Wild gloomy octopuses (Octopus tetricus), a medium-sized benthic octopus species common in temperate waters around Australia and New Zealand, frequently propel shells, silt, and algae through the water by releasing these materials from their arms while creating a forceful jet from the siphon held under the arm web. These ‘throws’ occur in several contexts at a site in Jervis Bay, Australia, including in interactions with other octopuses.
“The throwing of objects is an uncommon behavior in animals,” lead author Professor Peter Godfrey-Smith, a researcher at the University of Sydney, and his colleagues wrote in a paper in the journal PLoS ONE.
“A throw can be distinguished from other phenomena by the ballistic motion of a manipulable object or material, where ‘ballistic’ describes free motion with momentum.”
“Throwing with aiming has sometimes been seen as distinctively human, and it probably does have an important role in hominin evolution.”
“ But throwing at a target has also been observed in some non-human primates (especially chimps and capuchins), elephants, mongooses, and birds.”
“Related behaviors include the flicking of irritating hairs at threats by spiders, the squirting of water through the air at prey by archerfish, and the swinging of silk threads at prey by some bolas spiders.”
“We provide the first report for any octopus species of a behavior frequently seen at these aggregations: the throwing or projection of debris, both in social interactions and in other contexts.”
A gloomy octopus (Octopus tetricus) projects silt and kelp through the water. Image credit: Godfrey-Smith et al., doi: 10.1371/journal.pone.0276482.
Using underwater video cameras, the authors studied gloomy octopuses at a field site at 17 m depth in the southern part of Jervis Bay, Australia.
They analyzed 24 hours of footage across several days and identified 102 instances of debris throwing in a group of roughly 10 octopuses, although individual identification was not always possible.
The animals gathered material such as silt or shells, and released it while using a jet of water from their siphon to propel it between their arms and through the water, often throwing material several body lengths away.
To perform the throws, the octopuses had to move their siphon into an unusual position, suggesting the behavior was deliberate.
Both sexes were observed throwing, but 66% of throws were performed by females.
Around half of throws occurred during or around the time of interactions with other octopuses, such as arm probes or mating attempts, and about 17% of throws hit other octopuses.
Octopuses can change their skin coloration, with dark colors generally associated with aggression, and the researchers found that dark-colored individuals tended to throw more forcefully and were more likely to hit another octopus.
Octopuses hit by thrown material often altered their behavior by ducking or raising their arms in the direction of the thrower.
“Although it is difficult to determine the intent of octopuses propelling debris through the water, the behaviors observed suggest that at least in some social contexts, octopuses are capable of targeted throws towards other individuals, a behavior that has only been observed previously in a few non-human animals,” the researchers said.
“Wild octopuses project various kinds of material through the water in jet-propelled ‘throws,’ and these throws sometimes hit other octopuses.”
“There is some evidence that some of these throws that hit others are targeted, and play a social role.”
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P. Godfrey-Smith et al. 2022. In the line of fire: Debris throwing by wild octopuses. PLoS ONE 17 (11): e0276482; doi: 10.1371/journal.pone.0276482
Source link: https://www.sci.news/biology/debris-throwing-octopuses-11382.html
