Article:
Scheel, D., Godfrey-Smith, P., & Lawrence, M. (2016). Signal Use by Octopuses in Agonistic Interactions. Current Biology. DOI: 10.1016/j.cub.2015.12.033
Introduction:
As you may have noticed, last week Oceanbites was all about love in the ocean. Though finding a mate is important (unless you are a hermaphrodite), marine animals may not always be in a loving mood. A fight between members of the same species can break loose at any time, especially if it involves food, shelter or the aforementioned mate (Fig. 1). But how do two organisms decide when it is time to fight or if it is better to flee? Sound does not always work so well in the noisy ocean, making it hard for competitors to simply “talk it out”.
Cephalopods, such as cuttlefish and squid, have found a way to bridge this gap in communication by changing their body color, pattern and orientation before engaging in combat. These changes by the initiator may help cue the weaker competitor of the impending conflict and offer them a chance to flee the scene before things get ugly.
How do octopuses, another type of cephalopod, deal with competition from other members of their species? The answer was largely unexplored because octopuses were thought to be solitary and non-social creatures. Researchers in this study set out to verify this claim and attempt to record interactions between octopuses in the wild. To do this, 53 hrs of video footage was collected off the coast of Australia at a known octopus site, using staged underwater GoPro cameras.
Results:
It turns out octopuses are a lot more social than previously thought. From a total of 186 octopus interactions, researchers recorded 345 body colors and patterns, along with 512 different actions. Here is a breakdown of the most commonly observed body signals between interacting octopuses:
1. Reaching:
When two octopuses began to interact, the most common action by far was “reaching”. In this context, the term reaching refers to one octopus extending an arm towards another octopus. However, actual contact is never made, so this action is more of a precursor to combat – think of it as “feeling” out your competitor. Reaching often occurred when one octopus was in the safety of its den. Touching or grappling between two octopuses was extremely rare, especially when there was a large difference in body color (Fig. 2B). The initiator of the reach was dark and the receiver pale in color. Fighting was more likely if two octopuses had similar body colors.
2. Standing tall on higher ground:
Aside from being darker, the more dominant octopus would sometimes display a “stand tall” posture by raising its head and mantle and seeking a higher position (Fig. 2C). Interestingly enough, the relative darkness of interacting octopuses seemed to correlate with their choice to either withdraw from a fight or stand their ground. For instance, say one octopus was the initiator and approached another octopus called the reactor. When the reactor stood its ground (either by standing tall or reaching), the initiator was lighter and the reactor darker. If the initiator was darker and stood taller, the reactor would withdraw from the fight and flee the scene (Fig. 2D). Clearly, color seems to matter.
3. Mating:
There was some love to be found after all, but not in large quantities. Mating attempts comprised only 11% of the recorded interactions and on average lasted 6 minutes. Though difficult to identify the sex of the octopuses on film, researchers could provide estimates based on the types of body signals they saw. Males were typically pale, with dark eyes and would reach the right third arm toward the female (Fig. 2A). The third arm would make contact with the female who had a mottled body pattern.
Discussion and Significance:
Prior to this study, octopuses were thought to be solitary creatures that rarely interacted with members of their own species. It appears that some octopuses are highly interactive and use a complex array of body patterns and colors to communicate. Researchers captured footage from mounted GoPro cameras that revealed social behaviors before the onset of a fight. Overall, the more dominant octopus was darker in color and raised its body position to appear taller, while the weaker octopus appeared paler and not as physically dominant (Fig. 3)
Regardless of who initiates, it seems octopuses have found a way to determine the outcome of a fight before it happens. Why may it be beneficial to have this sort of communication? If you are a weaker octopus, the costs of entering and losing a fight seem too risky. It may also benefit initiators to not actually engage in unnecessary combat because they may become injured themselves or may waste important resources. This unique type of signaling may be a way of minimizing injury and or death of the population that results from a fight. This exciting discovery begs the question: what other types of communication have we yet to uncover between members of other marine species?
I am a first year MS candidate at the University of Rhode Island, Graduate School of Oceanography. I am interested in plankton ecology and the dynamics within plankton food webs. My research interests include the behavioral and physiological responses of phytoplankton and heterotrophic predators.
