Concepts and contentions of coral snake resemblance: Batesian mimicry and its alternatives (article review)

This review paper combines all previous studies regarding mimicry and color similarities between venomous coral snakes and their lookalikes. The authors report the current understanding of the relationship between snakes with ringed coloration and predator avoidance or lack thereof. In more recent literature on topics such as this, Batesian mimicry is assumed to be the primary explanation as to why aposematic coloration has persisted in mimics. However, the authors of this paper point out that a lack of empirical data and evidence that may prove alternative hypotheses further complicates scientific understanding of complex mimetic systems.

The first alternative hypothesis is thought to be the use of illusionary color patterns to visually confuse potential predators. This is enabled through critical flicker fusion (CFF) in which fast moving patterns blur in the same way strobe lights begin to appear as non-flickering to the human eye after prolonged exposure. When moving fast, the predator’s eyes aren’t able to keep up, therefore the ring patterns blend into one solid color. When not in motion, the ring patterns become a cryptic characteristic, especially on a mottled background which allows the snake to escape predation. While this theory makes sense, there is little to no empirical evidence of this occurring within coral snakes and their predators. 

Second, there is doubt placed on the predator’s learned avoidance because of the lethality of coral snake venom. Predators that die due to fast-acting lethal venom are unable to learn avoidance behaviors of similarly colored prey items. Alternatively, empathic learning via a third-party observer could be responsible for learned avoidance yet the assumptions of this occurring are highly implausible. For example, a large number of predators must avoid the coral snakes and lookalikes in order for mimicry to persist and the lack of knowledge regarding coral snake predators further contradicts this hypothesis. 

In typical mimicry systems, the mimic and the model species live in sympatry with each other because in a shared environment the mimic is able to benefit from predator avoidance of aposematic coloration. However, in some parts of the ranges of coral snakes and their lookalikes, they live in allopatry. For example, in the northern range of the scarlet kingsnake, there is no overlap in range with the venomous eastern coral snake. Further research needs to be conducted in order to provide inside into phenotypic similarity and geographical distribution.

In terms of supporting evidence for Batesian mimicry being a primary force to the evolution of coral snake lookalikes, there are three hypotheses mentioned in this paper. First, an experiment concluded that environmental variability does not affect predation rates among ringed snake species. Their findings highlight that patterned snakes are overall predated upon less than uniformly colored snakes. This contradicts the CFF hypotheses previously mentioned. 

Another plausible possibility of predator avoidance of aposematic colored snakes could be due to an innate predator avoidance due to neophobia. An experiment highlighted in this paper that illustrates this hypothesis showed that naïve chicks of a predatory bird species actively avoided ringed snakes even though they had never previously been exposed to coral snakes and their harmful consequences. However, a caveat is that while neophobia is present in some predator species of coral snakes, it is not ubiquitous among all predator species. 

Finally, the last argument for Batesian mimicry in coral snake lookalikes is the geographical distribution of both mimic and model species. Through experimentation, it was found that attacks on ringed snakes increased as allopatry increased, meaning that the protection gained from Batesian mimicry decreases. Further, the greater the resemblance of a mimic species to its model species counterparts also increases the higher the level of sympatry. This doesn’t explain the maintained presence of allopatric lookalikes however, and some explanation as to why this still occurs despite evidence for the contrary is also outlined in this paper- range contraction of coral snakes, range expansion of lookalikes, and gene flow that maintains this mimetic coloration. 

After reading this paper, it is clear further research must be conducted in order to reach a consensus and better understanding of Batesian mimicry in coral snakes and their lookalikes. There still remains uncertainty about whether or not Batesian mimicry is a main cause of coloration similarities in snakes. Rather than positing whether or not mimicry occurs or not within coral snakes and their lookalikes, the authors conclude that the similarities in coloration are most likely due to a suite of environmental factors. In order for future research opportunities to gain more understanding of this relationship, the authors also provided a clear definition of what constitutes a Batesian mimicry system: 

-        Systems consist of model, mimic, and signal receiver

-        Model is toxic or unpalatable

-        Signal receiver associates ringed coloration with harmful stimulus of the model

-        Model and mimic are sympatric

-        Signal receiver is the main selective pressure for persistence of the avoidance of mimetic phenotype

This review paper further emphasizes the scientific inquiry process and how information gained through experimentation is always susceptible to change through new methods and knowledge. While it is unclear whether or not Batesian mimicry is a main reason behind similarities in snake color patterns, we can deduce that the answer is not simple. 

Source

Sena, Anthony Thomas, and Sara Ruane. "Concepts and contentions of coral snake resemblance: Batesian mimicry and its alternatives." Biological Journal of the Linnean Society(2022). 

https://academic.oup.com/biolinnean/article-abstract/135/4/631/6513742