Sciences

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Sciences

Natural history - from animals to minerals, fossils to sea slugs. MV's scientists use the state's collections in important research.

Bugs within bugs, part 1

Author
by Patrick
Publish date
28 April 2014
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To support our collection of almost 100 invertebrate species on display at Melbourne Museum, Live Exhibits staff must occasionally collect bugs from the wild, and some of these can hold unwanted surprises inside.

Chalcid w A Chalcid wasp, newly emerged from the cocoon of its host caterpillar.
Image: Patrick Honan
Source: Museum Victorai
 

At least one in every ten insect species is a parasite on other insects. In Australia this adds up to several tens of thousands of parasitic insect species, all living their lives on the outside or, more commonly the inside, of other insects. Most of these parasites are wasps and flies, and most of their hosts are butterflies, moths and beetles.

Tachinid fly eggs on beetle Tachinid fly eggs on the outside of a doomed Leaf Beetle larva (Paropsis species).
Image: Patrick Honan
Source: Museum Victoria
 

Parasitic insects usually lay their eggs directly onto or into the body of their host, but may lay eggs on a food plant in the hope that they will later be ingested by a potential host. Once inside, the parasitic larva consumes the host’s internal tissues while the host continues to go about its business. The parasite usually avoids the vital organs until the last minute – then polishes these off and finally kills its host.

Aphid ‘mummies’ Aphid ‘mummies’ – aphids that have been parasitised and glued to the leaf by Braconid wasps. When fully developed, the wasps will cut a perfectly circular hole in the back and emerge as adults.
Image: Patrick Honan
Source: Museum Victoria
 

Parasitic wasps are able to find their hosts no matter where they might hide. In order to lay eggs on its host – Sirex Wood Wasp (Sirex noctilio) – Megarhyssa (Megarhyssa nortoni) can drill through 9cm of solid wood with its ovipositor (egg-laying organ). Megarhyssa females find their hosts using infrared detectors on their antennae; the outer bark of a tree is 0.5oC warmer where a larva lies underneath.

female Megarhyssa A female Megarhyssa (Megarhyssa nortoni) drills through a pine tree to deposit an egg on the Sirex Wood Wasp within.
Image: Patrick Honan
Source: Museum Victoria
 

A parasitic wasp will sometimes inject venom that paralyses the host but keeps it alive, allowing the wasp to hide it away for its offspring as a sort of living larder. A large wasp dragging a larger, paralysed, huntsman across open ground is a familiar sight during summer.

Pompilid wasp drags a huntsman A Pompilid wasp drags a huntsman (Isopeda species) from its hiding place under bark, before paralysing it and inserting an egg.
Image: Patrick Honan
Source: Museum Victoria
 

A caterpillar can sometimes dislodge a parasite’s eggs with its mandibles, but wasps usually lay their eggs just behind the caterpillar’s head where they can’t be reached. Many hosts are able to ‘encapsulate’ a parasite already inside their bodies, localising its damage and starving it of oxygen. When more than one parasite is laid inside a host, the larvae fight to the death within the host’s body for the rights to its organs.

wasp cocoons inside the empty shell of a Cabbage White Butterfly caterpillar Thousands of parasitic wasp cocoons inside the empty shell of a Cabbage White Butterfly caterpillar (Pieris rapae). Each cocoon will soon produce a tiny wasp that flies off to find other caterpillars to parasitise.
Image: Patrick Honan
Source: Museum Victoria
 

Parasites are themselves subject to attack from hyperparasites, insects that lay eggs inside an already-occupied host. The emerging larva seeks out the parasite in residence and burrows into its body. These in turn may be parasitised by superhyperparasites, and so on.

“Great fleas have little fleas upon their backs to bite 'em,

And little fleas have lesser fleas, and so ad infinitum…”

Augustus de Morgan (after Jonathan Swift)

Death by coitus

Author
by Alice
Publish date
14 April 2014
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The other week I attended Isabella Rossellini’s comic and educational monologue Green Porno, a fascinating lecture on the sexual escapades of the natural world. It really got me thinking about the various and bizarre methods of animal reproduction that I've encountered since commencing my role at the Discovery Centre. We see an intriguing array of specimens brought in to be identified and in some cases even added to the collection. Many of these animals would be well-deserving of a feature episode on Isabella’s show, but none have captivated my attention more than our recent acquisition of a male phascogale. 

