The Ensatina ring species represents a classic example of locally adapted lineages. The Monterey Ensatina (Ensatina eschscholtzii eschscholtzii) is a cryptic subspecies with brown coloration, however, a recently discovered polymorphic population within a wind-blown sand region also contains leucistic (pink) and xanthistic (orange) morphs. Leucism/xanthism frequency was mapped across the subspecies’ range revealing that these morphs are generally rare or absent except within regions containing light-colored substrate. Attack rates were estimated using clay models of the three morphs, deployed only at the crepuscular period and during the night, on both light and dark substrates at a site within the dune sand region. Model selection found that the interaction between morph and substrate color best predicted attack rates. Typical morphs had equal attack rates on both substrates while xanthistic and leucistic morphs incurred significantly fewer attacks on light versus dark substrate, and there was no significant difference in attack rates among morphs on light substrates. These results support the idea that xanthistic and leucistic morphs are poorly adapted for dark substrates compared to typical morphs, but they are more or less equally adapted for light substrates. We suggest that this microgeographic island of relaxed selection on light-colored morphs helps explain the existence of this polymorphic population.

Appendix S1 - Morph frequencies were estimated visually by examining georeferenced photographs depisted on iNaturalist (iNaturalist.org). Details can be found in the methods section of the published paper.

Appendix S2 - Raw data from the clay model predation study. Details can be found in the methods section of the published paper.

R Code - Used to generate heat maps from the georeferenced morph data.  Details can be found in the methods section of the published paper.