Holbrookia maculata processing dataThis file contains data for all Holbrookia maculata used in the study, including individual capture date/location, morphology data, trials each individual was included in, and whether the individual survived the trials.hmaculataprocessingdata.csvEnclosure recapture dataThis file contains recapture data for individual enclosure replicates. For each enclosure replicate, data are included on when the trial was run, which enclosure the trial was run in, and the number of substrate-matched and substrate-mismatched lizards that were recaptured.enclosuredata.csvThermal preference dataThis file contains data from thermal preference trials. Thermal preference trials were 90 minutes long, and we recorded data at 30 minute intervals throughout trials. For each lizard in the thermal preference trials, data are included on the lizard body temperature and distance of the lizard from the light source at each data collection point.thermalpreference.csvSpectrometer data 2011This file contains spectrometer data for painted and unpainted Holbrookia maculata collected in 2011. For each individual lizard that we measured with the spectrometer, data are included on percent transmittance at each wavelength when the lizard was unpainted, as well as after the lizard was painted.specdata2011.csvSpectrometer data 2012This file contains spectrometer data for painted and unpainted Holbrookia maculata collected in 2012. For each individual lizard that we measured with the spectrometer, data are included on percent transmittance at each wavelength when the lizard was unpainted, as well as after the lizard was painted.specdata2012.csv

Determining the adaptive significance of phenotypic traits is key for understanding evolution and diversification in natural populations. However, evolutionary biologists have an incomplete understanding of how specific traits affect fitness in most populations. The White Sands system provides an opportunity to study the adaptive significance of traits in an experimental context. Blanched color evolved recently in three species of lizards inhabiting the gypsum dunes of White Sands and is likely an adaptation to avoid predation. To determine whether there is a relationship between color and susceptibility to predation in White Sands lizards, we conducted enclosure experiments, quantifying survivorship of Holbrookia maculate exhibiting substrate-matched and substrate-mismatched phenotypes. Lizards in our study experienced strong predation. Color did not have a significant effect on survival, but we found several unexpected relationships including variation in predation over small spatial and temporal scales. In addition, we detected a marginally significant interaction between sex and color, suggesting selection for substrate matching may be stronger for males than females. We use our results as a case study to examine six major challenges frequently encountered in field-based studies of natural selection, and suggest that insight into the complexities of selection often results when experiments turn out differently than expected.