Processing pickled pepeketua – how many frogs can you fit in a jar?

Processing pickled pepeketua – how many frogs can you fit in a jar?

How do museum curators decide what specimens to keep, dispose of, or give to the beetles to be reduced to bones? As Natural History summer interns, Ben Carson and Tobia Dale were tasked with the job of processing three recently acquired research collections from prominent herpetologists Ben Bell, Ruth Ainsworth, and Phil Bishop.

Supervised by Vertebrate Curator Colin Miskelly and Collection Manager Tom Schultz, we began with frog expert Ben Bell’s collection, transferring specimens to new jars with fresh 70% ethanol. Most of the ‘herp’ tissue or whole animal specimens at Te Papa are stored in ethanol in jars of various sizes, which is why they are often referred to as fluid or spirit specimens.

The jars of specimens are shelved in air-conditioned rooms within our Tory Street research collections building, which holds nearly 900,000 (mainly fishes) specimens in its state-of-the-art Spirit Collection Area.

For tissue specimens, an ethanol concentration of 70% ensures the preservation of tissues without causing damage to the specimen. As we worked through the donated collections, we found that many of the specimens were in ethanol that was below this concentration, which meant we needed to take a few extra steps. If specimens previously stored in more dilute ethanol are placed directly into 70% ethanol, water leaches out of them, causing the specimens to shrink.

Therefore, specimens are ‘stepped’ by transferring them incrementally into higher concentrations of ethanol, allowing them to reach equilibrium gradually, thereby minimising damage.

This massive jar of tadpoles was amongst the specimens that required stepping.

Several small frogs in a glass jar with a white lid.
Whistling brown tree frogs (Litoria ewingii). Te Papa

Although Te Papa’s spirit collection is by no means small, the native frog collection will be significantly bolstered by these new acquisitions. There are three species of native frog, pepeketua, In New Zealand: Hochstetter’s frog (Leiopelma hochstetteri), Archey’s frog (Leiopelma archeyi), and Hamilton’s frog (Leiopelma hamiltoni).

No croaks, not even a ribbit

Our native frogs diverged from most other frogs very early in evolutionary history and have maintained primitive features such as vestigial tail-wagging muscles (more on this in a future blog). Our frogs also lack prominent eardrums and don’t croak.

Archey’s and Hamilton’s frogs lack a tadpole stage, with the fathers carrying newly hatched froglets on their backs until they’re ready to venture into the bush on their own. Only Hochstetter’s frog has slight webbing between its hind toes and a tadpole-like stage, revealing a semi-aquatic lifestyle. The other two species live more terrestrial lives in damp native forests.

A valuable aspect of Ben Bell’s collection is that it contained all three native frog species at each life stage, from egg to froglet and adult.

One of our favourite specimens in the collection contained five adult Archey’s frogs collected from Whareorino forest in 1993. We discovered that these specimens were connected to a scientific paper, which provided the first documented evidence of predation upon our native frogs on the mainland. We’ve found it super rewarding when we’re able to match specimens to original research.

Five dead frogs laid out on a white card. They are in varying states of wholeness.
Five adult Whareorino frogs found dead in December 1993. Habitat distribution and predation on a western population of terrestrial Leiopelma (Anura: Leiopelmatidae) in the northern King Country, New Zealand

What’s in and what’s out

A valuable skill we are learning whilst processing these acquisitions is how museum curators decide what to add to the research collection as intact specimens, what to skeletonise, and the importance of recording good data.

If a museum receives a specimen with a collector’s name, collection date and location, the specimen is of higher value in comparison to a specimen without these data. So, a key consideration when suggesting the fate of a specimen was the data associated with it.

Some specimens looked to be in perfect order but had little to no collection data, significantly reducing their value to researchers. We learnt that, excepting species that are rare in the museum collection, specimens lacking data would likely be disposed of rather than retained.

Many specimens in the three collections were in excellent condition; however, some specimens were in far poorer condition and will have greater value as skeletons. We learnt that when trying to skeletonise an amphibian or reptile with tiny bones, one of the most effective practices is to use a colony of dermestid beetles to remove excess tissue.

We have both loved working here so far, learning from leading experts and viewing highly important collections of natural history. Keep an eye out for future updates from us as we finish processing Ruth Ainsworth and Phil Bishop’s collections!

Find out more

Find out about the dermestid beetles used at Te Papa

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