Next, we used a phylogenetic framework to reconstruct origins of mimicry and rates of colour evolution across snakes at multiple time scales to characterize transitions between cryptic and conspicuous coloration, and test for temporal correlations with coral snake co-occurrence. We created geographic range polygons for over 1,000 New World snake species from both published records and occurrence data ( n=299,376 specimens) to test for a positive spatial correlation between coral snakes and their presumed mimics while controlling for geographic variation in species richness. Here, we leverage large-scale digitization of vertebrate museum records with advances in our understanding of the phylogenetic relationships among squamates 29 to reconcile the conflict between theoretical predictions and empirical observations, and provide a comprehensive test of mimicry in space and time. Because species are distributed non-randomly in space 25 and phenotypic traits often show phylogenetic signal 26, convincing tests of mimicry should incorporate biogeographic data in an evolutionary framework 3, 27, 28, especially across large clades. Although these effects are presumed to be minimal relative to the rate of natural selection within populations, they have not been well tested because most species occurrence records remain non-digitized and precise taxonomic relationships unknown, especially for insects. As both taxa share birds as a key predator class, the failure to meet these predictions in coral snakes and their mimics remains a puzzling evolutionary paradox.Ĭurrent theoretical models, however, ignore the contribution of both (a) large-scale biogeographic patterns of species diversity and (b) the evolutionary history of the mimetic phenotype to the current distribution of species with conspicuous colour patterns. Typically, model-mimic pairs show only narrow zones of mismatch in geographic distribution of coloration 18, 20, 21, 22, 23 and models are often more common than mimics 24. Although there is empirical evidence in insect mimicry that model abundances can be lower than mimics 17, 18 and a few species are found outside the range of their models 19, insects generally conform to these theoretical predictions. In fact, snakes include the only known example of a Batesian mimic that occurs entirely outside the geographic range of any model species (the California Mountain Kingsnake, Lampropeltis zonata 16). However, many researchers still question the extent, or even existence, of coral snake mimicry because snakes clearly violate two major theoretical predictions that should hold true for mimicry to persist over long periods of time 1, 9, 10: (1) that mimics should not occur outside the geographic range of the model species, and (2) that models should be more abundant than mimics, or at least near a ratio of 1:1 (refs 11, 12, 13, 14, 15). This striking convergence between distantly related species has motivated a century of experimental research demonstrating that predators innately avoid coral snake-like colour patterns and that this avoidance provides a selective advantage to mimetic coloration over other colour patterns 5, 6, 7, 8. Similar to well-known examples of toxic butterfly 2 and wasp 3 mimicry, the conspicuous red–black banded (RBB) colour pattern in some harmless snakes is thought to arise through mimicry of highly venomous coral snakes throughout North and South America 4. 1), brightly banded neotropical snakes were presented as the flagship example of ‘true mimicry' in vertebrates. In the first formalization of mimicry theory in the 1860s (ref. We also find that bidirectional transitions between mimetic and cryptic coloration are unexpectedly frequent over both long- and short-time scales, challenging traditional views of mimicry as a stable evolutionary ‘end point' and suggesting that insect and snake mimicry may have different evolutionary dynamics. Here we integrate distributional, phenotypic and phylogenetic data across all New World snake species to demonstrate that shifts to mimetic coloration in nonvenomous snakes are highly correlated with coral snakes in both space and time, providing overwhelming support for Batesian mimicry. However, mimicry of venomous coral snakes has remained controversial because of unresolved conflict between the predictions of mimicry theory and empirical patterns in the distribution and abundance of snakes. Batesian mimicry, in which harmless species (mimics) deter predators by deceitfully imitating the warning signals of noxious species (models), generates striking cases of phenotypic convergence that are classic examples of evolution by natural selection.
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