Melanin under a foldscope!

Nov 11, 2020 • 11:15 AM UTC

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zemimahossain

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I conducted this project as part of Professor Pringle’s EEB321 class at Princeton University
While I was studying outside this past weekend to try to take advantage of the gorgeous weather, one of the kids that I babysit for came rushing to me with excitement. He was holding a shriveled up, relatively small bird feather in his hand, which he found during his walk around the block here in Princeton, New Jersey. Soon after, I decided to observe the feather using my foldscope, and although the photo I was able to capture is quite mediocre (as looking through the foldscope and getting a semi-decent photo was a lot harder than I anticipated), this is what it looked like:

Going off of what I learned earlier in the semester in EEB 329: Sensory Ecology (an amazing class that I highly recommend to all of you juniors who can take it next year!), I believe the thick shaft that we see in the middle of the photo is the rachis. The rachis resembles the shaft of a tree in that it appears as though there are branches coming off it; these branch-like structures that we observe in the photo are called barbs. The twigs coming off the barbs are called barbules; they are not super discernible in the photo, as between the barbs we just see some lighter-colored, fuzzy shadings. Although we cannot really tell based on the photo, barbules look as though they connect with each other, as shown in the diagram below. I was thrilled that I was able to see these structures that I learned so much about up close; these nanometer-scale structures in the feathers are significant due to the roles they play in the various light scattering mechanisms that give rise to structural colors (which is not the case of this feather, as it is primarily dark brown, rather than being white, non-iridescent blues, and iridescent structural colors).

I’ve always been fascinated by the evolution of avian plumage color gamut, and so I loved being able to observe the colors of this bird’s feather through the lens of the foldscope. Based on the photo, the bird’s feather primarily consists of dark-colored pigments, which are referred to as melanins. Seeing as though the feather is mostly dark and light brown (on the far left, the photo makes it appear as though there’s some orange, but it’s more of a tawny or caramel shade of brown), we can classify these pigments as eumelanins. The feather itself was beautiful; I took this photo days ago, so I do not have access to the feather anymore, but I remember half of the feather being primarily a light brown, while the other half was the darker brown captured in the photo. What also intrigues me is that towards the ends of the barbs, we see a shift from a dark brown to a lighter brown. If anyone has any guess of which bird this might be, let me know! Melanin is quite interesting because although it is a pigment, it can help contribute to the feather’s structural properties, specifically in that iridescent colors are produced by coherent light scattering from the arrays of melanin granules arranged in regular layers in the feather barbules. Really cool stuff! With all of that being said, one question I still have trouble answering is the following: in the case of feathers consisting of these melanin light-scattering granules, are these feathers considered pigmentary because it includes melanin or are they solely structural?
Overall, I really enjoyed this lab! Paper microscopes are truly revolutionary, and I’m sure this won’t be my last time using one.

Melanin under a foldscope!

zemimahossain

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