The penis of an echidna has 4 heads however solely two turn into erect at anyone time. Now, Australian researchers have uncovered why.
Scientists found the marsupial has uncommon reproductive anatomy that causes male echidnas to ejaculate from solely two of their 4 penile heads at one time.
The analysis, printed within the peer-reviewed journal Sexual Growth, discovered that echidna penises have comparable options to these of different mammals, together with platypuses, but additionally similarities to reptiles.
The scientists studied the inner anatomy of a number of echidnas that had been introduced into the Currumbin Wildlife Sanctuary in Queensland with extreme accidents and needed to be euthanised.
Male echidnas don’t have any scrotum and retailer their penis internally when not utilizing it. Every of the 4 suggestions of the echidna penis has a department of their urethra however solely semen passes by.
The researchers discovered that in echidnas, the foremost blood vessel of the penis splits into two essential branches, which every provide two of the penile heads.
Jane Fenelon of the College of Melbourne, the examine’s lead writer, mentioned beforehand it was suspected that male echidnas alternated between two of their 4 penile heads by way of a valve mechanism on the urethra, however that they didn’t discover any proof of this.
As an alternative, they discovered the spongy tissue of the penis, which turns into erect when crammed with blood, was separated by a septum – which means the echidna penis has two distinct halves. By directing blood stream down one of many essential artery branches, the echidna is ready to management which half – and which two heads – turns into erect.
“Their penis is definitely appearing like two separate penises that simply occur to be merged collectively,” mentioned Fenelon.
“It’s the primary time we’ve seen this in mammals. We all know that in different species with actually elaborate penises, it usually occurs due to male–male competitors for females.” In that case, a multi-headed penis would possibly lower the time wanted between mating classes, however the evolutionary purpose for the behaviour in echidnas has not been confirmed definitively.
Fenelon mentioned the analysis was motivated by the behaviour of an echidna on the wildlife sanctuary, who had been noticed alternating using his penile heads as much as 10 instances in a row.
“Internally, we expect it’s fairly just like an echidna, however no one’s ever seen an erect platypus penis, so we’re undecided in the event that they solely use one among their two heads at one time,” she mentioned.
Two-pronged penises are frequent in lots of different marsupial species, together with kangaroos, koalas, bilbies and wombats.
There have been additionally anatomical similarities between the male echidna’s reproductive tracts and people of crocodiles and turtles, significantly in how the sperm enters the penis.
Feminine echidnas have a cloaca – a single opening that they use to urinate, defaecate, and mate. Internally, the cloaca branches into completely different methods, together with a two-branched reproductive tract.
“We expect when the penis is erect that it’s lengthy sufficient to achieve the place the uterus branches off,” mentioned Fenelon. Males additionally use their cloaca to urinate and defaecate.
Unusually, earlier research have proven that echidna sperm cells work cooperatively, swimming in linked bundles of as much as 100 sperm to achieve the egg.