page_title: Evidence of common descent
section_title: White Sands lizards
hierarchical_section_title: Evidence of common descent / Evidence from selection / Vertebrates / White Sands lizards
caption_attribution_description: Bleached earless lizard (Holbrookia maculata ruthveni)
context_page_description: Evidence of common descent of living organisms has been discovered by scientists researching in a variety of disciplines over many decades, demonstrating that all life on Earth comes from a single ancestor. This forms an important part of the evidence on which evolutionary theory rests, demonstrates that evolution does occur, and illustrates the processes that created Earth's biodiversity. It supports the modern evolutionary synthesis—the current scientific theory that explains how and why life changes over time. Evolutionary biologists document evidence of common descent, all the way back to the last universal common ancestor, by developing testable predictions, testing hypotheses, and constructing theories that illustrate and describe its causes.
  Comparison of the DNA genetic sequences of organisms has revealed that organisms that are phylogenetically close have a higher degree of DNA sequence similarity than organisms that are phylogenetically distant.
context_section_description: Animals that exhibit ecotonal variations allow for research concerning the mechanisms that maintain population differentiation. A wealth of information about natural selection, genotypic, and phenotypic variation; adaptation and ecomorphology; and social signaling has been acquired from the studies of three species of lizards located in the White Sands desert of New Mexico. Holbrookia maculata, Aspidoscelis inornatus, and Sceloporus undulatus exhibit ecotonal populations that match both the dark soils and the white sands in the region. Research conducted on these species has found significant phenotypic and genotypic differences between the dark and light populations due to strong selection pressures. For example, H. maculata exhibits the strongest phenotypic difference (matches best with the substrate) of the light colored population coinciding with the least amount of gene flow between the populations and the highest genetic differences when compared to the other two lizard species.
  New Mexico's White Sands are a recent geologic formation (approximately 6000 years old to possibly 2000 years old). This recent origin of these gypsum sand dunes suggests that species exhibiting lighter-colored variations have evolved in a relatively short time frame. The three lizard species previously mentioned have been found to display variable social signal coloration in coexistence with their ecotonal variants. Not only have the three species convergently evolved their lighter variants due to the selection pressures from the environment, they've also evolved ecomorphological differences: morphology, behavior (in is case, escape behavior), and performance (in this case, sprint speed) collectively. Roches' work found surprising results in the escape behavior of H. maculata and S. undulatus. When dark morphs were placed on white sands, their startle response was significantly diminished. This result could be due to varying factors relating to sand temperature or visual acuity; however, regardless of the cause, "…failure of mismatched lizards to sprint could be maladaptive when faced with a predator".
caption: Figure 5c: H. m. ruthveni, a White Sands ecotonal variant of Holbrookia maculata
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