New research could lead to a pregnancy test for endangered marsupials



Knew you were coming: a koala cub on the back of the mother.
Shutterstock/PARFENOV

Oliver Griffith, University of Melbourne

Many women realise they are pregnant before they’ve even done the test – perhaps feeling a touch of nausea, or tender, larger-than-usual breasts.

For a long time, biologists had thought most marsupials lacked a way to recognise a pregnancy.

But new research published today shows a marsupial mum knows – in a biological sense – when she’s carrying a young one before they make their journey to the pouch.




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This knowledge changes how we think pregnancy evolved in mammals. It may also help in breeding programs for threatened or endangered marsupials by contributing to new technologies such as a marsupial pregnancy test.

Marsupials do things differently

When people think of marsupials – animals that mostly rear their young in a pouch (although not all marsupials have a pouch) – kangaroos and koalas tend to spring to mind. But marsupials come in a range of shapes and sizes.

A red-necked wallaby with a joey.
Pixabay/sandid

Australia has about 250 species of marsupials, including wombats, possums, sugar gliders, the extinct Tasmanian tiger, and several endangered species such as the Tasmanian devil.

In addition to Australia’s marsupial diversity, there are also 120 marsupial species in South America – most of which are opossums – and just one species in North America, the Virginia opossum.

One thing all marsupials have in common is they give birth to very small, almost embryonic, young.

An opossum with two day old young.
Oliver Griffith, Author provided

Because marsupial pregnancy passes so quickly (12-40 days, depending on the species), and marsupial young are so small and underdeveloped at birth, biologists had thought the biological changes required to support the fetus through a pregnancy happened as a follow on from releasing an egg (ovulation), rather than a response to the presence of a fetus.

Marsupial pregnancy is quick

One way to explore the question of whether it is an egg or a fetus that tells the marsupial female to be ready for pregnancy is to look at the uterus and the placenta.

In marsupials, just like in humans, embryos develop inside the uterus where they are nourished by a placenta.

Previously, biologists thought all of the physiological changes required for pregnancy in marsupials were regulated by hormones produced in the ovary after ovulation.

If this hypothesis is right, then the uterus of pregnant opossums should look the same as the uterus of opossums that ovulate but don’t have the opportunity to mate with a male.

To test this hypothesis, my colleagues at Yale’s Systems Biology Institute and I examined reproduction in the grey short-tailed opossum.

Grey short tailed opossum with young.
Oliver Griffith

Signs of pregnancy

We looked at two groups of opossums: females that were exposed to male pheromones to induce ovulation, and females that were put with males so they could mate and become pregnant.

We then used microscopy and molecular techniques to compare females from the two groups. Contrary to the current dogma, we found that the uterus in pregnancy looked very different to those females that did not mate.

In particular, we found the blood vessels that bring blood from the mother to the placenta interface were only present in pregnancy. We also noticed that the machinery responsible for nutrient transport (nutrient transporting molecules) from the mother to the fetus was only produced in pregnancy.

While hormones may be regulating some aspects of maternal physiology, the mother is certainly detecting the presence of embryos and responding in a way that shows she is recognising pregnancy.

How this knowledge can help others

Given that recognition of pregnancy has now been found in both eutherian (formerly known as placental) mammals like ourselves and marsupials with the more ancestral reproductive characters, it appears likely that recognition of pregnancy is a common feature of all live bearing mammals.




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But this knowledge does more than satisfy our curiosity. It could lead to new technologies to better manage marsupial conservation. Several marsupials face threats in the wild, and captive breeding programs are an important way to secure the future of several species.

Two Tasmanian devils.
Pixabay/pen_ash

One such species is the Tasmanian devil, which faces extinction from a dangerous contagious cancer. Captive breeding programs may be one of the only mechanisms to ensure the species survives.

But management can be made more difficult when we don’t know which animals are pregnant. Our research shows that maternal signals are produced in response to the presence of developing embryos. With a bit more research, it may be possible to test for these signals directly.