Phascolgales belong to the same group of marsupials as the Tasmanian Devil and the quolls. But unlike their relatives they have managed to keep a very low profile. Considering that male phascogales live fast, die young, and have such a frantic sex life that it kills them, I was really surprised that the first time I became aware of this genus was through the arrival of a neatly wrapped frozen specimen.

  Mount of Phascogale tapoatafa, Brush-tailed Phascogale  Mount of Brush-tailed Phascogale
Image: Benjamin Healley
Source: Copyright Museum Victoria 2003
 

Phascogales are among a rare breed of mammals that practice suicidal reproduction, or semelparity, where one or both sexes die after a single episode of mating. This strategy is seen in some invertebrate and plant species, but is extremely rare in mammals, only occurring in a few marsupials native to Australia, South America and Papua New Guinea. In Australia the male Phascogale, Antechinus, Dasykaluta and Parantechinus are the only mammals where the males literally mate themselves to death.

Mating season for these dasyurid marsupials lasts only a few short weeks, during which promiscuous females and anxious males copulate for hours at a time (Antechinus have been known to go at it for up to 14 hours!). During this concentrated period of breeding the males’ levels of testosterone and stress hormones become so extreme that even their muscles start to break down to help fuel the act. The intensity of prolonged mating causes the males' bodily functions such as their immune system to shut down, exposing their exhausted bodies to infection, internal bleeding and disease shortly after. The males will not even get to see the fruits of their labour, as they all die before their young are born.

Phascogale tapoatafa: Brush-tailed Phascogale Brush-tailed Phascogale from J. Gould's Mammals of Australia, 1863, vol 1, pl 31
Image: Artist: John Gould; Lithographer: H.C. Richter
Source: Out of Copyright
 

So why do you think male phascogales have been programmed to pursue such a life ending labour of love?

The answer lies in their sperm. For phascogales sexual selection occurs after copulating, where the sperm compete inside the female for fertilisation. Rather than fighting to gain access to mate with a female, males need to put all of their energy into fertilising as many females with as much sperm as possible. This also explains the lengthy duration of the mating spree – the more time one male spends mating with a female, the less opportunity other males have at gaining access to her. Combine this with the promiscuous frenzy of their breeding period and many females may nurture offspring from multiple fathers. 

I can only imagine the field day that Isabella would have illuminating the fascinating science behind the phascogale's reproductive biology. A glimpse at any of her online videos will give you an idea.

Links:

Diana O. Fisher, Christopher R. Dickman, Menna E. Jones, and Simon P. Blomberg (2013) Sperm competition drives the evolution of suicidal reproduction in mammals Proceedings of the National Academy of Sciences, published ahead of print 7 October 2013: doi:10.1073/pnas.1310691110

Two eclipses for April

Author
by Tanya
Publish date
11 April 2014
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Not one, but two eclipses will occur this month and both are partially visible from Melbourne.

Just before sunset on the 15th April, the Moon will rise already totally eclipsed. It should look quite eerie to see a red moon rising above the eastern horizon and it's always amazing how bright the Moon appears as it moves out of the Earth's shadow and returns to its usual splendour. While you are watching the eclipse, be sure to take a look at Mars, which will be just to the left of the Moon and the bright star Spica (in the constellation of Virgo) that will be found just above.

Lunar Eclipse The progression of a total lunar eclipse in August 2007.
Image: Phil Hart
Source: http://www.philhart.com/
 

Two weeks later on the 29th April, the Moon and Sun will come together in the sky and we'll see a partial solar eclipse. The eclipse will begin during the afternoon and reach its maximum point just before sunset. At the height of the eclipse 64% of the Sun's diameter will be covered by the Moon. The Sun will still be partially eclipsed as it sets below the western horizon.

Solar Eclipse The Moon takes a bite out of the Sun.
Image: Phil Hart
Source: http://www.philhart.com/
 

The timings for both the lunar and solar eclipse can be found from the Planetarium's monthly newsletter – Skynotes – which is a great guide for finding your way around the night sky.

