• Adaptation;
  • gene flow;
  • genetic clustering;
  • lizards;
  • speciation by selection

Understanding the factors that promote or inhibit species formation remains a central focus in evolutionary biology. It has been difficult to make generalities about the process of ecological speciation in particular given that each example is somewhat idiosyncratic. Here we use a case study of replicated ecological speciation in the same selective environment to assess factors that account for similarities and differences across taxa in progress towards ecological speciation. We study three different species of lizards on the gypsum sand dunes of White Sands, New Mexico, and present evidence that all three fulfill the essential factors for ecological speciation. We use multilocus nuclear data to show that progress toward ecological speciation is unequal across the three species. We also use morphometric data to show that traits other than color are likely under selection and that selection at White Sands is both strong and multifarious. Finally, we implicate geographic context to explain difference in progress toward speciation in the three species. We suggest that evaluating cases from the natural world that are “same same but different” can reveal the mechanisms of ecological speciation.