Population differences in the roles of size and coloration in intra- and intersexual selection in the collared lizard, Crotaphytus collaris: influence of habitat and social organization

Previous studies have shown that in three Oklahoma populations of collared lizards, Wichita Mountains (WM), class Mountains (GM), and Arcadia Lake (AL), sexual dimorphism in body size varies as WM>AL>GM, whereas dorsal color dimorphism varies as GM>WM>AL. Social organization at these sites also differs such that the environmental potential for sexual selection varies as AL>WM>GM, We conducted female choice and male competition laboratory trials to assess whether advantages to large or bright males correlate best with the interpopulation pattern of sexual dimorphism or with that of the environmental potential for sexual selection. Between-population trials involved bright-colored WM males and dull-colored AL males that were matched for size. AL females preferred bright WM males, but WM females did not. WM males had higher agonistic scores in intrasexual contests when aggression was low, but AL males consistently had higher scores when aggression escalated. Within-population trials involved males that were disparate in color but size matched and disparate in size but color matched. Size was important in male contests in all populations. Color brightness was a factor in male trials only at AL. Also, only AL females preferred brighter males, and larger males were not preferred in any population. The importance of intra- and intersexual selection in these populations cannot be inferred from the observed pattern of size and color dimorphism. Rather, interpopulation differences in the environmental potential for females to assess and choose from among multiple males, and for males to interact, are most consistent with the observed outcomes.