Importantly, lunar eclipses are lovely to watch and you don't need any special equipment. Solar eclipses, on the other hand, require a bit of care and planning. Never look directly at the Sun.

There are safe ways to watch a solar eclipse and the easiest is to purchase special eclipse glasses. They are available from the Scienceworks shop and will allow you to watch the event, while protecting your eyesight.

You can also create a simple "pinhole" projection. It's as easy as making a small pinhole in a piece of paper or cardboard. Do not look through the hole, but allow the Sun to shine through and project an image onto a second piece of cardboard. Even a blank wall or a clear patch of ground can make a good surface for projection.

And as I've mentioned previously on the Museum's blog, sometimes nature helps out too. If you can see sunlight travelling through the leaves of a tree, you’ve got yourself some ready-made pinhole projections. Check the ground and it might be covered with little crescent Sun images, just like this great example from the Astronomy magazine website.

An Aztec pterosaur?

Author
by Erich Fitzgerald
Publish date
3 April 2014
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Dr Erich Fitzgerald is our Senior Curator of Vertebrate Palaeontology.

Next time you visit the Dinosaur Walk exhibition at Melbourne Museum, look up, and prepare to be gob-smacked. Behold, Quetzalcoatlus, largest of those magnificent Mesozoic aeronauts; the pterosaurs! With a 10-metre wingspan, Quetzalcoatlus was perhaps the largest flying animal ever…or perhaps not. But before delving into that palaeontological puzzle, another question will no doubt be on your lips: how do you pronounce “Quetzalcoatlus” and what does it mean anyway?! The answer lies in Mexico, about 1,000 years ago, at the dawn of the civilization that would eventually become the Aztec Empire.

The Nahua people, who gave rise to Aztec culture, believed in a feathered serpent god of the sky called Quetzalcoatl (pronounced ‘ket-sal-ko-ah-tell’). Aztecs inherited the worship of Quetzalcoatl as one of their chief deities: a dragon-like god that linked the earth with the heavens and created humans.

Aztec god Quetzalcoatl The Aztec god Quetzalcoatl as depicted in the Codex Telleriano-Remensis (16th century).
Source: via Wikimedia Commons
 

The feathered serpent god returned in 1971 with the discovery in Texas of the fossilized wing bones of a truly colossal pterosaur of late Cretaceous age (about 65 to 70 million years ago). In light of their location near Mexico and their suggestion of a reptile that dominated the skies, these extraordinary fossils were named Quetzalcoatlus (pronounced ‘ket-sal-ko-atlas’) after the Aztec god Quetzalcoatl.

Quetzalcoatlus illustration Life restoration of a group of giant azhdarchids, Quetzalcoatlus northropi, foraging on a Cretaceous fern prairie. A juvenile titanosaur has been caught by one pterosaur, while the others stalk through the scrub in search of small vertebrates and other food.
Image: Mark Witton and Darren Naish
Source: CC BY 3.0 via Wikimedia Commons
 

As impossible as it may seem, Quetzalcoatlus and its kin (collectively dubbed azhdarchids) were capable of getting airborne, then sustaining flight through long-distance gliding on thermal air columns. Yet recent research on the skeleton of azhdarchid pterosaurs has suggested that they actually spent a substantial amount of time on the ground, stalking prey while walking stilt-like on all fours. For now, the feathered serpent god of the Aztecs may have been brought down to earth, but in a twist of the serpent’s tale, its legacy continues thanks to fossils from an even more ancient world, long ago.

Links

Aztecs opens at Melbourne Museum on 9 April 2014

Pterosaurs: Flight in the Age of Dinosaurs exhibition at the American Museum of Natural History 

Town Skull, Country Skull

Author
by Max
Publish date
1 April 2014
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Skulls in the DC showcase. Skulls in the DC showcase.
Image: Max Strating
Source: Museum Victoria
 

One of the advantages of working in the Discovery Centre is that you’re in the box seat, so to speak, when you need something identified. I recently found a Teeny Weeny Skull behind the skirting board whilst doing renovations at the family holiday house on the South Gippsland coast. I immediately thought it could be a Microbat (Microchiroptera) as we had a colony in the laundry wall years ago.  I put the Teeny Weeny Skull in a matchbox and took it home with me. 

