The penis of an echidna has 4 heads but only two turn out to be erect at any one time. Now, Australian scientists have uncovered why.
Researchers discovered the marsupial has abnormal reproductive anatomy that triggers male echidnas to ejaculate from only two of their 4 penile heads at one time.
The investigation, released in the peer-reviewed journal Sexual Advancement, observed that echidna penises have identical functions to people of other mammals, together with platypuses, but also similarities to reptiles.
The researchers examined the inside anatomy of quite a few echidnas that had been brought into the Currumbin Wildlife Sanctuary in Queensland with significant injuries and had to be euthanised.
Male echidnas have no scrotum and retail outlet their penis internally when not employing it. Each and every of the 4 strategies of the echidna penis has a branch of their urethra but only semen passes by way of.
The scientists observed that in echidnas, the big blood vessel of the penis splits into two key branches, which every supply two of the penile heads.
Jane Fenelon of the University of Melbourne, the study’s guide creator, mentioned beforehand it was suspected that male echidnas alternated amongst two of their 4 penile heads by way of a valve mechanism on the urethra, but that they did not uncover any evidence of this.
As an alternative, they observed the spongy tissue of the penis, which results in being erect when stuffed with blood, was divided by a septum – that means the echidna penis has two unique halves. By directing blood stream down one of the key artery branches, the echidna is equipped to management which 50 percent – and which two heads – results in being erect.
“Their penis is really performing like two independent penises that just occur to be merged alongside one another,” mentioned Fenelon.
“It’s the 1st time we’ve noticed this in mammals. We know that in other species with truly elaborate penises, it normally transpires for the reason that of male–male levels of competition for females.” In that case, a multi-headed penis may lower the time desired amongst mating periods, but the evolutionary motive for the behaviour in echidnas has not been confirmed definitively.
Fenelon mentioned the investigation was determined by the behaviour of an echidna at the wildlife sanctuary, who had been observed alternating the use of his penile heads up to ten instances in a row.
“Internally, we assume it’s very identical to an echidna, but nobody’s ever noticed an erect platypus penis, so we’re not absolutely sure if they only use one of their two heads at one time,” she mentioned.
Two-pronged penises are common in numerous other marsupial species, together with kangaroos, koalas, bilbies and wombats.
There were also anatomical similarities amongst the male echidna’s reproductive tracts and people of crocodiles and turtles, notably in how the sperm enters the penis.
Woman echidnas have a cloaca – a solitary opening that they use to urinate, defaecate, and mate. Internally, the cloaca branches into various devices, together with a two-branched reproductive tract.
“We assume when the penis is erect that it’s lengthy more than enough to achieve where the uterus branches off,” mentioned Fenelon. Males also use their cloaca to urinate and defaecate.
Unusually, prior studies have revealed that echidna sperm cells do the job cooperatively, swimming in linked bundles of up to one hundred sperm to achieve the egg.