Adaptive Color Variation in the Ensatina "Ring Species" Complex: Implications for Ecological Speciation and Mimicry

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The salamander Ensatina eschscholtzii is a model ring species because it forms a ring of populations around the arid Central Valley of California, with reproductively isolated forms overlapping in southern CA but hybridization where other populations contact. Color patterns of these salamanders are thought to have evolved in response to two conflicting ecological pressures: selection favoring bright warning coloration that mimics highly toxic California Newts versus selection favoring cryptic patterns that blend into forest litter (camouflage). Where these forms come into contact there should be strong selection that favors reproductive isolation and that restricts mating within each subspecies. Color patterns of salamanders at contact zones will be studied with spectroradiographic measurements that record light wavelengths to determine how cryptic forms are camouflaged on the background and how warning-colored forms stand out against background patterns. Color patterns will be manipulated on models to assess predator attacks on pure and hybrid forms. This study addresses basic theories of crypsis and animal perception. It will provide data on how ecological interactions shape evolution of cryptic and warning-colored forms in the evolutionary long term. Such information is important in a general explanation of the evolution of diversity in natural populations.