More than mimicry? Evaluating scope for flicker-fusion as a defensive strategy in coral snake mimics

Abstract

Coral snakes and their mimics often have brightly colored banded patterns, generally associated with warning coloration or mimicry. However, such color patterns have also been hypothesized to aid snakes in escaping predators through a “flicker-fusion” effect. According to this hypothesis, banded color patterns confuse potential predators when a snake transitions from resting to moving because its bands blur together to form a different color. To produce this motion blur, a moving snake’s bands must transition faster than the critical flicker-fusion rate at which a predator’s photoreceptors can refresh. It is unknown if coral snakes or their mimics meet this requirement. We tested this hypothesis by measuring the movement speed and color patterns of two coral snake mimics, Lampropeltis triangulum campbelli and L. elapsoides, and comparing the frequency of color transitions to the photoreceptor activity of the avian eye. We found that snakes often produced a motion blur, but moving snakes created a blurring effect more often in darker conditions, such as sunrise, sunset, and nighttime when these snakes are often active. Thus, at least two species of coral snake mimics are capable of achieving flicker-fiision, indicating that their color patterns may confer an additional defense aside from mimicry.

Unravelling the illusion of flicker fusion

“…[29,30]), the problem is that there have been no tests with actual predators. So far, the evidence for the anti-predator function of the flicker fusion effect comes from indirect observations in snakes [22,31]. For example, the 'zigzag' morphs of adequate speed is required for blurring of pattern elements to occur stripe width thinner stripes will blur at lower speeds as they produce more rapid temporal frequency pattern internal contrast low contrast patterns blur at lower speeds than high contrast ones orientation of pattern elements blurring occurs when elements are repeated along the vector of motion predator vision spatio-temporal acuity increasing spatio-temporal acuity of the predator requires higher speeds for the flicker fusion effect to occur (in figure 2b, TFF will shift towards higher temporal and spatial frequencies)…”

“…This is [18,30] hide the final resting location a sudden change in appearance from the moving to the static prey pattern makes it difficult for a predator to locate resting prey [17,22,29] deter predators a sudden change in appearance caused by the flicker fusion effect may cause the attacking predator to show neophobia or hesitate, giving the prey an increased opportunity to escape rsbl.royalsocietypublishing.org Biol. Lett.…”

“…For example, some researchers refer to a 'flicker fusion hypothesis'; however, it is not clear what this is. Sometimes, it refers to the mechanism and whether or not it is possible that blurring occurs through the flicker fusion effect [22,30], while other times it refers to whether or not the blurring could confer a survival advantage [29,31]. While this is confusing in itself, there is of course the additional problem that there are multiple functional hypotheses relating to how it might reduce predation (table 2).…”

“…Blurring through the flicker fusion effect may be occurring more often in nature than previously thought (e.g. [22]), and occur in slower moving prey, not just those performing a rapid escape.…”

“…When animal eyes become adapted to low lighting conditions, spatial acuity can also decrease [25]. This means that the flicker fusion effect is more likely to occur under dim compared with bright conditions [22], because prey do not need to be moving as fast for blurring to occur. While for a given speed, finer stripes will produce faster alternation (and more likely exceed the TFF), other things being equal, the speed necessary for the flicker fusion effect will always be lower for prey patterns of lower internal contrast.…”