm placed inside the mouth cavity can be stored for much longer than the sperm placed inside the mantle cavity. The sperm inside the mantle cavity lasts less than a day, so the only opportunity the large male has is within that day, usually just a couple of hours to inseminate the female. But sperm placed inside the seminal receptacle, or mouth cavity can last for several months and is viable during that time. It is not really understood yet how the sperm of the 'sneaker' male are kept alive and what sort of nutrients are provided by the female for many squid species to be able to keep that sperm alive.
The interesting repercussions from these two alternative mating tactics for fisheries, which was really the subject of my thesis work, is to try to estimate the reproductive fitness from these two alternative mating tactics over time. That the large males have a greater reproductive fitness in the short term, because their sperm is used right away, but the small males have a greater reproductive fitness over the long term. So by using a combination of fieldwork and laboratory mating trials and genetics, we can try to figure out just how reproductively fit the different size classes of males are over time. This will allow us to better manage the fishery.
Log by Genevieve Johnson