The penis of an echidna has four heads, but only two become erect at a time. Now Australian researchers have found out why.
Scientists have discovered that the marsupial has an unusual reproductive anatomy that causes male echidnas to ejaculate from only two of their four penile heads at a time.
The research, published in the peer-reviewed journal Sexual development, found that echidna penises have similar characteristics to those of other mammals, including platypuses, but also similarities to reptiles.
Scientists have studied the internal anatomy of several echidnas that had been introduced into the Currumbin Wildlife Queensland Sanctuary with serious injuries and had to be euthanized.
Male echidnas do not have a scrotum and store their penises inside when not in use. Each of the four ends of the echidna’s penis has a branch of their urethra but only semen passes through.
Researchers found that in echidnas, the main blood vessel of the penis divides into two main branches, which each supply two of the heads of the penis.
Jane Fenelon of the University of Melbourne, the lead author of the study, previously said it was suspected that male echidnas alternated between two of their four penile heads via a valve mechanism on the urethra, but that ‘they had found no evidence of this.
Instead, they found that the spongy tissue in the penis, which becomes erect when filled with blood, was separated by a septum – meaning the echidna’s penis has two distinct halves. By directing blood flow to one of the main branches of the artery, the echidna is able to control which half – and which two heads – stands.
“Their penis actually acts like two separate penises that happen to be fused together,” Fenelon said.
“This is the first time we’ve seen this in mammals. We know that in other species with very elaborate penises this normally occurs because of male-male competition for females. In this case, a multi-headed penis could reduce the time it takes between mating sessions, but the evolutionary reason for the behavior of echidnas has not been definitively confirmed.
Fenelon said the research was motivated by the behavior of an echidna in the wildlife sanctuary, which has been observed alternating the use of its penile heads up to 10 times in a row.
“Internally we think it’s quite similar to an echidna, but no one has ever seen an erect platypus penis, so we don’t know if they are only using one of their two heads to both, ”she said.
Bifold penises are common in many other marsupial species, including kangaroos, koalas, bilbies, and wombats.
There were also anatomical similarities between the reproductive systems of the male echidna and those of crocodiles and turtles, particularly in the way sperm enters the penis.
Female echidnas have a cloaca – a single opening that they use to urinate, defecate, and mate. Inside, the cloaca branches out into different systems, including a two-branched reproductive system.
“We believe that when the penis is erect, it is long enough to reach where the uterus branches off,” Fenelon said. Males also use their cesspool to urinate and defecate.
Unusually, previous studies have shown that echidna sperm work cooperatively, swimming in connected bundles of up to 100 sperm to reach the egg.
Australian researchers discover why only two heads of echidna penis stand at once | Australia News
Source link Australian researchers discover why only two heads of echidna penis stand at once | Australia News