While the fiendish intelligence of the octopus is something well documented, scientists suggest that we may have overlooked the mental dexterity of the kind of company it keeps. Particularly when it comes to hunting.

Because according to the latest research, it turns out that predatory fish are taking more of a leading role when working alongside octopuses to ambush their dinner than we may have been led to believe; offering yet more insight into the cognitive agility of various underwater species.

Observing methods in which some animals cooperate with members of other species, researchers from the University of Konstanz in Germany, Cambridge University, and the Max Planck Institute for Animal Behaviour, have found the hunting dynamic between fish and octopus to be one of varying levels of complexity.

Findings have been laid bare in an article published this month in Current Biology in which researchers explore the possible cognitive foundations of cross-species social behaviour, using the octopus and reef fish dynamic as a prime example of cooperative hunting.

“When octopuses and reef fish hunt together, they coordinate their attacks to outwit their prey,” said Eduardo Sampaio, a biologist from the Cluster of Excellence ‘Collective Behaviour’ at the University of Konstanz, and lead author on the study titled Cognition in multi-species sociality.

“The fish don’t just tag along with the octopus; they play an active role by showing the octopus where the prey is hiding. The octopus then either wraps its arms around the prey to catch it or chases it out of its hiding place, thereby increasing the potential hunting success of the entire hunting party.

“What’s more, the octopus flexibly adapts its behaviour depending on its hunting partners, and a fish that exploits the cooperation even risks being ‘beaten up’ by the octopus for punishment.”

Foraging associations between octopus and fish have been observed for decades, with such interactions reported across various species and habitats. The traditional line of thinking has been, however, that the octopus was the ‘nucleus’ of the operation: the brains that were merely followed by opportunistic fish looking to capture dislodged prey.

This, Sampaio published in his paper, implied a ‘simple role for the fish’ as well as ‘minimal cognitive engagement between the species’. Recent studies have, however, subverted these beliefs – none more so ever than in the dynamic between the day octopus (Octopus cyanea) and its associations with species like coral trout (Plectropomus spp) and the goatfish (Parupeneus spp).

In both instances it was observed that rather than simply trailing behind, the fish in these partnerships actually take on an active role, locating prey and visually signalling its location to the octopus. The octopus then uses its arms to envelope elements of the substrate – a manoeuvre the scientists observed – that allows it to ensnare the prey and flush it out from its hiding spot, enhancing the chances of capture for both parties.

“Partnerships like these challenge traditional views of intelligence and cooperation in the animal kingdom,” said Sampaio. “They involve a two-way flow of information and coordinated behaviour as well as an ability to interpret both subtle behavioural cues and signals from other species. 

The study’s authors have suggested that these interactions are made “all the more intriguing” when it’s considered just how large the evolutionary distance is between the hunting partners as well as – crucially – the solitary lifestyles that octopuses lead.

Unlike social animals that live in groups and benefit from frequent interactions, octopuses are predominantly solitary and typically avoid interactions with others of their own kind, except for mating at the end of their life history.

“From an evolutionary perspective, social complexity, problem solving, and communication do not only arise within one’s own group, but can also be shaped by the need to collaborate across species boundaries,” said Sampaio.

The study has gone deeper still into just how complex these interspecies, cooperative relationships can be. And it comes down to how the octopus selects its hunting partner.

In cases where predatory fish simply attempt to exploit the octopus’ actions, rather than work alongside them, the researchers have observed octopus deploying defensive strategies including punching them to discourage a wayward fish. 

The authors have suggested that in this regard, species-level recognition is critical to these interactions; it benefits individuals to recognise the species with whom they can collaborate, as well as those that might exploit or pose a threat to them. 

“While most species tend to discriminate against or interact with species that resemble themselves, octopuses and partner fish are capable of doing so despite their dramatic differences in morphology and body plan,” Sampaio said. “In fact, they adapt their behaviour when hunting with collaborative species and direct negative feedback towards exploiter species such as ambush predators.

“Understanding how octopuses discriminate between relatively similar-looking species that look radically different from themselves (and do not pose a threat) is an exciting question moving forward.”

Sampaio and the team also wish to explore further the question left hanging over whether individuals in these multispecies hunting groups can recognise one another. 

“With moray eels, coral trout can distinguish between ‘good’ and ‘bad’ cooperators; however it is not known if they can identify specific individuals within these two categories of partners,” he said. “In the case of the octopus, evidence suggests that individual recognition is possible, as many punches appear directed at specific individuals from exploiter species.

“However, as before, it still remains unclear whether this response arises from individual recognition or rather from repeated opportunistic behaviour exhibited by certain individuals during a given hunt.”

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