At the shark end of fertility
Scientists are trying to save a slow breeder by accelerating its bizarre reproduction method, reports Emma Young
Thursday February 17, 2005
There's something amiss in the main tank at Melbourne aquarium. Moving effortlessly above the transparent viewing tunnel are giant rays, sharks, gleaming silver trevally - and four divers in black wetsuits, carrying what looks like a big plastic bag. Quickly, they make for the narrowest part of the tank, where they ambush a seven-gilled shark.
With a gentle touch to the head, the 2.5m fish is in the bag, and the opening taped shut. In the next 10 minutes, she will have her reproductive system scanned using ultrasound, and cells will be scraped from her vaginal opening before she is released safely back into the tank. She doesn't know it, but she is part of an urgent research project to save a relative, the grey nurse shark, from extinction.
There are only 500 to 1,000 eastern grey nurse sharks left in the wild. They look mean, with bulky, muscular bodies, rows of sharp teeth and tiny eyes. Though they were once believed to be dangerous to humans, and consequently hunted indiscriminately, they are not. And unless something dramatic is done, they will be extinct in 10 to 15 years.
But scientists at the aquarium and the nearby Monash Institute of Reproduction and Development hope to help by interfering with their bizarre, and painfully slow, reproduction method.
At some point after fertilisation (no one is sure when), as many as 12 eggs hatch in each of the two horns of the uterus. Then, from day one, it's a fight for survival. The bigger, stronger embryos cannibalise their brothers and sisters until there are only two left. This process takes about a year, and it takes another year for the mother to recover sufficiently to go through it all again.
"That unusual reproductive strategy has become a threat to their survival," says Nick Kirby, curator at the aquarium.
One option for boosting numbers might be to rescue embryos from the uterus before most of them are eaten. "We might be able to use drugs to do this, or, as the uterus is open to the water, flush them out with seawater," says Ian Gunn of the institute, who is leading the project. The immature sharks might then be raised in tanks.
To do this, the team needs to get its hands on a pregnant female. So far the two females and one male at the aquarium have shown no inclination to mate.
So the first important step is to try to develop assisted reproduction techniques. The team needs to identify when the female ovulates and when the eggs hatch, approximately three months later. They also want to be able to collect and preserve sperm to inseminate females artificially.
Ideally, they would like to scan the grey nurse sharks in the aquarium regularly. But there are so few of the species left, they are afraid of causing them too much stress, which itself can impede willingness to mate. So they are scanned only once or twice a year. The team is focusing its detailed research on weekly scans of the seven- gilled sharks, which also have young that develop in the uterus.
"The grey nurse reproductive system is fairly unique," says Jonathan Daly, a masters student at Monash. "This is about as close as you can get."
Upstairs, in a part of the aquarium visitors do not usually see, the seven-gilled shark is in a shallow holding tank, adjacent to its home. It is an industrial scene, with pipes running all over the walls and the noise of tank filters forcing voices to be raised
Quickly, the taped bag is opened. It takes five people to turn her on her back and hold her still inside the bag. One of the team monitors the oxygen content of the water while Daly grabs the ultrasound wand and moves it across her white belly. Images of her egg follicles appear on the monitor. David Galloway, also of the institute, takes a scraping from her cloaca.
It is good news. The follicles are twice the size they were a few weeks ago, indicating that she could be about to ovulate. "In other animals, there are changes in the vaginal cells just before ovulation," says Galloway. "We don't know yet if it will be the same with sharks."
But if it is, the team might be able to use a non-invasive ultrasound study or a vaginal scraping test to determine when the grey nurse is ovulating - the moment to try artificial insemination. The team also hope they will see some mating behaviour from the seven-gilled female. If they can date this, along with the time of hatching, they can begin to estimate how long the shark might store sperm before using it and what might trigger them to use it. Whatever they find for the seven-gilled species, they hope will follow for the grey nurse.
Gunn's group has previously worked on assisted reproduction techniques for a range of endangered animals, from the hairy-nosed wombat to the black rhino. He hopes that in this case, he will be able to adapt human techniques to help fish. It's a tough challenge. The future of the grey nurse shark could depend on it.
