An echidna’s penis has four heads, but only two become erect at a time. Now Australian researchers have discovered why.
Scientists discovered that the marsupial has unusual reproductive anatomy that causes male echidnas to ejaculate from only two of their four penis heads at a time.
The research, published in the peer-reviewed journal Sexual development, found that echidna penises have characteristics similar to those of other mammals, including platypus, but also similarities to reptiles.
The scientists studied the internal anatomy of several echidnas that had been brought to the Currumbin Wildlife Sanctuary in Queensland with serious injuries and had to be euthanized.
Male echidnas do not have a scrotum and store their penis internally when not in use. Each of the four tips of the echidna penis has a branch from its urethra, but only semen passes.
The researchers found that in echidnas, the penile’s main blood vessel splits into two main branches, each of which supplies two of the penis heads.
Jane Fenelon of the University of Melbourne, lead author of the study, previously said that male echidnas were suspected of alternating between two of their four penis heads via a valve mechanism in the urethra, but that they found no evidence for this. .
Instead, they found that the spongy tissue of the penis, which becomes erect when filled with blood, was separated by a septum, meaning that the echidna penis has two distinct halves. By directing blood flow to one of the branches of the main artery, the echidna can control which half and which two heads become erect.
“Your penis is actually acting like two separate penises that just merge,” Fenelon said.
“This is the first time we have seen this in mammals. We know that in other species with really elaborate penises, it usually occurs due to male-male competition for females ”. In that case, a multi-headed penis might decrease the time needed between mating sessions, but the evolutionary reason for the behavior in echidnas has not been definitively confirmed.
Fenelon said the research was prompted by the behavior of an echidna at the wildlife sanctuary, which had been observed alternating use of the head of the penis up to 10 times in a row.
Fenelon noted similarities between echidnas and platypus that have a two-headed penis covered in spines.
“Internally, we think it is quite similar to an echidna, but no one has ever seen an erect platypus penis, so we are not sure if they only use one of their two heads at a time,” he said.
Echidnas and platypuses are the only two living monotremes – marsupials that lay eggs rather than give birth to live young.
Double-ended penises are common in many other species of marsupials, including kangaroos, koalas, bilbies, and wombats.
There were also anatomical similarities between the reproductive tracts of the male echidna and those of crocodiles and turtles, particularly in the way sperm enter the penis.
Female echidnas have a cloaca, a single opening that they use to urinate, defecate, and mate. Internally, the cloaca branches into different systems, including a two-branch reproductive tract.
“We think that when the penis is erect it is long enough to reach where the uterus branches,” Fenelon said. Males also use their cloaca to urinate and defecate.
Unusually, previous studies have shown that echidna sperm work cooperatively, swimming in connected packets of up to 100 sperm to reach the egg.
George is Digismak’s reported cum editor with 13 years of experience in Journalism