In Batesian mimicry, a harmless animal resembles a dangerous one to deceive its predators. Natural selection for mimicry is strong, but we do not know how species? responses to selection are mediated by the genetic and biochemical mechanisms available to them for adaptation, or how the selection imposed by predators is affected by their sensory systems. This project will explore these questions in the scarlet king snake (Lampropeltis elapsoides), which imperfectly mimics the deadly eastern coral snake (Micrurus fulvius). The first part of this project will examine the chemicals that models and mimics use to produce their deceptive coloration, and how this deceptive coloration is perceived by their predators. The second part of the project will explore the possibility that mimicry can evolve via phenotypic plasticity (when the same genes produce different phenotypes in different environments).
This project will help us understand how species produce their adaptations from different genes, why species do not always evolve to fit the demands of selection perfectly, and how the interactions between organisms are shaped by their preexisting characteristics. At the same time, this project will provide educational outreach for young scientists by providing them with opportunities to experience research first-hand, and will broaden access to science by actively recruiting members of under-represented groups.
Three core phenomena that the theory of evolution can explain are why organisms are well adapted to their environments, why they are complex, and why they are diverse. Our interest in this grant was exploring how well adapted organisms are to their environments. The biological system that we chose to address this question was coral snake mimicry. In this mimicry system, harmless snakes have evolved to resemble deadly coral snakes because looking dangerous reduces predation. We sought to determine whether shared ancestry or independent evolution best explained the colorful patterns of coral snakes and their mimics. If coral snakes and their mimics shared pigments and developmental mechanisms that were present in ancestral snakes, it might make mimicry relatively easy to evolve. However, if models and mimics each arrived at different evolutionary solutions to the problem of producing the same color pattern, it would imply that differences that result from using alternate developmental mechanisms are overcome by natural selection. We differentiated between these two hypotheses for adaptation by examining how coral snakes and their mimics produce coloration. In one study, we focused on the eastern coral snake (Micurus fulvius) and its mimic the scarlet kingsnake (Lampropeltis elapsoides). We used transmission electron microscopy to characterized the distribution of pigmentation cells in the skin, and thin-layer chromatography and absorbance spectroscopy to identify specific pigments. We found that both snakes used the same tissue structures and pigments to produce their coloration. This indicated that precise color mimicry between the two species was facilitated by shared developmental systems. However, without knowing what mechanisms were present in a larger sampling of snakes, it was impossible to say whether this remarkable similarity between model and mimic was an instance of adaptation facilitated by ancestry or a spectacular instance of convergence. Therefore, we conducted another study in Arizona. We enlarged our sampling of snakes to include the Arizona coral snake (Micruroides euryxanthus) and its mimics, as well as several snakes that were not involved in mimicry. We found that these snakes all used the same pigments as those found in our earlier study. Therefore, it appears that color mimicry in snakes can evolve relatively easily due to the palette of coloring agents that they share as a group due to common ancestry. The work that we have completed on this grant underscores the importance of understanding the context of adaptive evolution. Adaptations are often facilitated by developmental systems inherited by descent, rather than created from scratch in response to a particular selective regime.
