杏吧原创

Hagfish literally tie themselves in knots to escape a tricky situation 鈥� and that includes tying their bodies into complicated three-twist knots.

In many ways, hagfish聽are extraordinary. They are long, eel-like marine animals that carry far more blood relative to their body volume , have 鈥� and .

It is partly because of this last feature that it is so useful for hagfish to tie knots in their long bodies. When the animal ties a knot at its tail end and slips it along the body to the head, it forms a broad flat surface that the hagfish鈥檚 upper jaw can work against, creating a makeshift lower jaw. Slipping a thick body knot along its body can also help a hagfish pull its head out of a tight spot if it gets stuck during hunting or feeding.

But although we have known for decades that hagfish tie themselves in knots, it has been difficult to confirm what types of knot they tie. 鈥淭hree-dimensional knots are difficult to visualise at the best of times,鈥� says Theodore Uyeno at Valdosta State University in Georgia. 鈥淏ut when it鈥檚 a squirmy self-manipulating knot that鈥檚 thrashing about, it鈥檚 impossible.鈥�

Uyeno and his colleagues came up with a solution. They anaesthetised a hagfish and gently inserted its head into a restraining device. When the hagfish woke, it slipped knots down its body to pull its head free. The researchers recorded the behaviour using high-speed cameras, and then analysed the knots. They repeated the procedure 100 times, capturing the knot-tying behaviour of three hagfish species.

Given the length and width of the hagfish body, mathematically they should be capable of tying any one of the . But the researchers suspected hagfish would choose not to tie the very simplest knots because the loops in these knots are so tight they might prove painful.

鈥淲hen you tighten a knot, more complex knots are less pinching,鈥� says Uyeno.

It turned out that 45 per cent of the time hagfish tie trefoil knots, where the hagfish has a single loop along its body, and slightly more complicated figure-eight knots 33 per cent of the time. Some other hagfish knots were difficult to classify, but they did occasionally 鈥� about 4 per cent of the time 鈥� tie a more complicated three-twist knot.

Although some other vertebrate animals including , as far as Uyeno knows none of them can tie three-twist knots. 鈥淚 guess I鈥檝e always had faith in hagfish brains,鈥� says Uyeno. 鈥淚 posited that if they have the [the physical dimensions] to tie more complicated knots, nature will find a way to evolve the control parameters to tie them.鈥