Xerophilic Flightless Grasshoppers (Orthoptera: Acrididae: Melanoplinae: Melanoplus: the Puer Group) of the Southeastern U.S.A.: an Evolutionary History
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The 27 flightless grasshopper species of the Puer Group (Orthoptera: Acrididae: Melanoplinae: Melanoplus) comprise a biological system of fascinating complexity in the southeastern U.S.A. that was heavily influenced by sea level fluctuations during the Pliocene and Pleistocene, especially during the latter. These shifts resulted in an oceanic island system that can now be classified as a landlocked archipelago, one that still reflects the patterns of its ancestral roots in terms of speciation and dispersal. To better understand speciation patterns in this group, I used several synergistic methods: molecular-based phylogenetic reconstruction, divergence time estimation, correlative microscopy and 3D model reconstruction of copulation, and shape analysis of male genitalia in an evolutionary time-based phylogenetic framework. As predicted, aside from general sea level changes, my evidence indicates that the biogeographical and speciation history of this system was shaped dominantly by allopatry in the form of oceanic islands in the past and, more recently, sympatry via sexual selection, especially for the species in peninsular Florida. My quantitative evidence also added strong support for the concept, especially in light of evolutionary time, that sexual selection can drive genital evolution divergently and rapidly. My investigation of the function of genital components (some new to science) during copulation was combined with shape analyses of five of those genital components to reveal that sexual selection’s evolutionary tempo on these components is accelerating and/or decelerating. The relative speed was found to be dependent upon the component and its associated function(s). I also discovered that one of the youngest Puer Group clades has speciated at a rapid rate that may possibly be the highest yet for insects. The obvious complexity of this biological system requires additional investigation at finer scales to further dissect the intriguing patterns and processes of evolution herein revealed to be at work. Continued analyses of the Puer Group, both quantitative and descriptive, are encouraged, especially because the threat of destruction and fragmentation of the group’s xeric habitats (especially scrub) looms large. Speciation is still largely a biological black box, but its inner workings will continue to be slowly revealed with further illuminating studies like this one.
Woller, Derek Alexander (2017). Xerophilic Flightless Grasshoppers (Orthoptera: Acrididae: Melanoplinae: Melanoplus: the Puer Group) of the Southeastern U.S.A.: an Evolutionary History. Doctoral dissertation, Texas A & M University. Available electronically from