Visual Signals of the Eastern Pacific Red Octopus (Octopus rubescens) During Conspecific Interactions
Historically, octopuses have been considered solitary, asocial individuals (Barbato et al., 2007; Hanlon and Messenger, 2018); however, recent studies suggest that octopuses use a unique and systematic arrangement of visual signals to communicate with conspecifics (Huffard, 2007; Caldwell et al., 2015; Scheel et al., 2016). These visual signals include chromatic and textural changes, postures, different forms of locomotion, and inking, which can be combined or used consecutively to create specific displays.
Some of the most complex signals octopuses use are chromatic signals. Since octopuses have direct neural control of pigment-containing cells, called chromatophores, octopuses can quickly change chromatic signals, adjust signal strength, and even perform bilateral signaling (Barbato et al., 2007; Hanlon and Messenger, 2018). Although colorblind, octopuses have excellent vision – consequently, by using highly contrasting chromatic signals, octopuses can clearly display their intent (e.g., to show dominance or submissiveness) toward a conspecific (Tricarico et al., 2011; Hanlon and Messenger, 2018).
Many visual signals that octopuses utilize are species-specific, therefore characterizing and documenting visual signals of octopuses via ethograms provides useful supplementary information for validating species identification (Barbato et al., 2007; Huffard, 2007). Ethograms are useful libraries of information that document the behaviors of organisms. For octopuses, ethograms can act as resources for scientists studying how ecological influences, such as conspecific interactions or habitat availability, may affect the evolution of signal development or communication.
Octopus rubescens is a subtidal species found along the west coast of North America (from Alaska to California), sheltering in kelp beds and rocky areas, and are commonly found in Admiralty Bay, WA (Cowles, 2005). The benthic habitat of this bay is generally barren and flat, characterized by mud, sand, and small rocks, with few hiding places for this non-burrowing octopus species. However, the bay is littered with discarded glass bottles which O. rubescens opportunistically use as dens (Anderson et al., 1999). Octopus rubescens have capitalized on this new habitat source which may have inadvertently concentrated individuals of this species within the bay (Chase and Verde, 2011). Consequently, O. rubescens may interact with conspecifics more frequently within this “artificial” environment and these interactions may be characterized by visual signals used by octopuses to communicate with each other.
Given that octopuses use visual signals to interact, the purpose of this study was to determine the frequency of such signals used by O. rubescens individuals to communicate with conspecifics, and to document those visual signals in an ethogram. As such, this study addressed the following questions:
1) What are the visual signals that O. rubescens use during interactions with conspecifics?
2) Is the frequency of interactions influenced by the sex of octopuses?
3) Do the type or frequency of visual signals differ between initiators and reactors of an interaction?
Octopus rubescens individuals were collected via SCUBA from Admiralty Bay, WA and housed at the Rosario Beach Marine Laboratory (RBML), Anacortes, WA. Individual octopuses were housed in plastic containers with constant flowing ambient seawater via a manifold system (Figure 1). Rocks were placed on top of the containers as additional measures to prevent octopuses from escaping. The total sample size (N) for this experiment was 20 octopuses (10 males & 10 females).
To identify the visual signals of O. rubescens, GoPro cameras (Figure 2) recorded videos of octopuses interacting for 15 min in an observation tank (Figure 3).
VLC Media Player was utilized to observe and analyze videos recorded by the GoPro cameras. Snapshots from the videos were used to create an ethogram. Any octopus interaction that lasted at least 5 s was analyzed for the use of visual signals (chromatic, textural, locomotor, and postural).
Octopus rubescens used a variety of visual signals to communicate and interact with conspecifics during the 15 min trials. These visual signals included chromatic (Figures 5 & 6), textural (Figure 7), inking (Figure 8), locomotor (Figure 9), and postural cues (Figure 10). The frequency of interactions differed by 1 interaction per test between the M/M octopus combinations (5.2 interactions per test) and M/F and F/F octopus combinations (4.2 interactions per test).
Octopus interactions (Figure 11) were typically characterized by the locomotor signals ‘stationary’ (45.9%), ‘approach’ (21.7%), and ‘flee’ (24.6%) by one or both octopuses for all sex combinations (M/M, M/F, F/F). The most common chromatic signals included ‘ochre’ (44.3%), ‘dark ochre’ (21.9%), and ‘pale’ (16.4%); octopuses appeared to primarily use ‘ochre’ as a resting pattern of pigmentation. The most common postures included ‘upright’ (33.6%) and ‘curled arms’ (23.9%). Textural signals were predominantly ‘smooth’ (77.2%) and octopuses rarely inked.
