Nav: Home

Scientists solve mystery of a fish called Mary's 'virgin' birth

February 20, 2019

A female stickleback fish, nick-named 'Mary', has produced offspring from eggs that appear to have been fertilised while they were still inside her, according to scientists at the University of Nottingham.

The team of researchers from the School of Life Sciences collected Mary on an expedition to the Outer Hebrides to gather wild sticklebacks which are fully genome-sequenced models for a wide range of scientific research.

In a paper published in Scientific Reports they present the first ever discovery of internal fertilisation and development of babies inside a normally egg-laying species, and their successful delivery.

The three-spined stickleback, Gasterosteus aculeatus, is a small fish that is common to both fresh and coastal waters in the Northern Hemisphere. In normal reproduction, the male stickleback builds a nest and, by performing a zig-zagging dance routine, lures a female to lay her eggs inside it. The male then chases the female away and fertilises the cluster. He then guards and takes care of the eggs by fanning them with his fins to aerate them for around 2 weeks until they hatch.

Mary's unusual pregnancy meant that the 'virgin' stickleback was egg-bound and close to death when her predicament was noticed so the decision was taken to save the lives of her young, by putting her to sleep and delivering the near-complete embryos by Caesarean section. 54 embryos were successfully delivered, hatched into fry and grew to adulthood in the aquaria in Nottingham where around 20 still survive nearly three years on. The team has also successfully bred from Mary's offspring in normal aquarium conditions.

Dr Laura Dean, from the School of Life Sciences, said: "We were astounded at what we found when we examined Mary in our lab in the Outer Hebrides. She looked like an ordinary egg-bound fish so we couldn't believe it when we found she had almost completely developed embryos inside her ovaries. This is pretty much unheard of in an egg laying species. The embryos were perfectly healthy, not deformed in any way, and most have gone on to live a normal adult lifespan."

This discovery is currently the only record of this kind of fertilisation and delivery of live offspring in any fish ever so the research team was very keen to investigate how this might have happened. There are three known mechanisms by which abnormal type of reproduction in fish can occur. The first is parthenogenesis which is where the fish clones herself, the second is that she could be hermaphrodite with both male and female sex organs.

Laura said: "We were able to rule these two possibilities out because, in parthenogenesis, her offspring would have been genetically identical to the mother, or, if hermaphroditism, they would have only had versions of genes that she had, with no genetic input from anywhere else. So, we did some very simple genetic testing on the offspring and found that they had versions of genes that Mary didn't have and so must have had a father.

"Our theory is that somehow sperm had got into the fish, fertilised the eggs and they developed into normal two-parent embryos. What has probably happened is that she has gone into a nest to lay her eggs where another female had already laid her eggs which had been covered with sperm by a male stickleback. Somehow some of the sperm in the nest must have got into Mary, presumably through her egg tube, and fertilised the eggs inside her but she never laid the eggs."

Andrew MacColl, Associate Professor of Evolutionary Biology, said:" Although this almost accidental find revealed a vanishingly rare phenomenon, it might help us to understand a really important change that has happened throughout the tree of life. Most animals lay eggs, but some (including almost all mammals, but few fish) retain their eggs inside and give birth to live young. Although this appears to be a difficult thing to achieve in evolution, this one little fish seems to have got there almost by itself!"

The finding of fertilised eggs inside a stickleback has only been recorded once before, in a paper published in the 1950s, but it was just recorded as a picture of the fish with no delivery of the embryos.

The researchers are now actively looking, on subsequent fishing expeditions to Scotland, for more female sticklebacks who may display the same phenomenon to see if there is a chance it may not just be a freak incident but could be an indication of an evolutionary or genetic change in the reproductive mechanism of the species.

They are also hoping to secure funding to investigate the internal mechanisms which allowed the embryos, which would normally have developed in water and been fanned and cared for by the father, to develop within ovarian fluid and without this care.
-end-


University of Nottingham

Related Embryos Articles:

Animal embryos evolved before animals
A new study by an international team of researchers, led by scientists from the University of Bristol and Nanjing Institute of Geology and Palaeontology, has discovered that animal-like embryos evolved long before the first animals appear in the fossil record.
Choosing the best embryos
Struggling with infertility? You are not alone. Infertility affects one out of every six Canadian couples.
Turtle embryos play a role in determining their own sex
In certain turtle species, the temperature of the egg determines whether the offspring is female or male.
Early in vitro testing for adverse effects on embryos
ETH researchers have combined embryonic cells and liver cells in a new cell culture test.
Embryos' signals take multiple paths
Rice University bioscientists uncover details about how embryonic stem cells respond to the collection of signals that direct their differentiation into blood, bone and tissue.
Are mosaic embryos the 'dark horse' of IVF?
New research conducted by scientists at the Oregon National Primate Research Center at OHSU is the first to confirm in a nonhuman primate model, that mosaic embryos can adapt to their abnormalities and persist in development, resulting in positive IVF outcomes.
Embryos' signaling proteins go with the flow
Protein signaling in the rapidly differentiating cells of embryos is far more complex than previously thought, as pathways take cues from many other players.
Making better embryos
One out of every six Canadian couples experiences infertility. Some resort to in vitro fertilization.
Embryos remember the chemicals that they encounter
A new study shows that embryonic cells retain a memory of the chemical signals to which they are exposed.
Stem cells organize themselves into pseudo-embryos
The three axes of the mammalian body, established shortly after implantation of the embryo in the uterus, becomes organized under the control of gene networks that coordinate the transcription of DNA.
More Embryos News and Embryos Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Clint Smith
The killing of George Floyd by a police officer has sparked massive protests nationwide. This hour, writer and scholar Clint Smith reflects on this moment, through conversation, letters, and poetry.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Nina
Producer Tracie Hunte stumbled into a duet between Nina Simone and the sounds of protest outside her apartment. Then she discovered a performance by Nina on April 7, 1968 - three days after the assassination of Dr. Martin Luther King Jr. Tracie talks about what Nina's music, born during another time when our country was facing questions that seemed to have no answer, meant then and why it still resonates today.  Listen to Nina's brother, Samuel Waymon, talk about that April 7th concert here.