Friday, May 12, 2017
I know what you’re thinking: “Why hasn’t she written about cuttlefish mating systems?” I understand, cuttlefish are ridiculously cool and you just need to know more about them. You are in luck as a brand new study has been published online about just that topic!
Cuttlefish are cephalopods, which are all predatory, marine animals that have at least eight arms, a siphon for jet-propulsion, and highly developed nervous and sensory systems (specifically the most sophisticated eye of all invertebrates). Those last characteristics make them highly intelligent, with complex learning behavior, to the point that many consider them to be “conscious.” Unlike other cephalopods, all of their hard parts (if any) are internal. That means all of their outside parts are soft, squishy and covered in color-changing skin. Their ability to change color is absolutely amazing, particularly in cuttlefish (just google ‘Flamboyant Cuttlefish’!). Located in their skin are tons of chromatophores (pigment filled bags) that expand or contract to reveal/hide their color. And it’s crazy-fast too. They can alter their appearance in as little as half a second! They use this color change for camouflage, courtship rituals, or just to show you how they feel about you interrupting them with your dive camera (a little personal experience with a mama octopus thrown in there).
Cuttlefish are in the clade Coloidea that also includes squid and octopuses, and a sister group to the Nautilus. They look like squid but have stouter bodies and a fin fringe that runs around their body that they undulate to move. They have separate sexes and an often elaborate courtship ritual. Should a female find a male worthy, she accepts his spermatophore (sperm packet), which he transfers to her with a specially modified arm (hectocotylus). Then the females will use the contents of this packet to fertilize their eggs and lay them in clusters.
Cuttlefish can be seasonal in their mating habits, with some species gathering in the hundreds to find their special someone. Where animals gather to mate, they also gather to strut their stuff. One of the ways they do this is through shear brawn. Basically, the strongest guy gets the girl. A study currently in press in The American Naturalist describes competition between male cuttlefish. Males compete vigorously for female mates. The researchers took a close look at the Common Cuttlefish (Sepia officinalis), a species “renowned for its visual capabilities, rapid adaptive camouflage, learning, and memory.” All those amazing qualities and yet oddly lacking in its ability to identify individual mates or rivals. Seriously, telling boy from girl is a challenge. This means that they must use a signal-response system to recognize each other. This system employs the use of intense zebra-stripe displays. Respond to a zebra with a zebra and you are male. If you don’t want to fight, darken your whole body (sign of alarm), ink and jet away. But extend your fourth arm, darken the skin around your eyes, and dilate your pupils and you know that shit is about to get real: inking, swiping, grappling, lunging, rolling, and biting. An all-out cuttlefish brawl.
A lot of this information is known from lab studies of cuttlefish, but how do they act in their natural environment. To test this, the researchers went to the Aegean Sea near Çeşmealtı, Turkey and filmed a bunch of cuttlefish. They brought the footage back to the lab to analyze mate guarding and fighting behaviors, frequencies of a series of agnoistic behaviors in individual males, and aggressive behaviors (e.g., bar room brawl scenario). Since it all starts with the zebra stripes, they also compared the intensity between males. They found a generalized sequence of events that correlated to the amount of aggression. For example, just a dark ring around the eye is low-level aggression, adding a dilated pupil ramps it up to medium-level aggression, intensifying the zebra pattern and arching and tilting the body ramps it up even more. The more medium- to high-level aggressive behaviors the more likely the male was to win. The researchers summarize it this way: “weak zebra banding, fourth arm extension, dark eye ring > dark eye ring with dilated pupil, dark face, strong zebra banding, inking > intense zebra display > swiping, grappling > biting, rolling.” This makes sense if you think about it. Fighting may result in injury and injury is costly, sometimes fatal. So you need to make sure you can win. The series of stages allow each male to assess both themselves and their opponent to see if an actual brawl is worth it.
Now, take what you’ve just learned and apply it to this video. It shows exactly the type of bout the authors describe. You may need to watch it twice, once to read the descriptions of what is going on and another to watch for the subtle differences described above. Can you see the color and eye changes?
Just imagine what we will find out as camera systems get faster. Considering the extremely fast rate at which cuttlefish are able to change their colors, it is very likely that we are missing a lot of the more subtle details in communications between males (and probably with females too). We’ll have to revisit this subject in the future.
Allen, J., Akkaynak, D., Schnell, A., & Hanlon, R. (2017). Dramatic Fighting by Male Cuttlefish for a Female Mate The American Naturalist DOI: 10.1086/692009
Learn more about Cephalopods at the University of California Berkeley’s Museum of Palentology and the Monterey Bay Aquarium
Image from the Monterey Bay Aquarium
Posted by Melissa Chernick at 5/12/2017