Animal coloration can influences multiple aspects of performance, including mating success and predator avoidance. In addition, coloration can have a large impact on thermal budgets by mediating how much radiative energy an organism absorbs. As a result, color evolution is likely to be mediated by a balance of selection on multiple functions of coloration. Lizards within the White Sands Desert of New Mexico provide an ideal system to investigate the multi-faceted consequences of color evolution. The White Sands is home to three lizards species (Holbrookia maculata, Sceloporus cowlesi, and Aspidoscelis inornatus) that have independently evolved blanched coloration relative to more melanized wild-type populations from adjacent dark soils. This color evolution is thought to result from predation pressure, as the pale coloration of White Sands populations increases background matching with the white gypsum sands that make up the substrate. However, it is currently unknown if this color evolution in thermally beneficial or detrimental in these systems. In other words, is color evolution thermally adaptive, or non-adaptive but maintained due to the greater selective pressure from predation on background matching?
Results/Conclusions
We applied a biophysical modeling approach to estimate operative thermal environments for lizards in the White Sands or dark soils with either blanched or wild-type integument. We also measured physiological thermal limits and behavioral thermal preferences of all species to estimate performance consequences of the different thermal environments. We found that blanched coloration reduces the annual number of hours that lizards need to find shaded refuges to avoid overheating in both White Sands and dark soil habitat, particularly during the wet season when activity is most intense. These results indicate that the blanched coloration of White Sands lizards may simultaneously be an adaptation to avoid predation and a thermal adaptation to avoid overheating and reduce the need for behavioral thermoregulation in desert habitat. These results highlight that multiple ecological forces can sometimes push animal color evolution in the same direction.