Monday, April 21, 2014

Spots and Specks: Elephant Freckles

by Rebecca Shoer              

                  One of the most obvious differences between African and Asian elephants has something to do with their skin.  What color is an elephant?  You may be tempted to answer "grey," but after a quick perusal of the different species of elephants (savannah, forest, and Asian), you'll see a wide variation in colors.  Savannah elephants are the greyest of the three, and they typically remain stubbornly grey their entire lives.  Forest elephants are more of a brown tint, and some even trend towards a red-brown; however, they will stay solidly one color their entire lives.  Asian elephants, and the various sub-populations of Asian elephants, also range in color-- from grey to brown to red.  Still, a characteristic that all Asian elephants have in common is the way in which their skin color changes during their lifetimes.  Unlike humans, who go grey as they age, Asian elephants go pink!
Photo by Rebecca Shoer

               Once an Asian elephant becomes fully grown, around 15 to 20 years of age, she begins to develop pink freckles on the thin skin around her trunk, ears, and face.  Just like humans, some elephants go pink earlier than others, but by age 30 Asian elephants will have a full spread of lovely freckles.  But what are these beauty marks, exactly?  Do they resemble the freckles that some humans get, or are they more like the spots on a dog?  First, we need to understand just what freckles are, and why calling these elephant marks "freckles" is actually somewhat of a misnomer.
               Freckles, like those on our lovely RA Elise (pictured below), are concentrations of melanin that form in a person's skin.  Melanin is a natural skin pigment found in humans, variations in which result in the amazing range of skin colors seen across the world.  These freckles can be found anywhere on a person's body, but are commonly found on the face because sunlight triggers their formation.  After being out in the sun, people with freckles will develop freckle-lines along with tan-lines, where their skin was exposed to the sun.  Thus, though someone may have freckles year-round, the freckles will become more prominent in summer.  Finally, anyone can have freckles, though the number of freckles you have is related to how many freckles your parents have. 

     
Photo by Lisa Barrett

               Do animals have freckles? Animals obviously come in a wide range of colors and patterns--some of these colors are caused by differences in color pigments like melanin.  First, animals like dogs and cats can certainly develop freckles on their skin, though they are often hidden by fur.  Spots on fur, and not the skin, are not freckles (as the underlying skin may not be spotted).  Fur color can be caused by differences in pigments produced by the animal, but in other animal species, the colors are actually the result of what an animal feeds on!  Flamingoes, for example, eat a type of pink shrimp, the pigments of which then color the feathers of the flamingo.  In addition, other animals actually vary the color of their scales and feathers by manipulating the physical structure--the light reflects off of variations on the scales or feathers in such a way as to create many different colors.  In fact, the pigments of a peacock's feathers are actually brown, but the structure of the feathers results in an amazing range of blues and greens.

File:Peacock feathers closeup.jpg
Photo from Wikimedia Commons

               Clearly, there is a tremendous range in how animals create colors.  So what about these elephant "freckles?"  Turns out, elephants develop freckles through a process called depigmentation.  As you may have guessed, this means that elephants actually lose pigment over time, resulting in spots that are lighter than the surrounding skin.  Animals that completely lack skin pigment are albino, while those that lack most (but not all) of their skin pigmentation are leucistic.  So elephant freckles are in fact reverse-freckles: rather than being caused by a concentration of melanin, they are the caused by a reduction in melanin in select areas. 

               Although freckles are clearly passed along genetically, scientists don't know why Asian elephants, and not African elephants, have freckles.  Can elephants use these spots to distinguish between individuals like we do?  Could they indicate age, and thus seniority, in a herd?  Do more freckles make a mate more desirable?  It's unlikely, since TEI's research has shown that elephants don't attend to visual cues as much as olfactory cues (Plotnik et al., 2013, Plotnik et al., 2013). Freckling may simply have arisen in ancient Asian elephants after they had diverged from African elephants.  As having freckles does not seem to harm the elephants in any way, they were passed down through the generations until modern times.  There is some variation in the number of freckles elephants may have between individuals and between entire populations; some subpopulations of elephants, like those in India, have fewer freckles than others.  
               Regardless of the reason, these spots make these animals even more lovely, adding to their individuality and uniqueness! There is so much that we still don't know about elephants, and we must work to study and understand these spectacular individuals before they (and their freckles) vanish altogether.

References

Plotnik JM, Pokorny JJ, Keratimanochaya T, Webb C, Beronja HF, et al. (2013) Visual Cues Given by Humans Are Not Sufficient for Asian Elephants (Elephas maximus) to Find Hidden Food. PLoS ONE 8(4): e61174. doi:10.1371/journal.pone.0061174

Plotnik, Joshua M., Shaw, Rachael C., Brubaker, Daniel L., Tiller, Lydia N., and Clayton, Nicola S. (2014) Thinking with their trunks: elephants use smell but not sound to locate food and exclude nonrewarding alternatives. Animal Behaviour. 88:91-98.

Wikipedia.org

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