The evolution of phenotype has historically been studied by classifying traits into categories, as traits within each category often exhibit close associations. However, these categories are not independent of one another. Thus, the phenotype may function as an integrated set of traits rather than as isolated units. In this study, we employed various phylogenetic comparative methods to explore evolutionary correlations among traits, estimate and compare phylogenetic signals, and evaluate evolutionary models to assess the validity of the historical categorization of phenotypic traits in spiny lizards of the genus Sceloporus. We categorized these traits as either morphological or life-history traits, including eight morphological traits and seven life-history traits, such as trunk length, head width, snout-vent length, clutch size, hatchling length, and size at maturity. Our analyses revealed covariation in the evolution of traits both within and across categories. Differences in phylogenetic signals between categories were also observed, though these results should be interpreted with caution. Additionally, the evolutionary models varied between categories. Our findings suggest that estimates of phylogenetic signals and covariation between morphological and life-history traits are independent of historically assigned categories. Therefore, this supports the notion that traits should be compared and analyzed in an integrated manner, regardless of their category. We discuss how evolutionary mechanisms, such as fecundity selection, may influence traits across different categories (e.g., trunk length, hatchling length, and clutch size), challenging the appropriateness of traditional phenotypic categorization in evolutionary studies of Sceloporus.

The evolution of the phenotype has historically been studied by segregating it into categories, as traits within a category often exhibit close associations. However, individuals can be considered as integrated phenotypes, suggesting that their analysis may not correspond to an artificial categorization. Nonetheless, variations in the intensity or persistence of selective pressures over time can lead to mismatches in phenotypic evolution. Despite the potential for selective pressures to induce phenotypic changes, closely related species tend to exhibit similarities due to their common ancestry. In this study, we calculated and compared the phylogenetic signal of phenotypic traits of lizard species in the genus Sceloporus. We categorized these traits as either morphological or life-history traits, with a total of eight traits in each category. These traits include trunk length, limb length, head length, clutch size, hatchling length, age at first brood, and size at maturity. We found that the amount of phylogenetic signal varies across Sceloporus traits. The intensity of the phylogenetic signal was higher in traits derived from morphometric measurements, regardless of their category. The remaining traits exhibited notable variation, ranging from phylogenetically conserved traits such as reproductive mode to the absence of phylogenetic signal, as seen in relative clutch mass. Furthermore, we observed that traits possibly influenced by the same evolutionary mechanism exhibit similar amount of phylogenetic signal, regardless of category. Finally, we discuss the potential implications of phylogenetic signal in the evolution of Sceloporus phenotypes.