Sunday, May 8, 2016

[Herpetology • 2016] Coral Snakes predict the Evolution of Mimicry across New World Snakes

Scientific illustration of a harmless mimic (Pliocercus elapoides, left) and venomous coral snake (Micrurus nigrocinctus, right) drawn from preserved specimens caught at the same field site in 1940 on a U-M Museum of Zoology expedition to Guatemala.
Illustration: John Megahan  |  DOI: 10.1038/ncomms11484


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. 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. 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. 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.

Figure 3: Repeated evolutionary transitions among colour patterns in snakes.
(a) Ancestral state reconstructions show that RBB colouration has evolved independently at least 26 times across snakes, including six times outside of New World (NW) colubrids and Elapid coral snakes. Numbers denote phylogenetic placement of corresponding snake images. Species 3 and 6 have sympatric colour polymorphism.
(b) Colubrid mimicry arose after both arrival in the NW (oldest black points) and sympatry with coral snakes (red arrow), with increasing accumulation of mimetic lineages over time.
 (c) Addition of missing taxa to a single clade recovers greater colour variation and faster phenotypic evolution. Tip state symbols show presence and absence of the red and black colour pattern components, with bicoloured points representing colour polymorphism (grey for absence). Asterisks denote co-occurrence with coral snakes.
(d) Trait mapping of intraspecific colour variation shows that polymorphism is the most common state and that RBB coloration does not depend on sympatry with coral snakes. Righthand images show four sympatric colour morphs found in populations with RBB polymorphism. The species names, photo credits (used with permission), and field collector/tissue numbers (when available) for the images in a are as follows: (1) Oxyrhopus trigeminus, Laurie J. Vitt, LJV-17825; (2) Erythrolamprus mimus, Edmund D. Brodie III; (3) Sonora mutabilis, Thomas J. Devitt, JAC-23362 and JAC-23363; (4) Micrurus brasiliensis, Donald B. Shepard; (5) Micrurus diastema, Jonathan A. Campbell, JAC-23126; (6) Micrurus multifasciatus, Edmund D. Brodie III; (7) Anilius scytale, Donald B. Shepard. For d the Sonora semiannulata colour morphs have the following credits from top to bottom: (1) mimetic morph, Yann Surget-Groba, ADR-BAL1M; (2) banded morph, Yann Surget-Groba, ADR-HIL1B; (3) striped morph, Yann Surget-Groba, ADR-Tor1S; (4) uniform morph, Alison R. Davis Rabosky and Christian L. Cox, CLC-291.

Alison R. Davis Rabosky, Christian L. Cox, Daniel L. Rabosky, Pascal O. Title, Iris A. Holmes, Anat Feldman and Jimmy A. McGuire. 2016. Coral Snakes predict the Evolution of Mimicry across New World Snakes. Nature Communications. 7(11484). DOI: 10.1038/ncomms11484

Deadly snakes or just pretending? The evolution of mimicry via @physorg_com