| The systematics of Cyrtacanthacridinae (Orthoptera: Acrididae) is investigated to study the evolution of locust phase polyphenism, biogeography, and the evolution of male genitalia. In Chapter Two, I present a comprehensive taxonomic synopsis of the genus Schistocerca Stal. I review the taxonomic history, include an identification key to species, revise the species concepts of six species and describe a new species. In Chapter Three, I present a morphological phylogeny of Schistocerca, focusing on the biogeography. The phylogeny places the desert locust S. gregaria deep within the New World clade, suggesting that the desert locust originated from the New World. In Chapter Four, I review the systematics of Cyrtacanthacridinae and present a phylogeny based on morphology. Evolution of taxonomically important characters is investigated using a character optimization analysis. The biogeography of the subfamily is also addressed. In Chapter Five, I present a comprehensive review the recent advances in the study of locust phase polyphenism from various disciplines. The review reveals that locust phase polyphenism is a complex phenomenon consisting of numerous density-dependent phenotypically plastic traits. The evolution of locust phase polyphenism is investigated from a phylogenetic perspective. I show that different components of locust phase polyphenism evolved independently and often phylogenetically conserved. In Chapter Six, I address some philosophical issues in the study of genital evolution. I show that the fundamental assumptions in the field of genital evolution are often violated and need to be tested more rigorously. |