New reproductive technologies are likely crucial for improving outcomes of conservation programs, and this work shows, that to do this we first need a better understanding of the biology of the animals we are trying to save.The Conversation

Oliver Griffith, ARC DECRA Fellow, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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‘Give us a sniff, love’: giving marsupials scents from suitors helps breeding programs



File 20190315 28499 dyfjo3.png?ixlib=rb 1.1
A baby eastern barred bandicoot pokes its head out of its mother’s pouch.
M. Parrott, Zoos Victoria, Author provided

Marissa Parrott, University of Melbourne

Smell is a vital part of sexual attraction for all kinds of animals (including humans). We may be able to use smell to improve breeding programs by giving the female animal a sample sniff of potential mates and letting her choose the best one before introducing them.

Our new research found female marsupials paired with the male of their choice in captive breeding programs had a higher chance of becoming pregnant, a shorter time to pregnancy and may produce healthier young.




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Ladies’ choice

Zoos and breeding institutions traditionally pair animals based on their relatedness and pedigree so they can manage the overall genetic health of the population. It’s expensive and often not possible to transport multiple males just to give a female some options – but if she refuses her solitary suitor when he arrives, it can cause major problems.

Our research shows that presenting the female with a range of scent samples and letting her pick her favourite dramatically increased compatibility.

This simple 10-minute test more than doubled the number of pregnancies and shortened the time to becoming pregnant in a small carnivorous marsupial, the stripe-faced dunnart.

Marissa Parrott with a captive-bred mountain pygmy-possum released to the wild.
Author provided

Using the same technique in the critically endangered mountain pygmy-possum at Healesville Sanctuary, we showed that females had significantly higher breeding success with males they liked during their choice tests. We have shown a similar effect of increasing breeding success and shortening the time to pregnancy in the endangered eastern barred bandicoot at Zoos Victoria through scent and interactions.

How are female marsupials choosing mates?

Put simply, they are following their noses. We gave females a choice of male smell and allowed her to sniff out the best mate.

In the first published study of marsupial mate choice, we found female agile antechinus chose the most genetically suitable male based on his smell. Females preferred males that were genetically dissimilar to themselves (avoiding in-breeding), but not too dissimilar (avoiding genetic out-breeding).

There is a sweet spot to female choice. If you can provide a female with a suite of males, they can choose their most compatible suitor, which in turn is likely to produce the healthiest and fittest young.

Better yet, females are choosing males compared with their own genes, so each female may like a different male, which is good for managing the overall population. However, care must be taken with sisters, as they are likely to have the same choices.




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This information is particularly helpful for global programs that have endangered species spread across different institutions and zoos, such as tree kangaroos.

In the dunnarts, we found that freezing and storing the scents of males for up to 40 days did not affect a female’s choice or interest in a scent. Thus, if you have a female tree kangaroo at Melbourne Zoo and are uncertain which male should be sent from overseas, you could freeze scents from eligible bachelors and send them to her in advance for her approval. This could reduce the stress, time and cost associated with sending males between zoos, especially if the male you sent ended up being the wrong choice!

A stripe-faced dunnart in the captive breeding colony at the University of Melbourne.
M Parrott, Author provided

But why focus on females?

In marsupials, females provide the majority of the care of the young. In the extreme case of the antechinus, all males die after mating, leaving the females with all the work raising the offspring. Thus, females are generally the choosier sex, ensuring they get the maximum benefit from appropriate mate choice.

In other species, such as the critically endangered plains wanderer whose females lay eggs and leave them with stay-at-home fathers, you may expect the male bird’s choice to be more important. He is providing the care to the growing chicks and thus will want to maximise their success through choosing the best mate.

Can people learn from the marsupial approach?

Female mate choice is a perennial issue for many humans. A study that supplied 49 women with T-shirts worn by different men found the women could sniff out the men in their genetic “sweet spot” – not too similar or dissimilar – and found those scents most attractive.

We are not so different to the endangered marsupials we are working to recover. Perhaps in the future, instead of swiping right on an image, we can be sent a palette of smells to choose a potential suitor. Instead of speed dating, could we use smell dating?




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Certainly, when used in conservation breeding programs, allowing a female to choose her own mate can help find the best pairings, reduce the time to produce young and hopefully help produce the healthiest offspring to fight extinction for their species.The Conversation

Marissa Parrott, Reproductive Biologist, Wildlife Conservation & Science, Zoos Victoria, and Honorary Research Associate, BioSciences, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.