Interactions between octopuses were also divided between the initiator and reactor within each sex combination (M/M, M/F, F/F) and these results can be viewed in the full manuscript, provided in a link at the end of this post.
The ethogram produced in this study portrays a variety of visual signals that O. rubescens used during conspecific interactions and suggests that communication was occurring between individuals. The number of interactions per test for all sex combinations (M/M, M/F, F/F) of octopus was similar which suggests that sex had little influence on the frequency of interactions between octopuses. While O. rubescens may gather in an area for a specific habitat resource, such as the bottles used as dens in Admiralty Bay, the species demonstrated predominantly aggressive behavior toward conspecifics during this study, suggesting that they are not a social species even if they are not solitary.
Nonetheless, visual signals are especially important for octopuses to use during aggressive interactions because they can clearly display an octopus’s intentions to attack or submit, depending on the likelihood of winning or losing a fight (Barbato et al., 2007; Scheel et al., 2016). Having the ability to display such intent helps octopuses avoid unnecessary harm.
One aggressive signal, ‘grappling’, was not as frequent as other postural or locomotor signals, but did occur during interactions and most frequently between males. Increased aggression between males perhaps could be attributed to their need to compete for females in their natural habitat.
Although the behaviors documented were in a laboratory setting, the ethogram produced in this study may still serve as a useful reference. Future studies can document the visual signals of O. rubescens collected from other habitats and reveal potential variations in visual signals used by this species. Since the sample of octopuses used in this study was from a population in Admiralty Bay, these octopuses may use a specialized system of visual signaling during interactions, as opposed to more solitary octopuses. This may allow scientists to hypothesize that the visual signals used by O. rubescens are influenced by surrounding habitats, like Admiralty Bay, or population density. The basic ethogram created in this study can also act as an additional resource of comparison between octopus species, regardless of the fact that the visual cues identified were during conspecific interactions.
Link to full manuscript - Download PDF
Anderson, R., P. Hughes, J. Mather, and C. Steele, C. 1999. Determination of the Diet of Octopus rubescens Berry, 1953 (Cephalopoda: Octopodidae), Through Examination of its Beer Bottle Dens in Puget Sound. Malacologia, 41:455–460.
Barbato, M., M. Bernard, L. Borrelli, and G. Fiorito. 2007. Body Patterns in Cephalopods: ‘‘Polyphenism’’ as a Way of Information Exchange. Pattern Recognition Letters, 28:1854–1864.
Caldwell, R., R. Ross, A. Rodaniche, and C. Huffard. 2015. Behavior and Body Patterns of the Larger Pacific Striped Octopus. PLoS One, 10: e0134152.
Chase, E, and A. Verde A. 2011. Population Density and Choice of Den and Food Made by Octopus rubescens Collected from Admiralty Bay, Washington, in July 2011. American Academy of Underwater Sciences, 30:110–116.
Cowles, D. 2005. Octopus rubescens Berry, 1953 [Internet]. College Place (WA): Walla Walla University; [cited 2018 Feb 6]; https://inverts.wallawalla.edu/Mollusca/Cephalopoda/Octopus_rubescens.html
Hanlon, R. and J. Messenger. 2018. Cephalopod Behaviour. Cambridge (England): Cambridge University Press.
Huffard, C. 2007. Ethogram of Abdopus aculeatus (D’Orbigny, 1834) (Cephalopoda: Octopodidae): Can Behavioral Characteristics Inform Octopodid Taxonomy and Systematics? Journal of Molluscan Studies, 73:185–193.
Scheel, D., P. Godfrey-Smith,and M. Lawrence. 2016. Signal Use by Octopus in Agonistic Interactions. Current Biology, 26:1–6.
Tricarico, E., L. Borrelli, F. Gherardi, and G. Fiorito. 2011. I Know my Neighbour: Individual Recognition in Octopus vulgaris. PLoS One, 6: e18710.
Authors: Rachel L. Borisko, Kirt L. Onthank, E. Alan Verde