With a gentle touch to the head, the 2.5m fish is in the bag, and the opening taped shut. In the next 10 minutes, she will have her reproductive system scanned using ultrasound, and cells will be scraped from her vaginal opening before she is released safely back into the tank. She doesn't know it, but she is part of an urgent research project to save a relative, the grey nurse shark, from extinction.
There are only 500 to 1,000 eastern grey nurse sharks left in the wild. They look mean, with bulky, muscular bodies, rows of sharp teeth and tiny eyes. Though they were once believed to be dangerous to humans, and consequently hunted indiscriminately, they are not. And unless something dramatic is done, they will be extinct in 10 to 15 years.
But scientists at the aquarium and the nearby Monash Institute of Reproduction and Development hope to help by interfering with their bizarre, and painfully slow, reproduction method.
At some point after fertilisation (no one is sure when), as many as 12 eggs hatch in each of the two horns of the uterus. Then, from day one, it's a fight for survival. The bigger, stronger embryos cannibalise their brothers and sisters until there are only two left. This process takes about a year, and it takes another year for the mother to recover sufficiently to go through it all again.
"That unusual reproductive strategy has become a threat to their survival," says Nick Kirby, curator at the aquarium.
One option for boosting numbers might be to rescue embryos from the uterus before most of them are eaten. "We might be able to use drugs to do this, or, as the uterus is open to the water, flush them out with seawater," says Ian Gunn of the institute, who is leading the project. The immature sharks might then be raised in tanks.
To do this, the team needs to get its hands on a pregnant female. So far the two females and one male at the aquarium have shown no inclination to mate.
So the first important step is to try to develop assisted reproduction techniques. The team needs to identify when the female ovulates and when the eggs hatch, approximately three months later. They also want to be able to collect and preserve sperm to inseminate females artificially.
Ideally, they would like to scan the grey nurse sharks in the aquarium regularly. But there are so few of the species left, they are afraid of causing them too much stress, which itself can impede willingness to mate. So they are scanned only once or twice a year. The team is focusing its detailed research on weekly scans of the seven- gilled sharks, which also have young that develop in the uterus.
"The grey nurse reproductive system is fairly unique," says Jonathan Daly, a masters student at Monash. "This is about as close as you can get."
Upstairs, in a part of the aquarium visitors do not usually see, the seven-gilled shark is in a shallow holding tank, adjacent to its home. It is an industrial scene, with pipes running all over the walls and the noise of tank filters forcing voices to be raised
Quickly, the taped bag is opened. It takes five people to turn her on her back and hold her still inside the bag. One of the team monitors the oxygen content of the water while Daly grabs the ultrasound wand and moves it across her white belly. Images of her egg follicles appear on the monitor. David Galloway, also of the institute, takes a scraping from her cloaca.
It is good news. The follicles are twice the size they were a few weeks ago, indicating that she could be about to ovulate. "In other animals, there are changes in the vaginal cells just before ovulation," says Galloway. "We don't know yet if it will be the same with sharks."
But if it is, the team might be able to use a non-invasive ultrasound study or a vaginal scraping test to determine when the grey nurse is ovulating - the moment to try artificial insemination. The team also hope they will see some mating behaviour from the seven-gilled female. If they can date this, along with the time of hatching, they can begin to estimate how long the shark might store sperm before using it and what might trigger them to use it. Whatever they find for the seven-gilled species, they hope will follow for the grey nurse.
Gunn's group has previously worked on assisted reproduction techniques for a range of endangered animals, from the hairy-nosed wombat to the black rhino. He hopes that in this case, he will be able to adapt human techniques to help fish. It's a tough challenge. The future of the grey nurse shark could depend on it.
1 comment:
Considering how unhappy I feel after I go to gynocologist appointments, I wouldn't want to have to do one on a shark, that's for sure!
I think it's funny that they call the uterus deal of the nurse sharks bizarre, other sharks have much stranger systems.
Post a Comment