Hoppin’ into some frog investigations

Moving into my second week of research, I decided to focus on organisms that uses aposematic coloration strategies and are also prone to predation. I learn from the first week that I was looking in the wrong sector of aposematic species. Even though wasps are small and at risk for being accidentally killed by creatures to large to notice them, they are still a predator species, like the Coral snake. I need to refocus and look towards species that are aposematic prey animals. A classic example of this type of aposematism is the monarch butterfly and its larvae.

The Monarch butterfly, both in caterpillar and adult form, uses its bright coloration to say to predators, “You don’t want to eat me!”. This species’ diet consists primarily of milkweed, a plant that is high a heart-arresting chemical similar to digitalis. These toxins are processed and retained within the body of the butterfly. Predators that makes the mistake of attacking the Monarch butterfly end up with a foul taste in their mouths and often discontinue their attack. Similar to the case of the Coral snake and the Milk snake, another species, the Viceroy butterfly exhibits strikingly similar color patterning to the Monarch in an attempt to reap the benefits of a confused predator. While their bodies do not contain the same toxins, their mimicry of the Monarch offers protection through misidentification.

While Monarchs are interesting aposematic animals that are prone to predation, I do not feel that their coloration is diverse enough to allow for the customization that is desired by human cyclists. However, I’ve come across another creature that seems to be perfect for my needs: The Poison Dart Frog.

Based on the National Geographic Society’s web entry about these incredible organisms, the Poison Dart Frog is found in the tropical environments of Central and South America. They are very small creatures, ranging in size from about half an inch to 2 inches and weighing on average only 1 ounce.

Their small size belies a powerful and deadly defense. Similar to the Monarch butterfly, these frogs are able to process and retain toxins from the insects they eat and then secrete these toxins through their skin. Not all types of dart frog are poisonous with some innocuous types just pretending to be their dangerous cousins. However, given that certain types of dart frogs have enough poison to kill 10 adult humans, it seems like a good plan to just avoid the creatures entirely. Indigenous groups sharing the environment with the dart frogs realized the value of these animals unique defense mechanism and began producing arrows tipped with the poison, hence the name poison “dart”, or sometimes “arrow” frog.

And so, I began visual analysis of poison dart frog patterns, specifically color analysis. They’re unique strategy of making themselves highly visible to their predators in an attempt to avoid predation. This is a very different strategy from those implemented by other prey animals who practice concealment behaviors.

Visual Analysis

This exercise in color analysis is more formal than the one I conducted with the wasps and represents my effort to capture the range of colors exhibited and to better understand the efficacy of different exhibited color combinations.

I started by compiling photographs of various dart frog color morphs. For each distinct color combination (20 individuals), I pulled out the colors utilized, noting that the quality of the hue has some variability across the organism’s form. From these colors, I created swatches that show the general proportion of color use for each organism.

Each color exhibited (non-black and non-white) is pulled into an unorganized palette and then further arranged loosely by hue into a second visualization that seeks to show the distribution of hues across the color spectrum. I’m still setting the rules for this. I have non-black meaning that the black pigment within the hue is less than 60% and I have non-white meaning that the saturation of the hue is greater than 10%; however, there are a few colors in the palettes that do not fit the criteria for non-white that I feel should be included.

Findings:

• The hue of the exhibited colors do not matter as long as they are high in brightness and saturation and are paired with a color that provides strong contrast (such as black).
• This would be useful in that it is aligned with my interest in allowing cyclists to customize their gear to suit their cycling identities. If specific hues do no matter, merely the saturation and brightness, more options will be available to cyclists using the gear. Fluorescent yellow-green (while the easiest color for humans to see quickly) is just not an option for everyone.

I further categorize the colors by organizing them around how they are manifested on the organism (i.e. body versus extremities, top of body versus bottom of body, main color versus accent color).

I organized all of the color proportion swatches by number of colors used (dyads, triads, tetrads) to better understand which color strategy is more common. I’ve discovered that there are far more dyads and triads than tetrads. There are only two monads that I found in my research, but given that they does not utilize pattern in their strategy, I have excluded them from my study.

I further analyzed the dyads, triads, and tetrads to understand how each are implemented on the organism and have written general rules for their use. For example, in triads, a primary color is generally found on the body and head. It is paired with an accent color that provides the highest level of contrast, both within pattern and to environment. A secondary color is found on the extremities and is paired with the same accent color as the primary color. The contrast between the secondary color and the accent color is generally low. It is also most common for the primary color to be warmer than the secondary color, causing the body of the organism to be brought forward visually, whereas the extremities, exhibiting the cooler color, will fall back.

Findings:

• Poison dart frogs seem to offer a different value in that they employ a randomized, reaction-diffusion pattern. I believe this use of bright colors abutting black shapes increases the number of “edges” between the high contrast color combination, causing an increase in the vibrative quality of the pattern; thus, drawing more attention to the organism. This is just a theory, but I’d like to investigate it further.
• I think reaction-diffusion modeling will be a crucial element of my project and have begun looking into ways to generate these patterns using algorithms so that I may increase the number I can produce and allow for easy manipulation of the patterns. This would be useful for testing and would align with my interest in allowing cyclists to customize their gear to suit their cycling identities.

I began researching the environments in which dart frogs live and where in those environments they are more commonly found. They are often found on the ground floor of tropical rainforests, so their colors help them to stand out against dark brown leaf litter. They only leave the ground cover to rear young amongst the lower canopy, mostly greens. Additionally, I’ve begun researching the predators of dart frogs and how they see, which brought me to interesting article from National Geographic that validates my finding about the importance of having high contrast markings. Snakes have limited color vision; however, they are able to perceive the amount light reflected of the prey animal (luminance contrast) and are hardwired to perceive high contrasting patterns as warnings. While I want to investigate how this works further, I also want to better understand how humans perceive colors, especially at different times of day (a huge factor in cycling accidents).

I’ve also begun read Visual Perception by Vicki Bruce. I anticipate this text will help me make the jump from rainforest frog strategies to that of humans.