Hi, Chris here. I previously posted on frogblog about the non-invasive research I’m doing with Andrew and Mark looking at the unique optical properties of tree frogs held in the collection at Manchester Museum. Well, I’ve now done a very preliminary investigation, so thought it’s time to report back!To start the investigation I’ve been using a technique known as reflection spectrometry. This allows me to see how much light of each wavelength is reflected back from the frog’s skin. What makes this particularly interesting is that a few frogs show an increase in the amount of light reflected in the near infrared (wavelengths just longer than we can see). The graph (just above) shows a typical reflection spectra from one of the phyllomedusine frogs.
Human vision can only see up to about 700 nm, so the very high reflection just beyond that level in the graph we humans just can’t see – if we could see that far into the spectrum then the frogs would appear bright red to us!
So far only 18 species of frog, mostly of the family Hylidae, have ever been identified as having an abnormally high reflection in the near infrared. Of these 18, 12 can be found right here at the museum! The purpose of this reflection is still unknown, although we suspect it is related to thermoregulation and crypticity (camouflage).
One thing we are hoping to do is try and refine our understanding of the interrelatedness and evolution of these species. The increased infrared reflectance has been found in frogs from at least two distinct regions, Central America and Northern Australia, and at the moment we don’t know whether this trait evolved once, a long time ago, and frogs that possessed it travelled to those regions when still joined, or whether the trait has evolved independently.
We have found that the spectra of the frogs certainly appears to be a defining feature of each species and have now developed a computer programme that can identify the species of a frog just from its spectra. The next challenge is to see under what conditions those spectra change, and see if that can help us learn more about how the frogs respond and interact with their environment. This may help us identify possible changes that can occur between wild and captive raised frogs, such as the Endangered Lemur Leaf Frog.
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