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DISPLAYING POSTS TAGGED: dna (2)

So many specimens

Author
by Kate C
Publish date
13 April 2012
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Tucked away from public view, kept in unlit, climate-controlled storage, the museum has millions of zoological specimens. Most of these are insects and other invertebrates but thousands are fish, birds, mammals, reptiles and amphibians. On top of that, we have huge tissue collection: tiny pieces of animal tissue preserved in a sort of genetic library.

Learning this, you might ponder: why do we collect and keep so many specimens, and often, multiple specimens of the same species? As Victoria's official repository for examples of our state's fauna, wouldn't one of each species be enough? And why would we want specimens from outside Victoria?

These are very good questions and there are several reasons why.

Defining a species

Let's say you were out hiking and you found a hidden canyon that wasn't on your map. Within the canyon, you spot an unusual butterfly that's not in your field guide. In fact, it's not like anything you have ever seen before. How would you verify that it is species new to science? You would need to compare it with properly identified examples of other species. You'd probably find those examples in a museum.

There are strict rules for describing and naming new species; the International Commission of Zoological Nomenclature oversees the process worldwide. To describe a new animal species you must lodge a holotype – the irreplaceable, single specimen that stands as the official representative of that species. It might take a few specimens, called a type series, to properly describe the species but there is only ever one holotype. Museum Victoria counts several thousand holotypes among our collections, including the Leadbeater's Possum, the Baw Baw Frog, and numerous invertebrates.

However one specimen can't possibly represent a whole species: what about the other sex? What if males and females are very different? Or the animal changes over its life cycle? Or the individuals from over here are slightly different to the individuals from over there? To get a full picture of all the variation within a species, we need many examples of that species.

trays of butterfly specimens Multiple examples of a few species of butterfly. Each individual specimen records the variation within a species.
Image: David Paul
Source: Museum Victoria
 

Changes through time

Preserving five individuals of our hypothetical new butterfly that you caught during your hike is a good start. You might have examples of slightly different sizes or varying wing patterns. But what about next month or next year? How early do the butterflies emerge in spring, and when do they disappear in winter? Maybe next year the canyon receives lots of rain, the butterfly's food plant is plentiful, and the population is twice as large and each individual butterfly is fatter. You'll need some examples of this, too.

Collecting specimens over time records all sorts of useful information. It can indicate the incoming wave of an invasive species or the decline of a rare one. Physical changes in the animals themselves – their size, colour, pattern – can reflect changes in their environment but it requires a large number of data points over many years to detect patterns and work out why those changes might be occurring.

marine crustacean collection The museum's wet collection contains specimens in alcohol. These are marine crustaceans.
Image: David Paul
Source: Museum Victoria
 

Future research

Natural history collectors of a century ago could not have imagined how we would use their specimens today. They didn't even know that DNA existed, let alone that it would one day help define and analyse species. Emerging technologies mean that we can return to old specimens again and again and keep learning new things. So-called 'next generation sequencing' means we can now look at the entire genome of an individual, every gene in their cells, where just a decade ago we could only look at a few marker genes. Genetic analysis can identify cryptic species – ones that can't otherwise be distinguished from closely-related species – and is useful for forensic questions such as determining the origin of smuggled wildlife. Museum collections are the source of tissue and reference specimens for these activities.

Freezers containing tissue collection The museum's banks of freezers contain thousands of tissue samples.
Image: David Paul
Source: Museum Victoria
 

Just like those collectors of old, we can only guess at the importance of today's collecting. Perhaps our hypothetical butterfly might experience a population explosion in the changing climate and become an important indicator of local conditions. That data set begins with those five specimens you collected on your weekend hike.

Links:

Lyman Entomological Museum: Why so many specimens?

The John Curtis British Insects Collection

The Field Museum: From Finches to Ostriches

Leo Joseph, 2011. Museum collections in ornithology: today's record of avianbiodiversity for tomorrow's world, Emu 111, i–xii  (PDF, 417 KB)

Chimp and human DNA

Author
by Kate C
Publish date
11 October 2011
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Exhibitions about science and technology are notoriously difficult to keep up-to date because those scientists just won't stop discovering and inventing things! Curator Kate Phillips encountered an example of this last week, after someone spotted a discrepancy between two Melbourne Museum exhibitions, Darwin to DNA (2000) and 600 Million Years: Victoria Evolves (2010).

Both exhibitions compare the similarity of DNA between chimpanzees and humans. The earlier exhibition states that there is less than two per cent difference while the more recent exhibition declares a 96 per cent similarity. While the numbers don't seem to agree, they're not necessarily incorrect because they compare different aspects of the genomes.

Face of young adult male chimpanzee. Young adult male chimpanzee.
Image: Frans de Waal, Emory University
Source: Used under Creative Commons CC BY-NC-SA 2.0 from Wikimedia Commons.
 

Kate explains:

"The discrepancy comes about because these two exhibitions were developed ten years apart and the understanding of DNA has changed over that time. In 2001 the draft human genome was published and a final version in 2004. In 2005 the draft chimp genome was published and could be accurately compared to the human one. The percentage similarity that came out of this comparison was 96 per cent. Before this time the similarity was probably based on comparing known genes, and therefore was working with less information."

"However the percentage you come up with also depends on how you make the comparison – on which bits of the genome you compare and that could also account for the discrepancy. If you compare genes, we are more similar, if you include the non-coding sequences, we are slightly less similar. Really 98 per cent and 96 per cent are both indicate great genetic similarity."

Set of chromosomes of a human male. Chromosomes of a human male. Humans have 23 pairs of chromosomes and chimpanzees have 24 pairs.
Source: National Human Genome Research Institute
 

We love that someone noticed this because it means that people are reading exhibition text closely, and keeps us on our toes. It's also, as Kate concludes, a pointed demonstration of "the scale of scientific discovery in the area of genome research over the last ten to twenty years."

Links:

The Chimpanzee Sequencing and Analysis Consortium (2005) 'Initial sequence of the chimpanzee genome and comparison with the human genome' Nature, Vol 437 pp 69-87.  (PDF, 4.3 MB)

Media release from NIH News, 'New Genome Comparison Finds Chimps, Humans Very Similar at the DNA Level' (2005)

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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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