Male octopuses can fertilise a mate, even if they cannot see their sexual partner.
When octopuses mate, the male keeps the female quite literally at arm’s length.
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For the act, the male has a special arm called a hectocotylus, which it uses to deposit a sack of sperm inside the female’s reproductive system.
However, scientists have not been clear about how exactly this arm locates the right place when the male cannot see what he is doing. Now, a new study has discovered how hectocotylus is guided.
Male octopuses ‘taste’ female hormones
During sex, the male octopus inserts the hectocotylus inside the female’s mantle - a bag-like structure behind the eyes that holds all of her major organs, including reproductive ones - and feels around until he finds her oviduct.
How he does this has been revealed in a paper published in the journal Science this week.
Researchers found that the mating arm is a sensory organ which, like octopuses’ other arms, is loaded with suckers that contain chemotactile receptors.
In the other seven arms, the receptors help the creatures to ‘taste’ their surroundings, functioning like a tongue to locate food or identify harmful microbes.
But in the hectocotylus, which is normally held close to the body when not mating, their function hasn’t been clear.
During their research, scientists found that the female octopus’s oviduct produces enzymes that generate the sex hormone progesterone.
They discovered that the receptors allow the males’ mating arm to detect the progesterone, meaning they can fertilise a mate, even if they cannot see their sexual partner.
The researchers also found that amputated specialist arms of male octopuses moved in response to progesterone – but not when in contact with other, similar hormones.
After examining hectocotylus cells from three individuals, the team detected up to three times more chemotactile receptors and three times more neurons in the mating arm than in a normal arm.
Octopuses can mate without seeing
It is common for animals to use hormone detection during mating processes, but the sensory detection organ is usually different from the one that releases the sperm.
In male octopuses, however, the hectocotylus is responsible for both jobs, which the researchers suggested was linked to octopuses’ solitary nature.
“It makes sense that the arm is both the sensor and the mating organ because in these chance encounters, the arm has to be able to both localise the female, localise the oviduct and very quickly initiate the mating or move on,” Professor Nicholas Bellono, senior author of the study at Harvard University, tells UK newspaper The Guardian.
Octopuses’ preference for independence was also a challenge for the researchers’ lab experiments.
A male and female pair was placed in a tank and separated by a divider, as they are prone to becoming aggressive and killing each other.
The divider contained holes that allowed the octopuses to reach through and ‘warm up’ to each other.
The scientists had planned to remove the dividers once the octopuses were acquainted, but were surprised to find the male reaching its mating arm through one of the holes and inserting it into the female’s mantle.
The researchers placed other couples in the same setup and found that the same result occurred.
Importantly, the behaviour was also the same in total darkness, supporting the hypothesis that octopuses are able to mate without even setting eyes on each other.