Antechinus skull in the DC showcase. Antechinus skull in the DC showcase.
Image: Max Strating
Source: Museum Victoria
 

The next time I was in the Discovery Centre I went to our showcase that contains skulls, skeletons, insects and assorted animals in order for people to do their own identifications. I scanned the case and noticed one that initially looked very much like the Teeny Weeny Skull. It was an Antechinus. If my specimen was an Antechinus, this was exciting; a friend who also had a property near mine had found an Antechinus (a Swamp Antechinus Antechinus minimus). They had given it to me to have it identified by our experts. It was duly examined, identity confirmed and a sample of its DNA was taken. It was also placed on the Atlas of Living Australia as one had not been registered from that location before.

Black Rat, Water Rat and House mouse skulls in the DC showcase. Black Rat, Water Rat and House mouse skulls in the DC showcase.
Image: Max Strating
Source: Museum Victoria
 

But my excitement was short-lived - alas, there were differences between my specimen and the Antechinus skull – the bones of the eye orbit weren’t the same, the teeth were quite different and the snout of the Teeny Weeny Skull was shorter. A further scan of the case revealed a match – Mus musculus – a House mouse! That’s right: an ordinary, garden variety mouse, not its more exciting native Australian (sort-of) counterpart. Mind you, if I had just consulted Bioinformatics Skull Views I might have worked it out sooner…

House Mouse skull The Teeny Weeny Skull: a House Mouse
Image: Max Strating
Source: Museum Victoria
 

Rings around an asteroid

Author
by Tanya
Publish date
31 March 2014
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In a surprise discovery, two rings have been found around the asteroid Chariklo, making it the first small Solar System body known to have rings.

Saturn is known for its magnificent rings and the other gas giants - Jupiter, Uranus and Neptune - have ring systems too, though not quite as impressive. Careful searches had not found any other ring systems within the Solar System and many astronomers were beginning to think that rings might only exist around large objects, until now.

Rings from Chariklo An artist's impression of the newly discovered rings around Chariklo.
Source: ESO/L. Calçada/Nick Risinger (skysurvey.org)
 

Chariklo is just 250km across and lies beyond Saturn, at a billion kilometres away. It is much too small and far away for the rings themselves to be seen, but amazing detail is now known about them. The rings are dense but narrow, just three and seven kilometres wide, and are separated by a clear gap of nine kilometres. If you were standing on the surface of Chariklo, the rings would appear as wide as our Full Moon and stretch from horizon to horizon.

The discovery was made possible because last June, Chariklo passed in front of an obscure star (UCAC4 248-108672). Not only did Chariklo block the star's light for 5 seconds, but two tiny dips in the starlight were seen, just before and after Chariklo moved by. This video from the European Southern Observatory (ESO) shows faint dimming caused by the rings, just before and after Chariklo blocks the star completely.

 

This event, known as an occultation, could only be seen from South America and an observing campaign was coordinated across seven observatories, including two telescopes operated by the ESO at La Silla, Chile. Having observations from all seven observatories, ruled out other possible explanations, except for a ring system.

What I really love is the data from the new high-resolution camera on ESO's 1.54m Danish telescope. (Anyone who has been to my Discover the Night Sky series knows that I am particularly fond of beautiful graphs!) This new camera was developed to search for exoplanets and can take up to 40 images per second. It was actually able to see the gap between the two rings – now that's beautiful science!

Chariklo Data The data captured by ESO's 1.54m Danish telescope, showing Chariklo blocking out the light of the star (the main dip). On either side are two small, double dips, as the rings also passed in front of the star.
Image: F. Braga-Ribas et al.
Source: Reprinted by permission from Macmillan Publishers Ltd: Nature (March, 2014)
 

The Planetarium's astronomer, Dr Tanya Hill, was recently appointed the Australian representative of the European Southern Observatory's Science Outreach Network.

Links:

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Updates on what's happening at Melbourne Museum, the Immigration Museum, Scienceworks, the Royal Exhibition Building, and beyond.

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