Differing rates of character evolution in Schistocerca lineata Scudder, 1899 (Orthoptera: Acrididae: Cyrtacanthacridinae)

The spotted bird grasshopper, Schistocerca lineata, is a widely distributed species found throughout most of the continental United States and southern Canada. This species is known to be highly variable in morphology, with many distinct ecotypes across its native range. These ecotypes display high levels of association with type-specific host plants. A phylogeographic analysis of the nine known populations of S. lineata was unable to resolve a signal of population-level genetic divergence, based on three mitochondrial genes. Understanding the evolutionary relationships among different ecotypes is crucial groundwork for studying the process of host-associated differentiation. The wide range of morphological differences across populations suggests that, in this species, morphological divergence may have preceded genetic divergence. To test this hypothesis, we analyzed the previously generated molecular data in a population genetics framework, and quantified the sizes and shapes of morphological features in each population. Two size-dependent measures (hind femur length and pronotum length) and one size-independent measure (male cercus) of morphology were used to evaluate differences between populations, including the degree of sexual dimorphism. The results of the molecular and morphological analyses were then compared and contrasted to illuminate the relative rates of character evolution of S. lineata.